EO-Topics - 2015 to 2014
EO-Topics1 (Time frame: 2015-2014)
Climate Change Warming World’s Lakes
• December 2015: Climate change is rapidly warming lakes around the world, threatening freshwater supplies and ecosystems, according to a new NASA and NSF (National Science Foundation)-funded study of more than half of the world’s freshwater supply. 1)
Using more than 25 years of satellite temperature data and ground measurements of 235 lakes on six continents, this study — the largest of its kind — found lakes are warming an average of 0.34º Celsius per decade. The scientists say this is greater than the warming rate of either the ocean or the atmosphere, and it can have profound effects.
The research, published in Geophysical Research Letters, was announced at the American Geophysical Union meeting in San Francisco in December 2015. 2)
As warming rates increase over the next century, algal blooms, which can rob water of oxygen, are projected to increase 20 percent in lakes. Algal blooms that are toxic to fish and animals are expected to increase by 5 percent. Emissions of methane, a greenhouse gas 25 times more powerful than carbon dioxide on 100-year time scales, will increase 4 percent over the next decade, if these rates continue.
“Society depends on surface water for the vast majority of human uses,” said co-author Stephanie Hampton, director of Washington State University’s Center for Environmental Research, Education and Outreach in Pullman. “Not just for drinking water, but manufacturing, for energy production, for irrigation of our crops. Protein from freshwater fish is especially important in the developing world.”
Water temperature influences a host of its other properties critical to the health and viability of ecosystems. When temperatures swing quickly and widely from the norm, life forms in a lake can change dramatically and even disappear. “These results suggest that large changes in our lakes are not only unavoidable, but are probably already happening,” said lead author Catherine O'Reilly, associate professor of geology at Illinois State University, Normal, IL. Earlier research by O’Reilly has seen declining productivity in lakes with rising temperatures.
Study co-author Simon Hook, science division manager at NASA/JPL ( Jet Propulsion Laboratory) in Pasadena, California, said satellite measurements provide a broad view of lake temperatures over the entire globe. But they only measure surface temperature, while ground measurements can detect temperature changes throughout a lake. Also, while satellite measurements go back 30 years, some lake measurements go back more than a century. “Combining the ground and satellite measurements provides the most comprehensive view of how lake temperatures are changing around the world,” he said.
Figure 1: Global changes in lake temperatures over the past 25 years. Red shades indicate warming; blue shades indicate cooling. The study found Earth’s lakes are warming about 0.61 degrees Fahrenheit (0.34 degrees Celsius) per decade on average, faster than overall warming rates for the ocean and atmosphere (image credit: Illinois State University, USGS/California, University of Pennsylvania)
Various climate factors are associated with the warming trend. In northern climates, lakes are losing their ice cover earlier in the spring and many areas of the world have less cloud cover, exposing their waters more to the sun’s warming rays.
Previous work by Hook, using satellite data, indicated many lake temperatures were warming faster than air temperature and that the greatest warming was observed at high latitudes, as seen in other climate warming studies. This new research confirmed those observations, with average warming rates of 1.3º Fahrenheit (0.72º Celsius) per decade at high latitudes.
Warm-water tropical lakes may be seeing less dramatic temperature increases, but increased warming of these lakes still can have significant negative impacts on fish. That can be particularly important in the African Great Lakes, where fish are a major source of food. In general, the researchers write, “The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.”
Figure 2: This image of Lake Tahoe, from the ASTER instrument on Terra, shows the lake’s temperature variations (cold is blue, warm is red), image credit: NASA
Figure 3: A combination of satellite data and ground measurements, such as from instrumented buoys like this one in Lake Tahoe on the California/Nevada border, were used to provide a comprehensive view of changing lake temperatures worldwide. The buoy measures the water temperature from above and below. image credit: Limnotech)
Human Fingerprint on Global Air Quality
• December 14, 2015: Using new, high-resolution global satellite maps of air quality indicators, NASA scientists tracked air pollution trends over the last decade in various regions and 195 cities around the globe. According to recent NASA research findings, the United States, Europe and Japan have improved air quality thanks to emission control regulations, while China, India and the Middle East, with their fast-growing economies and expanding industry, have seen more air pollution. 3)
Scientists examined observations made from 2005 to 2014 by the Ozone Monitoring Instrument aboard NASA's Aura satellite. One of the atmospheric gases the instrument detects is nitrogen dioxide, a yellow-brown gas that is a common emission from cars, power plants and industrial activity. Nitrogen dioxide can quickly transform into ground-level ozone, a major respiratory pollutant in urban smog. Nitrogen dioxide hotspots, used as an indicator of general air quality, occur over most major cities in developed and developing nations.
The following visualizations include two types of data. The absolute concentrations show the concentration of tropospheric nitrogen dioxide (Figures 4, 6, 7 and 8), with blue and green colors denoting lower concentrations and orange and red areas indicating higher concentrations.
The second type of data is the trend data from 2005 to 2014 (Figures 9 and 11), which shows the observed change in concentration over the ten-year period. Blue indicated an observed decrease in nitrogen dioxide, and orange indicates an observed increase. Please note that the range on the color bars (text is in white) changes from location to location in order to highlight features seen in the different geographic regions.
Bryan Duncan and his team at NASA/GSFC examined observations made from 2005 to 2014 by the Dutch-Finnish Ozone Monitoring Instrument aboard NASA's Aura satellite. One of the atmospheric gases the instrument detects is nitrogen dioxide, a yellow-brown gas that is a common emission from cars, power plants and industrial activity. Nitrogen dioxide can quickly transform into ground-level ozone, a major respiratory pollutant in urban smog. Nitrogen dioxide hotspots, used as an indicator of general air quality, occur over most major cities in developed and developing nations. 4)
The science team analyzed year-to-year trends in nitrogen dioxide levels around the world. To look for possible explanations for the trends, the researchers compared the satellite record to information about emission controls regulations, national gross domestic product and urban growth. "With the new high-resolution data, we are now able to zoom down to study pollution changes within cities, including from some individual sources, like large power plants," said Duncan.
Previous work using satellites at lower resolution missed variations over short distances. This new space-based view offers consistent information on pollution for cities or countries that may have limited ground-based air monitoring stations. The resulting trend maps tell a unique story for each region.
The United States and Europe are among the largest emitters of nitrogen dioxide. Both regions also showed the most dramatic reductions between 2005 and 2014. Nitrogen dioxide has decreased from 20 to 50 percent in the United States, and by as much as 50 percent in Western Europe. Researchers concluded that the reductions are largely due to the effects of environmental regulations that require technological improvements to reduce pollution emissions from cars and power plants.
China, the world's growing manufacturing hub, saw an increase of 20 to 50 percent in nitrogen dioxide, much of it occurring over the North China Plain. Three major Chinese metropolitan areas — Beijing, Shanghai, and the Pearl River Delta — saw nitrogen dioxide reductions of as much as 40 percent.
The South African region encompassing Johannesburg and Pretoria has the highest nitrogen dioxide levels in the Southern Hemisphere, but the high-resolution trend map shows a complex situation playing out between the two cities and neighboring power plants and industrial areas.
In the Middle East, increased nitrogen dioxide levels since 2005 in Iraq, Kuwait and Iran likely correspond to economic growth in those countries. However, in Syria, nitrogen dioxide levels decreased since 2011, most likely because of the civil war, which has interrupted economic activity and displaced millions of people.
Figure 4: This global map shows the concentration of nitrogen dioxide in the troposphere as detected by the Ozone Monitoring Instrument aboard the NASA Aura satellite, averaged over 2014 (image credit: NASA/GSFC)
Figure 6: This global map shows the concentration of nitrogen dioxide in the atmosphere as detected by the Ozone Monitoring Instrument aboard the NASA Aura satellite, averaged over 2005 (image credit: NASA/GSFC)
Figure 10: Color bar for the trend in nitrogen dioxide concentrations changes across the United Sates
Figure 12: Color bar for the trend in nitrogen dioxide concentrations changes across Europe (image credit: NASA/GSFC)
In Greenland, another major glacier comes undone
• November, 2015: One of Greenland’s glaciers is losing five billion tons of ice a year to the ocean, according to researchers. While these new findings may be disturbing, they are reinforced by a concerted effort to map changes in ice sheets with different sensors from space agencies around the world. It is estimated that the entire Zachariae Isstrom glacier in northeast Greenland holds enough water to raise the global sea levels by more than 46 cm. 5) 6) 7)
- Jeremie Mouginot, from UCI (University of California Irvine), USA and lead author of the paper published in the journal Science, said, “The shape and dynamics of Zachariae Isstrom have changed dramatically over the last few years. The glacier is now breaking up and calving high volumes of icebergs into the ocean, which will result in rising sea levels for decades to come.” Mouginot and his colleagues from NASA/JPL and the University of Kansas, Lawrence, set out to study the changes taking place at Zachariae Isstrom.
- As one of the first regions to experience and visibly demonstrate the effects of climate change, the Arctic serves as a barometer for change in the rest of the world. It is therefore critical that polar ice is monitored comprehensively and in a sustained manner. - The value of international organizations joining forces to understand aspects of our planet such as this cannot be underestimated.
- These current findings are a prime example of how different satellite observations and measurements from aerial surveys are being used from various space agencies including ESA (European Space Agency), CSA (Canadian Space Agency), NASA (National Aeronautics and Space Administration), DLR (German Aerospace Center), JAXA (Japan Aerospace Exploration Agency) and Italy’s space agency, ASI (Agenzia Spaziale Italiana).
- Over the last nine years the Polar Space Task Group has been coordinating the collection of radar data over Greenland and Antarctica. ESA radar observations going back to the ERS and Envisat satellites through to Sentinel-1A were used in the new study. In addition, the group relied heavily on data from Canada’s RADARSAT-1 and -2, Germany’s TerraSAR-X and TanDEM-X, Japan’s ALOS and Italy’s Cosmo-SkyMed constellation to ensure a continuous record of ice-sheet changes through to the launch of Sentinel-1A.
- Using these many sources, scientists determined that the bottom of Zachariae Isstrom is being rapidly eroded by warmer ocean water mixed with growing amounts of meltwater from the ice sheet surface. Jeremie Mouginot said, “Ocean warming has likely played a major role in triggering the glacier’s retreat, but we need more oceanographic observations in this critical sector of Greenland to determine its future.”
Figure 13: Ice velocity map (magnitude, in logarithmic scale) of the Greenland Ice Sheet derived from SAR data of the Sentinel-1A satellite, acquired in Interferometric Wide Swath Mode (IW) between January and March 2015 (color scale in meters per day), image credit: ESA .
Legend to Figure 13: This map of Greenland ice sheet velocity was created using data from Sentinel-1A in January–March 2015 and complemented by the routine 12-day repeat acquisitions of the margins since June 2015. About 1200 radar scenes from the satellite’s wide-swath mode were used to produce the map, which clearly shows dynamic glacier outlets around the Greenland coast. In particular, the Zachariae Isstrom glacier in the northeast is changing rapidly, and recently reported as having become unmoored from a stabilizing sill and now crumbling into the North Atlantic Ocean.
