EO Topics on Climate Change
EO (Earth Observation) Topics on Climate Change
Since the start of the space age, Earth observation is providing its share of evidence for a better perception and understanding of our Earth System and its response to natural or human-induced changes.
Earth is a complex, dynamic system we do not yet fully understand. The Earth system comprises diverse components that interact in complex ways. We need to understand the Earth's atmosphere, lithosphere, hydrosphere, cryosphere, and biosphere as a single connected system. Our planet is changing on all spatial and temporal scales.
Over the years, the entire Earth Observation community, the space agencies as well as other governmental bodies, and many international organizations (UN, etc.) are cooperating on a global scale to come to grips with the modeling of the Earth system, including a continuous process of re-assessment and improvement of these models. The goal is to provide scientific evidence to help guide society onto a sustainable pathway during rapid global change.
In the second decade of the 21st century, there is alarming evidence that important tipping points, leading to irreversible changes in major ecosystems and the planetary climate system, may already have been reached or passed. Ecosystems as diverse as the Amazon rainforest and the Arctic tundra, may be approaching thresholds of dramatic change through warming and drying. Mountain glaciers are in alarming retreat and the downstream effects of reduced water supply in the driest months will have repercussions that transcend generations. 1)
Table 1: Overview of some major international bodies involved in global-change research programs 2)
The UN Framework Convention on Climate Change (UNFCCC) is an intergovernmental treaty developed to address the problem of climate change. The Convention, which sets out an agreed framework for dealing with the issue, was negotiated from February 1991 to May 1992 and opened for signature at the June 1992 UN Conference on Environment and Development (UNCED) — also known as the Rio Earth Summit. The UNFCCC entered into force on 21 March 1994, ninety days after the 50th country’s ratification had been received. By December 2007, the convention had been ratified by 192 countries.
In the meantime, there were many UN conferences on Climate Change, starting with the UN climate conference in Kyoto, Japan, in December 1997. The Kyoto Protocol set standards for certain industrialized countries. Those targets expired in 2012.
Meanwhile, greenhouse gas emissions from both developed and developing countries have been increasing rapidly. Even today, those nations with the highest percentage of environment pollution, are not willing to enforce stricter environmental standards in their countries in order to protect their global business interests. It's a vicious cycle between these national interests and the deteriorating environment, resulting in more frequent and violent catastrophes on a global scale. All people on Earth are effected, even those who abide by their strict environmental rules.
The short descriptions in the following chapters are presented in reverse order on some topics of climate change to give the reader community an overview of research results in this wide field of global climate and environmental change.
Note: As of May 2020, the previously single large EO-Topics file has been split into five files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the period 2020 + 2021
Nobel Prize in Physics honors research on climate, glass, and other complex systems
• October 5, 2021: Syukuro Manabe, Klaus Hasselmann, and Giorgio Parisi enriched our understanding of complex systems with models of Earth’s climate and disordered phenomena. 3)
Syukuro Manabe, Klaus Hasselmann, and Giorgio Parisi are to share the 2021 Nobel Prize in Physics for their work on complex systems, the Royal Swedish Academy of Sciences announced on Tuesday.
Manabe (Princeton University) developed early climate models to investigate the interplay of incoming radiation from the Sun, IR from Earth, convection in the atmosphere, and the latent heat of water vapor. His 1967 framework offered an initial estimate of the rise in global surface temperatures that would result from increased atmospheric carbon dioxide.
About a decade later, Hasselmann (Max Planck Institute for Meteorology in Hamburg, Germany) created a stochastic climate model that incorporated the weather’s fluctuations as noise. He also demonstrated how the fingerprints of discrete influences on the climate, including the impact of humans, can be identified and extracted.
Parisi (Sapienza University of Rome) tackled the spin-glass problem: How do magnetic spins orient themselves when subjected to competing energetic and geometric constraints? His solution, which found patterns in the possible configurations, has influenced mathematics, biology, neuroscience, and machine learning.
Manabe and Hasselmann will share half the 10 million Swedish kronor (roughly $1.1 million) prize; it is the first time the Nobel physics committee has recognized achievements in atmospheric or climate science. Parisi will receive the other half.
Figure 1: Left to right: Syukuro Manabe, Klaus Hasselmann, and Giorgio Parisi (image credits: Bengt Nyman, CC BY 2.0; Fundación BBVA; Barbara Sabatini/Sapienza University of Rome)
Climate modeling and attribution
Manabe received his PhD from the University of Tokyo in 1958. Soon after, he arrived at the US Weather Bureau in Washington, DC, as one of the first hires of Joseph Smagorinsky, who had been tasked with running numerical simulations on computers to develop re-creations, or general circulation models, of Earth’s atmosphere. Coming up with the physics equations was the easy part for Smagorinsky, Manabe, and colleagues; the challenge was replicating, with sufficient accuracy but only limited computing power, the complexity of the atmosphere and its interactions with land, ice, and sea.
Manabe dedicated a lot of time to studying specific hydrological processes, such as how different types of soil absorb water, according to historian Spencer Weart in his climate science history. But what set Manabe apart was his ability to simplify, says V. Balaji, a computational climate scientist at Princeton University and the Pierre-Simon Laplace Institute in France who has worked with Manabe. “He took a complicated system and reduced it to a few elements that were mathematically tractable,” Balaji says. For example, in 1964 Manabe and Robert Strickler devised an adjustment to account for the thermal effects as water vapor rises from the surface and releases heat when it condenses into clouds.
Three years later Manabe, by now working with NOAA’s Geophysical Fluid Dynamics Laboratory at Princeton, and Richard Wetherald published a numerical model of a 24-km-tall column of Earth’s atmosphere. Although far from being a global three-dimensional model, it described the atmosphere relatively well and represented a key step in incorporating basic physics and the effects of greenhouse gases, particularly water vapor and CO2. When the researchers doubled the concentration of CO2 in their simulated atmosphere, the temperature near the surface rose by about 2ºC. “This was the first time a greenhouse warming computation included enough of the essential factors, in particular the effects of water vapor, to seem plausible to the experts,” Weart writes.
In 1969 Manabe and colleague Kirk Bryan published the first coupled atmospheric and ocean model. And in 1975 Manabe and Wetherald built on their work from eight years earlier to create a primitive 3D general circulation model. This time they calculated an equilibrium climate sensitivity—the globally averaged surface temperature change resulting from a doubling of atmospheric CO2—of nearly 3ºC.
By the 1970s Manabe and others had successfully created models despite the inability to simulate many of the complex, chaotic processes, such as the year-to-year variability in the El Niño–Southern Oscillation, that contribute to Earth’s natural climate fluctuations. Yet considering the substantial cumulative impact of all those processes, climate scientists needed ways to quantify the variability in their models.
While on a flight to a conference in the mid 1970s, Hasselmann devised a solution. Inspired by Brownian motion, in which the observed motion of macroscopic particles is the result of continuous random movement at the microscopic level, Hasselmann developed a stochastic climate model that treated changes to the climate as the integrated effects of continuous random weather disturbances.
Hasselmann’s insights into deciphering the causes of observable effects at long time scales also led him to consider how to separate an anthropogenic climate signal from natural climate fluctuations. The models by Manabe and others had allowed researchers to explore the potential for global warming due to increased CO2, but it was unclear how much of that warming was the result of external radiative forcing (the signal) versus natural fluctuations (the noise). In a 1979 paper, Hasselmann provided a statistical blueprint for climate scientists to examine their model results and distinguish signals from noise. He also identified telltale data signatures that cannot be explained by natural fluctuations.
A 2019 review in Nature Climate Change calls Hasselmann’s work “the first serious effort to provide a sound statistical framework for identifying a human-caused warming signal.” In the decades since, climate scientists have been able to demonstrate with increasing confidence that rising global temperatures and other observed climatic effects are the direct result of human activities.
This year’s physics Nobel announcement comes several weeks before the United Nations’ 26th Climate Change Conference, to be held in Glasgow, Scotland, and two months after the partial release of the Sixth Assessment Report of the UN Intergovernmental Panel on Climate Change (IPCC). One of the report’s conclusions, which is based on the attribution studies so influenced by Hasselmann, is that it is “unequivocal that human influence has warmed the atmosphere, ocean, and land.”
In its report, the IPCC pegged the equilibrium climate sensitivity at 2.5–4 °C. Forty-two years earlier, in its Ad Hoc Study Group on Carbon Dioxide and Climate, the US National Research Council had relied on Manabe’s modeling work to estimate a probable range of 1.5–4.5 °C. “Everything goes back to those first calculations that Manabe made,” Balaji says.
A new spin on a complex problem
Complexity can be found not just on the planetary scale, but also in how particles arrange themselves on the microscale. Parisi’s 1979 mathematical description of how a collection of spins orient has wide-ranging applications.
Imagine a magnetic spin placed at each of the three corners of a triangle. If the spins have antiferromagnetic interactions, no single lowest-energy state exists. With one spin up and one spin down, the third spin can’t point antiparallel to both neighbors. The situation gets more complicated with additional spins and complex geometric arrangements. Because there’s no unique equilibrium, such so-called spin glasses settle into a multitude of metastable states that minimize the energy as best they can. Which of those states they enter, however, is difficult to predict.
In 1975 Sam Edwards and Philip Anderson reimagined the spin-glass problem in terms of averaging over the configurations of many replicas of the system. Rather than multiplying the complexity, that approach simplified the math by turning the problem into a thermodynamic calculation. David Sherrington and Scott Kirkpatrick extended that model to infinite dimensions, which once again paradoxically simplified the math. But the extension also predicted negative entropy at low temperatures, a clear sign of trouble. Jairo de Almeida and David Thouless realized in 1978 that the issue lay with the assumption of replica symmetry, which treats all replicas as equally related to one another. Despite that insight, a general solution eluded physicists.
Then, one year later, Parisi solved the problem. He introduced a parameter that describes how similar the states of two replicas are—in other words, how many of the N spins are pointing in the same direction in the two replicas. The underlying idea is represented in the tree shown below. Each colored point represents a state of the system. Any pair of states with the same color overlap to the same degree.
To assess how similar any two states are, you count how many nodes you pass moving from one state to the other in the tree. For example, the red states are all one node apart, and any given red state is three nodes away from either yellow state and five away from any of the blue or green states. For any three states chosen at random, at least two of them overlap by the same amount, or number of nodes. That insight leads to a tidy equation for the distribution of overlaps. (See the column by Philip Anderson, Physics Today, July 1989, page 9.)
Figure 2: Ultrametric tree. This structure is a convenient way to represent the degree of resemblance between spin glass states (colored dots), image credit: Philip Anderson
“The solution has a richness that I don’t think anyone anticipated in advance,” says A. Peter Young of the University of California, Santa Cruz. “It has influenced much of the spin-glass literature for the last 40 years.”
The applications of Parisi’s approach have reached far beyond spin glasses. “It appears, for instance, when we want to understand the performance of modern artificial intelligence systems that learn by neural networks,” explains Lenka Zdeborová of the Swiss Federal Institute of Technology, Lausanne.
She is just one member of what she characterized as the “large community of researchers that use [Parisi’s] science every day in a broad range of areas from physics, to mathematics, computer science, materials science, neuroscience, and biology.”
Satellite data provide valuable support for IPCC climate report
• August 31, 2021: Earlier this month, the Intergovernmental Panel on Climate Change (IPCC) published its latest assessment report laying out the accumulating evidence of the climate crisis. The report identifies Earth observing satellites as a critical tool to monitor the causes and effects of climate change and directly acknowledges the contribution of ESA’s Climate Change Initiative – a research program that draws on observations from multiple satellite missions. 4)
It is the strongest and most significant IPCC report to date, incorporating advances in climate observations, analysis methods and modelling, and will be a key input to climate negotiations and decision-making.
Drawn from 14 000 scientific publications, the report concludes that ‘it is unequivocal that human influence has warmed the atmosphere, ocean and land’ and warns that the changes to the state of many parts of the climate system are ‘unprecedented over many centuries to many thousands of years.’
Carbon dioxide is now at its highest level in at least two million years, and every tonne adds to global heating. This is causing widespread and rapid changes to the atmosphere, ocean, cryosphere and biosphere.
Across many chapters, the report highlights the valuable contribution that satellites provide in tracking change and improving models for climate prediction. New and improved observational data records, which are longer since the IPCC’s previous report in 2013, support greater confidence in climate attribution assessments.
“The latest IPCC report clearly demonstrates the value of ESA programs in providing the evidence base for monitoring and understanding climate change.” said Josef Aschbacher, ESA’s Director General. “These hard facts are also highly appreciated by political decision makers in Europe and globally.”
The report explicitly acknowledges ESA’s Climate Change Initiative (CCI), which supports science teams to create long-term datasets spanning up to four decades for key aspects of the climate, known as Essential Climate Variables.
These variables underpin the ‘headline indicators’ for climate monitoring. Fifteen scientists from ESA’s CCI program worked as contributing authors to the report, with five taking lead and coordinating author roles.
Remote sensing has revolutionized our knowledge of the world’s frozen areas, particularly near the poles where conditions make surface observations difficult.
September Arctic sea ice extent continues its long-term decline – a trend tracked from space since 1979. Model simulations shown in the report alongside the satellite-based observational dataset supported by ESA CCI predict that the Arctic sea will be practically ‘ice free’ in summer at least once by 2050.
Most of the world’s glaciers are in retreat. Glacial ice loss has accelerated since the 1990s and is ‘very likely’ driven by human influence. Satellite records, and research supported by CCI, which contribute to global glacier inventories, provide crucial lines of evidence in the report. These data track glacier mass balance and elevation changes across thousands of remote glaciers worldwide and assess their contribution to sea level rise.
Figure 3: The Upsala Glacier is the third largest glacier in the Southern Patagonian Ice Field. Many glaciers in the Patagonian Ice Field, including Upsala, have been retreating over the last 50 years owing to rising temperatures. Earth observing satellites, including the Copernicus Sentinel-2 mission, have been closely monitoring the Upsala Glacier and have revealed that it has retreated approximately 9 km between 1985 and 2021. Satellite data can help monitor changes in glacier mass and, subsequently, their contribution to rising sea levels (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
Ice sheet melt
While summer sea ice decline can be reversed within decades if greenhouse gas emissions are cut rapidly, many other changes will continue for hundreds to thousands of years. Most notably these are the melting of the ice sheets, sea level rise, ocean warming and acidification.
The Greenland Ice Sheet lost an estimated 4890 Gt of ice since the 1990s owing to surface melting and run-off. The Antarctic Ice Sheet loss is around 2670 Gt for a similar period, dominated by the melt of the West Antarctic Ice Sheet.
The new insights since the IPCC’s latest report have been enabled by combining observations with modelling to understand the surface processes driving ice loss. The rate of ice sheet loss is accelerating – the report notes a four-fold increase in ice sheet loss between 1992-1999 and 2010-2019.
Observations from multiple missions, including data from ESA’s ERS-1, ERS-2, Envisat and CryoSat missions, as well as the EU’s Copernicus Sentinel-1 mission, have proven critical for monitoring changes to the ice sheets, which together with glacier mass loss, are now the dominant contributors to global sea level rise. The ESA-supported Ice Sheet Mass Balance Inter-Comparison Exercise, also known as IMBIE, provided updated, reconciled satellite estimates of ice sheet contributions to sea level rise.
Permafrost and snow cover
Substantial reductions in permafrost and seasonal snow cover are expected as the planet continues to warm. Both are the subject of study by CCI research projects, whose new data products such as snow water equivalent have made ‘substantial improvements to assessments of large-scale change.’ Each project has released satellite-based records to characterize change across recent decades (see Figure 40).
Sea level rise
Since 1901, sea level has risen by 20 cm, with the rate of increase accelerating to a high of 3.7 mm per year since 2006. Depending on future carbon emissions, mean sea level could rise a further 28-101 cm by 2100, and possibly by up to 2 m if the ice sheets become more unstable.
Satellite altimetry techniques provide a precise measurement of sea-level change. Global observations over the past three decades are consistent with the contribution of sea level rise from ice losses – in addition to the role of thermal expansion.
In order to closely monitor sea-level rise, the Copernicus Sentinel-6 Michael Freilich satellite was launched into orbit in November 2020. Using the latest radar altimetry technology, the satellite is set to provide a new overview of ocean topography and advance the long-term record of sea-surface height measurements that began in 1992 making it the most advanced mission dedicated to measuring sea-level rise.
These are shown alongside satellite-based data for ice sheet dynamics, sea surface temperature, sea ice and sea level, as well as improved representation of cloud, soil moisture and ocean biogeochemistry and regional carbon budgets. Many of these comparisons and model outputs are supported by CCI datasets and members of the CCI Climate Modelling User Group, as well as projects such as RECCAP-2 that make use of multiple satellite datasets to improve intercomparisons and how climate variables are represented in Earth System models.
Figure 4: Above ground biomass. Vegetation biomass is a crucial ecological variable for understanding the evolution and potential future changes of the climate system, on a local, regional and even global scale. A series of new maps, generated by ESA’s Climate Change Initiative, is set to help our understanding of global carbon cycling and support forest management, emissions reduction and sustainable development policy goals (image credit: ESA, CCI Biomass project)
Looking ahead to the 2021 United Nations Climate Change Conference (COP26), ESA will be releasing new maps of global above ground biomass, which will help support the first global stocktake of the world’s climate mitigation and adaptation efforts as part of the goals of the Paris Agreement.
Figure 5: Changing faces of Earth. Thanks to the satellite era we are better placed to understand our changing world. These globes show (from top left) global land cover with ocean color data, significant wave height, regional mean sea-level trends, sea-surface temperature, magnetic field variations, the NASA blue marble, global urban footprint, gravity geoid, ocean currents, ozone, nitrogen dioxide, fire hotspots (video credit: ESA/CCI/CNES/LOGOS/CLS/DLR/NASA/CNES/KNMI)
Protecting the Ozone Layer Also Protects Earth’s Ability to Sequester Carbon
• August 25, 2021: Protecting the ozone layer also protects Earth’s vegetation and has prevented the planet from an additional 0.85º Celsius of warming, according to new research from Lancaster University (UK), NASA, and others. This new study in Nature demonstrates that by protecting the ozone layer, which blocks harmful ultraviolet (UV) radiation, the Montreal Protocol regulating ozone-depleting substances also protects plants – and their ability to pull carbon from the atmosphere. The impact from plants has not been accounted for in previous climate change research. 5) 6)
“We know the ozone layer is connected to climate. We know greenhouse gases affect the ozone layer. But what we’ve never done before this is connect the ozone layer to the terrestrial carbon cycle,” said lead author Paul Young, an atmospheric and climate scientist at Lancaster University in the United Kingdom.
The ozone layer in the upper atmosphere, or stratosphere, blocks UV radiation that can damage living tissue, including plants. The ozone “hole,” discovered in 1985, is the result of humans emitting chlorofluorocarbons (CFCs), which are ozone-depleting chemicals and greenhouse gases that were once commonly used as coolants in refrigerators and in aerosols like hairspray. They were then phased out of use by the Montreal Protocol signed in 1987 and its subsequent amendments.
Scientists have previously simulated the world that we avoided by banning CFCs. Now, the new study returns to the same question – what would happen if CFCs continued to be emitted? – and looked at the effect on plants.
Figure 6: Previous “world-avoided” experiments have shown that, without the Montreal Protocol, ozone levels would be depleted globally by the mid-twentieth century (image credits: NASA/Goddard Space Flight Center Scientific Visualization Studio)
“Past world-avoided experiments have never considered the impacts of increased UV radiation on plants, and what that would mean for the plants’ ability to sequester carbon,” said Young.
Figure 7: Nearly 200 countries came together to sign the Montreal Protocol in 1987, which limited CFC emissions. The production of CFCs was eventually phased out, and the ozone layer is recovering as a result (video credits: NASA's Goddard Space Flight Center, Katy Mersmann)
The team used a series of models to gain a more complete picture and simulate two hypothetical scenarios: the world projected and the world avoided. “The world projected is similar to the path we’re currently on,” said Luke Oman, a research physical scientist focusing on atmospheric chemistry and dynamics at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The world avoided represents a path not taken.”
For the world-avoided scenario, the researchers assumed that CFC emissions would increase at the same rate, 3% every year, from the 1970s onward. The models show that there would be a huge thinning of the ozone layer across the globe by 2050. By 2100, ozone holes forming in the tropics would be worse than what has been observed in the Antarctic ozone hole.
In their models of the world-avoided, a depleted ozone layer would let more harmful ultraviolet (UV) radiation reach the surface, inhibiting plants from storing carbon in their tissue and in the soil. As a result, atmospheric CO2 levels are estimated to be 30% higher than they would likely be under Earth’s current trajectory. Consequently, Earth would likely be an additional 0.85ºC hotter in that “world-avoided” scenario solely because of the impact on plants.
This global thinning of the ozone layer would allow significantly more harmful UV radiation from the sun to reach the surface, which would effectively sunburn the plants on Earth, said Young. Earth’s trees and vegetation would be much less efficient at photosynthesis, hindering their ability to absorb carbon out of the atmosphere and sequester it, storing carbon in plant tissue and the soil for many years. Overall, the damage to plants would result in 580 billion metric tons less carbon stored in forests, soil and vegetation. It would instead be released into the atmosphere, increasing atmospheric CO2 levels by 30% on average compared to the world projected scenario.
That huge increase in atmospheric CO2 alone would cause global temperatures to rise 0.85ºC by 2100, according to the models. That’s on top of the warming Earth may experience due to prior and expected emissions of CO2 and other greenhouse gases, as well as the 1.7°C of direct warming due to increased CFC emissions in this scenario.
But how do we know this “world-avoided” scenario is anything like the world that would come to be without the Montreal Protocol? The team checked their models against historical data collected by NASA satellites and other available data from NASA’s partners. For example, they looked at ozone levels recorded by the Ozone Monitoring Instrument (OMI) aboard NASA’s Aura satellite and compared them to what the models ‘predicted’ would have happened. What happened in the model was very close to what actually happened in the past, giving the scientists confidence that their model could accurately project what may happen in the future.
NASA at Your Table: Where Food Meets Methane
• August 13, 2021: Today, human sources are responsible for 60% of global methane emissions, coming primarily from the burning of fossil fuels, decomposition in landfills and the agriculture sector. Nearly a quarter of methane emissions can be attributed to agriculture, much of which is from raising livestock. Rice cultivation and food waste are also important sources of agricultural methane, as nearly a third of all food produced for human consumption is lost or wasted. 7)
At NASA, scientists study the global methane budget to better understand the primary sources of methane emissions and how they contribute to climate change. In addition to the human sources, methane is also produced in natural settings. The greatest natural source of methane is wetlands, which contribute 30% of global methane emissions. Other natural sources of methane emissions include the oceans, termites, permafrost, vegetation and wildfires.
Atmospheric methane concentrations have more than doubled since the Industrial Revolution because of intensive use of oil, gas and coal, rising demand for beef and dairy products and increased production of food and organic waste. Although the increase in atmospheric methane concentrations slowed appreciably near the end of the 20th Century, concentrations have been increasing substantially since 2006, likely as a result of rising emissions from raising livestock, renewed reliance on natural gas and, in recent years, wetlands and global warming.
Figure 8: NASA’s new three-dimensional portrait of methane shows the world’s second-largest contributor to greenhouse warming as it travels through the atmosphere. Combining multiple data sets from emissions inventories and simulations of wetlands into a high-resolution computer model, researchers now have an additional tool for understanding this complex gas and its role in Earth’s carbon cycle, atmospheric composition and climate system. The new data visualization builds a fuller picture of the diversity of methane sources on the ground as well as the behavior of the gas as it moves through the atmosphere (video credit: NASA's Goddard Space Flight Center/Scientific Visualization Studio)
The Greenhouse Effect and Methane
Greenhouse gases, including methane, contribute to chemical reactions and climate feedbacks. The greenhouse gas molecules trap solar energy by acting like a thermal blanket. Energy from the sun is absorbed by Earth’s surface, though some of this energy is reflected into the atmosphere. The absorbed energy is also re-emitted at infrared wavelengths. Some of the reflected and re-emitted energy re-enters space, but the rest is trapped in the atmosphere by greenhouse gases. Over time, the captured heat warms our climate, increasing global temperatures.
Figure 9: Greenhouse gases in our atmosphere act like a blanket trapping heat from the Sun. This causes global temperatures to rise as the amount of greenhouse gases increases (image credit: NASA, Jesse Kirsch)
The human-driven temperature increases can have an impact on methane released from natural sources. For example, permafrost can thaw naturally and emit methane into the atmosphere, but humans have increased the rate at which permafrost thaws due to human-caused warming.
Methane is the world’s second largest contributor to global warming, after carbon dioxide. Although carbon dioxide is more abundant than methane in the atmosphere, a single molecule of methane more effectively traps heat than a single molecule of carbon dioxide.
However, the lifetime of a molecule of methane is shorter than a molecule of carbon dioxide because of natural chemical processes that are quicker at scrubbing methane out of the atmosphere than carbon dioxide. This means that if methane emissions were to decline and the natural chemical scrubbing of methane maintained, atmospheric methane could decrease dramatically in just ten years. Decreasing the amount of methane put into the atmosphere could have a significant and nearly immediate impact on reducing the near-term effects of climate change and may contribute to keeping global temperature change below 2º Celsius.
Why Cows Produce Methane
Cattle, such as dairy cows or beef cattle produce methane as a by-product of digestion. Cattle are ruminant animals, meaning they have specialized digestive systems that allow them to process foods that cannot be digested by humans and most other animals, like fresh grass and uncooked grain. When food enters a bovine’s stomach, it undergoes a process called enteric fermentation: microbes and bacteria partially break down the food particles, which then ferment in the part of the stomach called the rumen. As the food particles ferment, they produce methane. Every time cattle belch - and, to a smaller extent, flatulate - methane is expelled and enters the atmosphere, where it acts as a greenhouse gas.
Figure 10: Methane fast facts: Methane is responsible for 20% of global warming since the Industrial Revolution; In 2018, the food system contributed 33% of all human-caused GHG emissions; In 2015, livestock contributed to 10% of US methane emissions; Methane is about 30 times more potent than CO2 over the span of a century; Europe and the Arctic are the only two regions whose methane emissions decreased from 2000 to 2018; Atmospheric methane concentrations have more than doubled in the last 200 years (image credit: NASA, Jesse Kirsch)
NASA’s Eyes on Methane
While methane concentrations are well observed, emissions have to be inferred based on a variety of factors. NASA scientists use a variety of methods to track methane emissions. To get the most accurate estimates possible, they use emissions inventories from countries around the world, simulate wetland methane emissions, and combine this with ground-based, airborne and satellite data using atmospheric models.
