NASA Study Finds Earth’s Ocean Abyss Has Not Warmed

While the upper part of the world’s oceans continue to absorb heat from global warming, ocean depths have not warmed measurably in the last decade. This image shows heat radiating from the Pacific Ocean as imaged by the NASA’s Clouds and the Earth's Radiant Energy System instrument on the Terra satellite. (Blue regions indicate thick cloud cover.) Image Credit: NASA

The cold waters of Earth’s deep ocean have not warmed measurably since 2005, according to a new NASA study, leaving unsolved the mystery of why global warming appears to have slowed in recent years.

Scientists at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, analyzed satellite and direct ocean temperature data from 2005 to 2013 and found the ocean abyss below 1.24 miles (1,995 meters) has not warmed measurably. Study coauthor Josh Willis of JPL said these findings do not throw suspicion on climate change itself.

"The sea level is still rising," Willis noted. "We're just trying to understand the nitty-gritty details."

In the 21st century, greenhouse gases have continued to accumulate in the atmosphere, just as they did in the 20th century, but global average surface air temperatures have stopped rising in tandem with the gases. The temperature of the top half of the world's oceans -- above the 1.24-mile mark -- is still climbing, but not fast enough to account for the stalled air temperatures.

Many processes on land, air and sea have been invoked to explain what is happening to the "missing" heat. One of the most prominent ideas is that the bottom half of the ocean is taking up the slack, but supporting evidence is slim. This latest study is the first to test the idea using satellite observations, as well as direct temperature measurements of the upper ocean. Scientists have been taking the temperature of the top half of the ocean directly since 2005, using a network of 3,000 floating temperature probes called the Argo array.

"The deep parts of the ocean are harder to measure," said JPL's William Llovel, lead author of the study published Sunday in the journal Nature Climate Change. "The combination of satellite and direct temperature data gives us a glimpse of how much sea level rise is due to deep warming. The answer is -- not much."

Deep sea creatures, like these anemones at a hydrothermal vent, are not yet feeling the heat from global climate change. Although the top half of the ocean continues to warm, the bottom half has not increased measurably in temperature in the last decade. Image Credit: NERC

The study took advantage of the fact that water expands as it gets warmer. The sea level is rising because of this expansion and the water added by glacier and ice sheet melt.
To arrive at their conclusion, the JPL scientists did a straightforward subtraction calculation, using data for 2005-2013 from the Argo buoys, NASA's Jason-1 and Jason-2 satellites, and the agency’s Gravity Recovery and Climate Experiment (GRACE) satellites. 
From the total amount of sea level rise, they subtracted the amount of rise from the expansion in the upper ocean, and the amount of rise that came from added meltwater. The remainder represented the amount of sea level rise caused by warming in the deep ocean.
The remainder was essentially zero. Deep ocean warming contributed virtually nothing to sea level rise during this period.

Coauthor Felix Landerer of JPL noted that during the same period warming in the top half of the ocean continued unabated, an unequivocal sign that our planet is heating up. Some recent studies reporting deep-ocean warming were, in fact, referring to the warming in the upper half of the ocean but below the topmost layer, which ends about 0.4 mile (700 meters) down.

Landerer also is a coauthor of another paper in the same journal issue on 1970-2005 ocean warming in the Southern Hemisphere. Before Argo floats were deployed, temperature measurements in the Southern Ocean were spotty, at best. Using satellite measurements and climate simulations of sea level changes around the world, the new study found the global ocean absorbed far more heat in those 35 years than previously thought -- a whopping 24 to 58 percent more than early estimates.

Both papers result from the work of the newly formed NASA Sea Level Change Team, an interdisciplinary group tasked with using NASA satellite data to improve the accuracy and scale of current and future estimates of sea level change. The Southern Hemisphere paper was led by three scientists at Lawrence Livermore National Laboratory in Livermore, California.

NASA monitors Earth's vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

Source: Nasa

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Hox cluster found in Crown of Thorns starfish a surprise

A Crown of Thorns starfish, Acanthaster planci, feeding on several species of Montipora corals. The image was taken off the coast of Okinawa near Sesoko Island. Credit: Yuna Zayasu

New research published in the journal genesis, by Kenneth Baughman, Dr. Eiichi Shoguchi, Professor Noriyuki Satoh of the Marine Genomics Unit at the Okinawa Institute of Science and Technology Graduate University, and collaborators from Australia, reports an intact Hox cluster in the Crown of Thorns starfish, Acanthaster planci. This surprising result contrasts with the relatively disorganized Hox cluster found in sea urchins, which are also echinoderms, classification of animals including starfish, sea lilies, and sea cucumbers. Stanford University Professor Christopher Lowe, who studies developmental biology in echinoderms, summarizes the paper: "The translocation of the Hox cluster in echinoderms has been a major red herring for understanding their evolution. It's really good to have some hard data showing that some echinoderms exhibit some oddities that are not representative of all echinoderms."

The Hox cluster is a classic example of an 'evo-devo' genetic toolkit. The term "evo-devo" refers to the study of genetic programs that control development, which can be compared between species, and thus, across evolutionary time. 

The Hox genes coordinate segmental identity along the head to tail (anterior-posterior) axis. The Hox cluster is evolutionarily conserved and has been 

repurposed repeatedly during the evolution of the animal body plan, or how animals are shaped. Past studies have shown that Hox clusters organize the development of brain and central nervous system regions in chordates, limb bud identity in vertebrates, and, classically, antennae or wing segment identity in fruit flies.