The Sentinel-1 map of the surface velocity is displayed in north polar stereographic projection centered on Greenland, with an origin at 90°N, 45°W, a standard parallel of 70°N, and a reference to the WGS84 ellipsoid, corresponding to the projection used for the GIMP DEM. Figure 13 shows the magnitude of the horizontal surface velocity. The velocity mosaic provides near complete coverage of the ice sheet areas west of the main ice divide. Some gaps exist in the interior eastern and southeastern sections of the ice sheet. The terminus sections of all outlet glaciers are covered. Whereas on outlet glaciers the matching signal for offset tracking is based primarily on amplitude features related to surface structure and roughness, distinct amplitude features are sparse in the interior of the ice sheet and stable speckle patterns are required for correlation of image chips. Preservation of speckle requires temporal coherence. In areas exposed to high snowfall and strong winds the temporal decorrelation of the phase signal limits the availability of suitable repeat pass pairs. Most of the gaps in the January to March, 2015 data set could be filled with additional S-1 data acquisition during the following months.
On some tracks, in particular in the northern section, stripes are evident being aligned approximately perpendicular to the satellite flight direction. These patterns are due to azimuth shifts induced by fluctuations in ionospheric electron density. The ionosphere-induced noise is mainly of relevance for slow motion areas. It can be efficiently reduced by merging velocity data of multiple tracks.
Seven Case Studies in Carbon and Climate
• November 2015: Every part of the mosaic of Earth's surface — ocean and land, Arctic and tropics, forest and grassland — absorbs and releases carbon in a different way. Wild-card events such as massive wildfires and drought complicate the global picture even more. To better predict future climate, we need to understand how Earth's ecosystems will change as the climate warms and how extreme events will shape and interact with the future environment. Here are seven pressing concerns. 8)
1) The Arctic:
The Far North is warming twice as fast as the rest of Earth, on average. With a 5-year Arctic airborne observing campaign just wrapping up and a 10-year campaign just starting that will integrate airborne, satellite and surface measurements, NASA is using unprecedented resources to discover how the drastic changes in Arctic carbon are likely to influence our climatic future.
Wildfires have become common in the North. Because firefighting is so difficult in remote areas, many of these fires burn unchecked for months, throwing huge plumes of carbon into the atmosphere. A recent report found a nearly 10-fold increase in the number of large fires in the Arctic region over the last 50 years, and the total area burned by fires is increasing annually.
Organic carbon from plant and animal remains is preserved for millennia in frozen Arctic soil, too cold to decompose. Arctic soils known as permafrost contain more carbon than there is in Earth's atmosphere today. As the frozen landscape continues to thaw, the likelihood increases that not only fires but decomposition will create Arctic atmospheric emissions rivaling those of fossil fuels. The chemical form these emissions take — carbon dioxide or methane — will make a big difference in how much greenhouse warming they create.
Initial results from NASA's CARVE (Carbon in Arctic Reservoirs Vulnerability Experiment) airborne campaign have allayed concerns that large bursts of methane, a more potent greenhouse gas, are already being released from thawing Arctic soils. CARVE principal investigator Charles Miller of NASA/JPL (Jet Propulsion Laboratory), Pasadena, California, is looking forward to NASA's ABoVE (Arctic Boreal Vulnerability Experiment) field campaign to gain more insight. "CARVE just scratched the surface, compared to what ABoVE will do," Miller said.
Figure 14: Runoff in Alaska (image credit: NOAA)
Methane (CH4) is the Billy the Kid of carbon-containing greenhouse gases: it does a lot of damage in a short life. There's much less of it in Earth's atmosphere than there is carbon dioxide, but molecule for molecule, it causes far more greenhouse warming than CO2 does over its average 10-year life span in the atmosphere.
Methane is produced by bacteria that decompose organic material in damp places with little or no oxygen, such as freshwater marshes and the stomachs of cows. Currently, over half of atmospheric methane comes from human-related sources, such as livestock, rice farming, landfills and leaks of natural gas. Natural sources include termites and wetlands. Because of increasing human sources, the atmospheric concentration of methane has doubled in the last 200 years to a level not seen on our planet for 650,000 years.
Locating and measuring human emissions of methane are significant challenges. NASA's Carbon Monitoring System is funding several projects testing new technologies and techniques to improve our ability to monitor the colorless gas and help decision makers pinpoint sources of emissions. One project, led by Daniel Jacob of Harvard University, used satellite observations of methane to infer emissions over North America. The research found that human methane emissions in eastern Texas were 50 to 100 percent higher than previous estimates. "This study shows the potential of satellite observations to assess how methane emissions are changing," said Kevin Bowman, a JPL research scientist who was a coauthor of the study.
3) Tropical Forests:
Tropical forests are carbon storage heavyweights. The Amazon in South America alone absorbs a quarter of all carbon dioxide that ends up on land. Forests in Asia and Africa also do their part in "breathing in" as much carbon dioxide as possible and using it to grow.
However, there is evidence that tropical forests may be reaching some kind of limit to growth. While growth rates in temperate and boreal forests continue to increase, trees in the Amazon have been growing more slowly in recent years. They've also been dying sooner. That's partly because the forest was stressed by two severe droughts in 2005 and 2010 — so severe that the Amazon emitted more carbon overall than it absorbed during those years, due to increased fires and reduced growth. Those unprecedented droughts may have been only a foretaste of what is ahead, because models predict that droughts will increase in frequency and severity in the future.
In the past 40-50 years, the greatest threat to tropical rainforests has been not climate but humans, and here the news from the Amazon is better. Brazil has reduced Amazon deforestation in its territory by 60 to 70 percent since 2004, despite troubling increases in the last three years. According to Doug Morton, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, further reductions may not make a marked difference in the global carbon budget. "No one wants to abandon efforts to preserve and protect the tropical forests," he said. "But doing that with the expectation that [it] is a meaningful way to address global greenhouse gas emissions has become less defensible."
In the last few years, Brazil's progress has left Indonesia the distinction of being the nation with the highest deforestation rate and also with the largest overall area of forest cleared in the world. Although Indonesia's forests are only a quarter to a fifth the extent of the Amazon, fires there emit massive amounts of carbon, because about half of the Indonesian forests grow on carbon-rich peat. A recent study estimated that this fall, daily greenhouse gas emissions from recent Indonesian fires regularly surpassed daily emissions from the entire United States.
Wildfires are natural and necessary for some forest ecosystems, keeping them healthy by fertilizing soil, clearing ground for young plants, and allowing species to germinate and reproduce. Like the carbon cycle itself, fires are being pushed out of their normal roles by climate change. Shorter winters and higher temperatures during the other seasons lead to drier vegetation and soils. Globally, fire seasons are almost 20 percent longer today, on average, than they were 35 years ago.
Currently, wildfires are estimated to spew 2 to 4 billion tons of carbon into the atmosphere each year on average — about half as much as is emitted by fossil fuel burning. Large as that number is, it's just the beginning of the impact of fires on the carbon cycle. As a burned forest regrows, decades will pass before it reaches its former levels of carbon absorption. If the area is cleared for agriculture, the croplands will never absorb as much carbon as the forest did.
As atmospheric carbon dioxide continues to increase and global temperatures warm, climate models show the threat of wildfires increasing throughout this century. In Earth's more arid regions like the U.S. West, rising temperatures will continue to dry out vegetation so fires start and burn more easily. In Arctic and boreal ecosystems, intense wildfires are burning not just the trees, but also the carbon-rich soil itself, accelerating the thaw of permafrost, and dumping even more carbon dioxide and methane into the atmosphere.
5) North American Forests:
With decades of Landsat satellite imagery at their fingertips, researchers can track changes to North American forests since the mid-1980s. A warming climate is making its presence known.
Through the North American Forest Dynamics project, and a dataset based on Landsat imagery released this earlier this month, researchers can track where tree cover is disappearing through logging, wildfires, windstorms, insect outbreaks, drought, mountaintop mining, and people clearing land for development and agriculture. Equally, they can see where forests are growing back over past logging projects, abandoned croplands and other previously disturbed areas.
"One takeaway from the project is how active U.S. forests are, and how young American forests are," said Jeff Masek of Goddard, one of the project's principal investigators along with researchers from the University of Maryland and the U.S. Forest Service. In the Southeast, fast-growing tree farms illustrate a human influence on the forest life cycle. In the West, however, much of the forest disturbance is directly or indirectly tied to climate. Wildfires stretched across more acres in Alaska this year than they have in any other year in the satellite record. Insects and drought have turned green forests brown in the Rocky Mountains. In the Southwest, pinyon-juniper forests have died back due to drought.
Scientists are studying North American forests and the carbon they store with other remote sensing instruments. With radars and lidars, which measure height of vegetation from satellite or airborne platforms, they can calculate how much biomass — the total amount of plant material, like trunks, stems and leaves — these forests contain. Then, models looking at how fast forests are growing or shrinking can calculate carbon uptake and release into the atmosphere. An instrument planned to fly on the ISS (International Space Station), called the GEDI (Global Ecosystem Dynamics Investigation) lidar, will measure tree height from orbit, and a second ISS mission called the ECOSTRESS (Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station) will monitor how forests are using water, an indicator of their carbon uptake during growth. Two other upcoming radar satellite missions (the NASA-ISRO SAR radar, or NISAR, and the European Space Agency's BIOMASS radar) will provide even more complementary, comprehensive information on vegetation.
6) Ocean Carbon Absorption:
When carbon-dioxide-rich air meets seawater containing less carbon dioxide, the greenhouse gas diffuses from the atmosphere into the ocean as irresistibly as a ball rolls downhill. Today, about a quarter of human-produced carbon dioxide emissions get absorbed into the ocean. Once the carbon is in the water, it can stay there for hundreds of years.
Warm, CO2-rich surface water flows in ocean currents to colder parts of the globe, releasing its heat along the way. In the polar regions, the now-cool water sinks several miles deep, carrying its carbon burden to the depths. Eventually, that same water wells up far away and returns carbon to the surface; but the entire trip is thought to take about a thousand years. In other words, water upwelling today dates from the Middle Ages - long before fossil fuel emissions.
That's good for the atmosphere, but the ocean pays a heavy price for absorbing so much carbon: acidification. Carbon dioxide reacts chemically with seawater to make the water more acidic. This fundamental change threatens many marine creatures. The chain of chemical reactions ends up reducing the amount of a particular form of carbon — the carbonate ion — that these organisms need to make shells and skeletons. Dubbed the "other carbon dioxide problem," ocean acidification has potential impacts on millions of people who depend on the ocean for food and resources.
Microscopic, aquatic plants called phytoplankton are another way that ocean ecosystems absorb carbon dioxide emissions. Phytoplankton float with currents, consuming carbon dioxide as they grow. They are at the base of the ocean's food chain, eaten by tiny animals called zooplankton that are then consumed by larger species. When phytoplankton and zooplankton die, they may sink to the ocean floor, taking the carbon stored in their bodies with them.
Satellite instruments like MODIS (Moderate resolution Imaging Spectroradiometer) on NASA's Terra and Aqua spacecraft let us observe ocean color, which researchers can use to estimate abundance — more green equals more phytoplankton. But not all phytoplankton are equal. Some bigger species, like diatoms, need more nutrients in the surface waters. The bigger species also are generally heavier so more readily sink to the ocean floor.