In California (and some other regions), researchers fly aircraft equipped with NASA’s Airborne Visible Infrared Imaging Spectrometer – Next Generation, or AVIRIS-NG, and collect highly calibrated data. This data is used in the California Methane Survey, a project jointly funded by NASA, the California Air Resources Board and the California Energy Commission to rapidly identify and report methane leaks.
In Alaska and Northwestern Canada, NASA researchers use satellites, aircraft and field research to better understand methane emissions from thawing permafrost as part of the ABoVE (Arctic Boreal and Vulnerability Experiment). Researchers have discovered that carbon-rich permafrost is thawing at increasingly high rates, likely as a result of human-induced climate change, making the Arctic an important potential source of methane emissions. According to scientific estimates, this region’s soils store five times more carbon than has been emitted by all human activities in the last 200 years.
NASA researchers combine the data from missions like ABoVE and the California Methane Survey with their knowledge of how methane behaves in the atmosphere to create methane computer models. These models can help scientists and policy makers understand past, current, and future atmospheric methane patterns.
Paths Toward Reduced Methane Emissions
Researchers in a variety of fields have looked into potential solutions to decrease global methane emissions. For example, biogas systems reduce methane emissions by transforming waste from livestock, crops, water and food into energy. Biogas is produced through the same natural process that occurs in landfills to break down organic waste. However, biogas systems harness the gas that is produced and use it as a clean, renewable and reliable energy source rather than let it release into the atmosphere as a greenhouse gas.
A study led by Professor Ermias Kebreab from the University of California-Davis discovered that introducing a few ounces of seaweed into beef cattle diets could reduce their methane emissions by over 82%. 8)
Russia’s forests store more carbon than previously thought
• August 4, 2021: Russia has the largest area of forest on the planet, with more than a fifth of the world's trees. A new study, led by Russian scientists using data from ESA’s Climate Change Initiative (CCI), has produced new estimates of biomass contained in Russian forests, and confirms that the vast forested area is storing more carbon than previously estimated. 9)
The study, published last month in Nature Scientific Reports, estimates that Russian forests contain 111 billion m3 of wood as of 2014 – which equates to 39% higher than the value reported to the Food and Agriculture Organization of the United Nations (FAO) and the United Nations Framework Convention on Climate Change (UNFCC). 10)
The study uses satellite-based maps of forest biomass, produced by ESA’s Climate Change Initiative (CCI) Biomass project, combined with Russian ground-based measurements, such as data from the National Forest Inventory and the ESA-supported Forest Observation System, to obtain more accurate figures of carbon stored in forests.
Remote-sensing studies have already indicated increases in vegetation productivity and tree cover over the past decades. Yet Russia has reported almost no change in growing stock (+ 1.8%) and biomass (+ 0.6%) since the collapse of the Soviet Union and transition to a new forest inventory system.
This new estimate is in line with the results from the National Forest Inventory, but expands its capacity in terms of spatial and temporal representation. It is expected to have a major impact on how Russia reports its forest carbon stock.
“The paper demonstrates that the current methodology for UNFCCC reporting needs updating. The method of using satellite-based data that is validated with ground-based measurements is best-placed to help with this,” says the study’s lead author Dmitry Schepaschenko, a researcher with the International Institute for Applied Systems Analysis in Austria (IIASA).
Figure 11: The map shows the above ground biomass in Russia, using data generated by ESA’s Climate Change Initiative (CCI) Biomass project [image credit: ESA (data source: CCI Biomass project)]
“Ground surveying is crucial in measuring biomass. However, the first forest national inventory cycle took 14 years in a country that’s as large as Russia, and is expected to provide a robust estimate at a national scale only. The combination of ground and space-based data has allowed us to provide the results for specific years in a higher spatial resolution and reduce uncertainties of the estimates.”
He continues: “Our team include representatives of Russian academic institutes, people from the National Forest Inventory and Forestry Agency – which insures the impact on national policy.”
The authors use the last Soviet Union report as a reference, and they found that Russian forests accumulated 1 billion m3 per year between 1988–2014, which balances the net forest stock losses reported in tropical countries.
The team found that the sequestered carbon over the same period was 47% higher than that reported in Russia’s UNFCCC National Greenhouse Gases Inventory.
But they warn that the forest gains won’t necessarily continue in the long-term: “While we found that Russian forests have been a more important carbon stock than previously thought, the situation is changing after 2014 because of the increasing severity of forest disturbances,” says Schepaschenko.
Figure 12: The team collecting samples of dead wood to quantify the carbon pool and associated fluxes (image credit: WRan Kong)
Forest disturbances can include forest fires, including those currently taking place in the Sakha-Yakutia region of Siberia, which have burned through 1.5 million hectares of land. The fires have shrouded Yakutia’s cities and towns in thick smoke, suspending all flights at the regional capital’s airport. In response to the wildfire, the International Charter Space and Major Disasters has been activated.
The new national estimate and uncertainty make an important contribution to improving ESA’s maps of above ground biomass stored by forests on a global-scale via ESA’s Climate Change Initiative Biomass project. The authors’ ground-based measurements will also help validate new satellite observations of biomass that will be provided by ESA’s upcoming Biomass mission.
Figure 13: This image captured by the Copernicus Sentinel-2 mission shows one of the many forest fires in the Sakha Republic, Siberia, on 25 July 2021. The image has been processed using the mission’s shortwave-infrared band to identify the active fires. Large clouds of smoke can be seen blowing in a southeast direction, while burn scars are visible in dark brown (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO) 11)
Index Ranks Rainforests’ Vulnerability to Climate and Human Impacts
• July 26, 2021: A new index shows that the world’s rainforests are responding differently to threats like a warming climate and deforestation. 12)
Scientists from NASA’s Jet Propulsion Laboratory in Southern California and other international research institutions have created a tropical rainforest vulnerability index. It will detect and evaluate the vulnerability of these diverse ecosystems to two main categories of threats: the warming and drying climate, and the consequences of human land use such as deforestation and fragmentation from encroaching roads, agricultural fields, and logging.
The index shows that the world’s three major rainforest areas have different degrees of susceptibility to these threats. The Amazon Basin in South America is extremely vulnerable to both climate change and changes in human land use. The Congo Basin in Africa is undergoing the same warming and drying trends as the Amazon but is more resilient. Most Asian rainforests appear to be suffering more from changes in land use than from the changing climate.
“Rainforests are perhaps the most endangered habitat on Earth – the canary in the climate-change coal mine,” said Sassan Saatchi, a JPL scientist and lead author of the new study published July 23 in the journal OneEarth. 13)
These diverse ecosystems are home to more than half of the planet’s life forms and contain more than half of all the carbon in land vegetation. They serve as a natural brake on the rise of carbon dioxide in the atmosphere from fossil fuel burning because they “breathe in” carbon dioxide and store carbon as they grow.
But in the last century, 15 to 20% of rainforests have been cut down, and another 10% have been degraded. Today’s warmer climate, which has led to increasingly frequent and widespread forest fires, is limiting the forests’ capacity to absorb carbon dioxide as they grow while also increasing the rate at which forests release carbon to the atmosphere as they decay or burn.
Figure 14: A rainforest in Malaysia (image credit: Wikimedia Common)
The National Geographic Society convened a team of scientists and conservationists in 2019 to develop the new index. The index is based on multiple satellite observations and ground-based data from 1982 through 2018, such as Landsat and the Global Precipitation Measurement (GPM) mission, covering climate conditions, land use, and forest characteristics.
When an ecosystem can no longer recover from stress as quickly or as completely as it used to, that’s a sign of its vulnerability. The researchers correlated data on stressors, such as temperature, water availability, and the extent of degradation with data on how well the forests are functioning: the amount of live biomass, the amount of carbon dioxide plants were absorbing, the amount of water the forests transpire into the atmosphere, the intactness of a forest’s biodiversity, and more. The correlations show how different forests have responded to stressors and how vulnerable the forests are now.
The team then used statistical models to extend trends over time, looking for areas with increasing vulnerability and possible tipping points where rainforests will transition into dry forests or grassy plains.
The data from the tropical rainforest vulnerability index provides scientists with an opportunity to perform more in-depth examinations of natural rainforest processes, such as carbon storage and productivity, changes in energy and water cycles, and changes in biodiversity. Those studies will help scientists understand whether there are tipping points and what they are likely to be. The information can also help policy makers who are planning for conservation and forest restoration activities.
NASA Study Finds Tropical Forests’ Ability to Absorb Carbon Dioxide Is Waning
• July 20, 2021: The finding comes out of an effort to map where vegetation is emitting and soaking up carbon dioxide from the atmosphere. 14)
Earth’s trees and plants pull vast amounts of carbon dioxide out of the atmosphere during photosynthesis, incorporating some of that carbon into structures like wood. Areas that absorb more carbon than they emit are called carbon sinks. But plants can also emit the greenhouse gas during processes like respiration, when dead plants decay, or during combustion in the case of fires. Researchers are particularly interested in whether – and how – plants at the scale of an ecosystem like a forest act as sources or sinks in an increasingly warming world.
A recent study led by scientists at NASA’s Jet Propulsion Laboratory in Southern California identified whether vegetated areas like forests and savannas around the world were carbon sources or sinks every year from 2000 to 2019. The research found that over the course of those two decades, living woody plants were responsible for more than 80% of the sources and sinks on land, with soil, leaf litter, and decaying organic matter making up the rest. But they also saw that vegetation retained a far smaller fraction of the carbon than the scientists originally thought.
In addition, the researchers found that the total amount of carbon emitted and absorbed in the tropics was four times larger than in temperate regions and boreal areas (the northernmost forests) combined, but that the ability of tropical forests to absorb massive amounts of carbon has waned in recent years. The decline in this ability is because of large-scale deforestation, habitat degradation, and climate change effects, like more frequent droughts and fires. In fact, the study, published in Science Advances, showed that 90% of the carbon that forests around the world absorb from the atmosphere is offset by the amount of carbon released by such disturbances as deforestation and droughts. 15)
Figure 15: The Amazon rainforest is often called “the lungs of the world.” It produces oxygen and stores billions of tons of carbon every year (image credit: USDA Forest Service photo by Diego Perez)
The scientists created maps of carbon sources and sinks from land-use changes like deforestation, habitat degradation, and forest planting, as well as forest growth. They did so by analyzing data on global vegetation collected from space using instruments such as NASA’s Geoscience Laser Altimeter System (GLAS) on board ICESat and the agency’s Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra and Aqua satellites, respectively. The analysis used a machine-learning algorithm that the researchers first trained using vegetation data gathered on the ground and in the air using laser-scanning instruments.
“A lot of research that has come before hasn’t been spatially explicit – we haven’t had a map of where carbon fluxes were occurring,” said Nancy Harris, research director of the forest program at the World Resources Institute in Washington and one of the study authors.
Other ways of estimating how much carbon is exchanged between vegetated areas and the atmosphere include looking at how many plants or forests are in a particular region and studying land-use changes, combining that information with carbon emission estimates. But those methods have spatial or temporal limitations that the study authors tried to address with their machine-learning method.
Knowing where plants are taking up carbon and where they’re emitting it is important for monitoring how forests and other vegetated regions respond to a changing climate. “The Amazon was considered a substantial carbon sink because of large tracts of pristine forest that soak up carbon dioxide,” said Sassan Saatchi, principal scientist at JPL and the study lead investigator. “However, our results show that overall, the Amazon Basin is becoming almost neutral in terms of carbon balance because deforestation, degradation, and the impacts of warming, frequent droughts, and fires over the past two decades release carbon dioxide to the atmosphere.”
Saatchi and his colleagues developed their analysis so that it’s easier to track changes in vegetated areas based on data collected on the ground as well as remotely. “Our approach is designed to make sure we can systematically balance the global carbon budget every year, and that countries can use the results and methodology for carbon management and their own reporting needs,” he said.
Figure 16: This map shows the change in how much carbon a vegetated area stored or emitted between the years 2000 and 2019. Greener areas absorbed more carbon than they emitted, while more pink and purple regions released more carbon than they stored. One megagram of carbon (MgC) is one metric ton (image credit: NASA/JPL-Caltech)
This budgeting analysis helped the researchers better understand the dynamics of how forests and other vegetated areas around the world were storing the carbon that they’re absorbing from the atmosphere. “Many previous studies found that vegetation around the world absorbs a lot of atmospheric carbon dioxide,” said study lead author Alan Xu, a carbon researcher at JPL and UCLA. “It gives the impression that global forests are growing and getting bigger everywhere, but that’s not the case.”
This study helps to fill in the picture of where and how trees and plants are absorbing or emitting carbon, but there’s more work to be done. The satellite-based carbon maps in this study covered about 39 square miles (100 km2) at a time, but they couldn’t necessarily pick up changes happening on smaller scales. And there was some information about how forests stored and emitted carbon within those maps that wasn’t necessarily accounted for in the researchers’ source-sink calculations. Some of these information gaps should be remedied by higher-resolution carbon maps provided by newer satellites already in orbit, as well as upcoming missions like the NASA-Indian Space Research Organization’s NISAR.
Saatchi is hopeful that having a more systematic and consistent approach to keeping track of which parts of the world are acting as carbon sources or sinks will enable better monitoring across regions and countries. “It could allow countries around the world to use the data as guidance for meeting their national commitments to the Paris Climate Agreement.”
ESA and NASA join forces to understand climate change
• July 13, 2021: Climate change is, arguably, the biggest environmental challenge the global population faces today. To address this major issue, decision-makers not only need accurate information on how our world is changing now, but also predictions on what may happen in the future. A sound knowledge of how Earth behaves as one system is the foundation to all of this – and the pieces of this complex puzzle come largely from satellites orbiting our planet. To ensure that data from Earth-observing satellites are used to their best advantage, further science and, ultimately, bring the most benefit to humankind, ESA and NASA have formed a strategic partnership for Earth science and climate change. 16)
NASA and ESA (European Space Agency) have formed a first-of-its-kind strategic partnership to observe Earth and its changing environment. The global climate is rapidly changing and the demand for accurate, timely, and actionable knowledge is more pressing than ever. Recognizing that climate change is an urgent global challenge, the timing is right for NASA and ESA, as partners in space, to join forces to lead and support a global response to climate change. The partnership is an effort to help address and mitigate climate change through monitoring Earth with combined efforts of both agencies in Earth science observations, research, and applications. 17)
“Climate change is an all-hands-on deck, global challenge that requires action – now,” said NASA Administrator Bill Nelson. “NASA and ESA are leading the way in space, building an unprecedented strategic partnership in Earth science. This agreement will set the standard for future international collaboration, providing the information that is so essential for tackling the challenges posed by climate change and helping to answer and address the most pressing questions in Earth science for the benefit of the United States, Europe, and the world.”
Figure 17: NASA Deputy Administrator Pam Melroy, left, NASA Administrator Bill Nelson, NASA Associate Administrator for International and Interagency Relations Karen Feldstein, and NASA Associate Administrator for Science Thomas Zurbuchen (all left side of image) and ESA (European Space Agency) Director General Josef Aschbacher are seen in a screen capture from a signing ceremony for a new NASA-ESA joint statement of intent aimed at addressing global climate change July 13, 2021 (image credit: NASA)
This is not the first time ESA and NASA have joined forces. For example, ESA and NASA teams worked together on field campaigns in the Arctic to validate their respective CryoSat and ICESat missions. They also work together and with other partners on the recently launched Copernicus Sentinel-6 mission, which is a new mission to extend the long-term record of sea-level rise.
The partnership was formalized through a joint statement of intent, signed Tuesday (13 July), which outlines how the agencies will collaborate to ensure continuity of Earth observations; advance understanding of the Earth System, climate change and application of that knowledge; and collaborate on an open data policy that promotes open sharing of data, information, and knowledge within the scientific community and the wider public.
“Together, NASA and ESA provide most of the world’s Earth science coverage through our Earth-observing satellites,” said Thomas Zurbuchen, NASA associate administrator for science. “This transformative agreement will build on that capability, forging a critical international climate science partnership to tackle the most challenging climate questions in an integrated and strategic way. Not only will NASA and ESA work together to deliver unparalleled Earth science observations, research, and applications, but all of our findings will also be free and open for the benefit of the entire world as we work together to combat and mitigate climate change.”
NASA and ESA have a long and successful history working together to understand climate change. In 2020, NASA, National Oceanic and Atmospheric Administration (NOAA) and European partners, including ESA, launched the Sentinel-6 Michael Freilich satellite, which is collecting the most accurate data yet on global sea level and how oceans are rising in response to climate change. The mission also is collecting data of atmospheric temperature and humidity that will help improve climate models and weather forecasts.
“Without doubt, space is the best vantage point to measure and monitor climate change, but joining forces is also key to tackling this global issue,” said Josef Aschbacher, ESA director general. “This is why today’s agreement between our organizations is so crucial. Timing is also important, particularly as we look to the COP26 climate conference later this year, where we have the chance to further make space an integral part of the solution when it comes to climate-change mitigation.”
In May, NASA announced its Earth System Observatory, which will design a new set of Earth-focused missions to provide key information to guide efforts related to climate change, disaster mitigation, fighting forest fires, and improving real-time agricultural processes. The joint statement of intent complements activities underway for the Earth System Observatory.
Climate adaptation and mitigation efforts cannot succeed without robust climate observations and research. NASA has more than two dozen satellites and instruments observing how the planet is changing and measuring key climate indicators, such as the height of oceans and inland waters, clouds and precipitation, and carbon dioxide.
Study Projects a Surge in Coastal Flooding, Starting in 2030s
• July 7, 2021: In the mid-2030s, every U.S. coast will experience rapidly increasing high-tide floods, when a lunar cycle will amplify rising sea levels caused by climate change. 18)
- High-tide floods – also called nuisance floods or sunny day floods – are already a familiar problem in many cities on the U.S. Atlantic and Gulf coasts. The National Oceanic and Atmospheric Administration (NOAA) reported a total of more than 600 such floods in 2019. Starting in the mid-2030s, however, the alignment of rising sea levels with a lunar cycle will cause coastal cities all around the U.S. to begin a decade of dramatic increases in flood numbers, according to the first study that takes into account all known oceanic and astronomical causes for floods.
- Led by the members of the NASA Sea Level Change Science Team from the University of Hawaii, the new study shows that high tides will exceed known flooding thresholds around the country more often. What’s more, the floods will sometimes occur in clusters lasting a month or longer, depending on the positions of the Moon, Earth, and the Sun. When the Moon and Earth line up in specific ways with each other and the Sun, the resulting gravitational pull and the ocean’s corresponding response may leave city dwellers coping with floods every day or two.
- “Low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and it will only get worse,” said NASA Administrator Bill Nelson. “The combination of the Moon’s gravitational pull, rising sea levels, and climate change will continue to exacerbate coastal flooding on our coastlines and across the world. NASA’s Sea Level Change Team is providing crucial information so that we can plan, protect, and prevent damage to the environment and people’s livelihoods affected by flooding.”
- “It’s the accumulated effect over time that will have an impact,” said Phil Thompson, an assistant professor at the University of Hawaii and the lead author of the new study, published this month in Nature Climate Change. Thompson pointed out that because high-tide floods involve a small amount of water compared to hurricane storm surges, there’s a tendency to view them as a less significant problem overall. “But if it floods 10 or 15 times a month, a business can’t keep operating with its parking lot under water. People lose their jobs because they can’t get to work. Seeping cesspools become a public health issue.”
Figure 18: High-tide flooding in Honolulu (image credit: Hawaii Sea Grant King Tides Project)
- Why will cities on such widely separated coastlines begin to experience these higher rates of flooding at almost the same time? The main reason is a regular wobble in the Moon’s orbit that takes 18.6 years to complete. There’s nothing new or dangerous about the wobble; it was first reported in 1728. What’s new is how one of the wobble’s effects on the Moon’s gravitational pull – the main cause of Earth’s tides – will combine with rising sea levels resulting from the planet’s warming.
- In half of the Moon’s 18.6-year cycle, Earth’s regular daily tides are suppressed: High tides are lower than normal, and low tides are higher than normal. In the other half of the cycle, tides are amplified: High tides get higher, and low tides get lower. Global sea level rise pushes high tides in only one direction – higher. So half of the 18.6-year lunar cycle counteracts the effect of sea level rise on high tides, and the other half increases the effect.
- The Moon is in the tide-amplifying part of its cycle now. However, along most U.S. coastlines, sea levels have not risen so much that even with this lunar assist, high tides regularly top flooding thresholds. It will be a different story the next time the cycle comes around to amplify tides again, in the mid-2030s. Global sea level rise will have been at work for another decade. The higher seas, amplified by the lunar cycle, will cause a leap in flood numbers on almost all U.S. mainland coastlines, Hawaii, and Guam. Only far northern coastlines, including Alaska’s, will be spared for another decade or longer because these land areas are rising due to long-term geological processes.
- The researchers uncovered these tipping points in flood numbers by studying 89 tide gauge locations in every coastal U.S. state and territory but Alaska. They created a new statistical framework that mapped NOAA’s widely used sea level rise scenarios and flooding thresholds, the number of times those thresholds have been exceeded annually, astronomical cycles, and statistical representations of other processes, such as El Niño events, that are known to affect tides. They projected results to 2080.
- Ben Hamlington of NASA’s Jet Propulsion Laboratory in Southern California is a co-author of the paper and also the leader of NASA’s Sea Level Change Team. He notes that the findings of the new study are a vital resource for coastal urban planners, who may be focused on preparing for extreme events rather than more high-tide floods.
- “From a planning perspective, it’s important to know when we’ll see an increase,” Hamlington said. “Understanding that all your events are clustered in a particular month, or you might have more severe flooding in the second half of a year than the first – that’s useful information.” A high-tide flood tool developed by Thompson already exists on the NASA team’s sea level portal, a resource for decision-makers and the general public. The flood tool will be updated in the near future with the findings from this study. 19)
Ocean Circulation Helps Explain Uncertainties in Climate Change Predictions
• June 16, 2021: Thirty state-of-the-art International Panel on Climate Change (IPCC)–climate models predict dramatically different climates for the Northern Hemisphere, especially Europe. An analysis of the range of responses now reveals that the differences are mostly down to the individual model's simulations of changes to the North Atlantic ocean currents and not only—as normally assumed—atmospheric changes. 20)
The work, by Katinka Bellomo, National Research Council of Italy, Institute of Atmospheric Sciences and Climate, and colleagues is published in Nature Communications and is part of the European science collaboration, TiPES (Tipping Points in the Earth System), coordinated by the University of Copenhagen. 21)
All climate models vary in the details. Variables such as atmospheric pressure, cloud cover, temperature gradients, sea surface temperatures, and many more are tuned to interact slightly differently for every model. This means, the predictions of the many models also vary.
International modelling centers run a coordinated set of climate model simulations, which are then assessed by the IPCC and summarized in a balanced report. But naturally, an uncertainty remains, reflecting the many different details of models.
"We want to understand the differences among these models. Why does one model project an overall global temperature change of two degrees while another one of four degrees? Our objective is to narrow down this inter-model uncertainty. We also want to understand the differences in these models in terms of regional climate change," explains Bellomo.
Two types of climate scenarios
Bellomo and colleagues analyzed simulations from 30 different climate models and found an important difference. There is disagreement among the models on the rate of the decline in the Atlantic meridional overturning circulation (AMOC), a large system of ocean currents in the North Atlantic which overturns surface water to a deep ocean current and plays a crucial role in the distribution of heat from the tropics to the Northern Hemisphere.
"To see how this difference was reflected in projections of the future climate, we grouped together the top 10 models (from a total of 30) in which the AMOC decline is smaller. We then compared the group with the average of the 10 models that have the largest decline," explains Bellomo.
The analysis revealed two distinct types of climate scenarios. In models where the AMOC decline is large, Europe warms only slightly, but wind patterns in Europe and precipitation patterns in the tropics change dramatically. However, in models where the AMOC decline is smaller, the Northern hemisphere heats up considerably, and a well-known pattern of wet-regions-get- wetter, dry-get-dryer emerges.
Tease mechanisms apart
This means, that the uncertainties in predictions of the future climate may to a large degree depend on how climate models predict changes in the overturning circulation in the North Atlantic. Thus, the result challenges the previous understanding of mechanisms controlling climate change over the North Atlantic, in which parameterizations of the atmosphere have been suspected to cause the main part of the uncertainty.
"This is important because it points to the AMOC as one of the largest sources of uncertainties in climate prediction," says Bellomo.
"I am excited about this research because there is so much more that can be done in addition to this. We need to investigate the processes leading to the inter-model differences in the ocean circulation response, the link between the ocean circulation response and precipitation change, and we also need to compare this with near-future projections of climate change," says Bellomo.
The TiPES project, investigating tipping points in the Earth system has received funding from the EU Horizon 2020 Research and Innovation program.
Joint NASA, NOAA Study Finds Earth's Energy Imbalance Has Doubled
• June 15, 2021: Earth's climate is determined by a delicate balance between how much of the Sun's radiative energy is absorbed in the atmosphere and at the surface and how much thermal infrared radiation Earth emits to space. A positive energy imbalance means the Earth system is gaining energy, causing the planet to heat up. The doubling of the energy imbalance is the topic of a recent study, the results of which were published June 15 in Geophysical Research Letters. 22) 23)
- Scientists at NASA and NOAA compared data from two independent measurements. NASA's Clouds and the Earth's Radiant Energy System (CERES) suite of satellite sensors measure how much energy enters and leaves Earth's system. In addition, data from a global array of ocean floats, called Argo, enable an accurate estimate of the rate at which the world’s oceans are heating up. Since approximately 90 percent of the excess energy from an energy imbalance ends up in the ocean, the overall trends of incoming and outgoing radiation should broadly agree with changes in ocean heat content.
- "The two very independent ways of looking at changes in Earth's energy imbalance are in really, really good agreement, and they're both showing this very large trend, which gives us a lot of confidence that what we're seeing is a real phenomenon and not just an instrumental artifact, " said Norman Loeb, lead author for the study and principal investigator for CERES at NASA's Langley Research Center in Hampton, Virginia. "The trends we found were quite alarming in a sense."