As ocean currents change, however, the layers of surface water that have the right mix of sunlight, temperature and nutrients for phytoplankton to thrive are changing as well. "In the Northern Hemisphere, there's a declining trend in phytoplankton," said Cecile Rousseaux, an oceanographer with the Global Modeling and Assimilation Office at Goddard. She used models to determine that the decline at the highest latitudes was due to a decrease in abundance of diatoms. One future mission, the PACE (Pre-Aerosol, Clouds, and ocean Ecosystem) satellite, will use instruments designed to see shades of color in the ocean — and through that, allow scientists to better quantify different phytoplankton species.
In the Arctic, however, phytoplankton may be increasing due to climate change. The NASA-sponsored ICESCAPE (Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment) expedition on a U.S. Coast Guard icebreaker in 2010 and 2011 found unprecedented phytoplankton blooms under about three feet (a meter) of sea ice off Alaska. Scientists think this unusually thin ice allows sunlight to filter down to the water, catalyzing plant blooms where they had never been observed before.
Mass Gains of Antarctic Ice Sheet Greater than Losses
• In October 2015, a new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers. The research challenges the conclusions of other studies, including the IPCC (Intergovernmental Panel on Climate Change) 2013 report, which says that Antarctica is overall losing land ice. 9) 10)
According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed to 82 billion tons of ice per year between 2003 and 2008.
“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas.” Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”
Scientists calculate how much the ice sheet is growing or shrinking from the changes in surface height that are measured by the satellite altimeters. In locations where the amount of new snowfall accumulating on an ice sheet is not equal to the ice flow downward and outward to the ocean, the surface height changes and the ice-sheet mass grows or shrinks.
But it might only take a few decades for Antarctica’s growth to reverse, according to Zwally. “If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years — I don’t think there will be enough snowfall increase to offset these losses.”
The study analyzed changes in the surface height of the Antarctic ice sheet measured by radar altimeters on two ESA (European Space Agency) ERS-1 and -2 (European Remote Sensing) satellites, spanning from 1992 to 2001, and by the laser altimeter on NASA’s ICESat (Ice, Cloud, and land Elevation Satellite) from 2003 to 2008.
Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods. They also used information on snow accumulation for tens of thousands of years, derived by other scientists from ice cores, to conclude that East Antarctica has been thickening for a very long time. “At the end of the last Ice Age, the air became warmer and carried more moisture across the continent, doubling the amount of snow dropped on the ice sheet,” Zwally said.
The extra snowfall that began 10,000 years ago has been slowly accumulating on the ice sheet and compacting into solid ice over millennia, thickening the ice in East Antarctica and the interior of West Antarctica by an average of 1.7 cm per year. This small thickening, sustained over thousands of years and spread over the vast expanse of these sectors of Antarctica, corresponds to a very large gain of ice – enough to outweigh the losses from fast-flowing glaciers in other parts of the continent and reduce global sea level rise.
To help accurately measure changes in Antarctica, NASA is developing the successor to the ICESat mission, ICESat-2, which is scheduled to launch in 2018. “ICESat-2 will measure changes in the ice sheet within the thickness of a No. 2 pencil,” said Tom Neumann, a glaciologist at Goddard and deputy project scientist for ICESat-2. “It will contribute to solving the problem of Antarctica’s mass balance by providing a long-term record of elevation changes.”
Figure 15: The map is showing the rates of mass changes from ICESat 2003-2008 over Antarctica. Sums are for all of Antarctica: East Antarctica (EA, 2-17); interior West Antarctica (WA2, 1, 18, 19, and 23); coastal West Antarctica (WA1, 20-21); and the Antarctic Peninsula (24-27). A gigaton (Gt) corresponds to a billion metric tons (image credit:Jay Zwally, Journal of Glaciology)
Antarctic ozone hole nears record size again in 2015
• In October 2015, the ozone hole over Antarctica currently extends over 26 million km2 – an area larger than the North American continent. Currently, it is approximately 2.5 millionkm2 larger than at the same time in 2014. In 2006 it was larger than now, at 27 million km2. Researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Earth Observation Center (EOC) have discovered this trend using Earth observation satellites. They continuously monitor the protective ozone layer and analyze the changes they observe. 11)
Figure 16: The Antarctic ozone hole (false color view), as observed by the GOME-2 instrument on the MetOp spacecraft of EUMETSAT on October 2, 2015, appears as a nearly circular area (image credit: DLR)
Legend to Figure 16: The ozone concentrations are measured in Dobson units. If all the ozone molecules in the atmosphere were brought to the ground level, for example, an ozone concentration of 200 Dobson units would correspond to a layer thickness of only 2 mm. This shows that ozone is ,in fact, found only in trace amounts in the atmosphere - that is, it is a 'trace gas'. Small amounts of this trace gas can have a large impact, in the same way that a little salt in a soup can significantly affect the flavor.
Intense ozone depletion over Antarctica is a phenomenon that recurs annually. In the stratosphere, at an altitude of between 10 - 50 km, the concentration of chlorofluorocarbons (CFCs) becomes enriched while low temperatures prevail during the southern hemisphere winter. Currently, in the southern hemisphere is springtime, additional sunlight causes these substances to exert their ozone-depleting effect. For this reason, the ozone hole reaches its maximum annual expansion during the spring months in the southern hemisphere and then reduces in size again in the local late spring. In recent years, the ozone hole appeared to have stabilized, suggesting a very gradual recovery of the ozone layer. This year, however, the ozone hole has formed one month later and is now almost as large as it was nine years ago.
Figure 17: This image shows the areal extent of the ozone hole as detected by the DLR WDC-RSAT (World Data Center-Remote Sensing of the Atmosphere) in Oberpfaffenhofen, using daily satellite measurements. The ozone hole formed remarkably late in 2015 - during the last third of August (bold red line). Then in September, it reached an area the size of the North American continent. The magnitude of this expansion is the second largest measured until now. Only in 2006, the ozone hole was larger by about 1 million km2 than this year (image credit: DLR)
The 2015 Arctic Sea Ice Summertime Minimum Is Fourth Lowest on Record
• September 2015: According to a NASA analysis of satellite data, the 2015 Arctic sea ice minimum extent is the fourth lowest on record since observations from space began. The analysis by NASA and the NASA-supported NSIDC (National Snow and Ice Data Center) at the University of Colorado in Boulder showed the annual minimum extent was 4.41 million km2 on Sept. 11,2015. This year’s minimum is 1.81 million km2 lower, than the 1981-2010 average. 12)
The Arctic sea ice cover, made of frozen seawater that floats on top of the ocean, helps regulate the planet’s temperature by reflecting solar energy back to space. The sea ice cap grows and shrinks cyclically with the seasons. Its minimum summertime extent, which occurs at the end of the melt season, has been decreasing since the late 1970s in response to warming temperatures.
In some recent years, low sea-ice minimum extent has been at least in part exacerbated by meteorological factors, but that was not the case this year. “This year is the fourth lowest, and yet we haven’t seen any major weather event or persistent weather pattern in the Arctic this summer that helped push the extent lower as often happens,” said Walt Meier, a sea ice scientist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It was a bit warmer in some areas than last year, but it was cooler in other places, too.”
Figure 18: The 2015 Arctic sea ice summertime minimum is 1.81 million km2 below the 1981-2010 average, shown here as a gold line (image credit: NASA/GSFC Scientific Visualization Studio)
In contrast, the lowest year on record, 2012, saw a powerful August cyclone that fractured the ice cover, accelerating its decline. — The sea ice decline has accelerated since 1996. The 10 lowest minimum extents in the satellite record have occurred in the last 11 years. The 2014 minimum was 5.03 million km2, the seventh lowest on record. Although the 2015 minimum appears to have been reached, there is a chance that changing winds or late-season melt could reduce the Arctic extent even further in the next few days.
This year, the Arctic sea ice cover experienced relatively slow rates of melt in June, which is the month the Arctic receives the most solar energy. However, the rate of ice loss picked up during July, when the sun is still strong. Faster than normal ice loss rates continued through August, a transition month when ice loss typically begins to slow. A big “hole” appeared in August in the ice pack in the Beaufort and Chukchi seas, north of Alaska, when thinner seasonal ice surrounded by thicker, older ice melted. The huge opening allowed for the ocean to absorb more solar energy, accelerating the melt.
It’s unclear whether this year’s strong El Niño event, which is a naturally occurring phenomenon that typically occurs every two to seven years where the surface water of the eastern equatorial Pacific Ocean warms, has had any impact on the Arctic sea ice minimum extent.
Figure 19: Different projection of the minimum Arctic sea ice extend on Sept. 11, 2015, using data from the AMSR-2 instrument on GCOM-W1. The yellow outline on the map shows the median sea ice extent observed in September from 1981 through 2010 (image credit: NASA Earth Observatory, Jesse Allen) 13)
Long-term trend (14 years) of Carbon Monoxide Measurements from MOPITT on Terra
• June 2, 2015: Carbon monoxide is perhaps best known for the lethal effects it can have in homes with faulty appliances and poor ventilation. In the United States, the colorless, odorless gas kills about 430 people each year. However, the importance of carbon monoxide (CO) extends well beyond the indoor environment. Indoors or outdoors, the gas can disrupt the transport of oxygen by the blood, leading to heart and health problems. CO also contributes to the formation of tropospheric ozone, another air pollutant with unhealthy effects. And though carbon monoxide does not cause climate change directly, its presence affects the abundance of greenhouse gases such as methane and carbon dioxide. 14)
- Carbon monoxide forms whenever carbon-based fuels — including coal, oil, natural gas, and wood — are burned. As a result, many human activities and inventions emit carbon monoxide, including: the combustion engines in cars, trucks, planes, ships, and other vehicles; the fires lit by farmers to clear forests or fields; and industrial processes that involve the combustion of fossil fuels. In addition, wildfires and volcanoes are natural sources of the gas.
- Little was known about the global distribution of carbon monoxide until the launch of the Terra satellite in 1999. Terra carries a sensor MOPITT (Measurements of Pollution in the Troposphere) that can measure carbon monoxide in a consistent fashion on a global scale. With a swath width of 640 km, MOPITT scans the entire atmosphere of Earth every three days.
- Since CO has a lifetime in the troposphere of about one month, it persists long enough to be transported long distances by winds, but not long enough to mix evenly throughout the atmosphere. As a result, MOPITT’s maps show significant geographic variability and seasonality. To view month by month maps of carbon monoxide, visit the carbon monoxide page in Earth Observatory’s global maps section.
- In Africa, for example, agricultural burning shifts north and south of the equator with the seasons, leading to seasonal shifts in carbon monoxide. Fires are also the dominant source of carbon monoxide pollution in South America and Australia. In the United States, Europe, and eastern Asia, the highest carbon monoxide concentrations occur around urban areas and tend to be a result of vehicle and industrial emissions. However, wildfires burning over large areas in North America, Russia, and China also can be an important source.
- Terra has been in orbit long enough to observe significant changes over time. To illustrate how global carbon monoxide concentrations have changed, maps of the mission’s first (2000) and most recent full year (2014) of data are shown in Figure 20. The maps depict yearly average concentrations of tropospheric carbon monoxide at an altitude of 3,700 meters (12,000 feet). Concentrations are expressed in parts per billion by volume (ppbv). A concentration of 1 ppbv means that for every billion molecules of gas in a measured volume, one of them is a carbon monoxide molecule. Yellow areas have little or no carbon monoxide, while progressively higher concentrations are shown in orange and red. Places where data was not available are gray. For both years, the data has been averaged, which eliminates seasonal variations.