Figure 19: Researchers have found that Earth’s energy imbalance approximately doubled during the 14-year period from 2005 to 2019. Click image to animate: Comparison of overlapping one-year estimates at 6-month intervals of net top-of-the-atmosphere annual energy flux from CERES (solid orange line) and an in situ observational estimate of uptake of energy by Earth climate system (solid turquoise line), image credit: NASA/Tim Marvel
- Increases in emissions of greenhouse gases such as carbon dioxide and methane due to human activity trap heat in the atmosphere, capturing outgoing radiation that would otherwise escape into space. The warming drives other changes, such as snow and ice melt, and increased water vapor and cloud changes that can further enhance the warming. Earth’s energy imbalance is the net effect of all these factors. In order to determine the primary factors driving the imbalance, the investigators used a method that looked at changes in clouds, water vapor, combined contributions from trace gases and the output of light from the Sun, surface albedo (the amount of light reflected by the Earth's surface), tiny atmospheric particles called aerosols, and changes in surface and atmospheric temperature distributions.
- The study finds that the doubling of the imbalance is partially the result an increase in greenhouse gases due to human activity, also known as anthropogenic forcing, along with increases in water vapor are trapping more outgoing longwave radiation, further contributing to Earth’s energy imbalance. Additionally, the related decrease in clouds and sea ice lead to more absorption of solar energy.
- The researchers also found that a flip of the Pacific Decadal Oscillation (PDO) from a cool phase to a warm phase likely played a major role in the intensification of the energy imbalance. The PDO is a pattern of Pacific climate variability. Its fingerprint includes a massive wedge of water in the eastern Pacific that goes through cool and warm phases. This naturally occurring internal variability in the Earth system can have far-reaching effects on weather and climate. An intensely warm PDO phase that began around 2014 and continued until 2020 caused a widespread reduction in cloud coverage over the ocean and a corresponding increase in the absorption of solar radiation.
- "It's likely a mix of anthropogenic forcing and internal variability," said Loeb. "And over this period they're both causing warming, which leads to a fairly large change in Earth's energy imbalance. The magnitude of the increase is unprecedented."
- Loeb cautions that the study is only a snapshot relative to long-term climate change, and that it's not possible to predict with any certainty what the coming decades might look like for the balance of Earth's energy budget. The study does conclude, however, that unless the rate of heat uptake subsides, greater changes in climate than are already occurring should be expected.
- "The lengthening and highly complementary records from Argo and CERES have allowed us both to pin down Earth’s energy imbalance with increasing accuracy, and to study its variations and trends with increasing insight, as time goes on." said Gregory Johnson, co-author on the study and physical oceanographer at the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory in Seattle, Washington. "Observing the magnitude and variations of this energy imbalance are vital to understanding Earth’s changing climate."
The rocky road to accurate sea-level predictions
• June 11, 2021: The type of material present under glaciers has a big impact on how fast they slide towards the ocean. Scientists face a challenging task to acquire data of this under-ice landscape, let alone how to represent it accurately in models of future sea-level rise. “Choosing the wrong equations for the under-ice landscape can have the same effect on the predicted contribution to sea-level rise as a warming of several degrees,” says Henning Åkesson, who led a new published study on Petermann Glacier in Greenland. 24)
Figure 20: Swedish icebreaker Oden at the front of Petermann Ice Shelf in 2019. The new study shows that this ice shelf may break up if ocean warming continues. Photo: Martin Jakobsson)
- Glaciers and ice sheets around the world currently lose more than 700,000 Olympic swimming pools of water every day. Glaciers form by the transformation of snow into ice, which is later melted by the atmosphere in summer, or slides all the way into the sea. With climate change, glaciers are breaking up and drop icebergs into the ocean at an accelerating pace. Exactly how fast depends to a large extent on the bed below all the ice. Glaciers conceal a landscape under the ice covered by rocks, sediments and water. A new study shows that the way we represent this under-ice landscape in computer models means a great deal for our predictions of future sea-level rise. More specifically, how we incorporate the friction between the ground and the ice sliding over it in glacier models is what affects our predictions. This was found by a team of Swedish and American scientists, when they simulated the future of Petermann Glacier, the largest and fastest glacier in northern Greenland.
Figure 21: The 20 km-wide Petermann Fjord with the ice shelf in the far distance (Photo: Martin Jakobsson)
- Petermann is one of the few glaciers in the northern hemisphere with a remaining ice tongue, a type of floating glacier extension otherwise mainly found in Antarctica, where they are called ice shelves. These floating extensions have been found to be exposed to warm subsurface water flowing from the open ocean towards the glaciers. This happens both in Antarctica and in many fjords around Greenland, including the Petermann Fjord. “Petermann lost 40% of its floating ice tongue over the last decade. It still has a 45 km tongue, but we found that a slightly warmer ocean than today would lead to its break up, and trigger a retreat of the glacier”, says Henning Åkesson, a postdoctoral researcher at Stockholm University who led the study. 25)
- Many glaciers in Greenland and Antarctica flow towards the ocean much faster than they did a few decades ago, and therefore contribute more to global sea-level rise. Scientists have therefore mobilized great efforts into learning what is going on in these environments. This has spurred new insights into the landscape under glaciers and the shape of the seafloor where they drain. We now also know much more about what happens to the ice when glaciers meet the sea.
- Still, the remote polar regions are notoriously difficult to study because of sea ice, icebergs, and often harsh weather. The under-ice landscape is a particular challenge because, frankly, it is hard to measure something covered by a kilometer of ice on top. Even in areas of known under-ice topography, describing its physical properties using mathematical equations is difficult. Computer models are therefore still somewhat in the dark when it comes to how to represent things like sediments, rocks, ponds and rivers under glaciers in the equations that describe ice flow. These equations are ultimately the foundation of the models used by the IPCC to estimate how fast glaciers flow and how much sea levels will rise under future climate warming.
- “Choosing the wrong equations for the under-ice landscape can have the same effect on the contribution to sea-level rise as a warming of several degrees”, Åkesson says. “In fact, predicted sea-level rise for this Greenland glacier can quadruple depending on how we represent friction under the ice. We still don’t know which way is the best, but our study illustrates that ice-sheet models still need to progress in this respect, in order to improve our estimates of mass loss from Earth’s polar ice sheets.”
Local Lockdowns Brought Fast Global Ozone Reductions, NASA Finds
• June 09, 2021: When lockdowns during the coronavirus pandemic cut local nitrogen oxide emissions, the effect on ozone pollution was global and unexpectedly rapid. 26)
- As the coronavirus pandemic slowed global commerce to a crawl in early 2020, emissions of nitrogen oxides (NOx) – which create ozone, a danger to human health and to climate – decreased 15% globally, with local reductions as high as 50%, according to a study led by scientists at NASA’s Jet Propulsion Laboratory in Southern California. As a result of the lower NOx emissions, by June 2020, global ozone levels had dropped to a level that policymakers thought would take at least 15 years to reach by conventional means, such as regulations.
Figure 22: As the coronavirus pandemic slowed global commerce to a crawl in early 2020, emissions of nitrogen oxides (NOx) – which create ozone, a danger to human health and to climate – decreased 15% globally with local reductions as high as 50%, according to a study led by scientists at NASA's Jet Propulsion Laboratory (video credit: NASA's Goddard Space Flight Center, Scientific Visualization Studio)
- The study shows that innovative technologies and other solutions intended to decrease NOx locally have the potential to rapidly improve air quality and climate globally. It published today in Science Advances. 27)
- Ozone protects us from destructive solar radiation when it’s high above Earth in the stratosphere. Closer to the ground, though, it has other lasting impacts. Ozone at the surface was estimated to cause 365,000 deaths globally in 2019 by damaging the lungs of vulnerable people, such as young children and those with asthma. Similarly, it damages the breathing systems of plants – their ability to photosynthesize – reducing plant growth and crop yields. And at the top of the troposphere, it’s a potent greenhouse gas, increasing global temperatures.
- When the world went into lockdown, scientists had an unprecedented opportunity to study how human activity interacts with natural Earth system processes at regional and global scales. A team of international researchers led by JPL scientist Kazuyuki Miyazaki used this opportunity to research the two main oxides of nitrogen: nitrogen oxide and nitrogen dioxide, collectively called NOx. They charted the chain of events from reduced fossil fuel burning during lockdowns to reduced local NOx emissions and finally to reduced global tropospheric ozone pollution. The more stringent the lockdown a nation imposed, the greater the reduction in emissions. For example, China’s stay-at-home orders in early February 2020 produced a 50% drop in NOx emissions in some cities within a few weeks; most U.S. states achieved a 25% drop later in the spring.
- The total result of the reduced NOx emissions was a 2% drop in global ozone – half the amount that the most aggressive NOx emission controls considered by the Intergovernmental Panel on Climate Change, the authoritative body of international experts on climate, were expected to produce over a 30-year period.
- Ozone reductions from the reduced NOx emissions quickly spread both around the globe and from the surface upward more than 6 miles (10 kilometers). “I was really surprised at how large the impact on global ozone was,” said JPL scientist Jessica Neu, a co-author of the new study. “We expected more of a local response at the surface.”
- he reactions that transform NOx into ozone require sunlight and depend on many additional factors, such as weather and what other chemicals are in the air. These factors interact in so many ways that, in some circumstances, reducing NOx emissions actually increases ozone. So researchers can’t understand or predict ozone concentrations from NOx emissions data alone. That requires a more thorough analysis, like this study.
- The researchers used measurements of NOx, ozone, and other atmospheric gases from five NASA and ESA (European Space Agency) Earth-observing satellites. They fed the multiple satellite observations into four numerical models of atmospheric chemical reactions and weather, using a data analysis system developed at JPL. They found that the changes in the models’ atmospheres matched the satellite observations well and reproduced known increases and decreases in emissions as regions went into and out of lockdowns. These findings indicate that both NOx emissions and global ozone will climb again as the world economy revs back up.
- “I was very happy that our analysis system was able to capture the detailed changes in emissions across the world,” said Miyazaki. “The challenging and unprecedented nature of this work is a testament to improvements in satellite monitoring in service of societal needs.” This new capability of combining multiple types of satellite observations and models is already unlocking new understanding of Earth’s atmosphere and how it is changing.
- The research team also included scientists from the Japan Agency for Marine-Earth Science and Technology in Yokohama, Nagoya University in Japan, and the Royal Netherlands Meteorological Institute in De Bilt.
Satellites Show How Earth’s Water Cycle Is Ramping Up as Climate Warms
• May 27, 2021: NASA scientists have studied 17 years of gravity observations of our planet to understand how the global water cycle is changing. 28)
Figure 23: This image shows a forest giving off moisture into the air, or transpiring. When combined with moisture that evaporates from the land, both processes drive evapotranspiration, a key branch of the water cycle. As the climate warms, these processes are expected to intensify (image credit: © Acarapi / Adobe Stock)
The rate at which plants and the land surface release moisture into the air has increased on a global scale between 2003 and 2019. These processes are collectively known as evapotranspiration, and a new NASA study has calculated its increase by using observations from gravity satellites.
By gauging the mass change of water between the oceans and the continents, the researchers determined that evapotranspiration’s rate of increase is up to two times higher than previous estimates. This is important because evapotranspiration represents a critical branch of the global water cycle – a cycle that creates the conditions for life on land.
While it is known that a warming climate should increase the rate of evapotranspiration, accurate global measurements have, until now, been elusive.
“Our study found that evapotranspiration has increased by about 10% since 2003, which is more than previously estimated, and is mostly due to warming temperatures,” said Madeleine Pascolini-Campbell, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory in Southern California, who led the study. “We hope that this information about the water cycle will help to better inform the development and validation of climate models.” 29)
But how does the rate of evapotranspiration affect the global water cycle? As moisture from the oceans circulates through the atmosphere, a portion falls as precipitation over the continents. Some of this water goes into rivers as runoff, and some seeps into soils. The remaining water evaporates from the land and transpires from plants back into the air.
Finding that evapotranspiration is increasing at a faster rate than previously known has implications for understanding how climate change could impact Earth in the future. As the world warms, evapotranspiration will accelerate, speeding up the drying of land and vegetation. Weather patterns can also be affected: Increased evaporation from land can create droughts in some regions. This is a symptom of a warming world that can have major consequences for ecosystems and human societies as stress on surface and groundwater supplies increases.
“Images of melting glaciers and shrinking ice sheets are a palpable way for us to understand the impacts of global warming,” said Pascolini-Campbell. “But dramatic changes are also happening to other key components of our planet’s water cycle that aren’t so visible, such as when water evaporates from the land before it can enter the rivers as runoff.”
The Gravity of Water
To get a global estimate of how evapotranspiration is changing, researchers found a new way to leverage data collected by the pair of Gravity Recovery and Climate Experiment (GRACE) satellites that operated from 2002 to 2017, and the successor pair, GRACE Follow-On, that launched in 2018. The GRACE mission was launched by NASA and the German Aerospace Center (DLR), and GRACE-FO is a partnership between NASA and German Research Centre for Geosciences (GFZ).
Because water has mass and therefore contributes to the Earth’s gravity signal, these spacecraft are exquisitely sensitive to the movement of water around the world, from tracking changes in ice sheets to water stored on land to variations in ocean mass. Seeing an opportunity, the researchers studied the 17-year dataset from GRACE and GRACE-FO to see if it was possible to tease out the gravitational signal associated with the movement of water by evapotranspiration.
“With the combined record of GRACE and GRACE-FO, we now have a long-enough observational record to be able to monitor these critical signs of global change,” said J. T. Reager, a JPL scientist and an investigator on the study. “When the gravity signal decreases, it means the land is losing water. Some of that loss is through rivers flowing back into the oceans, but the rest of it goes up into the atmosphere as evapotranspiration.”
By subtracting all the water mass outputs from the inputs over land and then calculating the residual mass of water, the researchers were able to estimate the rate of evapotranspiration. They did this by subtracting independent estimates of global river discharge (in other words, the rate of water flowing through rivers to the ocean) and GRACE and GRACE-FO satellite data (that reveal the local changes in water mass on and in the ground) from global precipitation measurements to find out the mass of water being lost to the atmosphere.
Due to observational and measurement challenges, global estimates of evapotranspiration are typically approximated using models or by taking measurements from individual locations and then scaling those measurements up. But these methods can be prone to error. By measuring global mass changes using gravity satellite observations, however, the researchers were able to get a more precise estimate for the rate of global evapotranspiration.
Using this method, they found that evapotranspiration increased from 405 mm (about 16 inches) per year in 2003 to 444 mm (about 17.5 inches) per year in 2019. That represents an upward trend of 2.30 mm (about 0.1 inches) per year –a 10% increase – with a corresponding uncertainty of 0.5 mm (0.02 inches) per year, or 2%.
“For years, we’ve been looking for a way to measure gross changes in the global water cycle, and finally we’ve found it,” said Reager. “The magnitude of the evapotranspiration increases really surprised us: This is a sizable signal indicating our planet’s water cycle is changing.”
These results add to a growing body of research about our planet’s water cycle while also underlining the importance of continuity for Earth observations. Continuous satellite observations by satellites with a global view of water mass changes provide the long record necessary to observe the changing planet over the decades. These observations also help scientists track year-to-year variability in the water cycle caused by climate change and natural cycles.
What a Glacial River Reveals About the Greenland Ice Sheet
• April 5, 2021: With data from a 2016 expedition, scientists supported by NASA are shedding more light into the complex processes under the Greenland Ice Sheet that control how fast its glaciers slide toward the ocean and contribute to sea level rise. 30)
On the surface of the ice sheet, bottomless sinkholes called moulins can funnel meltwater into the base of the ice. As that water reaches the ice sheet’s underlying bed, it can make the ice detach slightly and flow more rapidly.
Glaciers that slide faster can eventually lead to the ice sheet melting a bit faster than expected, also increasing the amount of ice calved into the ocean. With a vast surface area roughly the size of Mexico, Greenland’s melting ice is the largest contributor to global sea level rise.
In a new study, published April 5 in Geophysical Research Letters, the authors concluded that the one important factor influencing the speed of a sliding glacier in southwest Greenland was how quickly water pressure changed within cavities at the base of the ice where meltwater met bedrock. 31)
Figure 24: At the fringes of the Greenland Ice Sheet, where glaciers are constantly melting, water rushes everywhere through an intricate system of lakes and streams that branch out like slip and slide shoots of super chilled, bright turquoise water. Some of that water eventually cascades straight into the surrounding land and ocean through channels and cracks. Some of it thunders off into sinkhole-like structures on the ice called moulins. Rumbling 24 hours a day, these holes swallow water from the surface and funnel it to the bedrock at the base of the ice (image credit: Laurence C. Smith)
“Even if the cavities are small, as long as the pressure is ramping up very fast, they will make the ice slide faster,” said Dr. Laurence C. Smith, a professor of environmental studies and Earth, environmental, and planetary sciences at Brown University in Providence, Rhode Island.
It’s the first time observations directly from field research show how changes in the volume of water under the Greenland Ice Sheet drive the flow velocities of a glacier.
The findings contradict a long-held view about ice sliding velocities and water stored under a glacier known as steady-state basal sliding law, which has helped scientists predict how fast ice sheets will slide based on the total volume of water underneath the ice.
Figure 25: Five years after a NASA-funded field study returned to to set up camp once again in the melt zone of the Greenland Ice Sheet, a new study adds to the rich findings from this innovative project. We look back on this bold undertaking, which featured helicopters, floating drifters plunging into holes in the ice, and all-night shifts operating a sonic boogie board under endless daylight. Scientist Larry Smith, at the time with UCLA and now with Brown University, takes us back to the challenges on the ice and the important findings made with the hard-won data (video credits: NASA's Goddard Space Flight Center/Scientific Visualization Studio; Additional field footage courtesy UCLA)
Dr. Lauren Andrews, a glaciologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, likes to explain the interactions between surface meltwater, basal ice, and the bedrock, as tires that slide very rapidly on a wet road because of hydroplaning.
“If you have a rapid perturbation of water going into the subglacial system, you overwhelm the system, and so you create essentially a layer of water at the interface that's not contained in channels or cavities anymore,” Andrews said.
It's not the actual volume in water that drives ice velocity, she explained, but the speed with which it builds up at a bedrock ice interface. For slow increases in water the subglacial system has time to evolve to accommodate the same amount of water.
Until recently, the lack of data directly from the ground had made it difficult for scientists to probe the interactions that speed up glaciers in Greenland. One of the trickiest aspects preventing scientists from fully understanding ice sliding dynamics is the need to pair measurements of the flow of meltwater into a glacier with observations of the motion of the ice at the surface.
The research team set camp on Russell Glacier near Kangerlussuaq, Greenland, and studied a glacial river named to honor the late NASA researcher Alberto Behar. By comparing GPS measurements of the motion of ice at the surface with the amount of meltwater discharging into a vertical shaft in the glacier, known as a moulin, as well as meltwater exiting the glacier’s edge, the team identified changes in water stored under the ice that corresponded with small accelerations in the ice at the surface. Past research on small alpine glaciers guided the design of the study.
“There's not a direct one-to-one relationship between the melting on the top and the meltwater exiting the ice sheet because the water is going through goodness knows what down below,” Smith said.
The new findings will be valuable for satellites such as the upcoming NISAR satellite mission, a joint Earth-observing mission between NASA and the Indian Space Research Organization (ISRO), which will measure changes in ice surface velocity with unprecedented resolution for the entire Greenland and Antarctic ice sheets, said Thorsten Markus, Cryospheric Science program manager at NASA. Projected to launch no earlier than 2022, NISAR may also enable further studies of ice surface velocities at much larger scales.
Eventually, combining satellite observations with data acquired from the ground can help scientists as they consider adjusting their models to represent the hydrology at the base of ice sheets more accurately.
Integrating new data in models is a gradual process, but Smith hopes the new findings can improve how climate models predict the pace of future sea level rise from Greenland’s ice in the face of climate change.
“The only tools that we have to predict the future are models,” Smith said. “We have remote sensing, and we have field campaigns, so if we can use both to improve our modeling capability, we'll be better able to adapt and mitigate sea level rise and climate change.”
The fieldwork is one of many projects NASA has supported over the last two decades to interpret satellite observations and study the Greenland Ice Sheet using local field data.
Satellite observations prove crucial in new climate science report
• February 2, 2021: With impacts from climate change threatening major disruption to society in the coming years, leading scientists have released a compilation of the 10 most important insights on climate to help inform collective action on the ongoing climate crisis, in which satellites have played a crucial role in aiding scientific understanding. 32)
The report, presented last week to Patricia Espinosa, Executive Secretary of the United Nations Framework Convention on Climate Change (UNFCCC), summarizes the most important results over the past 12 months within the field of climate science.
These findings range from improved models that underline the need for aggressive emission cuts in order to meet the Paris Agreement, to the impact of climate change on our mental health. The report also points out a number of growing risk factors, including the risk of weakening carbon uptake by land ecosystems, as well as significant emissions from abrupt thaw of permafrost.
The report was prepared by a consortium of 57 leading researchers from 21 countries as a partnership of Future Earth, the Earth League, and the World Climate Research Program (WCRP) and has been published annually since 2017.
Sophie Hebden, Future Earth liaison seconded to ESA’s Climate Office, commented, “This report is unique in providing a particularly broad view of the latest, most important climate research insights we should all be aware of. It highlights the current state of knowledge on the environmental risks posed by climate change, its impacts on society and human well-being, as well as the opportunities emerging from research into climate change economics and governance.”
Emissions of greenhouse gases from permafrost are likely to be worse than expected because of abrupt thaw processes, which are not yet included in global climate models. These abrupt thaw effects could as much as double the emissions from permafrost thaw under moderate and high emission scenarios (see Figure 40).
Satellite observations are fundamental in monitoring abrupt thaw of permafrost, which is visible as surfaces collapse across the Arctic landscape, producing slumps, gullies and wetland areas that are expected to substantially increase carbon emissions from permafrost this century as climate warms. Permafrost is one of the ‘essential climate variables’ defined by the Global Climate Observing System.
Through ESA’s Climate Change Initiative, research teams have compiled climate data records of permafrost temperature and extent over decades, as well as snow cover, that can be used to determine trends and understand more about how permafrost is changing and how it fits into the climate system.
In December 2020, ESA-funded researchers developed and released the longest satellite-derived permafrost record currently available. Long-term satellite-derived records, such as these, are a key tool to evaluate and improve global climate models and confidence in the predictions of both future emissions and change.
The new report also details the uptake of carbon by land ecosystems which is being eroded by human-driven land-use change, particularly in the tropics. Other factors, such as water stress and permafrost thaw, could further impede the land sink.
Several knowledge gaps exist regarding how climate change will affect the ability of land-based ecosystems to absorb greenhouse gases from the atmosphere. Better quantification of land-use change is therefore key for a better understanding of the natural land sink.
ESA is making significant contributions in monitoring the storage of carbon on land through its Climate Change Initiative (CCI) Biomass project which provides global maps of above-ground biomass.
As well as this, ESA’s CCI Land Cover Project releases annual maps of land cover types worldwide, helpful in tracking changes. These, combined with other CCI datasets such as land surface temperature and fire, can be used in climate and vegetation models, enabling researchers to improve their understanding of the ability of the land to store carbon.
Figure 26: Biomass: quantifying carbon. Satellite data was used to create a map of above-ground Biomass for 2017-18. The new map uses optical, lidar and radar data acquired in 2017 and 2018 from multiple Earth observation satellites, and is the first to integrate multiple acquisitions from the Copernicus Sentinel-1 mission and Japan’s ALOS mission (image credit: biomass_cci project funded under ESA's Climate Change Initiative)
Clement Albergel, Climate Applications Scientist at ESA’s Climate Office, commented, “Assuming a dynamic equilibrium, fire has a negligible net effect on the long-term carbon budget because fire-induced carbon loss is eventually compensated by subsequent vegetation growth as the ecosystem recovers. However, shifts in fire regimes could result in long-term carbon loss, or gain, if they lead to differing states of carbon pools.”
“By using satellite-derived products, such as burned areas and land cover changes from ESA’s CCI Fire and Land Cover projects, and combining these data into both fire emission and dynamic global vegetation models, allows us to determine land-use change carbon dioxide emissions.”
ESA’s Climate Change Initiative provides a wide range of stable, long-term, satellite-based essential climate variable data products derived from multiple satellite datasets, through international collaboration – not only key to understanding the changes taking place through climate change, but essential for climate policy.
Warming Seas Are Accelerating Greenland’s Glacier Retreat
• January 25, 2021: Scientists with NASA’s Oceans Melting Greenland (OMG) mission are probing deep below the island’s warming coastal waters to help us better predict the rising seas of the future. 33)
Greenland’s melting glaciers, which plunge into Arctic waters via steep-sided inlets, or fjords, are among the main contributors to global sea level rise in response to climate change. Gaining a better understanding of how warming ocean water affects these glaciers will help improve predictions of their fate. Such predictions could in turn be used by communities around the world to better prepare for flooding and mitigate coastal ecosystem damage.
But researchers have long lacked measurements of the depths of the fjords along Greenland’s craggy coast. Without this information, it’s extremely difficult to arrive at a precise assessment of how much ocean water is being allowed into the fjords and how that affects glacier melt. By measuring their fjords one by one, a new study published in Science Advances has quantified, for the first time, how the warming coastal waters are impacting Greenland’s glaciers.
Figure 27: To measure water depth and salinity, the OMG project dropped probes by plane into fjords along Greenland's coast. Shown here is one such fjord in which a glacier is undercut by warming water (image credit: NASA/JPL-Caltech)
For the past five years, scientists with the Oceans Melting Greenland (OMG) mission have been studying these marine-terminating glaciers from the air and by ship. They found that of the 226 glaciers surveyed, 74 in deep fjords accounted for nearly half of the total ice loss (as previously monitored by satellites) from Greenland between 1992 and 2017. These glaciers exhibited the most undercutting, which is when a layer of warm, salty water at the bottom of a fjord melts the base of a glacier, causing the ice above to break apart. In contrast, the 51 glaciers that extend into shallow fjords or onto shallow ridges experienced the least undercutting and contributed only 15% of the total ice loss.
“I was surprised by how lopsided these findings were. The biggest and deepest glaciers are undercut much faster than the smaller glaciers in shallow water,” said lead author Michael Wood, a post-doctoral researcher at NASA’s Jet Propulsion Laboratory in Southern California, who began this research as a doctoral student at the University of California, Irvine. “In other words, the biggest glaciers are the most sensitive to the warming waters, and those are the ones really driving Greenland’s ice loss.”
In the case of Greenland’s glaciers, the bigger they are, the faster they melt. And the culprit is the depth of the fjord they occupy: Deeper fjords allow in more warm ocean water than shallow fjords, hastening the undercutting process.
Undercutting and Calving
Greenland is home to one of Earth’s only two ice sheets. The ice there is over 2 miles (3 kilometers) thick in places. At the edges of Greenland, the vast glaciers extending from the ice sheet travel slowly down valleys like icy conveyor belts, which pour into the fjords and then melt or break off (or calve) as icebergs. The ice is replenished by snowfall that is compressed over time into the ice pack.
If the ice sheet were in balance, the amount of snow accumulating on the top would roughly equal the ice lost from melt, evaporation, and calving. But previous observations have shown that the ice sheet has been out of balance since the 1990’s: Melt has accelerated and calving has increased. In other words, the rate of ice being lost to the ocean is exceeding the supply from the ice sheet. This is causing the ice sheet to shrink and the glaciers to retreat toward land.
The main cause of such glacier retreat is the process of undercutting, which is driven by two factors: the amount of meltwater flowing from the glacier and the warm layer of salty water at the base of the fjord. During the summer months, increasing air temperatures heat the glacier’s surface, creating pools of meltwater. These pools leak through the ice and flow from the glacier in rivers below the surface. As the meltwater flows into the sea, it encounters the warmer salty water at the bottom of the fjord.
Glacial meltwater doesn’t contain salt, so it is less dense than saltwater and thus rises as a plume. The plume drags the warmer ocean water into contact with the glacier’s base. The amount of undercutting depends on the depth of the fjord, the warmth of the ocean water, and the amount of meltwater flowing out from beneath the glacier. As the climate warms, the amount of meltwater will increase and the ocean temperature will rise, two factors that boost the undercutting process.
Figure 28: The presence of warm ocean water and meltwater flowing off the glaciers that plunge into Greenland’s fjords combine to cause melting of the glaciers from below – a process known as undercutting – that causes pieces to break off as icebergs. OMG Principal Investigator Josh Willis explains how the process works in this animation (video credit: NASA/JPL-Caltech)
These findings suggest that climate models may underestimate glacial ice loss by at least a factor of two if they don’t account for undercutting by a warm ocean.
The study also lends insight into why many of Greenland’s glaciers never recovered after an abrupt warming of ocean water between 1998 and 2007, in which ocean temperature increased by nearly 2 degrees Celsius. Although ocean warming paused between 2008 and 2017, the glaciers had already experienced such extreme undercutting in the previous decade that they continued to retreat at an accelerated rate.
“We have known for well over a decade that the warmer ocean plays a major role in the evolution of Greenland glaciers,” said OMG Deputy Principal Investigator Eric Rignot of UCI and JPL, which manages the mission. “But for the first time, we have been able to quantify the undercutting effect and demonstrate its dominant impact on the glacier retreat over the past 20 years.”
Into the Icy Depths
Now in its sixth year, the OMG mission has carried out the mammoth task of measuring ocean temperature and salinity around the entire coast of Greenland. Each summer since 2016, the team has spent several weeks dropping between 250 and 300 probes from an aircraft to measure how water temperature and salinity change with depth while mapping the depth of otherwise-inaccessible fjords.
This data complements other surveys of the region – including OMG measurements via boat (which began in 2015) and observational data collected from the Landsat satellites from NASA and the U.S. Geologic Survey – and builds on a growing body of glacier research on ice-ocean interactions. During this time, the OMG team has been able to gain a detailed view of how quickly the 226 glaciers studied are melting and which are retreating the fastest.
OMG is planning its campaign for the summer of 2021. The team hopes that the ongoing measurements of ocean conditions will be invaluable for refining predictions of ice loss, ultimately helping the world prepare for a future of rising oceans.
“When the ocean speaks, the Greenland Ice Sheet listens,” said OMG Principal Investigator Josh Willis, also of JPL. “This gang of 74 glaciers in deep fjords is really feeling the influence of the ocean; it’s discoveries like these that will eventually help us predict how fast the ice will shrink. And that’s a critical tool for both this generation and the next.”
Our world is losing ice at record rate
• January 25, 2021: A research team – the first to carry out a survey of global ice loss using satellite data – has discovered that the rate at which ice is disappearing across the planet is speeding up. The findings also reveal that 28 trillion tons of ice was lost between 1994 and 2017 – equivalent to a sheet of ice 100 meters thick covering the whole of the UK. 34)
A paper, published today in The Cryosphere, describes how a team of researchers led by the University of Leeds in the UK used information from ESA’s ERS, Envisat and CryoSat satellites as well as the Copernicus Sentinel-1 and Sentinel-2 missions to find that the rate at which Earth has lost ice has increased markedly within the past three decades, from 0.8 trillion tons per year in the 1990s to 1.3 trillion tons per year by 2017. 35)
Figure 29: To put this into perspective, one trillion tonnes of ice can be thought of as a cube of ice measuring 10 x 10 x 10 km, which would be taller than Mount Everest – illustrated here as a cube of ice over New York (image credit: Planetary Visions)
The research shows that overall, there has been a 65% increase in the rate of ice loss over the 23-year survey. This has been driven mainly by steep rises in losses from the polar ice sheets in Antarctica and Greenland.
Ice melt from ice sheets and glaciers raises sea levels, increases the risk of flooding in coastal communities, which has severe consequences for society, the economy and the environment.
Lead author Thomas Slater, a research fellow at Leeds’ CPOM (Centre for Polar Observation and Modelling), said, “Although every region we studied lost ice, losses from the Antarctic and Greenland ice sheets have accelerated the most.
“The ice sheets are now following the worst-case climate warming scenarios set out by the IPCC (Intergovernmental Panel on Climate Change). Sea-level rise on this scale will have very serious impacts on coastal communities this century.”
The study is the first of its kind to examine all the ice that is disappearing on Earth, using satellite observations.
The survey covers 215,000 mountain glaciers spread around the planet, the polar ice sheets in Greenland and Antarctica, the ice shelves floating around Antarctica, and sea ice drifting in the Arctic and Southern Oceans.
Figure 30: A research team – the first to carry out a survey of global ice loss using satellite data – has discovered that the rate at which ice is disappearing across the planet is speeding up. The findings also reveal that 28 trillion tonnes of ice was lost between 1994 and 2017 (video credit: CPOM)
Dr Slater added, “Over the past three decades there’s been a huge international effort to understand what’s happening to individual components in Earth’s ice system. This has been revolutionized by satellites as they allow us to routinely monitor the vast and inhospitable regions where ice can be found.”
The increase in ice loss has been triggered by warming of the atmosphere and oceans, which have warmed by 0.26°C and 0.12°C per decade since 1980, respectively.
During the survey period, there was a loss of 7.6 trillion tons of Arctic sea ice and a loss of 6.5 trillion tons from Antarctic ices shelves, both of which float on the polar oceans.
Isobel Lawrence, also a research fellow at the CPOM (Centre for Polar Observation and Modelling), said, “Sea-ice loss doesn't contribute directly to sea-level rise, but it does have an indirect influence. One of the key roles of Arctic sea ice is to reflect solar radiation back into space, which helps keep the Arctic cool.
“As the sea ice shrinks, more solar energy is being absorbed by the oceans and atmosphere, causing the Arctic to warm faster than anywhere else on the planet.”
Half of all losses were from ice on land – including 6.1 trillion tons from mountain glaciers, 3.8 trillion tons from the Greenland ice sheet, and 2.5 trillion tons from the Antarctic ice sheet. These losses have raised global sea levels by 35 mm.
It is estimated that for every centimeter of sea-level rise, approximately a million people in low-lying regions are in danger of being displaced.
Despite storing only 1% of Earth's total ice volume, glaciers have contributed to almost a quarter of the global ice losses over the study period, with all glacier regions around the world losing ice.
Report co-author and PhD researcher Inès Otosaka, also from the CPOM, said, “As well as contributing to global mean sea-level rise, mountain glaciers are also critical as a freshwater resource for local communities.
“The retreat of glaciers around the world is therefore of crucial importance at both local and global scales.”
ESA’s Mark Drinkwater added, “The tap to the vast global icy reservoir has been well and truly opened by global warming. Continuity in satellite data is the key to predicting future ice losses, and to assist in mitigating the threats posed by sea-level rise, shrinking high mountain glaciers and further climate feedbacks. The Copernicus Expansion missions, CRISTAL, CIMR and ROSE-L have been designed to fill the gaps in current Sentinel capabilities for comprehensive monitoring of changes in the global ice cover.”
Figure 31: Ice lost between 1994–2017 (image credit: CPOM)
Lake heatwaves to increase due to climate change
• January 21, 2021: Lake heatwaves – periods of extreme warm surface water temperature in lakes – may become hotter and longer by the end of the 21st century, according to a new study published in Nature, increasing the link between climate change and extreme events. 36) 37)
The modelling study, which is validated using satellite observation records generated by ESA’s Climate Change Initiative, shows that under a high greenhouse gas emissions scenario, the average duration of lake heatwaves could increase by around three months on average, with some lakes reaching a permanent heatwave state.
The increasing frequency of marine and land heatwaves has been linked to global warming in previous studies. However, less is known about lake heatwaves and how they will be affected by global warming.
Figure 32: Lake heatwave projections. Historical and future projections of global lake heatwave strength for three different greenhouse gas emission scenarios: a is RCP (Representative Concentration Pathway) 2.6, b is RCP 6.0 and c is RCP 8.5 [image credit: Woolway et al., (2021)]
Iestyn Woolway, a research fellow with ESA’s Climate Office, and colleagues modelled the impact of heatwaves on 702 lakes all over the globe from 1901 to 2099 in this latest study. They show, for the first time, that heatwaves frequently occur in lakes, and that they are very sensitive to climatic variations.
Under future climate change, their multi-model projections demonstrate that lake heatwaves will become progressively worse as the century progresses, particularly under a high greenhouse gas emissions scenario. The average temperature of lake heatwaves is likely to increase from approximately 3.7ºC to 5.4ºC, while the average duration will increase from around a week to more than three months by the end of the 21st century.
Under the most conservative emissions scenario, the average increases in temperature and duration are around 4.0°C and one month, respectively. The authors found that heatwaves would be longer lasting but less intense in deeper lakes.
As lakes warm over the 21st century, heatwaves will extend across all seasons and some lakes will reach a permanent heatwave state, the authors suggest.
Iestyn Woolway commented, “Agencies from around the world recently reported that 2020 was part of the warmest decade on record, and climate projections suggest that this warming will continue. Unless climate change is mitigated, our projections suggest that lake heatwaves will become increasingly severe this century, threatening lake biodiversity and pushing ecosystems to the limits of their resilience.”
Given their ability to monitor lake properties on a global scale over multiple decades, satellites observations prove crucial in this study, with the authors using a long-term lakes satellite dataset generated by the ESA Climate Change Initiative (CCI).
Initially released last year, the CCI dataset provides information for 250 globally distributed lakes worldwide over the period 1995—2019. In addition to surface temperature, information on four other lake variables are also available, including daily observations for lake level, water extent, ice cover and reflectance, which help support studies related to lakes and climate.
The next version of the dataset, anticipated for release later this year, will increase the number of lakes for which data is provided to around 2000, to further support studies aimed at understanding the response of lakes to climate change.
ESA’s Climate Change Initiative is a research programme that merges multiple sources of satellite data, to create long time series for 21 key aspects of the climate, known as Essential Climate Variables, including lakes.
Figure 33: The percentage of studied lakes which are projected to experience a permanent heatwave state during the 21st century (image credit: ESA, Woolway et al., (2021))
2020 Tied for Warmest Year on Record, NASA Analysis Shows
• January 14, 2021: Earth’s global average surface temperature in 2020 tied with 2016 as the warmest year on record, according to an analysis by NASA. 38)
Continuing the planet’s long-term warming trend, the year’s globally averaged temperature was 1.84 degrees Fahrenheit (1.02 degrees Celsius) warmer than the baseline 1951-1980 mean, according to scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York. 2020 edged out 2016 by a very small amount, within the margin of error of the analysis, making the years effectively tied for the warmest year on record.
“The last seven years have been the warmest seven years on record, typifying the ongoing and dramatic warming trend,” said GISS Director Gavin Schmidt. “Whether one year is a record or not is not really that important – the important things are long-term trends. With these trends, and as the human impact on the climate increases, we have to expect that records will continue to be broken.”
Figure 34: Globally, 2020 was the hottest year on record, effectively tying 2016, the previous record. Overall, Earth’s average temperature has risen more than 2 degrees Fahrenheit since the 1880s. Temperatures are increasing due to human activities, specifically emissions of greenhouse gases, like carbon dioxide and methane (video credits: NASA’s Scientific Visualization Studio/Lori Perkins/Kathryn Mersmann)
A Warming, Changing World
Tracking global temperature trends provides a critical indicator of the impact of human activities – specifically, greenhouse gas emissions – on our planet. Earth's average temperature has risen more than 2 degrees Fahrenheit (1.2 degrees Celsius) since the late 19th century.
Rising temperatures are causing phenomena such as loss of sea ice and ice sheet mass, sea level rise, longer and more intense heat waves, and shifts in plant and animal habitats. Understanding such long-term climate trends is essential for the safety and quality of human life, allowing humans to adapt to the changing environment in ways such as planting different crops, managing our water resources and preparing for extreme weather events.
Ranking the Records
A separate, independent analysis by the National Oceanic and Atmospheric Administration (NOAA) concluded that 2020 was the second-warmest year in their record, behind 2016. NOAA scientists use much of the same raw temperature data in their analysis, but have a different baseline period (1901-2000) and methodology. Unlike NASA, NOAA also does not infer temperatures in polar regions lacking observations, which accounts for much of the difference between NASA and NOAA records.
Like all scientific data, these temperature findings contain a small amount of uncertainty – in this case, mainly due to changes in weather station locations and temperature measurement methods over time. The GISS temperature analysis (GISTEMP) is accurate to within 0.1 degrees Fahrenheit with a 95 percent confidence level for the most recent period.
Beyond a Global, Annual Average
While the long-term trend of warming continues, a variety of events and factors contribute to any particular year’s average temperature. Two separate events changed the amount of sunlight reaching the Earth’s surface. The Australian bush fires during the first half of the year burned 46 million acres of land, releasing smoke and other particles more than 18 miles high in the atmosphere, blocking sunlight and likely cooling the atmosphere slightly. In contrast, global shutdowns related to the ongoing coronavirus (COVID-19) pandemic reduced particulate air pollution in many areas, allowing more sunlight to reach the surface and producing a small but potentially significant warming effect. These shutdowns also appear to have reduced the amount of carbon dioxide (CO2) emissions last year, but overall CO2 concentrations continued to increase, and since warming is related to cumulative emissions, the overall amount of avoided warming will be minimal.
The largest source of year-to-year variability in global temperatures typically comes from the El Nino-Southern Oscillation (ENSO), a naturally occurring cycle of heat exchange between the ocean and atmosphere. While the year has ended in a negative (cool) phase of ENSO, it started in a slightly positive (warm) phase, which marginally increased the average overall temperature. The cooling influence from the negative phase is expected to have a larger influence on 2021 than 2020.
“The previous record warm year, 2016, received a significant boost from a strong El Nino. The lack of a similar assist from El Nino this year is evidence that the background climate continues to warm due to greenhouse gases,” Schmidt said.
The 2020 GISS values represent surface temperatures averaged over both the whole globe and the entire year. Local weather plays a role in regional temperature variations, so not every region on Earth experiences similar amounts of warming even in a record year. According to NOAA, parts of the continental United States experienced record high temperatures in 2020, while others did not.
In the long term, parts of the globe are also warming faster than others. Earth’s warming trends are most pronounced in the Arctic, which the GISTEMP analysis shows is warming more than three times as fast as the rest of the globe over the past 30 years, according to Schmidt. The loss of Arctic sea ice – whose annual minimum area is declining by about 13 percent per decade – makes the region less reflective, meaning more sunlight is absorbed by the oceans and temperatures rise further still. This phenomenon, known as Arctic amplification, is driving further sea ice loss, ice sheet melt and sea level rise, more intense Arctic fire seasons, and permafrost melt.
Land, Sea, Air and Space
NASA’s analysis incorporates surface temperature measurements from more than 26,000 weather stations and thousands of ship- and buoy-based observations of sea surface temperatures. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions if not taken into account. The result of these calculations is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.
Figure 35: This plot shows yearly temperature anomalies from 1880 to 2019, with respect to the 1951-1980 mean, as recorded by NASA, NOAA, the Berkeley Earth research group, and the Met Office Hadley Centre (UK). Though there are minor variations from year to year, all five temperature records show peaks and valleys in sync with each other. All show rapid warming in the past few decades, and all show the past decade has been the warmest (image credits: NASA GISS/Gavin Schmidt)
NASA measures Earth's vital signs from land, air, and space with a fleet of satellites, as well as airborne and ground-based observation campaigns. The satellite surface temperature record from the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA’s Aura satellite confirms the GISTEMP results of the past seven years being the warmest on record. Satellite measurements of air temperature, sea surface temperature, and sea levels, as well as other space-based observations, also reflect a warming, changing world. The agency develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. NASA shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.
NASA’s full surface temperature data set – and the complete methodology used to make the temperature calculation – are available at: https://data.giss.nasa.gov/gistemp
Shrinking Margins of Greenland
• January 2, 2021: A recent study of Greenland’s ice sheet found that glaciers are retreating in nearly every sector of the island, while also undergoing other physical changes. Some of those changes are causing the rerouting of freshwater rivers beneath the ice. 39)
In a study led by Twila Moon of the National Snow and Ice Data Center, researchers took a detailed look at physical changes to 225 of Greenland’s ocean-terminating glaciers—narrow fingers of ice that flow from the ice sheet interior to the ocean. They found that none of those glaciers has substantially advanced since the year 2000, and 200 of them have retreated. 40)
About 80 percent of Greenland is blanketed by an ice sheet, also known as a continental glacier, that reaches a thickness of up to 3 kilometers (2 miles). As glaciers flow toward the sea, they are usually replenished by new snowfall on the interior of the ice sheet that gets compacted into ice. Multiple studies have shown that the balance between glacier melting and replenishment is changing, as is the rate of iceberg calving. Due to rising air and ocean temperatures, the ice sheet is losing mass at an accelerating rate and additional meltwater is flowing into the sea.
Figure 36: At least 200 of the island’s coastal glaciers have retreated over the past 20 years. This map shows measurements of ice velocity across Greenland as measured by satellites. The data were compiled through the Inter-mission Time Series of Land Ice Velocity and Elevation project (ITS_LIVE), which brings together observations of glaciers collected by multiple Landsat satellites between 1985 and 2015 into a single dataset open to scientists and the public [image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey and the ITS_LIVE project at NASA/JPL-Caltech, and the General Bathymetric Chart of the Oceans (GEBCO). Story by Calla Cofield, Jet Propulsion Laboratory, with Mike Carlowicz]
“The coastal environment in Greenland is undergoing a major transformation,” said Alex Gardner, a snow and ice scientist at NASA’s Jet Propulsion Laboratory and co-author of the study. “We are already seeing new sections of the ocean and fjords opening up as the ice sheet retreats, and now we have evidence of changes to these freshwater flows. So losing ice is not just about changing sea level, it’s also about reshaping Greenland’s coastline and altering the coastal ecology.”
Though the findings by Moon, Gardner, and colleagues are in line with other Greenland observations, the new survey captures a trend that has not been apparent in previous work. As individual glaciers retreat, they are also changing in ways that are likely rerouting freshwater flows under the ice. For example, glaciers change in thickness not only as warmer air melts ice off of their surfaces, but also as their flow speed changes. Both scenarios can lead to changes in the distribution of pressure beneath the ice. This, in turn, can change the path of subglacial rivers, since water will always take the path of least resistance (lowest pressure).
Citing previous studies on the ecology of Greenland, the authors note that freshwater rivers under the ice sheet deliver nutrients to bays, deltas, and fjords around Greenland. In addition, the under-ice rivers enter the ocean where the ice and bedrock meet, which is often well below the ocean’s surface. The relatively buoyant freshwater rises, carrying nutrient-rich deep ocean water to the surface, where the nutrients can be consumed by phytoplankton. Research has shown that glacial meltwater rivers directly affect the productivity of phytoplankton, which serve as a foundation of the marine food chain. Combined with the opening of new fjords and sections of ocean as glaciers and ice shelves retreat, these changes amount to a transformation of the local environment.
“The speed of ice loss in Greenland is stunning,” said Moon. “As the ice sheet edge responds to rapid ice loss, the character and behavior of the system as a whole are changing, with the potential to influence ecosystems and people who depend on them.”
Figure 37: An aerial view of the Greenland ice sheet taken in September 1992. New research finds ice loss has accelerated significantly over the past two decades, transforming the shape of the ice sheet edge and therefore coastal Greenland (image credit: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research (Own work), CC BY-SA 2.5) 41)
Water Limitations in the Tropics Offset Carbon Uptake from Arctic Greening
• December 18, 2020: More plants and longer growing seasons in the northern latitudes have converted parts of Alaska, Canada and Siberia to deeper shades of green. Some studies translate this Arctic greening to a greater global carbon uptake. But new research shows that as Earth’s climate is changing, increased carbon absorption by plants in the Arctic is being offset by a corresponding decline in the tropics. 42)
"This is a new look at where we can expect carbon uptake to go in the future,” said scientist Rolf Reichle with the Global Modeling and Assimilation Office (GMAO) at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Reichle is one of the authors of a study, published Dec. 17 in AGU Advances, which combines satellite observations over 35 years from the National Oceanic and Atmospheric Administration (NOAA’s) Advanced Very High Resolution Radiometer (AVHRR) with computer models, including water limitation data from NASA’s Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). 43)
Together, these provide a more accurate estimate of global "primary productivity" – a measure of how well plants convert carbon dioxide and sunlight to energy and oxygen via photosynthesis, for the time span between 1982 to 2016.
Arctic gains and tropical losses
Plant productivity in the frigid Arctic landscape is limited by the lengthy periods of cold. As temperatures warm, the plants in these regions have been able to grow more densely and extend their growing season, leading to an overall increase in photosynthetic activity, and subsequently greater carbon absorption in the region over the 35-year time span.
However, buildup of atmospheric carbon concentrations has had several other rippling effects. Notably, as carbon has increased, global temperatures have risen, and the atmosphere in the tropics (where plant productivity is limited by the availability of water) has become drier. Recent increases in drought and tree mortality in the Amazon rainforest are one example of this, and productivity and carbon absorption over land near the equator have gone down over the same time period as Arctic greening has occurred, canceling out any net effect on global productivity.
Figure 38: A map of the world shows the changes in global gross primary productivity (GPP), an indicator of carbon uptake, from 1982–2016. Each dot indicates a region with a statistically significant trend (image credit: NASA/Nima Madani)
Adding Satellites to Productivity Models
Previous model estimates suggested that the increasing productivity of plants in the Arctic could partially compensate for human activities which release atmospheric carbon, like the burning of fossil fuels. But these estimates relied on models that calculate plant productivity based on the assumption that they photosynthesize (convert carbon and light) at a given efficiency rate.
In reality, many factors can affect plants’ productivity. Including satellite records like those from AVHRR provide scientists with consistent measurements of the global photosynthetic plant cover, and can help account for variable events such as pest outbreaks and deforestation that previous models do not capture. These can impact the global vegetation cover and productivity.
“There have been other studies that focused on plant productivity at global scales,” said Nima Madani from NASA’s Jet Propulsion Laboratory, (JPL) Pasadena, California, and lead author of the study, which also includes scientists from the University of Montana. “But we used an improved remote sensing model to have a better insight into changes in ecosystem productivity.” This model uses an enhanced light use efficiency algorithm, which combines multiple satellites’ observations of photosynthetic plant cover and variables such as surface meteorology.
“The satellite observations are critical especially in regions where our field observations are limited, and that’s the beauty of the satellites,” Madani said. “That’s why we are trying to use satellite remote sensing data as much as possible in our work.”
It was only recently that the satellite records began to show these emerging trends in shifting productivity. According to Reichle, “The modelling and the observations together, what we call data assimilation, is what really is needed.” The satellite observations train the models, while the models can help depict Earth system connections such as the opposing productivity trends observed in the Arctic and tropics.
Brown Is the New Green
The satellite data also revealed that water limitations and decline in productivity are not confined to the tropics. Recent observations show that the Arctic’s greening trend is weakening, with some regions already experiencing browning.
“I don’t expect that we have to wait another 35 years to see water limitations becoming a factor in the Arctic as well,” said Reichle. We can expect that the increasing air temperatures will reduce the carbon uptake capacity in the Arctic and boreal biomes in the future. Madani says Arctic boreal zones in the high latitudes that once contained ecosystems constrained by temperature are now evolving into zones limited by water availability like the tropics.
These ongoing shifts in productivity patterns across the globe could affect numerous plants and animals, altering entire ecosystems. That can impact food sources and habitats for various species, including endangered wildlife, and human populations.
The data produced from this study are publicly accessible at: https://doi.org/10.3334/ORNLDAAC/1789
NASA Finds What a Glacier’s Slope Reveals About Greenland Ice Sheet Thinning
• December 18, 2020: As glaciers flow outward from the Greenland Ice Sheet, what lies beneath them offers clues to their role in future ice thinning and sea-level rise contribution. 44)
Outlet glaciers are rivers of ice flowing within the cracks of the bedrock and draining into the surrounding sea. They retreat and start to thin as climate warms, and this thinning works its way toward the center of the ice sheet. Now, by looking at the bed topography beneath the ice, scientists have a better understanding of which glaciers could have a significant impact on the Greenland Ice Sheet’s contribution to sea-level rise in coming years. They found that some glaciers flowing over gentler slopes could have a greater impact than previously thought. The gentle slopes allow thinning to spread from the edge of the ice sheet far into the interior, whereas glaciers with steep drops in their bed topographies limit how far into the interior thinning can spread.
The research, which was published December 11th in Geophysical Research Letters, analyzed 141 outlet glaciers on the Greenland Ice Sheet to predict how far into the interior thinning may spread along their flow lines, starting from the ocean edge. 45)
“What we discovered is some glaciers flow over these steep drops in the bed, and some don’t,” said lead author Denis Felikson with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the Universities Space Research Association (USRA). “For the glaciers that do have that steep drop in the bed, thinning can’t make its way past those drops.” Borrowing a term from geomorphology – the study of Earth’s physical features – they coined these steep drop features “knickpoints.”