- According to MOPITT, carbon monoxide concentrations have declined since 2000 (Figure 20). The decrease is particularly noticeable in the Northern Hemisphere. Most air quality experts attribute the decline to technological and regulatory innovations that mean vehicles and industries are polluting less than they once did. Interestingly, while MOPITT observed slight decreases of carbon monoxide over China and India, satellites and emissions inventories have shown that other pollutants like sulfur dioxide and nitrogen dioxide have risen during the same period.
- “For China, nitrogen dioxide emissions are mostly from the power and transportation sectors and have grown significantly since 2000 with the increase in demand for electricity,” explained Helen Worden, an atmospheric scientist from the National Center for Atmospheric Research (NCAR). “Carbon monoxide emissions, however, have a relatively small contribution (less than 2 percent) from the power sector, so vehicle emissions standards and improved combustion efficiency for newer cars have lowered carbon monoxide in the atmosphere despite the fact that there are more vehicles on the road burning more fossil fuel.”
- As illustrated by the maps, the news is also generally positive for the Southern Hemisphere, where deforestation and agricultural fires are the primary source of carbon monoxide. In South America, MOPITT observed a slight decrease in carbon monoxide; other satellites have observed decreases in the number of small fires and areas burned, suggesting a decrease in deforestation fires since 2005. Likewise, MOPITT has observed decreases in the amount of carbon monoxide over Africa. “There have been fewer fires in Africa, so that is a big part of the story there,” explained Worden. “However, growing cities might be increasing of the amount of CO in some areas of equatorial Africa.”
- The line graph of Figure 21 shows the long-term trend as well as monthly variations in carbon monoxide concentrations. While the overall trend is downward, several peaks and valleys are visible. For instance, some researchers attribute the peak from around 2002 to 2003 to an unusually active fire season in the boreal forests of Russia. The dip in carbon monoxide emissions from 2007 to 2009 also matches a decline in global fire emissions. In addition, researchers have noted that this dip overlaps with a global financial crisis that started in late 2008 and caused global manufacturing output to decline.
2014 — Warmest Year in Modern Record
The year 2014 ranks as Earth’s warmest since 1880, according to two separate analyses by NASA and NOAA (National Oceanic and Atmospheric Administration) scientists. 15)
The 10 warmest years in the instrumental record, with the exception of 1998, have now occurred since 2000. This trend continues a long-term warming of the planet, according to an analysis of surface temperature measurements by scientists at NASA’s GISS (Goddard Institute of Space Studies) in New York. In an independent analysis of the raw data, also released on Jan. 16, 2015, NOAA scientists also found 2014 to be the warmest on record.
Since 1880, Earth’s average surface temperature has warmed by about 0.8º Celsius, a trend that is largely driven by the increase in carbon dioxide (CO2) and other human emissions into the planet’s atmosphere. The majority of that warming has occurred in the past three decades.
Figure 22: This color-coded map displays the global temperature anomaly data from 2014 (image credit: NASA/GSFC)
For understanding climate change, the long-term trend of rising temperatures across the planet is more important than any year’s individual ranking. These rankings can be sensitive to analysis methods and sampling. While 2014 ranks as the warmest year in NASA’s global temperature record, it is statistically close to the values from 2010 and 2005, the next warmest years.
While 2014 temperatures continue the planet’s long-term warming trend, scientists still expect to see year-to-year fluctuations in average global temperature caused by phenomena such as El Niño or La Niña. These phenomena warm or cool the tropical Pacific and are thought to have played a role in the flattening of the long-term warming trend over the past 15 years. However, 2014’s record warmth occurred during an El Niño-neutral year.
Regional differences in temperature are more strongly affected by weather dynamics than the global mean. For example, in the U.S. in 2014, parts of the Midwest and East Coast were unusually cool, while Alaska and three western states – California, Arizona and Nevada – experienced their warmest year on record, according to NOAA.
GISS (Goddard Institute of Space Studies) is a NASA laboratory managed by the Earth Sciences Division of the agency’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. 16)
The GISS analysis incorporates surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. This raw data is analyzed using an algorithm that takes into account the varied spacing of temperature stations around the globe and urban heating effects that could skew the calculation. The result is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.
• June 9, 2015: NASA has released data showing how temperature and rainfall patterns worldwide may change through the year 2100 because of growing concentrations of greenhouse gases in Earth’s atmosphere. The dataset, which is available to the public, shows projected changes worldwide on a regional level in response to different scenarios of increasing carbon dioxide simulated by 21 climate models. The high-resolution data, which can be viewed on a daily timescale at the scale of individual cities and towns, will help scientists and planners conduct climate risk assessments to better understand local and global effects of hazards, such as severe drought, floods, heat waves and losses in agriculture productivity. 17)
- “NASA is in the business of taking what we’ve learned about our planet from space and creating new products that help us all safeguard our future,” said Ellen Stofan, NASA chief scientist. “With this new global dataset, people around the world have a valuable new tool to use in planning how to cope with a warming planet.”
- The new dataset is the latest product from NEX (NASA Earth Exchange), a big-data research platform within the NASA Advanced Supercomputing Center at the agency's ARC (Ames Research Center) in Moffett Field, California. In 2013, NEX released similar climate projection data for the continental United States that is being used to quantify climate risks to the nation’s agriculture, forests, rivers and cities.
- "This is a fundamental dataset for climate research and assessment with a wide range of applications,” said Ramakrishna Nemani, NEX project scientist at Ames. “NASA continues to produce valuable community-based data products on the NEX platform to promote scientific collaboration, knowledge sharing, and research and development."
- This NASA dataset integrates actual measurements from around the world with data from climate simulations created by the international Fifth Coupled Model Intercomparison Project. These climate simulations used the best physical models of the climate system available to provide forecasts of what the global climate might look like under two different greenhouse gas emissions scenarios: a “business as usual” scenario based on current trends and an “extreme case” with a significant increase in emissions.
- The NASA climate projections provide a detailed view of future temperature and precipitation patterns around the world at a 25 km resolution, covering the time period from 1950 to 2100. The 11 TB dataset provides daily estimates of maximum and minimum temperatures and precipitation over the entire globe.
- NEX is a collaboration and analytical platform that combines state-of-the-art supercomputing, Earth system modeling, workflow management and NASA remote-sensing data. Through NEX, users can explore and analyze large Earth science data sets, run and share modeling algorithms and workflows, collaborate on new or existing projects and exchange workflows and results within and among other science communities.
- NEX data and analysis tools are available to the public through the OpenNEX project on Amazon Web Services. OpenNEX is a partnership between NASA and Amazon, Inc., to enhance public access to climate data, and support planning to increase climate resilience in the U.S. and internationally. OpenNEX is an extension of the NASA Earth Exchange in a public cloud-computing environment.
- NASA uses the vantage point of space to increase our understanding of our home planet, improve lives, and safeguard our future. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.
Figure 23: The new NASA global data set combines historical measurements with data from climate simulations using the best available computer models to provide forecasts of how global temperature (shown here) and precipitation might change up to 2100 under different greenhouse gas emissions scenarios (image credit: NASA)
• October 2014: Sunlight is the primary driver of Earth’s climate and weather. Averaged over the entire planet, roughly 340 W/m2 of energy from the Sun reach Earth. About one-third of that energy is reflected back into space, and the remaining 240 W/m2 is absorbed by land, ocean, and atmosphere. Exactly how much sunlight is absorbed depends on the reflectivity of the atmosphere and the surface. 18)
As scientists work to understand why global temperatures are rising and how carbon dioxide and other greenhouse gases are changing the climate system, they have been auditing Earth’s energy budget. Is more energy being absorbed by Earth than is being lost to space? If so, what happens to the excess energy?
For seventeen years, scientists have been examining this balance sheet with a series of space-based sensors known as CERES (Clouds and the Earth’s Radiant Energy System). The instruments use scanning radiometers to measure both the shortwave solar energy reflected by the planet (albedo) and the longwave thermal energy emitted by it. The first CERES went into space in 1997 on the TRMM (Tropical Rainfall Measuring Mission), and three more have gone up on Terra, Aqua, and Suomi-NPP. The last remaining CERES instrument will fly on the JPSS-1 (Joint Polar Satellite System-1) satellite (launch in 2017), and a follow-on, the RBI (Radiation Budget Instrument), will fly on JPSS-2 (launch in 2022).
If Earth was completely covered in ice, its albedo would be about 0.84, meaning it would reflect most (84%) of the sunlight that hit it. On the other hand, if Earth was covered by a dark green forest canopy, the albedo would be about 0.14 (most of the sunlight would get absorbed). Changes in ice cover, cloudiness, airborne pollution, or land cover (from forest to farmland, for instance) all have subtle effects on global albedo. Using satellite measurements accumulated since the late 1970s, scientists estimate Earth’s average albedo is about about 0.30.
The maps of Figure 24 show how the reflectivity of Earth—the amount of sunlight reflected back into space—changed between March 1, 2000, and December 31, 2011. This global picture of reflectivity (also called albedo) appears to be a muddle, with different areas reflecting more or less sunlight over the 12-year record. Shades of blue mark areas that reflected more sunlight over time (increasing albedo), and orange areas denote less reflection (lower albedo).
Taken across the planet, no significant global trend appears. As noted in the anomaly plot of Figure 25, the global albedo rose and fell in different years, but did not necessarily head in either direction for long.
In the maps of Figure 24, however, some regional patterns emerge. At the North Pole, reflectivity decreased markedly, a result of the declining sea ice on the Arctic Ocean and increasing dust and soot on top of the ice. Around the South Pole, reflectivity is down around West Antarctica and up slightly in parts of East Antarctica, but there is no net gain or loss. At the same time, Antarctic sea ice there has been increasing slightly each year.
One of the most compelling parts of the global map is the signature of the ENSO (El Niño–Southern Oscillation) pattern in the Pacific Ocean (right and left ends of the global map in Figure 24). The first seven years of the CERES data record were characterized by relatively weak El Niño events, but this soon gave way to some moderate-to-strong La Niña events in the latter part of the record. La Niña tends to bring more convection and cloudiness over the western Pacific Ocean, while El Niño brings those rain clouds to the central Pacific. In very strong El Niños, the convection can even travel to the eastern Pacific. The map of CERES reflectivity changes shows an increase in reflectivity in the western tropical Pacific (blue patches in the figure) and reduced reflectivity (orange colors) in the central Pacific—patterns consistent with a shift from El Niño to La Niña during the CERES period.
In the early 2000s, after the first few years of Terra-CERES measurements, it appeared that Earth’s albedo was declining, a phenomenon that was widely reported in scientific journals and on NASA Earth Observatory. But as more years of data accumulated, and as scientists began to better understand the data, they found that albedo was neither increasing nor declining over time. It was fluctuating a lot by year, though.
“What the results show is that even at global scales, Earth’s albedo fluctuates markedly over short time periods due to natural variations in the climate system,” said Norman Loeb, CERES principal investigator at NASA/LaRC ( Langley Research Center). Ice cover, cloud cover, and the amount of airborne particles—aerosols from pollution, volcanoes, and dust storms—can change reflectivity on scales from days to years. “We should not get fooled by short-term fluctuations in the data, as a longer record may reverse any short-term trend.”