When a river flows over a knickpoint, it often results in a waterfall or a lake. But for glaciers, steep is a relative term which in reality translates to just about three degrees of incline. “It’s not like the ice is going over a cliff,” said Felikson. “But in terms of glacier dynamics, they are very steep – an order of magnitude more steep than a typical bed that the ice flows over.”
The researchers were able to identify these “steep” changes in topography using digital elevation models of the ice sheet bed and surface topography. Surface topography came from the Greenland Ice Mapping Project, created using NASA’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument that flies aboard NASA’s Terra satellite, in conjunction with data from NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) mission. The bed topography digital elevation model, known as the BedMachine data set, is a high-resolution model of the bed beneath the Greenland Ice Sheet, created using data from NASA’s Operation IceBridge airborne surveys of polar ice.
“This bed topography data set was critical to us doing our work,” Felikson said. “And it is thanks to NASA remote sensing, namely the Operation IceBridge surveys, that we were able to do this.” Using the remote sensing data, scientists were able to compare topography measures to produce a single metric along a glacier’s flow line. This helped them identify a break point between the upstream and downstream parts of the glacial ice.
Ice below the knickpoint is susceptible to thinning from the glacier’s edge. But the thinning does not extend beyond this point upstream, so the interior of the ice sheet is not impacted.
Of all the glaciers observed, a majority (65 percent) had discernable knickpoints. Especially steep knickpoints are prevalent in the more mountainous regions of Greenland, where several of the biggest and fastest moving glaciers also show knickpoints that are relatively close to the coast. By sheer size alone these glaciers could contribute significantly to ice sheet thinning and melt, but because their knickpoints are near the coast, thinning is not expected to spread far inland.
Figure 39: GIF image showing the potential distances over which thinning can spread into Greenland’s interior. Glaciers in regions of higher elevation, tend to pervade less inland than those in regions of lower elevation (image credit: Denis Felikson)
However, glaciers that flow through gentle topography are found to either have gradual knickpoints, or no knickpoint at all. Such glaciers are of interest, and concern, because even those that are smaller in size have the potential to let thinning expand hundreds of kilometers inland, eroding the heart of the ice sheet.
“They could be impactful in terms of sea level rise, not because they are big and deep, but because they have access to more ice that they can eat away,” said Felikson. “It will take them a lot longer to respond, but over the long term they could end up contributing just as much to sea level rise, maybe, as the big glaciers.”
Over the gentle topography of the northwest coast of Greenland, nine of twelve neighboring glaciers are predicted to thin more than 250 km (155.3 miles) into the interior of the ice sheet, over a ~140 km (86.9 mile) wide region. The northwest sector of the ice sheet is also the only region experiencing an ongoing increase in ice discharge over the last couple decades, and Felikson predicts that it will continue to do so given the characteristics of these glaciers.
This work was started at the University of Texas as part of Felikson’s dissertation and has continued throughout his time at NASA Goddard. The origins of knickpoints and their implications for long-term thinning, as well as Greenland’s overall contribution to sea level rise, remain the basis for future research.
The data used in this study is available at: https://zenodo.org/record/4284759
Long-term permafrost record details Arctic thaw
• December 16, 2020: Frozen Arctic soils are set to release vast amounts of greenhouse gases to the atmosphere as they continue to thaw in coming decades. Despite concerns that this will fuel future global warming, the scale and speed of this important climate process remain uncertain. To help address this knowledge gap, ESA-funded researchers have developed and released a new permafrost dataset – the longest, satellite-derived permafrost record currently available. 46)
Covering 18 million km2, northern hemisphere permafrost areas have been warming since the 1980s, according to the Intergovernmental Panel on Climate Change’s latest report on oceans and cryosphere. The total carbon released each year may rival present-day emissions from all EU countries by the end of century – and are expected to amplify future climate change.
Figure 40: This animation shows the permafrost extent from 1997-2018.Frozen Arctic soils are set to release vast amounts of greenhouse gases to the atmosphere as they continue to thaw in coming decades. Despite concerns that this will fuel future global warming, the scale and speed of this important climate process remain uncertain. To help address this knowledge gap, ESA-funded researchers have developed and released a new permafrost dataset - the longest, satellite-derived permafrost record currently available [image credit: ESA (data source: Permafrost CCI, Obu, J. et al. 2020)]
The new 21-year satellite-derived record details the annual changes to the northern hemisphere permafrost soils from 1997—2018. This is the longest satellite permafrost record currently available, and extends the time-series by seven years.
Long-term satellite-derived records such as these are a key tool to evaluate and improve global climate models and confidence in the predictions of both future emissions and change.
Permafrost cannot be directly observed from space. Instead, the research team, led by Annett Bartsch from B.geos, combine global satellite data products for land surface temperature and land cover with in situ measurements and the ERA5 climate reanalysis to generate a picture of the permafrost ground conditions.
The resulting one-kilometer resolution dataset provides permafrost ground temperatures at 1 m, 2 m, 5 m and 10 m of the ‘active layer’ – the depth to which the top layer of soil thaws during the summer and freezes again during the autumn. The team also derive and provide permafrost extent data, a standard parameter used for a variety of related applications.
Figure 41: This animation shows the average subsurface temperatures from 1997-2018. Frozen Arctic soils are set to release vast amounts of greenhouse gases to the atmosphere as they continue to thaw in coming decades. Despite concerns that this will fuel future global warming, the scale and speed of this important climate process remain uncertain. To help address this knowledge gap, ESA-funded researchers have developed and released a new permafrost dataset – the longest, satellite-derived permafrost record currently available [ESA (data source: Permafrost CCI, Obu, J. et al. 2020)]
Although currently short of the three-decade minimum required to identify a climate signal, the 21-year record shows interesting trends, according to Dr Bartsch who points to rising ground temperatures, and greater variability along coastal areas and at high arctic latitudes.
“Average ground temperatures are rising at a rate of one degree Celsius per decade in the record,” explains Dr Bartsch, adding that, “Wider temperature variation can be observed along the coasts of east Russia and northwest Canada bordering the Chukchi sea – where rates of coastal erosion are some of the highest in the world, and are, in part, exacerbated by permafrost thaw conditions.”
An unusually warm summer in 2020 in northern Russia, led to ground conditions becoming unstable, contributing to a major diesel oil leak at a facility near the town of Norilsk. The incident threatened to pollute the Arctic Ocean and highlights some of the consequences of changing permafrost.
Figure 42: MAGT (Mean Annual Ground Temperature) at 2m depth for 2003-2017 at coastal Arctic locations in Canada and Russia. Vertical dashed lines indicate years with PALSAR acquisitions (image credit: Obu et al., 2019a)
“Although ground temperatures remained close to zero degrees, on-going slow seasonal ground ice melt and a deepening of the active layer can be observed in the data,” explains, Dr Bartsch’s colleague, Prof Westermann of the University of Oslo and the developer of the satellite-retrieval scheme.
The research-quality dataset is freely available from ESA’s CCI (Climate Change Initiative) Open Data Portal along with a suite of research-quality global, satellite data sets for Essential Climate Variables.
Moving forwards, the permafrost project team is working to integrate snow extent observations into their model to supplement or replace modelled snow data, and develop Arctic-specific land cover maps that will for example help to further improve represent soil and ground temperature further.
Greenland's Retreating Glaciers Could Impact Local Ecology
• October 27, 2020: A new study of Greenland's shrinking ice sheet reveals that many of the island's glaciers are not only retreating, but are also undergoing other physical changes. Some of those changes are causing the rerouting of freshwater rivers beneath the glaciers, where it meets the bedrock. These rivers carry nutrients into the ocean, so this reconfiguring has the potential to impact the local ecology as well as the human communities that depend on it. 47)
"The coastal environment in Greenland is undergoing a major transformation," said Alex Gardner, a research scientist at NASA's Jet Propulsion Laboratory and co-author of the study. "We are already seeing new sections of the ocean and fjords opening up as the ice sheet retreats, and now we have evidence of changes to these freshwater flows. So losing ice is not just about changing sea level, it's also about reshaping Greenland's coastline and altering the coastal ecology."
About 80% of Greenland is blanketed by an ice sheet, also known as a continental glacier, that reaches a thickness of up to 2.1 miles (3.4 km). Multiple studies have shown that the melting ice sheet is losing mass at an accelerating rate due to rising atmosphere and ocean temperatures, and that the additional meltwater is flowing into the sea.
Figure 43: Greenland appears in this image created using data from the ITS_LIVE project, hosted at NASA's Jet Propulsion Laboratory. The coloring around the coast of the arctic island shows the speed of outlet glaciers flowing into the ocean (image credit: NASA/JPL-Caltech/USGS)
This study, published on Oct. 27 in the Journal of Geophysical Research: Earth's Surface, provides a detailed look at physical changes to 225 of Greenland's ocean-terminating glaciers, which are narrow fingers of ice that flow from the ice sheet interior out into the ocean. The data used in the paper was compiled as part of a project based at JPL called Inter-mission Time Series of Land Ice Velocity and Elevation, or ITS_LIVE, which brings together observations of glaciers around the globe - collected by multiple satellites between 1985 and 2015 - into a single dataset open to scientists and the public. The satellites are all part of the Landsat program, which has sent a total of seven spacecraft into orbit to study Earth's surface since 1972. Managed by NASA and the U.S. Geological Survey, Landsat data reveals both natural and human-caused changes to Earth's surface, and is used by land managers and policymakers to make decisions about Earth's changing environment and natural resources. 48)
Figure 44: Glacier flow is imperceptible to the human eye, but this animation shows glaciers in Asia moving over a span of 11 years, from 1991 to 2002. The animation is composed of false-color images from Landsat 5 and 7 spacecraft. Moving ice is gray and blue; brighter blues are changing snow and ice cover (image credit: NASA/JPL-Caltech/USGS/Earth Observatory)
Advancing and Retreating
As glaciers flow toward the sea - albeit too slowly to be perceptible to the eye - they are replenished by new snowfall on the interior of the ice sheet that gets compacted into ice. Some glaciers extend past the coastline and can break off as icebergs. Due to rising atmospheric and ocean temperatures, the balance between glacier melting and replenishment, as well as iceberg calving, is changing. Over time, a glacier's front may naturally advance or retreat, but the new research shows that none of the 225 ocean-terminating glaciers surveyed has substantially advanced since 2000, while 200 have retreated.
Although this is in line with other Greenland findings, the new survey captures a trend that hasn't been apparent in previous work: As individual glaciers retreat, they are also changing in ways that are likely rerouting freshwater flows under the ice. For example, glaciers change in thickness not only as warmer air melts ice off their surfaces, but also as their flow speed changes in response to the ice front advancing or retreating.
Both scenarios were observed in the new study, and both can lead to changes in the distribution of pressure beneath the ice; scientists can infer these pressure changes based on changes in thickness analyzed in the study. This, in turn, can change the path of a subglacial river, since water will always take the path of least resistance, flowing in the direction of lowest pressure.
Citing previous studies on the ecology of Greenland, the authors note that freshwater rivers under the ice sheet deliver nutrients (such as nitrogen, phosphorus, iron, and silica) to bays, deltas, and fjords around Greenland. In addition, the under-ice rivers enter the ocean where the ice and bedrock meet, which is often well below the ocean's surface. The relatively buoyant fresh water rises, carrying nutrient-rich deep ocean water to the surface, where the nutrients can be consumed by phytoplankton. Research has shown that glacial meltwater rivers directly impact the productivity of phytoplankton - meaning the amount of biomass they produce - which serves as a foundation of the marine food chain. Combined with the opening up of new fjords and sections of ocean as glaciers retreat, these changes amount to a transformation of the local environment.
"The speed of ice loss in Greenland is stunning," said Twila Moon, deputy lead scientist of the National Snow and Ice Data Center and lead author on the study. "As the ice sheet edge responds to rapid ice loss, the character and behavior of the system as a whole are changing, with the potential to influence ecosystems and people who depend on them."
The changes described in the new study seem to depend on the unique features of its environment, such as the slope of the land that the glacier flows down, the properties of the ocean water that touch the glacier, as well as the glacier's interaction with neighboring glaciers. That suggests scientists would need detailed knowledge not only of the glacier itself, but also of the glacier's unique environment in order to predict how it will respond to continued ice loss.
"It makes modeling glacial evolution far more complex when we're trying to anticipate how these systems will evolve both in the short term and two or three decades out," Gardner said. "It's going to be more challenging than we previously thought, but we now have a better understanding of the processes driving the variety of responses, which will help us make better ice sheet models."
Space for Climate
• October 22, 2020: The scientific evidence of global climate change is irrefutable. The consequences of a warming climate are far-reaching – affecting fresh water resources, global food production, sea level and triggering an increase in extreme-weather events. 49)
Figure 45: In order to tackle climate change, scientists and governments need reliable data in order to understand how our planet is changing. ESA is a world-leader in Earth observation and remains dedicated to developing cutting-edge spaceborne technology to further understand the planet, improve daily lives, support effect policy-making for a more sustainable future, and benefit businesses and the economy (video credit: ESA)
Figure 46: To tackle climate change, a global perspective is needed and this can be provided by satellites. Their data is key if we want to prepare ourselves for the consequences of climate change. While our Earth Explorers gather data to understand how our planet works and understand the impact that climate change and human activity are having on the planet, the European Union’s Copernicus Sentinels provide systematic data for environmental services that help adapt to and mitigate change (video credit: ESA)
Figure 47: This image of Paris was captured by Sentinel-2A on 15 July 2015. The satellite carries an innovative high-resolution multispectral imager with 13 spectral bands for new perspective of our land and vegetation. It will provide information, for example, for agricultural practices and to help manage food security (image credit: Copernicus Sentinel data (2015)/ESA)
Climate change is the paramount environmental issue of our time, and the greatest challenge is obtaining a detailed understanding of the complex variables involved. It includes health and safety, food production, security, economic and other aspects of our lives. 50)
On 30 November to 11 December 2015 the world’s attention will be firmly on Paris in France as leaders meet for the COP21 climate conference to set the tone for the health of our planet for decades to come.
Satellites play a critical role in providing essential information – from mapping ice in the polar regions to monitoring deforestation and urban growth – so that informed decisions can be made.
By using Earth observation techniques from space, we can monitor global environmental change not possible with other techniques.
The observations provide unique information that greatly assist in the understanding and management of climate change. Space delivers data with regular, uniform and global coverage, and reliable assessments of trends over time for specific variables. It also observes remote regions possible that are under-sampled by conventional networks.
Earth observation has not only revolutionized the way we perceive our planet, but it has also changed the way we comprehend our profound impact on the environment. Current satellite missions are building a long-term archive of essential data for local and international policy and planning.
How can different types of missions, instruments and data be used to study changes of our atmosphere, land, oceans and ice?
To respond to the need for climate-quality satellite data, ESA set up the Climate Change Initiative.
The aim is to realize the full potential of the long-term global Earth observation archives that ESA, together with its member states, has established over the last 30 years, as a significant and timely contribution to the ECV (Essential Climate Variables) databases required by the UNFCCC (UN Framework Convention on Climate Change).
The goal is to provide stable, long-term, satellite-based ECV data products for climate researchers. The ECVs will be derived from multiple satellite datasets, through international collaboration, and will include specific information on the errors and uncertainties of the dataset.
ESA’s Climate Change Initiative is making full use of Europe’s Earth observation satellites to exploit robust long-term global records of ECVs, such as greenhouse-gas concentrations, sea-ice extent and thickness, and sea-surface temperature and salinity.
NASA Supercomputing Study Breaks Ground for Tree Mapping, Carbon Research
• October 19, 2020: Scientists from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and international collaborators demonstrated a new method for mapping the location and size of trees growing outside of forests, discovering billions of trees in arid and semi-arid regions and laying the groundwork for more accurate global measurement of carbon storage on land. 51)
Figure 48: Scientists from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and international collaborators demonstrated a new method for mapping the location and size of trees growing outside of forests, discovering surprisingly high numbers of trees in semi-arid regions and laying the groundwork for more accurate global measurement of carbon storage on land (video credit: NASA/GSFC, Scientific Visualization Studio)
- Using powerful supercomputers and machine learning algorithms, the team mapped the crown diameter – the width of a tree when viewed from above – of more than 1.8 billion trees across an area of more than 500,000 square miles, or 1,300,000 km2. The team mapped how tree crown diameter, coverage, and density varied depending on rainfall and land use.
- Mapping non-forest trees at this level of detail would take months or years with traditional analysis methods, the team said, compared to a few weeks for this study. The use of very high-resolution imagery and powerful artificial intelligence represents a technology breakthrough for mapping and measuring these trees. This study is intended to be the first in a series of papers whose goal is not only to map non-forest trees across a wide area, but also to calculate how much carbon they store – vital information for understanding the Earth’s carbon cycle and how it is changing over time. 52)
Measuring carbon in trees
- Carbon is one of the primary building blocks for all life on Earth, and this element circulates among the land, atmosphere, and oceans via the carbon cycle. Some natural processes and human activities release carbon into the atmosphere, while other processes draw it out of the atmosphere and store it on land or in the ocean. Trees and other green vegetation are carbon “sinks,” meaning they use carbon for growth and store it out of the atmosphere in their trunks, branches, leaves and roots. Human activities, like burning trees and fossil fuels or clearing forested land, release carbon into the atmosphere as carbon dioxide, and rising concentrations of atmospheric carbon dioxide are a main cause of climate change.
- Conservation experts working to mitigate climate change and other environmental threats have targeted deforestation for years, but these efforts do not always include trees that grow outside forests, said Compton Tucker, senior biospheric scientist in the Earth Sciences Division at NASA Goddard. Not only could these trees be significant carbon sinks, but they also contribute to the ecosystems and economies of nearby human, animal and plant populations. However, many current methods for studying trees’ carbon content only include forests, not trees that grow individually or in small clusters.
- Tucker and his NASA colleagues, together with an international team, used commercial satellite images from DigitalGlobe, which were high-resolution enough to spot individual trees and measure their crown size. The images came from the commercial QuickBird-2, GeoEye-1, WorldView-2, and WorldView-3 satellites. The team focused on the dryland regions – areas that receive less precipitation than what evaporates from plants each year – including the arid south side of the Sahara Desert, that stretches through the semi-arid Sahel Zone and into the humid sub-tropics of West Africa. By studying a variety of landscapes from few trees to nearly forested conditions, the team trained their computing algorithms to recognize trees across diverse terrain types, from deserts in the north to tree savannas in the south.
Figure 49: The team focused on the dryland regions of West Africa, including the arid south side of the Sahara Desert, stretching through the semi-arid Sahel Zone and into the humid sub-tropics. By studying a variety of landscapes from few trees to nearly forested conditions, the team trained their computing algorithms to recognize trees across diverse terrain types, from deserts in the north to tree savannas in the south [image credits: NASA's Scientific Visualization Studio; Blue Marble data is courtesy of Reto Stockli (NASA/GSFC)]
Learning on the job
- The team ran a powerful computing algorithm called a fully convolutional neural network (“deep learning”) on the University of Illinois’ Blue Waters, one of the world’s fastest supercomputers. The team trained the model by manually marking nearly 90,000 individual trees across a variety of terrain, then allowing it to “learn” which shapes and shadows indicated the presence of trees.
- The process of coding the training data took more than a year, said Martin Brandt, an assistant professor of geography at the University of Copenhagen and the study’s lead author. Brandt marked all 89,899 trees by himself and helped supervise training and running the model. Ankit Kariryaa of the University of Bremen led the development of the deep learning computer processing.
- “In one kilometer of terrain, say it’s a desert, many times there are no trees, but the program wants to find a tree,” Brandt said. “It will find a stone, and think it’s a tree. Further south, it will find houses that look like trees. It sounds easy, you’d think – there’s a tree, why shouldn’t the model know it’s a tree? But the challenges come with this level of detail. The more detail there is, the more challenges come.”
- Establishing an accurate count of trees in this area provides vital information for researchers, policymakers and conservationists. Additionally, measuring how tree size and density vary by rainfall – with wetter and more populated regions supporting more and larger trees – provides important data for on-the-ground conservation efforts.
- “There are important ecological processes, not only inside, but outside forests too,” said Jesse Meyer, a programmer at NASA Goddard who led the processing on Blue Waters. “For preservation, restoration, climate change, and other purposes, data like these are very important to establish a baseline. In a year or two or ten, the study could be repeated with new data and compared to data from today, to see if efforts to revitalize and reduce deforestation are effective or not. It has quite practical implications.”
- After gauging the program’s accuracy by comparing it to both manually coded data and field data from the region, the team ran the program across the full study area. The neural network identified more than 1.8 billion trees – surprising numbers for a region often assumed to support little vegetation, said Meyer and Tucker.
- “Future papers in the series will build on the foundation of counting trees, extend the areas studied, and look ways to calculate their carbon content,” said Tucker. NASA missions like GEDI (Global Ecosystem Dynamics Investigation), and ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2), are already collecting data that will be used to measure the height and biomass of forests. In the future, combining these data sources with the power of artificial intelligence could open up new research possibilities.
- “Our objective is to see how much carbon is in isolated trees in the vast arid and semi-arid portions of the world,” Tucker said. “Then we need to understand the mechanism which drives carbon storage in arid and semi-arid areas. Perhaps this information can be utilized to store more carbon in vegetation by taking more carbon dioxide out of the atmosphere.”
- “From a carbon cycle perspective, these dry areas are not well mapped, in terms of what density of trees and carbon is there,” Brandt said. “It’s a white area on maps. These dry areas are basically masked out. This is because normal satellites just don’t see the trees – they see a forest, but if the tree is isolated, they can’t see it. Now we’re on the way to filling these white spots on the maps. And that’s quite exciting.”
Figure 50: An astronaut aboard the International Space Station (ISS) took this oblique photograph that shows most of the West African country of Guinea-Bissau, along with neighboring Guinea, The Gambia and Senegal, and the southern part of Mauritania. This scene stretches from the green forest vegetation and wet climates of the Atlantic coast to the almost vegetation-less landscapes of the Sahara Desert (image credit: NASA)
EO Topics on Climate Change continued
Prior Weather Linked to Rapid Intensification of Hurricanes Near Landfall
• October 15, 2020: New study results show that ocean heat waves can provide enough fuel for hurricanes to gain momentum as they approach land. 53)
Although most hurricanes tend to weaken as they approach land, some rapidly increase in strength just prior to landfall - a phenomenon that is both dangerous and hard to forecast. As the climate continues to warm, the number of storms that fall into the latter category is likely to increase, presenting a stark reality for communities in their paths. Because current weather models can't accurately predict this sudden intensification, communities preparing for a lesser storm often don't have time to respond to the arrival of a much stronger one or to the magnitude of destruction it is likely to leave behind.
Figure 51: Hurricane Michael was captured from the International Space Station on Oct. 10, 2018, after the storm made landfall as a Category 4 hurricane over the Florida Panhandle. The National Hurricane Center reported maximum sustained winds near 145 mph (233 kph) with the potential to bring dangerous storm surge and heavy rains to the Florida Panhandle (image credit: NASA)
The good news? The results of a new study published in September in Nature Communications identify pre-storm conditions that can contribute to this rapid intensification - an important step in improving our ability to forecast it. 54)
"We analyzed the events that led up to Hurricane Michael in 2018 and found that the storm was preceded by a marine heat wave, an area of the coastal ocean water that had become abnormally warm," said Severine Fournier, a NASA Jet Propulsion Laboratory scientist and a co-author of the study. "Marine heat waves like this one can form in areas that have experienced back-to-back severe weather events in a short period of time."
In October 2018, Hurricane Michael intensified from a Category 2 to a Category 5 storm the day before it made landfall in the Florida Panhandle. Michael is the most intense storm on record to hit the area, having left some $25 billion in damage in its wake. Using a combination of data gathered from weather buoys and satellites, the science team behind the study examined ocean conditions before, during, and after the hurricane.
Figure 52: This map of the Gulf of Mexico shows areas with unusually high sea surface temperatures before Hurricane Michael. The area from land down to the green line, and the small, enclosed areas below the green line experienced an extreme ocean heat wave in this period. The smaller circles show the path of Tropical Storm Gordon (TS), which preceded Michael; larger, darker circles show Michael's track and intensification. The legend's first four icons mark data stations (image credit: NASA/JPL-Caltech/University of South Alabama/DISL)
About a month before the hurricane arrived, Tropical Storm Gordon moved through the Gulf of Mexico. Under normal circumstances, a tropical storm or hurricane - Gordon, in this case - mixes the ocean water over which it travels, bringing up the cold water that is deeper in the water column to the surface and pushing the warm surface water down toward the bottom. This newly present colder water at the surface typically causes the storm to weaken.
But Tropical Storm Gordon was immediately followed by a severe atmospheric heat wave during which the warm air heated the cooler ocean water that had recently been brought to the surface. This, combined with the warm water that Gordon had pushed down through the water column, ultimately produced plenty of warm-water fuel for an incoming hurricane.
"In that situation, basically the whole water column was made up of warm water," said Fournier. "So when the second storm - Hurricane Michael - moved in, the water it brought up during mixing was warm just like the surface water being pushed down. Hurricanes feed off the heat of the ocean, so this sequence of weather events created conditions that were ideal for hurricane intensification."
Although the study focuses in-depth on Hurricane Michael, the scientists note that the pattern of weather events leading up to a major storm - and the resulting storm intensification - doesn't appear to be unique to Michael.
"Both Hurricane Laura and Hurricane Sally, which impacted the U.S. Gulf Coast in 2020, appeared to have similar setups to Michael, with both storms being preceded by smaller storms [Hurricane Hanna and Hurricane Marco, respectively]," said lead author Brian Dzwonkowski of the University of South Alabama/Dauphin Island Sea Lab. "Combined with warmer-than-average summer conditions in the region, this pre-storm setup of the oceanic environment likely contributed to those intensifications prior to landfall as well."
NASA scientists have been tackling the question of what causes hurricanes to intensify rapidly just before landfall from multiple angles. Another recent study led by JPL's Hui Su found that other factors, including the rainfall rate inside a hurricane, are also good indicators that can help forecast if and how much a hurricane is likely to intensify in the hours that follow. Both studies bring us closer to understanding and being better able to forecast rapid intensification of hurricanes near landfall.
Global lake warming trend threatens freshwater species
• October 09, 2020: Holding over 80% of Earth’s surface freshwater, lakes support and sustain communities across the planet. A new study uses satellite data to underline the vulnerability of these inland water bodies to climate change and warns of serious future consequences for many freshwater species worldwide. 55)
Rising lake water temperatures, a consequence of climate change, strongly influences the distribution and abundance of freshwater species. A recent study, published in Nature Climate Change, estimates the rate of future global lake surface water temperature changes using the latest generation of climate projections from the Coupled Model Intercomparison Project (CMIP5) and compares this to the ability of some species to disperse to cooler areas. 56)
Figure 53: The velocity of climate change in European standing waters. Figure a depicts the surface water temperature trend, while b shows the two-dimensional spatial gradient of surface water temperature change. Figure c shows the velocity of climate change during the 1979 to 2018 period. White regions represent those where standing waters are absent within the global database (image credit: Nature: Climate velocity in inland standing waters)
The authors calculated the speed at which lake habitats are warming and the distance species would need to migrate or shift their distribution over time to maintain a suitable thermal habitat. Often referred to as climate change velocity, this latter figure is used by scientists to help understand the impacts of climate change.
In line with previous studies, the majority of lakes, 99%, were found to be warming by 0.13°C per decade on average between 1979 to 2018. Importantly, they show climate change velocity is expected to accelerate during the current century, with potentially serious consequences for freshwater species.
The study shows that the climate change velocity was 3.5 km per decade from 1861-2005 (with a standard deviation of 2.3 km). While this figure is similar to, or lower than, rates of dispersal of some motile species, the rate is expected to accelerate from now to the end of the century.
Under a future low greenhouse gas emissions scenario, the climate velocity increases to 8.7 km per decade (with a standard deviation of 5.5 km) and as high as 57 km per decade (standard deviation of 17 km) if the Intergovernmental Panel on Climate Change’s worst-case climate projections that assume high-levels of greenhouse gas emissions.
According to Iestyn Woolway, co-author of the study and ESA research fellow, “Lake temperatures are set to rise faster than the ability of some species to disperse to cooler areas. The consequences will be more serious for species that disperse less readily, such as freshwater molluscs, but even more motile species, such as some fish, which could migrate more rapidly are likely to be restricted by physical barriers.”
The researchers illustrate that while lake climate change velocity is half that of marine environments, the fragmented and often isolated distribution of lakes across the landscape limits dispersal and magnifies the negative outlook for freshwater species conservation, and the goods and services they provide.
Satellite observations play an important role in the development and validation of models. This study exploited the first global dataset for the lakes essential climate variable. Generated by ESA Climate Change Initiative’s lake project, the dataset addresses the urgent need for global, long-term observations required by the Global Climate Observing System (GCOS) needed to critically characterize Earth’s climate.
The freely available data covers the period 1992 to 2019 and provides information for five key lake variables, including daily observations of lake surface temperature, level, extent, ice cover and reflectance for 250 globally distributed lakes worldwide.
ESA's Climate Change Initiative generates accurate and long-term satellite-derived datasets for 21 Essential Climate Variables, to characterize the evolution of the Earth system.
Figure 54: Global relationship between the spatial temperature gradient and elevation. Shown is comparison of a, the two-dimensional spatial gradient of surface water temperature change, and b, elevation. White regions represent those where standing waters are absent within the global database (image credit: Nature: Climate velocity in inland standing waters)
Change in Tundra Greeness
• September 23, 2020: As Arctic summers warm, Earth’s northern landscapes are changing. Using satellite images to track global tundra ecosystems over decades, a team of researchers finds the region has become greener as warmer air and soil temperatures lead to increased plant growth. 57)
“The Arctic tundra is one of the coldest biomes on Earth, and it’s also one of the most rapidly warming,” said Logan Berner, assistant research professor with Northern Arizona University’s School of Informatics, Computing, and Cyber Systems (SICCS), who led the research in collaboration with scientists at eight other institutions in the United States, Canada, Finland and the United Kingdom. “This Arctic greening we see is really a bellwether of global climatic change—it’s this biome-scale response to rising air temperatures.”
The study, published this week in Nature Communications, is the first to measure vegetation changes across the Arctic tundra, from Alaska and Canada to Siberia, using satellite data from Landsat, a joint mission of NASA and the U.S. Geological Survey. Scientists use Landsat data to determine how much actively growing vegetation is on the ground—greening can represent plants growing more, becoming denser or shrubs encroaching on typical tundra grasses and moss. 58)
Figure 55: The study is the first to measure vegetation changes across the Arctic tundra, from Alaska and Canada to Siberia, using satellite data from Landsat (image credit: Northern Arizona University, NASA, USGS)
When the tundra vegetation changes, it impacts not only the wildlife that depend on certain plants, but also the people who live in the region and depend on local ecosystems for food. While active plants will absorb more carbon from the atmosphere, the warming temperatures are also thawing permafrost, releasing greenhouse gasses. The research is part NASA’s Arctic Boreal Vulnerability Experiment (ABoVE), which aims to better understand how ecosystems are responding in these warming environments and its broader implications.
Landsat data was used including additional calculations to estimate the peak greenness for a given year for each of 50,000 randomly selected sites across the tundra. Between 1985 and 2016, about 38 percent of the tundra sites across Alaska, Canada and western Eurasia showed greening. Only 3 percent showed the opposite browning effect, which would mean fewer actively growing plants.
To include eastern Eurasian sites, the team compared data starting in 2000, which was when Landsat satellites began collecting regular images of that region. With this global view, 22 percent of sites greened between 2000 and 2016, while 4 percent browned.
“Whether it’s since 1985 or 2000, we see this greening of the Arctic evident in the Landsat record,” Berner said. “And we see this biome-scale greening over the same period as we see really rapid increases in summer air temperatures.”
The researchers compared these greening patterns with other factors and found that they are also associated with higher soil temperatures and higher soil moisture. They confirmed these findings with plant growth measurements from field sites around the Arctic.
“Landsat is key is for these kinds of measurements because it gathers data on a much finer scale than what was previously used,” said Goetz, who contributed to the study and leads the ABoVE science team. That allows the researchers to investigate what is driving the changes to the tundra. “There’s a lot of microscale variability in the Arctic, so it’s important to work at finer resolution while also having a long data record. That’s why Landsat’s so valuable.”
Ocean salinity: Climate change is also changing the water cycle
• September 9, 2020: As the Earth is warming, the global water cycle amplifies. Researchers from the Chinese Academy of Science (CAS), ETH Zürich, the American National Center for Atmospheric Research (NCAR), the University of St. Thomas (St. Paul, Minnesota) and the Pennsylvania State University studying ocean salinity have found strong evidence of a substantial amplification of in the past 50 years. 59)
Water and its movements within or between atmosphere, land, and ocean defines the global water cycle, which is a central element of Earth’s climate system (Figure 56). Almost all weather and climate phenomena are in some way tied to the water cycle. Examples include extreme rainfall during thunderstorms, hurricanes and tropical cyclones, flooding, droughts, and sea level rise.
As the climate changes, the water cycle is changing in important ways as well. Theory and models suggest that as the Earth is warming, the global water cycle amplifies, i.e., more water is evaporated from the ocean, and consequently precipitation is increasing as well. Yet the observational confirmation of this prediction has been difficult, since past changes of the water cycle were poorly observed due to the difficulty of measuring global-scale evaporation and precipitation and the complexity of their spatial and temporal variability.
Figure 56: An illustration of the global water cycle and its change. The figure is adapted from https://gpm.nasa.gov/education/water-cycle. (image credit: NASA)
The meaning of salinity change
The study, published in Journal of Climate, overcomes many of the previous limitations, and derives an estimate of water cycle change based on a new salinity data product since 1960. From this, they provided strong evidence that the global water cycle has amplified substantially in the past 50 years, confirming theory and models. The study is led by Lijing Cheng from Institute of Atmospheric Physics of CAS, who collaborated with a group of international scientists. 60)
Changes in ocean salinity change can be used to estimate changes in Earth’s water cycle, because salinity variations very sensitively reflect the net exchange of freshwater between the ocean and the atmosphere. “Evaporation takes freshwater from the ocean into the atmosphere and increases the ocean salinity; precipitation puts freshwater into the ocean and reduces its salinity. Consequently, salinity changes integrate effects over broad areas and provide an excellent indicator for water cycle change,” according to Lijing Cheng.
Monthly gridded salinity fields deliver more accurate data
A number of previous studies have followed this approach, but their conclusions were limited by the fact that the underlying salinity datasets were subject to biases or limited to just the surface ocean. This new study provides new monthly gridded salinity fields for the upper 2000 m since 1960. “The new product is clearly more reliable for examining long-term salinity changes, as we show that this new salinity reconstruction has much better continuity through changes in the observing-system (from altimeters on satellites and profiling floats (Argo) in the ocean,” according to co-author, Kevin Trenberth from NCAR.
Figure 57: The 0-2000 mean salinity climatology (top) shows the relatively fresh Pacific versus the salty Atlantic northern Indian Ocean. Its long-term trend (middle) has a remarkably similar pattern (image credit: Ocean salinity study team)
The "Salinity Contrast (SC) index"
As the salinity changes are spatially complex, Cheng et al. use a simple index to synthesize these changes, named the Salinity Contrast (SC) index, which is defined as the difference between the salinity averaged over high-salinity and low-salinity regions (Figure 58). “This metric provides a simple but powerful means of synthesizing the observed salinity pattern changes” said Nicolas Gruber, a coauthor of this study from ETH: “We show that the 0-2000 m salinity pattern has amplified by 1.6% and and that at the surface by 7.5%. We also show that this increase is due to human influence, and that this anthropogenic signal has exceeded the natural background variability.”
By combining this improved estimate of the salinity changes with model simulations, the authors demonstrate that the water cycle must have amplified by 2~4 % per degree Celsius since 1960 in order to explain the magnitude and pattern of changes (Figure 56). This ocean-based result is broadly consistent with many recent atmospheric based estimates and strengthens the evidence that global warming intensifies the global water cycle.
Figure 58: Increasing salinity-contrast in the world’s ocean. The figure shows the salinity-contrast time series from 1960 to 2017 at the upper ocean 2000 m. Background photograph: Xilin Wang (image credit: Ocean salinity study team)
Consequences for the future climate
This result has important implications for future climate. This sensitivity to global warming implies an amplification by 4~8% in a world warmed by +2°C (the upper limit of the “Paris Agreement” target). This amplification will be even stronger if the aerosol impacts are smaller in the future than today (i.e. if the air pollution can be controlled). Consequently, there will be stronger evaporation: the drier regions will get even drier and further increase the odds of worsening drought. Droughts affect livestock and crops and increase risk of damaging and sometimes deadly wildfire in many regions, including the U.S., China, Australia, Brazil, and other countries, posing severe risks to food safety and human health.
There will also be greatly increased risk of heavy and extreme rains. The more intense rainstorms cause major problems like extreme flooding around the world. The rainfall associated with tropical cyclones and hurricanes will continue to grow and increase damage not only to coastal and small island communities, but far in the inland as well (as in Isaias).
“This study is a significant advance in the field”, said Michael Mann from Pennsylvania State University. “First, the new, more accurate estimates of salinity changes provide a better basis for comparison with climate model simulations. Secondly, the Salinity-Contrast (SC) index provides a key measure of climate change impact on the global water hydrological cycle and distinguishing the signal. We find that it takes a little more than a decade to isolate the climate change signal from background noise in this particular metric, suggesting it should be used more widely by the climate research community.”
This study was supported by the National Key R&D Program of China (2017YFA0603202), Key Deployment Project of Centre for Ocean Mega-Research of Science, CAS (COMS2019Q01), the European Union’s Horizon 2020 research and innovation program under grant agreements 821001 and 821003.
Ice sheet melt on track with ‘worst-case climate scenario’
• September 8, 2020: A recent report confirms that ice sheets in Greenland and Antarctica, whose mass-loss rates have been rapidly increasing, are matching the Intergovernmental Panel on Climate Change's worst-case sea-level rise scenarios. 61)
The study, published in Nature Climate Change, compares ice-sheet mass-balance results from satellite observations with projections from climate models. The results come from an international team of scientists from the University of Leeds (UK) and the Danish Meteorological Institute (DMI), who are also part of the ongoing IMBIE (Ice-Sheet Mass Balance Inter-comparison Exercise). 62)
IMBIE is an international collaboration between scientists, established in 2011 as a community effort to reduce uncertainties in different satellite-based measurements of ice sheet mass balance, and is co-funded by ESA and NASA.
Since the systematic monitoring of ice sheets began in the early 1990s, Greenland and Antarctica combined lost 6.4 trillion tons of ice between 1992 and 2017 – pushing global sea levels up by 17.8 mm. If these rates continue, ice sheets are expected to raise sea levels by a further 17 cm – exposing an additional 16 million people to annual coastal flooding by the end of the century.
Tom Slater, lead author of the study and climate researcher at the Centre for Polar Observation and Modelling at the University of Leeds, comments, “Satellites are our only means of routinely monitoring these vast and remote areas, so they are absolutely critical in providing measurements which we can use to validate ice sheet models.
“Satellite observations not only tell us how much ice is being lost, they also help us to identify and understand which parts of Antarctica and Greenland are losing ice and through what processes - both are key in helping us improve ice sheet models.”
Figure 59: The Antarctic and Greenland ice sheet contribution to global sea level according to IMBIE (black), compared to satellite observations and projections between 1992-2040 (left) and 2040-2100 (right), image credit: IMBIE
IMBIE uses data from various satellite missions – including ESA’s ERS-1, ERS-2, Envisat and CryoSat missions, as well as the EU’s Copernicus Sentinel-1 mission – to monitor changes in the ice sheet’s volume, flow and mass.
Ruth Mottram, co-author of the study and Climate Scientist at DMI, adds, “Data from ESA satellite missions have underpinned many advances in our understanding of ice sheet behavior over the past three decades. ESA’s family of satellite radar altimeters: ERS-1, ERS-2, Envisat and CryoSat have provided a long-term continuous record of ice sheet changes since the early 1990s.”
ESA’s Marcus Engdahl adds, “Satellite observations are showing us that the ice sheets are reacting surprisingly rapidly to environmental change. It is vital that scientists have access to data from future satellite missions that can observe polar areas, for example, the next high priority Copernicus candidate missions CRISTAL, ROSE-L and CIMR.”
IMBIE is supported by ESA's EO Science for Society program and ESA's Climate Change Initiative, which generates accurate and long-term satellite-derived datasets for 21 Essential Climate Variables, to characterize the evolution of the Earth system.
NASA-led Study Reveals the Causes of Sea Level Rise Since 1900
• August 21, 2020: To make better predictions about the future impacts of sea level rise, new techniques are being developed to fill gaps in the historic record of sea level measurements. We know the factors that play a role in sea level rise: Melting glaciers and ice sheets add water to the seas, and warmer temperatures cause water to expand. Other factors are known to slow the rise, such as dams impounding water on the land, stymying its flow into the sea. 63)
When each factor is added together, this estimate should match the sea level that scientists observe. Until now, however, the sea level "budget" has fallen short of the observed sea level rise, leading scientists to question why the budget wouldn't balance.
A new study published on Aug. 19 seeks to balance this budget. By gaining new insights to historic measurements, scientists can better forecast how each of these factors will affect sea level rise and how this rise will impact us in the future. 64)
For example, in its recent flooding report, the National Oceanic and Atmospheric Administration (NOAA) noted a rapid increase in sea level rise-related flooding events along U.S. coasts over the last 20 years, and they are expected to grow in extent, frequency, and depth as sea levels continue to rise.
Factors Driving Our Rising Seas
On reexamining each of the known contributors to sea level rise from 1900 to 2018, the research, led by NASA's Jet Propulsion Laboratory in Southern California, uses improved estimates and applies satellite data to better understand historic measurements.
The researchers found that estimates of global sea level variations based on tide-gauge observations had slightly overestimated global sea levels before the 1970s. (Located at coastal stations scattered around the globe, tide gauges are used to measure sea level height.) They also found that mountain glacier meltwater was adding more water to the oceans than previously realized but that the relative contribution of glaciers to sea level rise is slowly decreasing. And they discovered that glacier and Greenland ice sheet mass loss explain the increased rate of sea level rise before 1940.
Figure 60: This infographic shows the rise in sea levels since 1900. Pre-1940, glaciers and Greenland meltwater dominated the rise; dam projects slowed the rise in the 1970s. Now, ice sheet and glacier melt, plus thermal expansion, dominate the rise. Tide-gauge data shown in blue and satellite data in orange (image credit: NASA/JPL-Caltech)
In addition, the new study found that during the 1970s, when dam construction was at its peak, sea level rise slowed to a crawl. Dams create reservoirs that can impound freshwater that would normally flow straight into the sea.
"That was one of the biggest surprises for me," said lead researcher Thomas Frederikse, a postdoctoral fellow at JPL, referring to the peak in global dam projects at that time. "We impounded so much freshwater, humanity nearly brought sea level rise to a halt."
Since the 1990s, however, Greenland and Antarctic ice sheet mass loss and thermal expansion have accelerated sea level rise, while freshwater impoundment has decreased. As our climate continues to warm, the majority of this thermal energy is absorbed by the oceans, causing the volume of the water to expand. In fact, ice sheet melt and thermal expansion now account for about two-thirds of observed global mean sea level rise. Mountain glacier meltwater currently contributes another 20%, while declining freshwater water storage on land adds the remaining 10%.
All told, sea levels have risen on average 1.6 mm (0.063 inches) per year between 1900 and 2018. In fact, sea levels are rising at a faster rate than at any time in the 20th century. But previous estimates of the mass of melting ice and thermal expansion of the ocean fell short of explaining this rate, particularly before the era of precise satellite observations of the world's oceans, creating a deficit in the historic sea level budget.
Finding a Balance
In simple terms, the sea level budget should balance if the known factors are accurately estimated and added together. It's a bit like balancing the transactions in your bank account: Added together, all the transactions in your statement should match the total. If they don't, you may have overlooked a transaction or two.
The same logic can be applied to the sea level budget: When each factor that affects sea level is added together, this estimate should match the sea level that scientists observe. Until now, however, the sea level budget has fallen short of the observed sea level rise.
"That was a problem," said Frederikse. "How could we trust projections of future sea level change without fully understanding what factors are driving the changes that we have seen in the past?"
Frederikse led an international team of scientists to develop a state-of-the-art framework that pulls together the advances in each area of study - from sea level models to satellite observations - to improve our understanding of the factors affecting sea level rise for the past 120 years.
The latest satellite observations came from the pair of NASA - German Aerospace Center (DLR) Gravity Recovery and Climate Experiment (GRACE) satellites that operated from 2002-2017, and their successor pair, the NASA - German Research Centre for Geosciences (GFZ) GRACE Follow-On (launched in 2018). Additional data from the series of TOPEX/Jason satellites - a joint effort of NASA and the French space agency CNES (Centre National d'Etudes Spatiales) -that have operated continuously since 1992 were included in the analysis to enhance tide-gauge data.
"Tide-gauge data was the primary way to measure sea level before 1992, but sea level change isn't uniform around the globe, so there were uncertainties in the historic estimates," said Sönke Dangendorf, an assistant professor of oceanography at Old Dominion University in Norfolk, Virginia, and a coauthor of the study. "Also, measuring each of the factors that contribute to global mean sea levels was very difficult, so it was hard to gain an accurate picture."
But over the past two decades, scientists have been "flooded" with satellite data, added Dangendorf, which has helped them precisely track the physical processes that affect sea levels.
For example, GRACE and GRACE-FO measurements have accurately tracked global water mass changes, melting glaciers, ice sheets, and how much water is stored on land. Other satellite observations have tracked how regional ocean salinity changes and thermal expansion affect some parts of the world more than others. Up-and-down movements of Earth's crust influence the regional and global levels of the oceans as well, so these aspects were included in the team's analysis.
"With the GRACE and GRACE-FO data we can effectively back-extrapolate the relationship between these observations and how much sea level rises at a particular place," said Felix Landerer, project scientist at JPL for GRACE-FO and a coauthor of the study. "All observations together give us a pretty accurate idea of what contributed to sea level change since 1900, and by how much."
The study, titled "The Causes of Sea Level Rise Since 1900," was published Aug. 19 in Nature. In addition to scientists from JPL and Old Dominion University, the project involved researchers from Caltech, Université Catholique de Louvain in Belgium, University of Siegen in Germany, the National Oceanography Centre in the United Kingdom, Courant Institute in New York, Chinese Academy of Sciences, and Academia Sinica in Taiwan.
JPL managed the GRACE mission and manages the GRACE-FO mission for NASA's Earth Science Division of the Science Mission Directorate at NASA Headquarters in Washington. Based on Pasadena, California, Caltech manages JPL for NASA.
Methane Emissions Continue to Rise
Researchers synthesized all known data about methane from emissions inventories, atmospheric measurements, and models to assemble a global “methane budget” that details which processes add the gas to the atmosphere and which remove it. They found that global emissions of the potent greenhouse gas totaled 576 million metric tons per year for the 2008 to 2017 decade—a 9 percent increase compared to the previous decade.
The rapid growth builds upon the rise in the atmospheric concentration of the gas that has been happening for more than a century. (Emissions briefly stabilized between 2000 and 2006.) Concentrations of methane now exceed 1875 parts per billion, about 2.5 times as much as was in the atmosphere in the 1850s. Climate scientists estimate that the gas is responsible for about one quarter of the global warming that has happened since then.
Figure 61: This figure shows the changes in methane emissions from 2017 compared to the 2000–2006 average and sorted by region. Estimates were compiled through “top-down” methods—based on satellite and ground-based observations—and “bottom-up” methods—summing up all individual sources from global inventories and models. The two independent approaches are used and compared to one another as a way to see how well the methane budget is understood. In both cases, increases in methane emissions over the past two decades were widespread and statistically significant (image credit: NASA Earth Observatory image by Lauren Dauphin, using data from Jackson, R. et al. (2020). Story by Adam Voiland) 66)
“The increase was primarily fueled by human activities—especially agriculture and fossil fuels,” explained Benjamin Poulter, a NASA scientist and coordinator of the wetland methane emissions estimates for the Global Carbon Project. “The specific activities that we linked to the biggest increases were raising livestock, coal mining, waste disposal in landfills, and gas and oil production.”
Across the study years, wetlands contributed 30 percent of global methane emissions, with oil, gas, and coal activities accounting for 20 percent. Agriculture, including enteric fermentation and manure management, made up 24 percent of emissions, and landfills comprised 11 percent. Sixty-four percent of emissions came from tropical regions of South America, Asia, and Africa, with temperate regions accounting for 32 percent and the Arctic contributing 4 percent.
High-latitude ecosystems are particularly vulnerable to climate change. Large amounts of carbon are stored in frozen soils (permafrost) and in forest vegetation in the Arctic. As it thaws, water-logged soil becomes an ideal environment for methane production. “However, we have yet to detect abnormal methane emissions in higher-latitude regions,” said Poulter, “despite thawing permafrost and record-breaking air temperatures year-after-year.”
There is evidence that significant amounts of carbon from thawing permafrost may be entering rivers as dissolved carbon rather than being emitted to the atmosphere as methane. Also, the high-latitude warming may be drying out Arctic ecosystems, causing carbon to leave the soil as carbon dioxide rather than methane.
NASA’s Arctic Boreal Ecosystem Vulnerability Study (ABoVE) is one major effort to improve our understanding of how climate change is affecting Arctic methane emissions. For instance, ABoVE researchers recently made hyperspectral airborne observations that confirmed the existence of millions of sources of methane around small ponds and lakes in Alaska and western Canada.
Figure 62: This photograph shows a freshwater lake in Fairbanks, Alaska, that ABoVE researchers visited in July 2016. The lake showed signs of thawing permafrost below the surface, including “drunken trees” that had tipped over as the soil shifted around their roots (image credit: NASA Earth Observatory)
Figure 63: The video is a data visualization that highlights several different sources of methane emissions produced around the globe and throughout the year. It was created using output from a modeling system developed and maintained by NASA’s Global Modeling and Assimilation Office. Note that the height of Earth’s atmosphere and topography have been vertically exaggerated approximately 50 times higher than normal in order to show the complexity of the atmospheric flow (video credit: NASA Scientific Visualization Studio, NASA Earth Observatory)
Ice Melt Linked to Accelerated Regional Freshwater Depletion
• June 1, 2020: Continuous monitoring of glaciers and ice caps has provided unprecedented insights to global ice loss that could have serious socioeconomic impacts on some regions. 67)
Seven of the regions that dominate global ice mass losses are melting at an accelerated rate, a new study shows, and the quickened melt rate is depleting freshwater resources that millions of people depend on.
The impact of melting ice in Greenland and Antarctica on the world's oceans is well documented. But the largest contributors to sea level rise in the 20th century were melting ice caps and glaciers located in seven other regions: Alaska, the Canadian Arctic Archipelago, the Southern Andes, High Mountain Asia, the Russian Arctic, Iceland and the Norwegian archipelago Svalbard. The five Arctic regions accounted for the greatest share of ice loss.
Figure 64: A small glacier in the Arctic region of Norwegian archipelago Svalbard, as photographed by NASA's Airborne Tropical Tropopause Experiment (ATTREX). This is one of the seven regions where ice loss is accelerating, causing the depletion of freshwater resources (image credit: NASA/John Sonntag)
And this ice melt is accelerating, potentially affecting not just coastlines but agriculture and drinking water supplies in communities around the world, according to the study by scientists at NASA's Jet Propulsion Laboratory; the University of California, Irvine; and the National Center for Atmospheric Research in Boulder, Colorado. The study was led by Enrico Ciraci, a UCI graduate student researcher in Earth system science. 68)
"In the Andes Mountains in South America and in High Mountain Asia, glacier melt is a major source of drinking water and irrigation for several hundred million people," said study coauthor Isabella Velicogna, a senior scientist at JPL and professor of Earth system science at UCI. "Stress on this resource could have far-reaching effects on economic activity and political stability."
The researchers based their work on data from the recently decommissioned U.S.-German Gravity Recovery and Climate Experiment (GRACE) pair of satellites that operated from 2002 to 2017, and their successor pair, GRACE Follow On (launched in 2018). The researchers calculated that, on average, these seven regions lost more than 280 billion tons of ice per year.