“The results also suggest that in order to confidently detect changes in Earth’s albedo above natural variability, a much longer record is needed,” Loeb added. “It is paramount that we continue the CERES Terra, Aqua, and Suomi-NPP observations as long as possible, and launch follow-on Earth radiation budget instruments to ensure continued coverage of this fundamental property of the climate system.”
Sea ice retreat in the Arctic and sea ice advancement in the Antarctic as of 2014
• September 2014: Arctic sea ice coverage continued its below-average trend this year as the ice declined to its annual minimum on Sept. 17, according to the NASA-supported NSIDC (National Snow and Ice Data Center) at the University of Colorado, Boulder, CO. Over the 2014 summer, arctic sea ice melted back from its maximum extent reached in March 2014 to a coverage area of 5.02 million km2 , according to analysis from NASA and NSIDC scientists. This year’s minimum extent is similar to last year’s and below the 1981-2010 average of 6.22 million km2).19) 20) 21)
Arctic sea ice coverage in 2014 is the sixth lowest recorded since 1978. The summer started off relatively cool, and lacked the big storms or persistent winds that can break up ice and increase melting. This summer, the Northwest Passage above Canada and Alaska remained ice-bound. A finger of open water stretched north of Siberia in the Laptev Sea, reaching beyond 85 degrees north, which is the farthest north open ocean has reached since the late 1970s.
While summer sea ice has covered more of the Arctic in the last two years than in 2012’s record low summer, this is not an indication that the Arctic is returning to average conditions. This year’s minimum extent remains in line with a downward trend; the Arctic Ocean is losing about 13% of its sea ice per decade.
To measure sea ice extent, scientists include areas that are at least 15% ice-covered. The NASA-developed computer analysis, which is one of several methods scientists use to calculate extent, is based on data from NASA’s Nimbus 7 satellite, which operated from 1978 to 1987, and the U.S. Department of Defense’s DMSP (Defense Meteorological Satellite Program), which has provided information since 1987.
In addition to monitoring sea ice from space, NASA is conducting airborne field campaigns to track changes in Arctic sea ice and its impact on climate. Operation IceBridge flights have been measuring Arctic sea ice and ice sheets for the past several years during the spring. A new field experiment, ARISE (Arctic Radiation – IceBridge Sea and Ice Experiment), started in September 2014 to explore the relationship between retreating sea ice and the Arctic climate.
Figure 26: Arctic sea ice hit its annual minimum on Sept. 17, 2014. The red line in this image shows the 1981-2010 average minimum extent. The map is based from data of the AMSR2 instrument on the GCOM-W1 satellite of JAXA (Japan Aerospace Exploration Agency), image credit: NASA, NSIDC
Figure 27: Different projection of the minimum Arctic sea ice extend on Sept. 19, 2014. The yellow outline on the map shows the median sea ice extent observed in September from 1981 through 2010 (image credit: NASA Earth Observatory,, Jesse Allen, Ref. 21)
Antarctic sea ice extend:
Meanwhile, sea ice on the other side of the planet was headed in the opposite direction. Figure 28, also based on data from the AMSR2 (Advanced Microwave Scanning Radiometer -2) sensor, shows the Antarctic sea ice on September 17, 2014. While it was not yet possible to determine if the ice had reached its maximum extent for the year, the five-day average had already surpassed 20 million km2.
Figure 28: Antarctic sea ice extend on September 19, 2014. Sea ice around Antarctica has been increasing, but not by much. The overall trend of sea ice expansion in the Antarctic is only one-third of the magnitude of the decrease in arctic sea ice. The yellow outline on the map shows the median sea ice extent observed in September from 1981 through 2010 (image credit: NASA Earth Observatory,, Jesse Allen)
Antarctic sea ice develops and evolves under vastly different circumstances than Arctic sea ice. In the north, sea ice sits in a nearly land-locked ocean, while sea ice in the southern hemisphere exists in the open ocean surrounding an extensive land mass (the Antarctic continent). This geography affects how the ice expands and retreats in response to climate, leading in part to the differing sea ice scenarios at the two poles (Ref. 21).
Another study of long-term sea ice extend was published in December 2014 by Claire Parkinson of NASA/GSFC to create a global picture of sea ice extents and their changes over the 35-yr period 1979–2013. The results yield a global annual sea ice cycle more in line with the high-amplitude Antarctic annual cycle than the lower-amplitude Arctic annual cycle but trends more in line with the high-magnitude negative Arctic trends than the lower-magnitude positive Antarctic trends. 22)
Globally,the monthly sea ice extent reaches a minimum February and a maximum generally in October or November. All 12 months show negative trends over the 35-yr period, with the largest magnitude monthly trend being the September trend, at -68,200 ± 10,500 km2 yr-1 (2..62% ± 0.40%decade-1), and the yearly average trend being -35,000 ± 5,900 km2 yr-1 (-1.47% ± 0.25%decade-1).
Data sources: The data used for this study are from the SMMR (Scanning Multichannel Microwave Radiometer) on the Nimbus-7 satellite of NASA, the SSM/I (Special Sensor Microwave Imager), flown on the DMSP (Defense Meteorological Satellite Program) spacecraft F8, F11 and F13 of DoD, and SSM/IS (SSM/I Sounder) on the DMSP F17 satellite. These datasets begin shortly after the launch of the Nimbus 7 satellite in late October 1978 and continue to the present time (2014). The data from each sensor are mapped onto rectangular grids overlaid on polar stereographic projections with grid squares (or pixels) sized at approximately 25 km x 25 km. Ice concentration, defined as the percent areal coverage of ice, is calculated at each grid square through the NASA Team algorithm, and ice extent is calculated as the sum of the area of grid squares with ice concentration at least 15%.
The passive-microwave data have undergone rigorous intercalibration, first between the SMMR and SSM/I sensors in 1999 and then between the SSM/I and SSM/IS sensors in 2012, to create a homogeneous dataset for long-term trend studies. The resulting intercalibrated datasets are available from the NSIDC (National Snow and Ice Data Center) in Boulder, Colorado, and have been widely used. Most pertinently, Cavalieri and Parkinson (2012) have used the data for hemispheric studies of the Arctic and Antarctic sea ice extents, respectively, for the period November 1978–December 2010.
Results: Adding Arctic and Antarctic sea ice extents month by month for the period November 1978–December 2013 yields a global time series that shows a strong seasonal cycle with minimum global ice extent occurring in February of each year, maximum ice extent occurring in October or November of each year except 1979, and a minor secondary maximum often occurring in the June–July time frame (Figure 29). In the anomalous year 1979, the customary June/July secondary maximum is instead the primary maximum.
Figure 29: Monthly average global sea ice extents, November 1978–December 2013, as derived from satellite passive-microwave data. The February ice extents are marked by crosses, October ice extents by diamonds, November ice extents by squares aligned with the axes, and ice extents for all other months by circles. The x-axis tick marks are at January of each year, and the year labels are centered at the middle of the year (image credit: NASA, Claire Parkinson)
Examining 35 years of sea ice data, Parkinson has shown that increases around Antarctica do not make up for the accelerated Arctic sea ice loss of the last decades. Earth has been shedding sea ice at an average annual rate of 35,000 km2 since 1979 — the equivalent of losing an area of sea ice larger than the state of Maryland every year.
Even though Antarctic sea ice reached a new record maximum in September 2014, global sea ice is still decreasing. That’s because the decreases in Arctic sea ice far exceed the increases in Antarctic sea ice. The line graphs of Figure 30 plot the monthly deviations and overall trends in polar sea ice from 1979 to 2013 as measured by satellites. The top line shows the Arctic, the middle shows Antarctica, and the third line shows the global, combined total. The sparklines at the bottom of the graphs show each year separately, enabling month-to-month comparisons across each year. The thickness of each sparkline indicates the overall growth or loss in sea ice globally. The thinning of the sparklines is indicative of the downward trend in total polar sea ice.
Furthermore, the global sea ice loss has accelerated. From 1979 to 1996, the ice loss was 21,500 km2 per year. This rate from 1996 to 2013 was 50,000 km2 lost per year. Annual losses were larger than the states of Vermont and New Hampshire combined.
Figure 30: Despite Antarctic Gains, Global Sea Ice Is Shrinking (image credit: NASA) 23)
• March 19, 2015: The sea ice cap of the Arctic appeared to reach its annual maximum winter extent on Feb. 25, according to data from the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder. At 14.54 million km2, this year’s maximum extent was the smallest on the satellite record and also one of the earliest. 24)
Arctic sea ice, frozen seawater floating on top of the Arctic Ocean and its neighboring seas, is in constant change: it grows in the fall and winter, reaching its annual maximum between late February and early April, and then it shrinks in the spring and summer until it hits its annual minimum extent in September. The past decades have seen a downward trend in Arctic sea ice extent during both the growing and melting season, though the decline is steeper in the latter.
Figure 31: The 2015 maximum is compared to the 1979-2014 average maximum shown in yellow. A distance indicator shows the difference between the two in the Sea of Okhotsk north of Japan (image credit: NASA)
The main player in the wintertime maximum extent is the seasonal ice at the edges of the ice pack. This type of ice is thin and at the mercy of which direction the wind blows: warm winds from the south compact the ice northward and also bring heat that makes the ice melt, while cold winds from the north allow more sea ice to form and spread the ice edge southward.
Scientifically, the yearly maximum extent is not as interesting as the minimum. It is highly influenced by weather and we’re looking at the loss of thin, seasonal ice that is going to melt anyway in the summer and won’t become part of the permanent ice cover, according to Walt Meier of NASA/GSFC. With the summertime minimum, when the extent decreases it’s because we’re losing the thick ice component, and that is a better indicator of warming temperatures.
Global carbon dioxide emissions
• September 2014: World leaders face multiple barriers in their efforts to reach agreement on greenhouse gas emission policies. And, according to Arizona State University researchers, without globally consistent, independent emissions assessments, climate agreements will remain burdened by errors, self-reporting and the inability to verify emissions progress.
An international research team led by ASU (Arizona State University) scientists has developed a new approach to estimate CO2 emissions from burning fossil fuels – one that provides crucial information to policymakers. Called the FFDAS (Fossil Fuel Data Assimilation System), this new system was used to quantify 15 years of CO2 emissions, every hour, for the entire planet – down to the city scale. Until now, scientists have estimated greenhouse gas emissions at coarser scales or used less reliable techniques. 25) 26) 27)
Figure 32: Global fossil fuel CO2 emissions as represented by the FFDAS (Fossil Fuel Data Assimilation System), image credit: FFDAS research team
The FFDAS uses information from satellite feeds, national fuel accounts and a new global database on power plants to create high-resolution planetary maps. These maps provide a scientific, independent assessment of the planet’s greenhouse gas emissions – something policymakers can use and the public can understand.
The research team built upon the previously developed FFDAS for estimating global high-resolution fossil fuel CO2 emissions — improving the underlying observationally based data sources, expanding the approach through treatment of separate emitting sectors, including a new pointwise database of global power plants, and extending the results to cover a 1997 to 2010 time series at a spatial resolution of 0.1°. The long-term trend analysis of the resulting global emissions shows subnational spatial structure in large active economies such as the United States, China, and India. These three countries, in particular, show different long-term trends and exploration of the trends in nighttime lights, and population reveal a decoupling of population and emissions at the subnational level. Analysis of shorter-term variations reveals the impact of the 2008–2009 global financial crisis with widespread negative emission anomalies across the U.S. and Europe (Ref. 27).
The team used a center of mass (CM) calculation as a compact metric to express the time evolution of spatial patterns in fossil fuel CO2 emissions. The global emission CM has moved toward the east and somewhat south between 1997 and 2010, driven by the increase in emissions in China and South Asia over this time period. Analysis at the level of individual countries reveals a per capita CO2 emission migration in both Russia and India. The per capita emission CM holds potential as a way to succinctly analyze subnational shifts in carbon intensity over time. Uncertainties are generally lower than the previous version of FFDAS due mainly to an improved nightlight data set.
• In November 2014, NASA released an ultra-high-resolution computer model providing a stunning new look at how carbon dioxide in the atmosphere travels around the globe. Plumes of carbon dioxide in the simulation swirl and shift as winds disperse the greenhouse gas away from its sources. The simulation also illustrates differences in carbon dioxide levels in the northern and southern hemispheres and distinct swings in global carbon dioxide concentrations as the growth cycle of plants and trees changes with the seasons. 28) 29)
- The carbon dioxide visualization was produced by a computer model called GEOS-5, created by scientists at NASA Goddard’s Global Modeling and Assimilation Office. In particular, the visualization is part of a simulation called a “Nature Run.” The Nature Run ingests real data on atmospheric conditions and the emission of greenhouse gases and both natural and man-made particulates. The model is then is left to run on its own and simulate the natural behavior of the Earth’s atmosphere. This Nature Run simulates May 2005 to June 2007.
- In the spring of 2014, for the first time in modern history, atmospheric carbon dioxide – the key driver of global warming – exceeded 400 parts per million across most of the northern hemisphere. Prior to the Industrial Revolution, carbon dioxide concentrations were about 270 parts per million. Concentrations of the greenhouse gas in the atmosphere continue to increase, driven primarily by the burning of fossil fuels.
- Despite carbon dioxide’s significance, much remains unknown about the pathways it takes from emission source to the atmosphere or carbon reservoirs such as oceans and forests. Combined with satellite observations such as those from NASA’s recently launched OCO-2 (Orbiting Carbon Observatory-2), computer models will help scientists better understand the processes that drive carbon dioxide concentrations.
Figure 33: A still image of CO2 concentrations as of January 1, 2006 (image credit: NASA)
Note, the high-resolution visualization of the video representation (Ref. 28) provide a much better impression of the plumes of carbon dioxide as that swirl and shift with the global winds.
TCCON (Total Carbon Column Observing Network):
TCCON is a network of ground-based FTS (Fourier Transform Spectrometers) that record direct solar spectra in the near-infrared. From these spectra, accurate and precise column-averaged abundances of atmospheric constituents including CO2, CH4, N2O, HF, CO, H2O, and HDO, are retrieved. The TCCON is designed to investigate the flow (or flux) of carbon between the atmosphere, land, and ocean (the so-called carbon budget or carbon cycle). This is achieved by measuring the atmospheric mass of carbon (the airborne fraction). The TCCON measurements have improved the scientific community's understanding of the carbon cycle, and urban greenhouse gas emissions. The TCCON supports several satellite instruments by providing an independent measurement to compare (or validate) the satellite measurements of the atmosphere over the TCCON site locations. 30)
This network currently includes over a dozen stations, distributed over a range of latitudes spanning Lauder, New Zealand and Ny Alesund, Norway, and is continuing to grow. To relate TCCON measurements to the WMO CO2 standard, aircraft observations have been collected over several stations, using the same in situ CO2 measurement approaches used to define that standard. OCO-2 will target a TCCON site as often as once each day, acquiring thousands of measurements as it flies overhead. These measurements will be analyzed to reduce biases below 0.1% (0.3 ppm) at these sites. The spaceborne CO2 estimates will be further validated through comparisons with CO2 and surface pressure measurements from ground based sites with the aid of data assimilation models to provide a more complete global assessment of measurement accuracy 31).
In May 2004 a new approach for studying greenhouse gases in our atmosphere came from an unlikely source: a lone trailer in Park Falls, WI, USA. That site became the first station of the TCCON, a ground-based network of instruments providing measurements and data to help better understand the sources and sinks of carbon dioxide (CO2) and methane (CH4) to and from Earth’s atmosphere. Now, a decade after the first site became operational, TCCON has expanded and provides important information about regional and global atmospheric levels of carbon-containing gases from many stations, worldwide (Figure 34). 32)
Each of the TCCON stations accommodates a FTS (Fourier Transform Spectrometer) that provides precise measurements of the amount of direct sunlight absorbed by atmospheric gases. At each site, the FTS produces a spectrum of sunlight; from that spectrum, researchers determine the abundance of CO2, CH4, carbon monoxide (CO), and other gases in the atmospheric column extending from the surface of the Earth to the top of the atmosphere. In the absence of clouds, one measurement is made approximately every two minutes.
Data from the individual stations provide information about regional carbon sources and carbon sinks. Furthermore, by combining the data from all the stations, researchers can monitor carbon as it is exchanged—“circulates”—between the atmosphere, the land, and the ocean, explains atmospheric chemist Paul Wennberg at Caltech, who is the elected chair of TCCON.
The TCCON is a partnership arrangement. Although the TCCON stations are scattered around the globe and are overseen by numerous investigators, every partner has agreed on what instruments are used and how they are operated; everyone is using a common analysis software so that the measurements are comparable across the whole network.
Originally, data from each of these stations were intended to help validate measurements obtained from NASA’s OCO (Orbiting Carbon Observatory) satellite, which failed upon launch in 2009 due to a faulty fairing separation. OCO and TCCON [were to] provide a new type of data—a type of CO2 measure that had never been used before, called the column average mixing ratio. Measurements from TCCON provide the precise column average mixing ratio of CO2 at discrete locations around the world, and OCO would have provided a similar measurement from space; comparing the two at coincident times and locations were to provide an important evaluation of the satellite data.
Despite the loss of OCO, TCCON continued to expand in recognition of its importance in carbon cycle science and for validation of other remote sensing projects. TCCON provided the very first key observations regarding column average data, long before there were spaceborne estimates.
Table 1: TCCON station locations, lead investigators, and institutions
Figure 34: TCCON has expanded rapidly over the last decade and data have been obtained from 22 locations (red dots) spread around the globe. Blue squares indicate future stations (image credit: Caltech)
Ten Years of Data: Discoveries and Contributions: Over the years, studies using data from TCCON stations have revealed new information about the sources and sinks of CO2 and CH4. These include the discovery of elevated CH4 emissions from Los Angeles, CA, and Four Corners, NM, as well as regional enhancements of CO2 from fossil fuel emissions. Furthermore, TCCON has provided key observations on how uptake of CO2 by the boreal forest—northern forests that span the range from Alaska to Siberia—depends on surface temperature. More broadly, data from TCCON are also being used to evaluate large-scale carbon models and improve global estimates of the sources and sinks of CO2 and CH4 (Figure 35). Understanding the interactions between climate and carbon dynamics is critical for predicting future levels of atmospheric CO2.
The network’s ability to collect very precise data has also proved to be very useful for validating the European Space Agency’s SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY), which flew on Envisat, launched in 2002, and was the first instrument to yield global measurements of CO2 and CH4 from space. John Burrows, PI of SCIAMACHY remarks, that the creation of TCCON filled a key missing element in the observational system required to meet the challenge [of quantifying] greenhouse gases. In fact, the combination of the SCIAMACHY and TCCON datasets became a milestone in remote sensing, revealing important carbon sources and sinks in Europe, North America, and Siberia. The unprecedented combination of ground-based and spaceborne measurements helped to underscore the importance of wet-land sources of CH4 and the impact of increased CH4 from fracking and oil fields. TCCON has pioneered a key element of the ground segment measurements required to provide the evidence base for policy making for the next 100 years.
More recently, TCCON data have been the core of the validation effort for CO2 and CH4 measurements from the Japanese GOSAT (Greenhouse Gases Observing Satellite) that was launched in January 2009. Osamu Uchino of JAXA says that TCCON has been and will [continue to] be a key [player] in the GOSAT product validation, and together, both TCCON and GOSAT data are contributing significantly to carbon-cycle science.
Figure 35: [Top] Observations of CO2 from TCCON stations have shown that over the past decade, the column mole fraction of CO2 (XCO2) has increased by more than 20 parts per million (ppm). In fact, this past winter (2013-14) all sites in the Northern Hemisphere exceeded 400 ppm. [Bottom] TCCON observations indicate the CH4 concentrations have also increased substantially since 2006–07.
Figure 36: Plots of TCCON data over the period 2004-2013 (image credit: TCCON partners)
Figure 37: TCCON network precision and accuracy (image credit: TCCON partners, Ref. 33)
Table 2: Overview of NASA missions observing/contributing to the global Carbon Cycle measurements and Earth’s Changing Climate (NASA missions) 35)
Land Cover Change:
Background: The physical surface of the Earth is in constant change: abundant water resources give rise to new growth, cities expand, what was once forest is converted to farmland. Man causes some of these transformations; others are merely the result of the changing of the seasons. Most fundamentally, land cover is a way of portraying the surface of the Earth. Often this is done through a process of classification where regions of the Earth are identified according to some of their more prominent,quantifiable attributes. Researchers are frequently interested in how land cover changes in a given area through time.
The pace, magnitude and spatial reach of human alterations of the Earth's land surface are unprecedented. Land use and land cover change directly impacts biotic diversity worldwide, contributes to climate change, is the primary source of soil degradation, and, by altering ecosystem services, affects the ability of biological systems to support human needs. Such changes also determine, in part, the vulnerability of places and people to climatic, economic or socio-political perturbations. LUCC (Land Use and Cover Change) research, a program of IGBP, addresses the problem of land use dynamics through comparative case study analysis, addresses land cover dynamics through empirical observations and diagnostic models, and extends the understanding of cause-use-cover dynamics through integrated regional and global modeling. 36)
The LUCC objectives are:
• To develop a fundamental understanding of the human and biophysical dynamics of land-use changes ad the impacts of these changes on land cover.
• To develop robust and regionally sensitive global models of land-use/cover change with improved capacities to predict and project use/cover changes.
• To develop an understanding of land-use/cover dynamics through systematic and integrated case studies.
• To assist in the development of a global land-use classification scheme LUCC was completed in 2005.
The use of satellite imagery has made the mapping of land cover much more practical. Currently, it is possible to look at land cover from global to local scales. This type of analysis has proven helpful to a variety of disciplines, from archeology to forestry to hydrology.
The global land cover map of Figure 38 was created using data from ESA's Envisat mission for the 2010 epoch (2008–12). This is the most recent data product from the CCI (Climate Change Initiative) Land Cover team led by the Catholic University of Leuven, Belgium, showing 22 different types of global land cover classes, plus 14 regional land cover classes. 37)
Following the GCOS (Global Climate Observing System) Implementation Plan, the purpose of the CCI Land Cover project is to make the best use of available satellite sensor data to provide an accurate land-cover classification that can serve the climate modelling community. The maps propose a legend based on the FAO/UNEP Land Cover Classification System, in order to be compatible with previous products.
The land-cover maps are currently under validation by regional experts, coordinated by the European Commission’s JSC (Joint Research Centre).