This ice loss contributed a total of 13 mm (0.5 inches) in global sea level rise between 2002 and 2019, and the rate has increased from 0.7 mm (0.028 inches) per year in 2002 to 0.9 mm per year in 2019. 69)
As with GRACE, the GRACE-FO satellites continuously measure very slight changes in Earth's gravitational pull as they orbit the Earth. Over time, shifts in the distribution of water are the largest source of gravity changes on the planet, so scientists can use the measurements of gravity change to track variations in the mass of water as it cycles from the ice caps and glaciers to the oceans.
GRACE was a joint mission of NASA and the German Aerospace Center, in partnership with the University of Texas at Austin. GRACE-FO is a partnership between NASA and the German Research Centre for Geosciences. When it launched in May 2018, 11 months had passed since GRACE made its last measurements.
Velicogna and her coauthors closed the resulting data gap between the end of GRACE and the initiation of GRACE-FO by using a state-of-the-art modeling tool called Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) from NASA's Global Modeling and Assimilation Office. MERRA-2 utilizes a host of independent observational datasets to boost the precision of its estimates. For this study, the researchers noted how well the MERRA-2 results lined up with the GRACE and GRACE-FO data, giving them a high degree of confidence of what these satellites would have observed if one or both were operating in the period of the data gap.
Having a record based on the long-term, precision measurements of hundreds of thousands of the world's glaciers for over 18 years, Velicogna said, significantly enhances our understanding of their evolution.
"This paper demonstrates that GRACE-FO, in addition to GRACE, is providing precise, reliable, worldwide observations of the fate of mountain glaciers, which are not only important for understanding sea level change, but also for managing our freshwater resources," she said.
Shedding light on the ocean’s living carbon pump
• May 6, 2020: Phytoplankton play a crucial role in ocean biology and climate. Understanding the natural processes that influence phytoplankton primary production, and how they are changing as the planet warms, is vital. A new study, using data from the European Space Agency’s Climate Change Initiative, has produced a 20-year time-series of global primary production in the oceans – shedding new light on the ocean’s living carbon pump. 70)
Phytoplankton, microscopic, free-floating plants in aquatic systems, play an important role in the global carbon cycle by absorbing carbon dioxide on a scale equivalent to that of terrestrial plants. Primary production is an ecologic term used to describe the synthesis of organic material from carbon dioxide and water, in the presence of sunlight, through photosynthesis. Even small variations in primary productivity can affect carbon dioxide concentrations, as well as influencing biodiversity and fisheries.
As ocean surfaces warm in response to increasing atmospheric greenhouse gases, phytoplankton productivity will need to be monitored both consistently and systematically. Although in situ measurements are necessary in studying productivity, satellite data are fundamental to providing a global view of phytoplankton and their role in, and response to, climate change.
In a recent paper published in Remote Sensing, scientists used data from the OC-CCI (Ocean Color Climate Change Initiative) to study the long-term patterns of primary production and its interannual variability. Combining long-term satellite data with in situ measurements, they assessed global annual primary productivity from 1998-2018. 71)
Figure 65: This map shows the global annual primary productivity from 1998-2018 (video credit: Ocean Color CCI, Plymouth Marine Laboratory/ESA)
Changes in primary production varied location to location, season to season and year after year. They found that global annual primary production varied around 38 to 42 gigatons of carbon per year. They also observed several regional differences, with high production in coastal areas and low production in the open oceans.
Figure 66: Global monthly primary productivity. This animation shows the monthly average of primary productivity in 2018 (image credit: Ocean Color CCI, Plymouth Marine Laboratory/ESA)
The paper also highlighted that phytoplankton productivity levels increase and decrease coinciding with major Earth system processes – such as El Niño, Indian Ocean Dipole and North Atlantic Oscillation.
Gemma Kulk, from Plymouth Marine Laboratory and the lead author of the paper, comments “Everyone understands why the rainforests and trees are important – they are the lungs of the Earth, taking up carbon dioxide from the atmosphere. What is overlooked is that the oceans are of equal importance – every second breath you take comes from the oceans.”
Being able to observe and quantify primary production over long-time scales will help the scientific and modelling communities to determine the effect of climate variability on these processes, as well as to identify any residual trend that signals a shift in climate.
Co-author, Shubha Sathyendranath, from Plymouth Marine Laboratory and science leader of the Ocean Color CCI project, adds, “Although the data records span 20 years, it is important to wait at least 30 years to be able to identify any clear climate trend with sufficient confidence.
”It is critical that the ocean color dataset as part of the Climate Change Initiative be extended and maintained on a regular basis, so that we have an empirical record of the response of ocean biota to changes in climate. From this, we can develop reliable models, so we can accurately predict change in order to adapt to the impacts of a changing world.”
ESA’s Climate Change Initiative is a research and development program that merges and calibrates measurements from multiple satellite missions to generate a global time-series looking at 21 key components of the climate system. Spanning decades, these long-term data records enable scientists to identify climate trends, develop and test Earth system models that predict future change and inform decision-makers to mitigate and adapt to the impacts.
Figure 67: The Copernicus Sentinel-2 mission takes us over the green algae blooms swirling around the Baltic Sea. 'Algae bloom' is the term used to describe the rapid multiplying of phytoplankton – microscopic marine plants that drift on or near the surface of the sea. The chlorophyll that phytoplankton use for photosynthesis collectively tints the surrounding ocean waters, providing a way of detecting these tiny organisms from space. In most of the Baltic Sea, there are two annual blooms – the spring bloom and the cyanobacterial (also called blue-green algae) bloom in late summer. The Baltic Sea faces many serious challenges, including toxic pollutants, deep-water oxygen deficiencies, and toxic blooms of cyanobacteria affecting the ecosystem, aquaculture and tourism. Cyanobacteria have qualities similar to algae and thrive on phosphorus in the water. High water temperatures and sunny, calm weather often lead to particularly large blooms that pose problems to the ecosystem. - In this image captured on 20 July 2019, the streaks, eddies and whirls of the late summer blooms, mixed by winds and currents, are clearly visible. Without in situ measurements, it is difficult to distinguish the type of algae that covers the sea as many different types of algae grow in these waters. The highest concentrations of algal blooms are said to occur in the Central Baltic and around the island of Gotland, visible to the left in the image (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
Shrinking Snowcaps Fuel Harmful Algal Blooms in Arabian Sea
• May 4, 2020: A uniquely resilient organism all but unheard of in the Arabian Sea 20 years ago has been proliferating and spreading at an alarming pace, forming thick, malodorous green swirls and filaments that are visible even from space. This unusual organism is Noctiluca scintillans—a millimeter-size planktonic organism with an extraordinary capacity to survive, thrive and force out diatoms, the photosynthesizing plankton that have traditionally supported the Arabian Sea food web. Noctiluca is not a preferred food for larger organisms, so these large blooms, recurring annually and lasting for several months, are disrupting the base of the region’s marine food chain, threatening fisheries that sustain 150 million people, and possibly exacerbating the rise of criminal piracy in the region. 72)
New research published this week in Nature’s Scientific Reports describes how the continued loss of snow over the Himalayan-Tibetan Plateau region is fueling the expansion of this destructive algal bloom. Led by Joaquim I. Goes from Columbia University’s Lamont-Doherty Earth Observatory, the study uses field data, laboratory experiments, and decades of NASA satellite imagery to link the rise of Noctiluca in the Arabian Sea with melting glaciers and a weakened winter monsoon. 73)
Normally, cold winter monsoon winds blowing from the Himalayas cool the surface of the oceans. These colder waters sink and are replaced with nutrient-rich waters from below. This convective mixing is no different than putting an ice cube into a mug of hot coffee. During this time, phytoplankton, the primary producers of the food chain, thrive in the sunlit, nutrient-rich upper layers, and surrounding countries see a bounty of fish that feed directly or indirectly on the phytoplankton. But with the shrinking of glaciers and snow cover in the Himalayas, the monsoon winds blowing offshore from land are warmer and moister, resulting in diminished convective mixing and decreased fertilization of the upper layers.
In this scenario, phytoplankton such as diatoms are at a disadvantage, but not Noctiluca. Unlike diatoms, Noctiluca (also known as sea sparkle) doesn’t rely only on sunlight and nutrients; it can also survive by eating other microorganisms. Noctiluca hosts thousands of photosynthesizing endosymbionts within its bulbous, transparent, greenhouse-like cell. The green endosymbionts provide it with energy from photosynthesis, while its tail-like flagellum allows it to grab any microscopic plankton from the surrounding water as an additional source of food.
This dual mode of energy acquisition gives it a tremendous advantage to flourish and disrupt the classic food chain of the Arabian Sea. Noctiluca’s second advantage is that its endosymbionts accumulate a lot of ammonia in the cell, making the organism unpalatable to larger grazers. As a third advantage, the accumulated ammonia is also a repository of nitrogenous nutrients for the endosymbionts, making them less vulnerable to diminishing inputs of nutrients from a weakened convective mixing.
Noctiluca blooms first appeared in the late 1990s. The sheer size of their blooms, which occur annually, threaten the Arabian Sea’s already vulnerable food chain because its symbionts not only compete with phytoplankton for the annually replenished nutrients, but feed on the phytoplankton themselves. However, only jellyfish and salps seem to find Noctiluca palatable. In Oman, desalination plants, oil refineries and natural gas plants are forced to scale down operations because they are choked by Noctiluca blooms and the jellyfish that swarm to feed on them. The resulting pressure on the marine food supply and economic security may also have fueled the rise in piracy in countries like Yemen and Somalia.
Figure 68: Noctiluca blooms in the Arabian Sea, as seen from space (image credit: NASA, Norman Kuring)
Figure 69: Coauthor Khalid Al-Hashmi of Oman’s Sultan Qaboos University holds a Noctiluca-fouled bottle of seawater (photo credit: Columbia University/Lamont-Doherty Earth Observatory, Joaquim Goes)
Figure 70: The millimeter-size organisms can both perform photosynthesis and hunt down other organisms for food (Columbia University/Lamont-Doherty Earth Observatory, Kali McKee)
“This is probably one of the most dramatic changes that we have seen that’s related to climate change,” said Goes who, along with Lamont researcher Helga do Rosario Gomes, has been studying the rapid rise of this organism for more than 18 years. “We are seeing Noctiluca in Southeast Asia, off the coasts of Thailand and Vietnam, and as far south as the Seychelles, and everywhere it blooms it is becoming a problem. It also harms water quality and causes a lot of fish mortality.”
The study provides compelling new evidence of the cascading impacts of global warming on the Indian monsoons, with socioeconomic implications for large populations of the Indian sub-continent and the Middle East.
“Most studies related to climate change and ocean biology are focused on the polar and temperate waters, and changes in the tropics are going largely unnoticed,” said Goes.
The study highlights how tropical oceans are being disproportionately impacted, losing their biodiversity, and changing faster than conventional model predictions. This may portend dire consequences over the long term for countries in the region already gripped by socioeconomic problems from war, poverty and loss of livelihoods, said Goes.
Lamont-Doherty scientists O. Roger Anderson, Douglas G. Martinson, and high school students working with the observatory also contributed to the research. Other co-authors include researchers from Oman’s Ministry of Fisheries and Agricultural Wealth and Ministry of Foreign Affairs, as well as researchers from Oman’s Sultan Qaboos University, and from Tiangong and Xiamen universities in China.
The research was funded by NASA Earth Sciences, the Gordon and Betty Moore Foundation and the Sultan Qaboos Cultural Center.
Whatever Sea Level Rise Brings, NASA Will Be There
• April 21, 2020: Greenland and coastal Louisiana may not seem to have a lot in common. An autonomous territory of Denmark, Greenland is covered in snow most of the year and is home to about 56,000 people. On the other hand, more than 2 million people call coastal Louisiana home and the region rarely sees snow. 74)
But their economies, though 3,400 miles (5,400 km) apart, share a dependence on the sea. The majority of Greenland's residents rely on the territory's robust Arctic fishing industry. And in Louisiana, the coasts, ports and wetlands provide the basis for everything from shipping to fishing to tourism. As a result, both locales and the people who live in them are linked by a common environmental thread: melting ice and consequent sea level rise.
Figure 71: The Mississippi River Delta contains vast areas of marshes, swamps and barrier islands — important for wildlife and as protective buffers against storms and hurricanes. Rapid land subsidence due to sediment compaction and dewatering increases the rate of submergence in this system (image credit: K. L. McKee / U.S. Geological Survey)
Figure 72: Photo from a 2017 survey of Greenland conducted by NASA's Oceans Melting Greenland (OMG) mission (photo credit: NASA/JPL-Caltech)
NASA Sees the Seas
Thanks to altimetry missions, beginning with the U.S.-French TOPEX / Poseidon mission launched in 1992 and continuing through the present with the Jason series, we now have a nearly three-decade-long record of sea level change.
Similarly, because of missions like the U.S.-German Gravity Recovery and Climate Experiment (GRACE) and its successor, GRACE Follow-On, we know a lot more about what the ice is doing than we used to, especially at the poles. For instance, we know that Greenland lost 600 billion tons of ice last summer alone. That's enough to raise global sea levels by a tenth of an inch (2.2 millimeters). We also know that both Greenland and Antarctica are losing ice six times faster than they were in the 1990s.
These numbers matter because frozen within all of the glaciers and ice sheets is enough water to raise global sea levels by more than 195 feet (60 meters) — key word here being "global." Ice that melts in Greenland and Antarctica, for example, increases the volume of water in the ocean as a whole and can lead to flooding far from where the melting occurred, like in coastal communities half a world away.
In addition to using satellite data to monitor sea levels and ice melt, NASA scientists are observing the seas from a closer vantage point. "The satellites tell us it's happening. But we want to know why — what's causing it?" said Josh Willis of the agency's Jet Propulsion Laboratory in Southern California. "Generally speaking, it's global warming. But in a specific sense, how much is it the melting of polar ice sheets as opposed to glaciers? And how much is it ocean warming and thermal expansion?" he said, referring to how water expands as it warms. "Most importantly, what's going to happen in the future?"
Willis is the principal investigator for NASA's Ocean's Melting Greenland (OMG), an air and ship-borne mission designed to answer some of these questions. OMG maps and measures the height of glaciers along Greenland's coast each year. It also measures the temperature and salinity of the ocean around the coastline and has developed precision maps of the ocean floor there. Combined, these datasets reveal to scientists how Greenland's glaciers are responding to changes both in the warming waters below them and in the warming air above them.
"The satellites are telling us how much global sea level is rising, but the airborne and shipborne data are really telling us how much Greenland is contributing to it, and what's causing Greenland to contribute to it," Willis said. "It's a piece of a much bigger puzzle, but it's an important piece because Greenland alone has enough ice to raise global sea levels by 25 feet (7.6 meters)."
Melting Here, Flooding There
As the ice melts in one part of the world, elsewhere, coastal communities in particular wrangle with the consequences — the most common: flooding. High-tide flooding, where seawater spills onto land and into low-lying communities when the tide comes in, has doubled in the last 30 years. Other factors, such as ocean currents, the terrain and subsidence, or land sinking, also influence a region's susceptibility to flooding.
In addition to measuring global sea level changes, NASA scientists are working with land and resource managers to help them understand and mitigate these regional flooding risks.
"A lot of coastal communities are working to identify particular parts of their towns where there have been flooding issues, and they are trying to adopt strategies to lessen the impact of sea level rise and flooding in those areas," said JPL's Ben Hamlington, head of the Sea Level Change Science Team. "We're often able to provide the high-resolution information that they need to make important decisions, particularly in terms of subsidence, which can differ quite a bit over even short distances."
Because subsidence is so variable — it can occur in measurements of less than an inch to feet, and over areas of a few acres to many miles — it is an important factor in assessing and responding to flood risk. For example, in a 2017 study of Hampton Roads, Virginia, an area prone to flooding, NASA scientists, including Hamlington (who was with Old Dominion University at the time), detected major differences in the rate of subsidence in areas just a few miles apart.
"It highlights the fact that subsidence information should be incorporated into land use decisions and taken into consideration for future planning, including at the local level," Hamlington said.
In order to get crucial information like this into the hands of stakeholders, Hamlington's team is working on a new, interactive sea level assessment tool. Available in coming weeks on the agency's sea level website, it will provide quantitative information, based on NASA observations, on sea level rise in the coastal U.S. and the processes driving it.
One reason floods are among the most common natural disasters in the U.S., resulting in billions of dollars in damage each year, is that they can be caused by a number of factors, including excessive rainfall, snowmelt, levee or dam failures, or storm surges from hurricanes. In other words, flooding is a threat that effects nearly every region of the U.S.
NASA's role continues even after a flood has occurred. The agency regularly provides relief groups and response agencies, including the Federal Emergency Management Agency (FEMA), with crucial satellite-derived data and decision-support maps when flooding events occur.
"It can be difficult to assess the extent of flooding from the ground because flood waters can recede and flood extent can disappear in a matter of hours," said JPL's Sang-Ho Yun, Disaster Response lead on NASA's Advanced Rapid Imaging and Analysis (ARIA) team. "After an earthquake, damaged buildings stay damaged until they are repaired. But flood extent is like a ghost — it is there and then it disappears."
Earth-observing satellites can fill in some of the blanks. Using synthetic aperture radar (SAR) that penetrates clouds and rain, day and night, including data acquired by the European Space Agency's Sentinel-1 and Japan's ALOS-2 satellites, Yun and the ARIA team can identify areas that are likely flooded.
"In the satellite radar data, the bare ground has its own roughness, but when you cover the ground with smooth water, it becomes like a mirror," Yun said. "When the radar signal from the satellite hits the bare ground, it reflects back to the satellite. But when the signal hits water on the surface instead, it actually reflects away from the satellite, so flooded areas appear darker than normal."
Yun's team processes the satellite data to produce flood maps (like this one) that FEMA and other agencies can use in their disaster response efforts.
NASA's Disasters Program, in the agency's Earth Science Division, also provides extremely useful information on the use of Earth observations in the prediction of, preparation for, response to and recovery from natural disasters like flooding. The NASA Disasters Mapping Portal provides access to near real-time data products and maps of disaster areas. The flood dashboard, which brings together observations and products from NASA, the National Weather Service and the United States Geological Survey (USGS) to provide a more complete picture of the extent of flooding, is also publicly accessible.
In some way or other, the effects of sea level rise, whether direct or indirect, will touch us all. But from Greenland to Louisiana to coastal regions around the world, NASA continues to provide key insight into our rising seas and how to navigate the effects of sea level rise.
Unusually Clear Skies Drove Record Loss of Greenland Ice in 2019
• April 15, 2020: Last year was one of the worst years on record for the Greenland ice sheet, which shrunk by hundreds of billions of tons. According to a study published today in The Cryosphere, that mind-boggling ice loss wasn’t caused by warm temperatures alone; the new study identifies exceptional atmospheric circulation patterns that contributed in a major way to the ice sheet’s rapid loss of mass. 75) 76)
Because climate models that project the future melting of the Greenland ice sheet do not currently account for these atmospheric patterns, they may be underestimating future melting by about half, said lead author Marco Tedesco from Columbia University’s Lamont-Doherty Earth Observatory.
The study used satellite data, ground measurements, and climate models to analyze changes in the ice sheet during the summer of 2019.
The researchers found that while 2019 saw the second-highest amount of runoff from melting ice (2012 was worse), it brought the biggest drops in surface mass balance since record-keeping began in 1948. Surface mass balance takes into account gains in the ice sheet’s mass — such as through snowfall — as well as losses from surface meltwater runoff. “You can see the mass balance in Greenland as your bank account,” said Tedesco. “In some periods you spend more, and in some periods you earn more. If you spend too much you go negative. This is what happened to Greenland recently.”
Specifically, in 2019, the ice sheet’s surface mass balance dropped by about 320 billion tons below the average for 1981-2010 — the biggest drop since record-keeping began in 1948. Between 1981 and 2010, the surface mass “bank account” gained about 375 billion tons of ice per year, on average. In 2019, that number was closer to 50 billion tons. And while a gain of 50 billion tons may still sound like good news for an ice sheet, Fettweis explained that it is not, because of another factor: the ice sheet is also shedding hundreds of billions of tons as icebergs break off into the ocean. Under stable conditions, the gains in surface mass balance would be high enough to compensate for the ice that’s lost when icebergs calve off. Under the current conditions, the calving far outweighs the surface mass balance gains; Overall, the ice sheet lost an estimated 600 billion tons in 2019, representing a sea level rise of about 1.5 millimeters.
Before now, 2012 was Greenland’s worst year for surface mass balance, with a loss of 310 billion tons compared to the 1981-2010 baseline. Yet summer temperatures in Greenland were actually higher in 2012 than in 2019 — so why did the surface lose so much mass last year?
Tedesco and co-author Xavier Fettweis, from the University of Liège, found that the record-setting ice loss was linked to high-pressure conditions (called anticyclonic conditions) that prevailed over Greenland for unusually long periods of time in 2019.
The high pressure conditions inhibited the formation of clouds in the southern portion of Greenland. The resulting clear skies let in more sunlight to melt the surface of the ice sheet. And with fewer clouds, there was about 50 billion fewer tons of snowfall than usual to add to the mass of the ice sheet. The lack of snowfall also left dark, bare ice exposed in some places, and because ice doesn’t reflect as much sunlight as fresh snow, it absorbed more heat and exacerbated melting and runoff.
Figure 73: Average pressure over Greenland in summer 2019, with arrows showing wind direction (image credit: Tedesco and Fettweis, 2019)
Conditions were different, but no better, in the northern and western parts of Greenland, because as the high pressure system spun clockwise, it pulled up warm, moist air from the lower latitudes and channeled it into Greenland.
“Imagine this vortex rotating in the southern part of Greenland,” Tedesco explained, “and that is literally sucking in like a vacuum cleaner the moisture and heat of New York City, for example, and dumping it in the Arctic — in this case, along the west coast of Greenland. When that happened, because you have more moisture and more energy, it promoted the formation of clouds in the northern part.”
But instead of bringing snowfall, these warm and moist clouds trapped the heat that would normally radiate off of the ice, creating a small-scale greenhouse effect. These clouds also emitted their own heat, exacerbating melting.
Through these combined effects, the atmospheric conditions of the summer of 2019 led to the highest annual mass loss from Greenland’s surface since record-keeping began.
With the help of an artificial neural network, Tedesco and Fettweis found that 2019’s large number of days with these high-pressure atmospheric conditions was unprecedented. The summer of 2012, one of Greenland’s worst years, also saw anticyclonic conditions.
Figure 74: Summer 2019 anomalies in number of melting days (a), snowfall (b), albedo (c), cloudiness (d), and temperature two meters above the ice (e), image credit: Tedesco and Fettweis, 2019)
“These atmospheric conditions are becoming more and more frequent over the past few decades,” said Tedesco. “It is very likely that this is due to the waviness to the jet stream, which we think is related to, among other things, the disappearance of snow cover in Siberia, the disappearance of sea ice, and the difference in the rate at which temperature is increasing in the Arctic versus the mid-latitudes.” In other words, climate change may make the destructive high-pressure atmospheric conditions more common over Greenland.
Current global climate models are not able to capture these effects of a wavier jet stream. As a result, “simulations of future impacts are very likely underestimating the mass loss due to climate change,” said Tedesco. “It’s almost like missing half of the melting.”
The Greenland ice sheet contains enough frozen water to raise sea levels by as much as 23 feet (7 meters). Understanding the impacts of atmospheric circulation changes will be crucial for improving projections for how much of that water will flood the oceans in the future, said Tedesco.
NASA Study Adds a Pinch of Salt to El Niño Models
• April 7, 2020: When modeling the El Niño-Southern Oscillation (ENSO) ocean-climate cycle, adding satellite sea surface salinity — or saltiness — data significantly improves model accuracy, according to a new NASA study. 77)
ENSO is an irregular cycle of warm and cold climate events called El Niño and La Niña. In normal years, strong easterly trade winds blow from the Americas toward southeast Asia, but in an El Niño year, those winds are reduced and sometimes even reversed. Warm water that was “piled up” in the western Pacific flows back toward the Americas, changing atmospheric pressure and moisture to produce droughts in Asia and more frequent storms and floods in the Americas. The reverse pattern is called a La Niña, in which the ocean in the eastern Pacific is cooler than normal.
Figure 75: Watch as surface and subsurface ocean temperature anomalies in the Pacific show the rise and fall of an El Niño (video credit: NASA / Earth Observatory)
The team used NASA’s Global Modelling and Assimilation Office (GMAO) Sub-seasonal-To-Seasonal (S2S) coupled ocean/atmosphere forecasting system (GEOS-S2S-2) to model three past ENSO events: The strong 2015 El Niño, the 2017 La Niña and the weak 2018 El Niño.
The saltiness of the sea surface varies depending on where and when you're looking. Heavy rainfall, river outflows, ocean currents, sea ice melt, evaporation and other seasonal phenomena can all alter salinity—and scientists can now see these changes in clear detail. NASA's Aquarius mission has collected the agency's first full year of satellite ocean surface salinity measurements, revealing a colorful and dynamic portrait of our salty seas. Salinity shifts, a powerful driver of global ocean currents, are also a fingerprint of variations in Earth's fresh water cycle, providing valuable information on how a changing climate is altering global rainfall patterns. Before Aquarius, researchers had only snapshots of the ocean's salt content variations. With global satellite measurements, they will now be able to see how salinity changes over time. Watch the video to learn more about our ocean's salty motions.
Figure 76: Take a global tour of ocean salinity, courtesy of Aquarius data. Red represents the highest surface salinity; blue represents the lowest. NASA / CONAE's Aquarius satellite (2011-2015) collected sea surface salinity (saltiness) data over the entire globe. Today, the Soil Moisture Active Passive (SMAP) mission collects ocean salinity and soil moisture data (video credit: NASA / Greg Shirah)
Pulling from NASA’s SMAP ( Soil Moisture Active Passive) mission, the past NASA-CONAE (Argentinian Space Agency) Aquarius mission and the European Space Agency’s SMOS (Soil Moisture Ocean Salinity) mission, they compared the forecast model’s accuracy for each of the three events with and without assimilating SSS data into the models’ initialization. In other words: One model run’s initial conditions included SSS data, and the other did not.
Adding assimilation of SSS data to the GEOS model helped it to depict the depth and density of the ocean’s top layer more accurately, which led to better representations of large-scale circulation in response to ENSO. As a result, the models’ predictions for the three case studies more closely reflected actual observations, compared to what forecasting models predicted at the time.