Figure 38: Global land cover 2010 - the latest land-cover map for studying the effects of climate change, conserving biodiversity and managing natural resources (image credit: ESA, CCI Land Cover, Catholic University of Leuven)
Naturally, there are also many land cover change maps on a regional basis. An example is the “Land Cover Change in the Eastern United States,” provided by the USGS (United States Geological Survey). As part of a national assessment of U.S. land change, the USGS recently completed an analysis of 20 Eastern U.S. eco-regions (Figure 39). The 20 eco-regions spanan area of 1,650,930 km2, as defined by the EPA (Environmental Protection Agency). 38)
Ozone layer on the road to recovery in 2014 (UNEP/WMO)
• September 2014: Earth’s protective ozone layer is on track for recovery within the next few decades according to a new assessment by 282 scientists from 36 countries. The abundance of most ozone-depleting substances in the atmosphere has dropped since the last assessment in 2010, and stratospheric ozone depletion has leveled off and is showing some signs of recovery. These observations were the headlines of the recent “Assessment for Decision-Makers,” part of a larger report to be released in early 2015 by UNEP (United Nations Environment Program) and WMO (World Meteorological Organization). 39) 40) 41) 42)
The stratospheric ozone layer shields us from most of the damaging ultraviolet rays from the Sun. In 1974, scientists discovered that chlorine- and bromine-containing compounds such as chlorofluorocarbons (CFCs) and halons could deplete the ozone layer, and by the mid-1980s, they had observational evidence that it was happening. In 1987, international leaders crafted a treaty to phase out the production and consumption of these ozone-depleting chemicals. The Montreal Protocol was signed on September 16, 1987, and the date is celebrated each year as the International Day for the Preservation of the Ozone Layer.
Stratospheric ozone is typically measured in DU (Dobson Units), the number of molecules required to create a layer of pure ozone 0.01 mm thick at a temperature of 0º Celsius and an air pressure of 1 atmosphere (the pressure at the surface of the Earth). The average amount of ozone in Earth’s atmosphere is 300 Dobson Units, equivalent to a layer with the height of 2 pennies stacked together.
According to the UNEP/WMO assessment, total column ozone declined about 2.5% over most of the world during the 1980s and early 1990s, but has remained relatively unchanged since 2000. The amount of ozone-destroying chlorine and bromine compounds in the air has dropped by 10 to 15 % since a peak in the late 1990s. And by some accounts, ozone levels in the upper stratosphere may now be increasing slightly.
However, the road to recovery will be a long one. Ozone-depleting chemicals—which were once used for refrigerants, aerosol spray cans, insulation foam, and fire suppression—persist for decades in the atmosphere. Though CFCs and similar chemicals were phased out years ago, the existing gases in the stratosphere will take many years to decay. If nations continue to follow the guidelines of the Montreal Protocol, the UNEP/WMO report notes, ozone levels over most of the globe should recover to 1980 levels by 2050. The ozone hole over the South Pole will take longer to recover, ending by 2070.
Beyond the positive impact on the ozone layer, the banning of CFCs and similar compounds has had a positive effect on climate because such chemicals are also greenhouse gases. The UNEP/WMO team cautioned that one of the key replacements for CFCs—hydrofluorocarbons (HFCs)—do not harm the ozone layer but they are potent greenhouse gases that could contribute substantially to climate change in the coming decades.
GMSLR (Global Mean Sea Level Rise)
The IPCC (Intergovernmental Panel on Climate Change), set up by WMO and UNEP in 1988, is an international panel to advise policy makers. The IPCC organizes a number of meetings with different objectives and level of participation. They include Plenary sessions of the IPCC and IPCC Working Groups which are attended by representatives from governments and participating organizations, sessions of the IPCC Bureau, the Task Force Bureau and any task group set up by the Panel, as well as workshops, scoping and other expert meetings, and meetings of lead authors involved in preparing an IPCC report. The IPCC co-sponsors also meetings to support the assessment process, to disseminate its results and enhance interaction with scientists and users. Official documents of past and upcoming sessions of the IPCC and IPCC Working Groups, and approved reports of sessions of the IPCC and the IPCC Bureau can be found at the following reference. 43) (currently documents since 2001).
The Fourth Assessment Report of the IPCC in 2007 is intended to assess the scientific, technical and socio-economic information concerning climate change, its potential effects, and options for adaptation and mitigation. The report is the largest and most detailed summary of the climate change situation ever undertaken, produced by thousands of authors, editors, and reviewers from dozens of countries, citing over 6,000 peer-reviewed scientific studies. 44)
Some background: The ocean has an important role in climate variability and change. The ocean’s heat capacity is about 1,000 times larger than that of the atmosphere, and the oceans net heat uptake since 1960 is around 20 times greater than that of the atmosphere. This large amount of heat, which has been mainly stored in the upper layers of the ocean, plays a crucial role in climate change, in particular variations on seasonal to decadal time scales. The transport of heat and freshwater by ocean currents can have an important effect on regional climates, and the large-scale MOC (Meridional Overturning Circulation); also referred to as thermohaline circulation) influences the climate on a global scale. 45)
Life in the sea is dependent on the biogeochemical status of the ocean and is influenced by changes in the physical state and circulation. Changes in ocean biogeochemistry can directly feed back to the climate system, for example, through changes in the uptake or release of radiatively active gases such as carbon dioxide. Changes in sea level are also important for human society, and are linked to changes in ocean circulation. Finally, oceanic parameters can be useful for detecting climate change, in particular temperature and salinity changes in the deeper layers and in different regions where the short-term variability is smaller and the signal-to-noise ratio is higher.
The large-scale, three-dimensional
ocean circulation and the formation of water masses that ventilate the
main thermocline together create pathways for the transport of heat,
freshwater and dissolved gases such as carbon dioxide from the surface
ocean into the density-stratified deeper ocean, thereby isolating them
from further interaction with the atmosphere. These pathways are also
important for the transport of anomalies in these parameters caused by
changes in the surface conditions. Furthermore, changes in the storage
of heat and in the distribution
Changes in Sea Level: Present-day sea level change is of considerable interest because of its potential impact on human populations living in coastal regions and on islands. The focus is on global and regional sea level variations, over time spans ranging from the last decade to the past century.
Processes in several nonlinearly coupled components of the Earth system contribute to sea level change, and understanding these processes is therefore a highly interdisciplinary endeavor. On decadal and longer time scales, global mean sea level change results from two major processes, mostly related to recent climate change, that alter the volume of water in the global ocean: i) thermal expansion, and ii) the exchange of water between oceans and other reservoirs (glaciers and ice caps, ice sheets, other land water reservoirs - including through anthropogenic change in land hydrology, and the atmosphere.
All these processes cause geographically nonuniform sea level change as well as changes in the global mean; some oceanographic factors (e.g., changes in ocean circulation or atmospheric pressure) also affect sea level at the regional scale, while contributing negligibly to changes in the global mean. Vertical land movements such as resulting from GIA (Glacial Isostatic Adjustment), tectonics, subsidence and sedimentation influence local sea level measurements but do not alter ocean water volume; nonetheless, they affect global mean sea level through their alteration of the shape and hence, the volume of the ocean basins containing the water.
Measurements of present-day sea level change rely on two different techniques: tide gages and satellite altimetry.
• Tide gages provide sea level variations with respect to the land on which they lie. To extract the signal of sea level change due to ocean water volume and other oceanographic change, land motions need to be removed from the tide Gage measurement. Land motions related to GIA can be simulated in global geodynamic models. The estimation of other land motions is not generally possible unless there are adequate nearby geodetic or geological data, which is usually not the case. However, careful selection of tide gage sites such that records reflecting major tectonic activity are rejected, and averaging over all selected gages, results in a small uncertainty for global sea level estimates.
• Sea level change based on satellite altimetry is measured with respect to the Earth’s center of mass, and thus is not distorted by land motions, except for a small component due to large-scale deformation of ocean basins from GIA.
The global sea level rose by about 120 m during the several millennia that followed the end of the last ice age (approximately 21,000 years ago), and stabilized between 3,000 and 2,000 years ago. Sea level indicators suggest that global sea level did not change significantly from then until the late 19th century. The instrumental record of modern sea level change shows evidence for onset of sea level rise during the 19th century. Estimates for the 20th century show that global average sea level rose at a rate of about 1.7 mm/year.
Satellite observations available since the early 1990s provide more accurate sea level data with nearly global coverage. This decade-long satellite altimetry data set shows that since 1993, the sea level has been rising at a rate of around 3 mm/year, significantly higher than the average during the previous half century. Coastal tide gage measurements confirm this observation, and indicate that similar rates have occurred in some earlier decades.
In agreement with climate models, satellite data and hydrographic observations show that sea level is not rising uniformly around the world. In some regions, rates are up to several times the global mean rise, while in other regions sea level is falling. Substantial spatial variation in rates of sea level change is also inferred from hydrographic observations. Spatial variability of the rates of sea level rise is mostly due to non-uniform changes in temperature and salinity and related to changes in the ocean circulation.
Near-global ocean temperature data sets made available in recent years allow a direct calculation of thermal expansion. It is believed that on average, over the period from 1961 to 2003, thermal expansion contributed about 1/4 of the observed sea level rise, while melting of land ice accounted for less than half. Thus, the full magnitude of the observed sea level rise during that period was not satisfactorily explained by those data sets, as reported in the IPCC Third Assessment Report.
Global sea level is projected to rise during the 21st century at a greater rate than during 1961 to 2003. Under the IPCC Special Report on Emission Scenarios (SRES) A1B scenario by the mid-2090s 46), for instance, global sea level reaches 0.22 to 0.44 m above the 1990 levels, and is rising at about 4 mm/year. As in the past, sea level change in the future will not be geographically uniform, with regional sea level change varying within about ±0.15 m of the mean in a typical model projection. Thermal expansion is projected to contribute more than half of the average rise, but land ice will lose mass increasingly rapidly as the century progresses. An important uncertainty relates to whether discharge of ice from the ice sheets will continue to increase as a consequence of accelerated ice flow, as has been observed in recent years. This would add to the amount of sea level rise, but quantitative projections of how much it would add cannot be made with confidence, owing to limited understanding of the relevant processes.
Legend to Figure 41: Time series of global mean sea level (deviation from the 1980-1999 mean) in the past and as projected for the future. For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change. - The red line is a reconstruction of global mean sea level from tide gages, and the red shading denotes the range of variations from a smooth curve. - The green line shows global mean sea level observed from satellite altimetry. - The blue shading represents the range of model projections for the SRES A1B scenario for the 21st century, relative to the 1980 to 1999 mean, and has been calculated independently from the observations.
According to NOAA (National Oceanic and Atmospheric Administration), Washington, D.C., the current sea level rise is about 3 mm/year worldwide. This is a significantly larger rate than the sea-level rise averaged over the last several thousand years, and the rate may be increasing. Sea level rises can considerably influence human populations in coastal and island regions and natural environments like marine ecosystems. 47)
Legend to Figure 42: The data record built by the missions T/P, Jason-1, GFO, ERS-1 & -2, Envisat, and Jason-2 represents the first multi-decadal global record for addressing the issue of sea level rise - which has been identified by the 2007 IPCC (Inter-Governmental Panel for Climate Change) assessment as one of the most important consequences and indicators of global climate change.
Between 1870 and 2004, global average sea levels rose a total of 195 mm which is about 1.46 mm/year. From 1950 to 2009, measurements show an average annual rise in sea level of 1.7 ± 0.3 mm/year, with satellite data showing a rise of 3.3 ± 0.4 mm/year from 1993 to 2009.