“In our three case studies, we examined different phases of ENSO,” said Eric Hackert, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland and the study’s lead author. “For the big El Niño in 2015, assimilating the salinity data damped the signal — our original model was overestimating the amplitude of the event. For the other two ENSO events, the forecasts originally predicted the wrong sign: For example, in 2017, the model without salinity data forecasted an El Niño, while the real ocean produced a La Niña. However, for each case we examined, adding satellite salinity to the initialization improved the forecasts.”
The study is one of the first to incorporate SSS (Sea Surface Salinity) data into forecast initialization for a global coupled model of interactions between the ocean, atmosphere, land, aerosols and sea ice. GEOS and other models used to help predict ENSO events do not typically include SSS. However, ocean surface salinity plays an important role in ocean currents, evaporation and interaction with the atmosphere, and heat transfer from the tropics to the poles. Colder, saltier water is denser and heavier than warmer, fresher water, and the large-scale temperature and precipitation shifts of ENSO events change ocean circulation and interactions between the water and atmosphere.
“For example, forecasts and observations gave a strong indication that there would be a big El Niño in 1997, which would lead to drought in northeast Brazil,” he said. “This allowed the government of Brazil to issue a statement to subsistence farmers, encouraging them to plant drought-resistant corn instead of high-yield varieties. In this case, good ENSO forecasts along with government action may have saved many lives. This is just one example of many socio-economic benefits for extending useful El Niño predictions.”
Including satellite SSS data also makes models useful for longer periods — accurate ENSO forecasts without salinity data only extend out 4 months, while those with SSS data cover 7 months, Hackert said.
“Rather than having one season of confidence in your forecast, you have two seasons,” Hackert said. “If your growing season is six months down the line, a longer quality forecast gives you an improved understanding of whether you need to plant high-yield or drought-resistant varieties. Another example would be that you have plenty of time to fix your roof if you live in Southern California (since El Niño typically brings rainy conditions to the southern US).”
Having access to an ongoing record of satellite SSS data is essential for making forecasts accurate and reliable, Hackert said.
“In current forecast systems, satellite and ocean observations are optimally combined using models and data assimilation techniques to help define the state of the ocean,” he said. “This study shows that adding satellite SSS to the suite of current observations helps to characterize the near-surface ocean state, leading to improved seasonal forecasts. We recommend that other forecast model systems around the world adopt SSS into their systems.”
Figure 77: Ocean surface salinity plays an important role in ocean currents, evaporation and interaction with the atmosphere, and heat transfer from the tropics to the poles. Colder, saltier water is denser and heavier than warmer, fresher water (image credit: NASA)
New 3D View of Methane Tracks Sources and Movement around the Globe
• March 23, 2020: NASA’s new 3-dimensional portrait of methane concentrations shows the world’s second largest contributor to greenhouse warming, the diversity of sources on the ground, and the behavior of the gas as it moves through the atmosphere. Combining multiple data sets from emissions inventories, including fossil fuel, agricultural, biomass burning and biofuels, and simulations of wetland sources into a high-resolution computer model, researchers now have an additional tool for understanding this complex gas and its role in Earth’s carbon cycle, atmospheric composition, and climate system. 78)
Since the Industrial Revolution, methane concentrations in the atmosphere have more than doubled. After carbon dioxide, methane is the second most influential greenhouse gas, responsible for 20 to 30% of Earth’s rising temperatures to date.
“There’s an urgency in understanding where the sources are coming from so that we can be better prepared to mitigate methane emissions where there are opportunities to do so,” said research scientist Ben Poulter at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Figure 78: NASA’s new 3-dimensional portrait of methane shows the world’s second largest contributor to greenhouse warming as it travels through the atmosphere. Combining multiple data sets from emissions inventories and simulations of wetlands into a high-resolution computer model, researchers now have an additional tool for understanding this complex gas and its role in Earth’s carbon cycle, atmospheric composition, and climate system. The new data visualization builds a fuller picture of the diversity of methane sources on the ground as well as the behavior of the gas as it moves through the atmosphere (video credit: NASA/Scientific Visualization Studio)
A single molecule of methane is more efficient at trapping heat than a molecule of carbon dioxide, but because the lifetime of methane in the atmosphere is shorter and carbon dioxide concentrations are much higher, carbon dioxide still remains the main contributor to climate change. Methane also has many more sources than carbon dioxide, these include the energy and agricultural sectors, as well as natural sources from various types of wetlands and water bodies.
“Methane is a gas that’s produced under anaerobic conditions, so that means when there’s no oxygen available, you’ll likely find methane being produced,” said Poulter. In addition to fossil fuel activities, primarily from the coal, oil and gas sectors, sources of methane also include the ocean, flooded soils in vegetated wetlands along rivers and lakes, agriculture, such as rice cultivation, and the stomachs of ruminant livestock, including cattle.
“It is estimated that up to 60% of the current methane flux from land to the atmosphere is the result of human activities,” said Abhishek Chatterjee, a carbon cycle scientist with Universities Space Research Association based at Goddard. “Similar to carbon dioxide, human activity over long time periods is increasing atmospheric methane concentrations faster than the removal from natural ‘sinks’ can offset it. As human populations continue to grow, changes in energy use, agriculture and rice cultivation, livestock raising will influence methane emissions. However, it’s difficult to predict future trends due to both lack of measurements and incomplete understanding of the carbon-climate feedbacks.”
Researchers are using computer models to try to build a more complete picture of methane, said research meteorologist Lesley Ott with the Global Modeling and Assimilation Office at Goddard. “We have pieces that tell us about the emissions, we have pieces that tell us something about the atmospheric concentrations, and the models are basically the missing piece tying all that together and helping us understand where the methane is coming from and where it’s going.”
To create a global picture of methane, Ott, Chatterjee, Poulter and their colleagues used methane data from emissions inventories reported by countries, NASA field campaigns, like the Arctic Boreal Vulnerability Experiment (ABoVE) and observations from the Japanese Space Agency’s Greenhouse Gases Observing Satellite (GOSAT Ibuki) and the Tropospheric Monitoring Instrument aboard the European Space Agency’s Sentinel-5P satellite. They combined the data sets with a computer model that estimates methane emissions based on known processes for certain land-cover types, such as wetlands. The model also simulates the atmospheric chemistry that breaks down methane and removes it from the air. Then they used a weather model to see how methane traveled and behaved over time while in the atmosphere.
The data visualization of their results shows methane’s ethereal movements and illuminates its complexities both in space over various landscapes and with the seasons. Once methane emissions are lofted up into the atmosphere, high-altitude winds can transport it far beyond their sources.
The Arctic and high-latitude regions are responsible for about 20% of global methane emissions. “What happens in the Arctic, doesn’t always stay in the Arctic,” Ott said. “There’s a massive amount of carbon that’s stored in the northern high latitudes. One of the things scientists are really concerned about is whether or not, as the soils warm, more of that carbon could be released to the atmosphere. Right now, what you’re seeing in this visualization is not very strong pulses of methane, but we’re watching that very closely because we know that’s a place that is changing rapidly and that could change dramatically over time.”
“One of the challenges with understanding the global methane budget has been to reconcile the atmospheric perspective on where we think methane is being produced versus the bottom-up perspective, or how we use country-level reporting or land surface models to estimate methane emissions,” said Poulter. “The visualization that we have here can help us understand this top-down and bottom-up discrepancy and help us also reduce the uncertainties in our understanding of the global methane budget by giving us visual cues and a qualitative understanding of how methane moves around the atmosphere and where it’s produced.”
The model data of methane sources and transport will also help in the planning of both future field and satellite missions. Currently, NASA has a planned satellite called GeoCarb that will launch around 2023 to provide geostationary space-based observations of methane in the atmosphere over much of the western hemisphere.
Greenland, Antarctica Melting Six Times Faster Than in the 1990s
•March 16, 2020: Observations from 11 satellite missions monitoring the Greenland and Antarctic ice sheets have revealed that the regions are losing ice six times faster than they were in the 1990s. If the current melting trend continues, the regions will be on track to match the "worst-case" scenario of the Intergovernmental Panel on Climate Change (IPCC) of an extra 17 cm of sea level rise by 2100. 79) 80)
The two regions have lost 6.4 trillion (6.4 x 1012) tons of ice in three decades; unabated, this rate of melting could cause flooding that affects hundreds of millions of people by 2100.
The findings, published online March 12 in the journal Nature from an international team of 89 polar scientists from 50 organizations, are the most comprehensive assessment to date of the changing ice sheets. The Ice Sheet Mass Balance Intercomparison Exercise team combined 26 surveys to calculate changes in the mass of the Greenland and Antarctic ice sheets between 1992 and 2018. 81)
The assessment was supported by NASA and ESA (European Space Agency). The surveys used measurements from satellites including NASA's ICESat (Ice, Cloud, and land Elevation Satellite) missions and the joint NASA-German Aerospace Center GRACE (Gravity Recovery and Climate Experiment) mission. Andrew Shepherd at the University of Leeds in England and Erik Ivins at NASA's Jet Propulsion Laboratory in Southern California led the study.
Figure 79: An aerial view of the icebergs near Kulusuk Island, off the southeastern coastline of Greenland, a region that is exhibiting an accelerated rate of ice loss (image credit: NASA Goddard Space Flight Center)
The team calculated that the two ice sheets together lost 81 billion tons per year in the 1990s, compared with 475 billion tons of ice per year in the 2010s - a sixfold increase. All total, Greenland and Antarctica have lost 6.4 trillion tons of ice since the 1990s.
The resulting meltwater boosted global sea levels by 17.8 mm. Together, the melting polar ice sheets are responsible for a third of all sea level rise. Of this total sea level rise, 60% resulted from Greenland's ice loss and 40% resulted from Antarctica's.
"Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea level rise," said Ivins. "While computer simulations allow us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable, evidence."
The IPCC in its Fifth Assessment Report issued in 2014 predicted global sea levels would rise 71 cm by 2100. The Ice Sheet Mass Balance Intercomparison Exercise team's studies show that ice loss from Antarctica and Greenland tracks with the IPCC's worst-case scenario.
Combined losses from both ice sheets peaked at 552 billion tons per year in 2010 and averaged 475 billion tons per year for the remainder of the decade. The peak loss coincided with several years of intense surface melting in Greenland, and last summer's Arctic heat wave means that 2019 will likely set a new record for polar ice sheet loss, but further analysis is needed. IPCC projections indicate the resulting sea level rise could put 400 million people at risk of annual coastal flooding by the end of the century.
The IMBIE (Icesheet Mass Balance Inter-comparison Exercise) led by Andrew Shepherd from the University of Leeds and Erik Ivins at NASA’s Jet Propulsion Laboratory, compared and combined data from 11 satellites – including ESA’s ERS-1, ERS-2, Envisat and CryoSat missions, as well as the EU’s Copernicus Sentinel-1 and Sentinel-2 missions – to monitor changes in the ice sheet’s volume, flow and gravity.
Using observation data spanning three decades, the team has produced a single estimate of Greenland and Antarctica’s net gain or loss of ice – known as mass balance. "Every centimeter of sea level rise leads to coastal flooding and coastal erosion, disrupting people's lives around the planet," said Shepherd.
As to what is leading to the ice loss, Antarctica's outlet glaciers are being melted by the ocean, which causes them to speed up. Whereas this accounts for the majority of Antarctica's ice loss, it accounts for half of Greenland's ice loss; the rest is caused by rising air temperatures melting the surface of its ice sheet.
The Intergovernmental Panel on Climate Change (IPCC)’s latest report predicted that global sea levels will rise by 60 centimeters by 2100, and it is estimated that this would put 360 million people at risk of annual coastal flooding. However, the IMBIE teams studies shows that ice losses from Antarctica and Greenland are rising faster than expected, tracking the IPCC’s worst-case climate warming scenario. 82)
Figure 80: Antarctica and Greenland’s contribution to sea level change. Of the total sea level rise, around 60% (10.6 mm) was due to Greenland ice losses and 40% was due to Antarctica (7.2 mm), [video credit: CPOM (Center for Polar Observation and Modelling), University of Leeds]
Antarctic ice walls protect the climate
• February 26, 2020: The ocean can store much more heat than the atmosphere. The deep sea around Antarctica stores thermal energy that is the equivalent of heating the air above the continent by 400 degrees. Now, a Swedish-led international research group has explored the physics behind the ocean currents close to the floating glaciers that surround the Antarctic coast. 83)
“Current measurements indicate an increase in melting, particularly near the coast in some parts of Antarctica and Greenland. These increases can likely be linked to the warm, salty ocean currents that circulate on the continental shelf, melting the ice from below,” says Anna Wåhlin, lead author of the study and professor of oceanography at the University of Gothenburg.
”What we found here is a crucial feedback process: the ice shelves are their own best protection against warm water intrusions. If the ice thins, more oceanic heat comes in and melts the ice shelf, which becomes even thinner etc. It is worrying, as the ice shelves are already thinning because of global air and ocean warming”, says Céline Heuzé, climate researcher at the Department of Earth Sciences of Gothenburg University.
Figure 81: The Getz ice shelf. Inland Antarctic ice contains volumes of water that can raise global sea levels by several meters. A new study published in the journal Nature shows that glacier ice walls are vital for the climate, as they prevent rising ocean temperatures and melting glacier ice (image credit: Anna Wåhlin, University of Gothenburg) 84)
The stability of ice is a mystery
Inland Antarctic ice gradually moves towards the ocean. Despite the ice being so important, its stability remains a mystery – as does the answer to what could make it melt faster. Since the glaciers are difficult to access, researchers have been unable to find out much information about the active processes.
More knowledge has now been obtained from studying the measurement data collected from instruments that Anna Wåhlin and her researcher colleagues placed in the ocean around the Getz glacier in West Antarctica.
The ice’s edge blocks warm seawater
Getz has a floating section that is approximately 300 to 800 meters thick, beneath which there is seawater that connects to the ocean beyond. The glacier culminates in a vertical edge, a wall of ice that continues 300–400 meters down into the ocean. Warm seawater flows beneath this edge, towards the continent and the deeper ice further south", says Anna Wåhlin.
“Studying the measurement data from the instruments, we found that the ocean currents are blocked by the ice edge. This limits the extent to which the warm water can reach the continent. We have long been stumped in our attempts to establish a clear link between the transport of warm water up on the continental shelf and melting glaciers", says Anna Wåhlin.
Now, we understand that only a small amount of the current can make its way beneath the glacier. This means that around two-thirds of the thermal energy that travels up towards the continental shelf from the deep sea never reaches the ice.”
Can lead to better prognoses
The results of the studies have provided researchers with a greater understanding of how these glacier areas work.
“From the Getz glacier, we are receiving measurements of heat transport in the ocean that correspond with the melting ice being measured by satellites. This also means that the floating glaciers – the ice fronts in particular – are key areas that should be closely monitored. If the ice walls were to disappear, much greater levels of thermal energy would be released towards the ice on land."
"Consequently, we no longer expect to see a direct link between increasing westerly winds and growing levels of melting ice. Instead, the increased water levels can be caused by the processes that pump up warmer, heavier water to the continental shelf, for example as low-pressure systems move closer to the continent.”
Researchers believe that the studies have provided them with significantly better tools to be able to predict future water levels and create more accurate climate prognoses.
Picturing permafrost in the Arctic
• February 25, 2020: According to the latest Intergovernmental Panel on Climate Change Special Report, permafrost temperatures have increased to record high levels from the 1980s to present. As a consequence, concern is growing that significant amounts of greenhouse gases could be mobilized over the coming decades as it thaws, and potentially amplify climate change. 85)
According to the latest Intergovernmental Panel on Climate Change Special Report, permafrost temperatures have increased to record high levels from the 1980s to present. As a consequence, concern is growing that significant amounts of greenhouse gases could be mobilized over the coming decades as it thaws, and potentially amplify climate change.
Permafrost is any ground that remains completely frozen for at least two consecutive years – these permanently frozen grounds are most common in high latitude regions such as Alaska and Siberia, or at high altitudes like the Andes and Himalayas.
Near the surface, Arctic permafrost soils contain large quantities of organic carbon and materials leftover from dead plants that cannot decompose or rot, whereas permafrost layers deeper down contain soils made of minerals. When permafrost thaws, it releases methane and carbon dioxide – adding these greenhouse gases to the atmosphere.
Figure 82: Permafrost extent for the northern hemisphere in the period 2003 to 2017 (image credit: Permafrost CCI, Obu et al, 2019 via the CEDA archive)
Since permafrost is a subsurface phenomenon, understanding it is challenging without relying strictly on in situ measurements. Satellite sensors cannot measure permafrost directly, but a dedicated project as part of ESA’s Climate Change Initiative (CCI), has used complementary satellite measurements of landscape features such as land-surface temperature and land cover to estimate permafrost extent.
Figure 83: This animation shows the permafrost extent in the northern hemisphere from 2003 to 2017. The maps, produced by ESA’s Climate Change Initiative, are providing new insights into thawing permafrost in the Arctic. Continuous permafrost is defined as a continuous area with frozen material beneath the land surface, except for large bodies of water. None-continuous permafrost is broken up into separate areas and can either be discontinuous, isolated or sporadic. It is considered isolated if less than 10% of the surface has permafrost below, while sporadic means 10%-50% of the surface has permafrost below, while discontinuous is considered 50%-90% (video credit: Permafrost CCI, Obu et al,. 2019 via the CEDA archive)
These data combined with in situ observations allow the permafrost team to get a panoptic view – improving the understanding of permafrost dynamics and the ability to model its future climate impact.
Annett Bartsch, science lead of the Permafrost CCI project, comments, “The maps show there is a clear variability in the extent of permafrost. This can be seen in North America as well as Northern Eurasia.”
However, she is careful to point out, “Although the maps provide useful insight with regard to interannual variability over a 14-year period, drawing conclusions regarding climate trends is not possible.”
Dr Bartsch advises researchers, “To wait and use permafrost maps covering the full 30 year time-series, which are expected to be ready for release by the project around the mid-2020.”
The use of Earth observation data can provide spatially consistent permafrost data coverage, even in the most remote and inaccessible areas such as the Arctic. The maps are provided by the Permafrost CCI team and cover the period 2003-17 at a spatial resolution of 1 km. The Permafrost CCI data are available online.
ESA Director of Earth Observation Programs, Josef Aschbacher, adds, "The role of permafrost is believed to be underestimated in the climate change context. Therefore ESA and NASA have launched a joint initiative to call on the scientists in Europe and the US to study the impact of permafrost and other Arctic regions on global methane emissions. The initiative was jointly launched in December 2019 and a first science workshop is planned for June this year."
Figure 84: This animation shows the mean ground temperature of the northern hemisphere in 2017. The animation shows ground temperature at 2 m depth – the commonly used depth used to indicate presence of permafrost (video credit: Permafrost CCI, Obu et al, 2019 via the CEDA archive) 86)
Arctic Ice Melt Is Changing Ocean Currents
• February 6, 2020: A major ocean current in the Arctic is faster and more turbulent as a result of rapid sea ice melt, a new study from NASA shows. The current is part of a delicate Arctic environment that is now flooded with fresh water, an effect of human-caused climate change. 87) 88)
Using 12 years of satellite data, scientists have measured how this circular current, called the Beaufort Gyre, has precariously balanced an influx of unprecedented amounts of cold, fresh water — a change that could alter the currents in the Atlantic Ocean and cool the climate of Western Europe.
The Beaufort Gyre keeps the polar environment in equilibrium by storing fresh water near the surface of the ocean. Wind blows the gyre in a clockwise direction around the western Arctic Ocean, north of Canada and Alaska, where it naturally collects fresh water from glacial melt, river runoff and precipitation. This fresh water is important in the Arctic in part because it floats above the warmer, salty water and helps to protect the sea ice from melting, which in turn helps regulate Earth's climate. The gyre then slowly releases this fresh water into the Atlantic Ocean over a period of decades, allowing the Atlantic Ocean currents to carry it away in small amounts
Figure 85: Arctic sea ice was photographed in 2011 during NASA's ICESCAPE (Impacts of Climate on Ecosystems and Chemistry of the Arctic Pacific Environment) mission, a shipborne investigation to study how changing conditions in the Arctic affect the ocean's chemistry and ecosystems. The bulk of the research took place in the Beaufort and Chukchi seas in the summers of 2010 and 2011 (image credit: NASA/Kathryn Hansen)
But the since the 1990s, the gyre has accumulated a large amount of fresh water — 1,920 cubic miles (8,000 km3) — or almost twice the volume of Lake Michigan. The new study, published in Nature Communications, found that the cause of this gain in freshwater concentration is the loss of sea ice in summer and autumn. This decades-long decline of the Arctic's summertime sea ice cover has left the Beaufort Gyre more exposed to the wind, which spins the gyre faster and traps the fresh water in its current.
Persistent westerly winds have also dragged the current in one direction for over 20 years, increasing the speed and size of the clockwise current and preventing the fresh water from leaving the Arctic Ocean. This decades-long western wind is unusual for the region, where previously, the winds changed direction every five to seven years.
Scientists have been keeping an eye on the Beaufort Gyre in case the wind changes direction again. If the direction were to change, the wind would reverse the current, pulling it counterclockwise and releasing the water it has accumulated all at once.
"If the Beaufort Gyre were to release the excess fresh water into the Atlantic Ocean, it could potentially slow down its circulation. And that would have hemisphere-wide implications for the climate, especially in Western Europe," said Tom Armitage, lead author of the study and polar scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.
Fresh water released from the Arctic Ocean to the North Atlantic can change the density of surface waters. Normally, water from the Arctic loses heat and moisture to the atmosphere and sinks to the bottom of the ocean, where it drives water from the north Atlantic Ocean down to the tropics like a conveyor belt.
This important current is called the Atlantic Meridional Overturning Circulation and helps regulate the planet's climate by carrying heat from the tropically-warmed water to northern latitudes like Europe and North America. If slowed enough, it could negatively impact marine life and the communities that depend it.
"We don't expect a shutting down of the Gulf Stream, but we do expect impacts. That's why we're monitoring the Beaufort Gyre so closely," said Alek Petty, a co-author on the paper and polar scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
The study also found that, although the Beaufort Gyre is out of balance because of the added energy from the wind, the current expels that excess energy by forming small, circular eddies of water. While the increased turbulence has helped keep the system balanced, it has the potential to lead to further ice melt because it mixes layers of cold, fresh water with relatively warm, salt water below. The melting ice could, in turn, lead to changes in how nutrients and organic material in the ocean are mixed, significantly affecting the food chain and wildlife in the Arctic. The results reveal a delicate balance between wind and ocean as the sea ice pack recedes under climate change.
"What this study is showing is that the loss of sea ice has really important impacts on our climate system that we're only just discovering," said Petty.
NASA, NOAA Analyses Reveal 2019 Second Warmest Year on Record
• January 15, 2020: According to independent analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA), Earth's average global surface temperature in 2019 was the second warmest since modern record-keeping began in 1880. Globally, 2019's average temperature was second only to that of 2016 and continued the planet's long-term warming trend: the past five years have been the warmest of the last 140 years. 89)
This past year was 1.8 degrees Fahrenheit (0.98 degrees Celsius) warmer than the 1951 to 1980 mean, according to scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York.
“The decade that just ended is clearly the warmest decade on record,” said GISS Director Gavin Schmidt. “Every decade since the 1960s clearly has been warmer than the one before.”
Figure 86: The past five years have been the warmest of the past 140 years (image credit: NASA, GISS)
The average global surface temperature has risen since the 1880s and is now more than 2º Fahrenheit (a bit more than 1º Celsius) above that of the late 19th century. For reference, the last Ice Age was about 10º Fahrenheit colder than pre-industrial temperatures.
Figure 87: Earth’s long-term warming trend can be seen in this visualization of NASA’s global temperature record, which shows how the planet’s temperatures are changing over time, compared to a baseline average from 1951 to 1980. The record is shown as a running five-year average (video credit: NASA’s Scientific Visualization Studio/Kathryn Mersmann)
Using climate models and statistical analysis of global temperature data, scientists have concluded that this increase has been driven mostly by increased emissions into the atmosphere of carbon dioxide and other greenhouse gases produced by human activities.
Figure 88: This plot shows yearly temperature anomalies from 1880 to 2019, with respect to the 1951-1980 mean, as recorded by NASA, NOAA, the Berkeley Earth research group, the Met Office Hadley Centre (UK), and the Cowtan and Way analysis. Though there are minor variations from year to year, all five temperature records show peaks and valleys in sync with each other. All show rapid warming in the past few decades, and all show the past decade has been the warmest (image credit: NASA GISS/Gavin Schmidt)
“We crossed over into more than 2 degrees Fahrenheit warming territory in 2015 and we are unlikely to go back. This shows that what’s happening is persistent, not a fluke due to some weather phenomenon: we know that the long-term trends are being driven by the increasing levels of greenhouse gases in the atmosphere,” Schmidt said.
Because weather station locations and measurement practices change over time, the interpretation of specific year-to-year global mean temperature differences has some uncertainties. Taking this into account, NASA estimates that 2019’s global mean change is accurate to within 0.1 degrees Fahrenheit, with a 95 percent certainty level.
Weather dynamics often affect regional temperatures, so not every region on Earth experienced similar amounts of warming. NOAA found the 2019 annual mean temperature for the contiguous 48 United States was the 34th warmest on record, giving it a “warmer than average” classification. The Arctic region has warmed slightly more than three times faster than the rest of the world since 1970.
Rising temperatures in the atmosphere and ocean are contributing to the continued mass loss from Greenland and Antarctica and to increases in some extreme events, such as heat waves, wildfires and intense precipitation.
NASA’s temperature analyses incorporate surface temperature measurements from more than 20,000 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations.
These in-situ measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heat island effects that could skew the conclusions. These calculations produce the global average temperature deviations from the baseline period of 1951 to 1980.
NOAA scientists used much of the same raw temperature data, but with a different interpolation into the Earth’s poles and other data-poor regions. NOAA’s analysis found 2019's average global temperature was 1.7 degrees Fahrenheit (0.95 degrees Celsius) above the 20th century average.
NASA’s full 2019 surface temperature dataset and the complete methodology used for the temperature calculation and its uncertainties are available at: https://data.giss.nasa.gov/gistemp
GISS is a laboratory within the Earth Sciences Division of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The laboratory is affiliated with Columbia University’s Earth Institute and School of Engineering and Applied Science in New York.
NASA uses the unique vantage point of space to better understand Earth as an interconnected system. The agency also uses airborne and ground-based measurements, and develops new ways to observe and study Earth with long-term data records and computer analysis tools to better see how our planet is changing. NASA shares this knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).