The global mean sea level rise is caused by an increase in the volume of the global ocean. This in turn is caused by:
• Warming the ocean (thermal expansion)
• Loss of ice by glaciers and ice sheets
• Reduction of liquid water storage on land.
Sea level rise is one of several lines of evidence that support the view that the global climate has recently warmed. The global community of climate scientists confirms that it is very likely human-induced (anthropogenic) warming contributed to the sea level rise observed in the latter half of the 20th century.
Changes in the ocean and on land, including observed decreases in snow cover and Northern Hemisphere sea ice extent, thinner sea ice, shorter freezing seasons of lake and river ice, glacier melt, decreases in permafrost extent, increases in soil temperatures and borehole temperature profiles, and sea level rise, provide additional evidence that the world is warming.
Steve Cole, Alan Buis, Eric Sorensen, ”Study Shows Climate Change
Rapidly Warming World’s Lakes,” NASA Press Release 15, 239,
Dec. 16, 2015, URL: http://www.nasa.gov/press-release
2) Catherine M. O'Reilly, Sapna Sharma, Derek K. Gray, Stephanie E. Hampton, Jordan S. Read, Rex J. Rowley, Philipp Schneider, John D. Lenters, Peter B. McIntyre, Benjamin M. Kraemer, Gesa A. Weyhenmeyer, Ditmar Straile, Bo Dong, Rita Adrian, Mathew G. Allan, Orlane Anneville, Lauri Arvola, Jay Austin, John L. Bailey, Jill S. Baron, Justin D. Brokers, Elvira de Eyto, Martin T. Dokulil, David P. Hamilton, Karl Havens, et al., ”Rapid and highly variable warming of lake surface waters around the globe,” Geophysical Research Letters, Vol. 42, Issue 24, Dec. 28, 2015, pp: 10,773–10,781, doi:10.1002/2015GL066235, URL: http://onlinelibrary.wiley.com/doi/10.1002/2015GL066235/full
3) Trent L. Schindler, Ellen T. Gray, Kayvon Sharghi, Bryan Duncan, Lok Lamsal, ”NASA Images Show Human Fingerprint on Global Air Quality – Release Materials,” NASA Goddard Media Studios, Dec. 14, 2015, URL: http://svs.gsfc.nasa.gov/12094
Steve Cole, Ellen Gray, ”New NASA Satellite Maps Show Human
Fingerprint on Global Air Quality,” NASA, Release 15-233, Dec.
15, 2015, URL: https://www.nasa.gov/press-release
5) ”International effort reveals Greenland ice loss,” ESA, Nov. 13, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
6) Thomas Nagler, Helmut Rott, Markus Hetzenecker, Jan Wuite, Pierre Potin, ”The Sentinel-1 Mission: New Opportunities for Ice Sheet Observations,” Journal of Remote Sensing, Vol. 7, Issue 7, July 22, 2015, pp: 9371-9389; doi:10.3390/rs70709371, URL: http://www.mdpi.com/2072-4292/7/7/9371/pdf
Carol Rasmussen, Kate Ramsayer, Alan Buis, ”Seven Case Studies in
Carbon and Climate,” NASA News 2015-348, November 12, 2015, URL: http://www.jpl.nasa.gov/news/news.php?feature=4768&utm_source=iContact&
Maria-José Viñas, Rob Garner, ”NASA Study: Mass
Gains of Antarctic Ice Sheet Greater than Losses,” NASA, Oct. 30,
2015, URL: http://www.nasa.gov/feature/goddard
10) H. Jay Zwally, Jun Li, John W. Robbins, Jack L. Saba, Donghui Yi, Anita C. Brenner, ”Mass gains of the Antarctic ice sheet exceed losses,” Journal of Glaciology, October 29, 2015, DOI: http://dx.doi.org/10.3189/2015JoG15J071
11) Michael Bittner, ”Ozone hole nears record size again,” DLR, October 26, 2015, URL: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-15594/year-all/#/gallery/21005
12) Steve Cole, Rani Gran, “Arctic Sea Ice Summertime Minimum Is Fourth Lowest on Record,” NASA, Sept. 15, 2015, URL: https://www.nasa.gov/press-release
13) “Arctic Sea Ice Reaches Annual Low,” NASA Earth Observatory, Sept. 16, 2015, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=86607&src=eoa-iotd
14) Adam Volland, “Fourteen Years of Carbon Monoxide from MOPITT,” NASA, Earth Observatory, June 2, 2015, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=85967
Steve Cole, Leslie McCarthy, “NASA, NOAA Find 2014 Warmest Year
in Modern Record,” NASA Release 15-010, January 16, 2015, URL: http://www.nasa.gov/press/2015/january
Steve Cole, Darryl Waller, “NASA Releases Detailed Global Climate
Change Projections,” NASA, Release 15-115, June 9, 2015, URL: http://www.nasa.gov/press-release
18) “Measuring Earth’s Albedo,” NASA Earth Observatory, October 21,2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=84499
Steve Cole, Patrick Lynch, “2014 Arctic Sea Ice Minimum Sixth
Lowest on Record,” NASA News Release 14-261, Sept. 22, 2014, URL:
21) “A Tale of two Poles,” NASA Earth Observatory, Sept. 24, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=84418
22) Claire L. Parkinson, “Global Sea Ice Coverage from Satellite Data: Annual Cycle and 35-Yr Trends,” Journal of Climate, Vol. 27, 15 December 2014, pp: 9377-9382, DOI: 10.1175/JCLI-D-14-00605.1, URL: http://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-14-00605.1
23) “Despite Antarctic Gains, Global Sea Ice Is Shrinking,” NASA Earth Observatory, Feb. 11, 2015, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=85246&src=eoa-iotd
Maria-José Viñas, “2015 Arctic Sea Ice Maximum
Annual Extent Is Lowest On Record,” NASA, March 19, 2015, URL: http://www.nasa.gov/content/goddard
25) “Study maps 15 years of carbon dioxide emissions on Earth,” ASU News, Sept. 11, 2014, URL: https://asunews.asu.edu/20140911-carbon-dioxide-emissions-mapping
26) Kevin Gurney, Salvi Asefi-Najafabady, Peter Rayner, Bedrich Benes, “FFDAS data retrieval and visualization: Study maps 15 years of the planet’s carbon dioxide emissions at local scales, every hour,” Purdue University, Press release, Sept. 11, 2014, URL: http://hpcg.purdue.edu/FFDAS/index.php?page=media
27) S. Asefi-Najafabady, P. J. Rayner, K. R. Gurney, A. McRobert, Y. Song, K. Coltin, J. Huang, C. Elvidge, K. Baugh, “A multiyear, global gridded fossil fuel CO2 emission data product: Evaluation and analysis of results,” Journal of Geophysical Research: Atmospheres, Article first published online: 10 Sept. 2014, DOI: 10.1002/2013JD021296
28) Patrick Lynch, “NASA Computer Model Provides a New Portrait of Carbon Dioxide,” NASA, Nov. 17, 2014, URL: http://www.nasa.gov/press/goddard/2014/november
29) Patrick Lynch, “A Closer Look at Carbon Dioxide,” NASA, Nov. 17, 2014, URL: http://www.nasa.gov/content/goddard/a-closer-look-at-carbon-dioxide/
30) “Total Carbon Column Observing Network,” Wikipedia, URL: http://en.wikipedia.org/wiki/Total_Carbon_Column_Observing_Network
31) David Crisp, “Measuring CO2 from Space: The NASA Orbiting Carbon Observatory-2,” Proceedings of the 61st IAC (International Astronautical Congress), Prague, Czech Republic, Sept. 27-Oct. 1, 2010, IAC-10.B1.6.2
32) Jessica Stoller-Conrad, “Integrating Carbon from the Ground Up: TCCON Turns Ten,” The Earth Observer, July-August 2014, Volume 26, Issue 4, pp: 13-16, URL: http://eospso.gsfc.nasa.gov/earthobserver/jul-aug-2014
34) Debra Wunch, Geoffrey C. Toon, Jean-François L. Blavier, Rebecca A. Washenfelder, Justus Notholt, Brian J. Connor, David W. T. Griffith, Vanessa Sherlock, Paul O. Wennberg, “The Total Carbon Column Observing Network,” Philosophical Transactions of the Royal Society, A 2011, Vol. 369, pp: 2087-2112
35) Heather Hansen, Karen Yuen, David Crip, “Orbiting Carbon Observatory-2: Observing CO2 from Space,” NASA, The Earth Observer, July-August 2014, Volume 26, Issue 4, pp: 4-11, URL: http://eospso.gsfc.nasa.gov/sites/default/files/eo_pdfs/JulyAug_2014_color508.pdf
36) “Land Use and Cover Change,” IGBP, URL: http://www.igbp.net/researchprojects/pastprojects
37) “Land Cover 2010,” ESA, October 2, 2014, URL: http://www.esa.int/spaceinimages/Images/2014/10/Land_cover_2010
38) Thomas R. Loveland, William Acevedo, “Land Cover Change in the Eastern United States,” USGS, July 28, 2014, URL: http://landcovertrends.usgs.gov/east/regionalSummary.html
39) “UN Panel: Ozone Layer on the Road to Recovery,” NASA Earth Observatory, Sept. 17, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=84382
40) “Assessment for Decision-Makers Scientific Assessment of Ozone Depletion: 2014,” WMO/UNEP, Preprint for Public Release, 10 September 2014, URL: http://ozone.unep.org/Assessment_Panels/SAP/SAP2014_Assessment_for_Decision-Makers.pdf
42) “International Action Against Ozone Depleting Substances Yields Significant Gains,” NASA, Sept. 10, 2014, URL: http://www.nasa.gov/content/goddard
43) “IPCC Sessions & IPCC WGS Sessions,” URL: http://www.ipcc.ch/meeting_documentation
44) “Climate Change 2007: The Physical Science Basis,” IPCC Fourth Assessment Report (AR4), URL: http://www.ipcc.ch/publications_and_data
45) Vincenzo Artale (Italy), Anny Cazenave (France), Jonathan M. Gregory (UK), Sergey Gulev (Russian Federation), Kimio Hanawa (Japan), Corrine Le Quéré (UK, France, Canada), Sydney Levitus (USA), Yukihiro Nojiri (Japan), C.K. Shum (USA), Lynne D. Talley (USA), Alakkat S. Unnikrishnan (India), et. al., “Observations: Oceanic Climate Change and Sea Level,” Chapter 5 of The Fourth Assessment Report of the IPCC 2007, URL: http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter5.pdf
46) Nebojsa Nakicenovic, Ogunlade Davidson, Gerald Davis, Arnulf Grübler, Tom Kram, Emilio Lebre La Rovere, Bert Metz, Tsuneyuki Morita,William Pepper, Hugh Pitcher, Alexei Sankovski, Priyadarshi Shukla, Robert Swart, Robert Watson, Zhou Dadi, “Intergovernmental Panel on Climate Change- Summary for Policymakers - Emissions Scenarios -A Special Report of IPCC Working Group III,” WMO, UNEP, 2000, ISBN: 92-9169-113-5, URL: http://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf
47) “Current sea level rise,” Wikipedia, URL: http://en.wikipedia.org/wiki/Current_sea_level_rise
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).