Generally, the Hox cluster shows "colinearity," in which gene order correlates with the location of expression, or the developmental stage of expression. "For example, anterior Hox genes are expressed in regions that are closer to the head of an embryo, and are expressed sooner during development, versus the posterior Hox genes," explained Baughman. "Thus, we were surprised to see chordate-like Hox cluster organization in starfish, which have a radial body plan." Echinoderms are classical model organisms for embryology, and more recently evo-devo. Baughman added, "Interacting with the speakers and students of theOIST Winter Course 'Evolution of Complex Systems' (OWECS) allowed me to appreciate the importance of finding an intact Hox cluster in starfish."

The Crown of Thorns starfish, a predatory starfish which feeds on corals, is famous for its dramatic changes in population density on the reefs near Australia, as well as Okinawa. Over the past 50 years, this has resulted in a measurable loss of coral reefs. A recent 27-year reef monitoring study of the Great Barrier Reef estimated that the starfish accounts for 42% of the loss in coral cover, 2nd only to typhoons. While population control was the initial motivation for Crown of Thorns genome research, the Hox cluster report is one of the first to show that the species can be useful for studies in evolutionary-developmental biology. "We were excited to see the entire Hox cluster on a single genomic scaffold, a result which confirmed the remarkably high quality of the genomic data," said Prof. Satoh.

As is often the case with science, the discovery raises more questions than it answers. If starfish have a collinear Hox cluster, what accounts for their dramatic departures in body plan organization? Do starfish express Hox genes during development in a manner similar to chordates, as indicated by the organization of their Hox cluster? Baughman looks forward to addressing these questions and many more as part of his doctoral research. "I look forward to pursuing developmental biology studies that may suggest methods for mitigating damage to the coral reef caused by the Crown of Thorns starfish."

More research is being conducted at OIST on the Crown of Thorns starfish in the Marine Biophysics Unit by Masako Nakamura in cooperation with local fishermen. In addition to the research collaboration highlighted by the Hox publication, recent efforts by the Okinawa Prefectural Government and Australian Institute of Marine Science are also working on projects to protect the existing coral reefs from the Crown of Thorns starfish.

Source: Okinawa Institute of Science and Technology - OIST

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Long-running Jason-1 ocean satellite takes final bow

Artist's concept of the joint NASA/CNES Jason-1 ocean altimetry satellite. During its 11-1/2-year life, Jason-1 helped create a 20-plus-year climate record of global ocean surface topography, providing new insights into ocean circulation, tracking our rising seas and enabling more

The curtain has come down on a superstar of the satellite oceanography world that played the "Great Blue Way" of the world's ocean for 11-1/2 years. The successful joint NASA and Centre National d'Etudes Spatiales (CNES) Jason-1 ocean altimetry satellite was decommissioned this week following the loss of its last remaining transmitter.

Launched Dec. 7, 2001, and designed to last three to five years, Jason-1 helped create a revolutionary 20-plus-year climate data record of global ocean surface topography that began in 1992 with the launch of the NASA/CNES Topex/Poseidon satellite. For more than 53,500 orbits of our planet, Jason-1 precisely mapped sea level, wind speed and wave height for more than 95 percent of Earth's ice-free ocean every 10 days. The mission provided new insights into ocean circulation, tracked our rising seas and enabled more accurate weather, ocean and climate forecasts.

"Jason-1 has been a resounding scientific, technical and international success," said John Grunsfeld, associate administrator of NASA's Science Mission Directorate in Washington. 

"The mission met all of its requirements, performed an extended mission and demonstrated how a long-term climate data record should be established from successively launched satellites. Since launch, it has charted nearly 1.6 inches (4 centimeters) of rise in global sea levels, a critical measure of climate change and a direct result of global warming. The Jason satellite series provides the most accurate measure of this impact, which is felt all over the globe."

During parts of its mission, Jason-1 flew in carefully coordinated orbits with both its predecessor Topex/Poseidon and its successor, the Ocean Surface Topography Mission/Jason-2, launched in 2008. These coordinated orbit periods, which lasted about three years each, cross-calibrated the satellites, making possible a 20-plus-year unbroken climate record of sea level change. These coordination periods also doubled data coverage.

Combined with data from the European Space Agency's Envisat mission, which also measured sea level from space, these data allow scientists to study smaller-scale ocean circulation phenomena, such as coastal tides, ocean eddies, currents and fronts. These small-scale features are thought to be responsible for transporting and mixing heat and other properties, such as nutrients and dissolved carbon dioxide, within the ocean.

"Jason-1 was an exemplary and multi-faceted altimeter mission and contributed so much to so many scientific disciplines," said Jean-Yves Le Gall, CNES president in Paris. "Not only did Jason-1 extend the precise climate record established by Topex/Poseidon, it made invaluable observations for mesoscale ocean studies on its second, interleaved orbit. Even from its 'graveyard' orbit, Jason-1 continued to make unprecedented new observations of the Earth's gravity field, with precise measurements right till the end."

The in-orbit Jason-2 mission, operated by the meteorological agencies of the United States and Europe (the National Oceanic and Atmospheric Administration and EUMETSAT, respectively) in collaboration with NASA and CNES, is in good health and continues to collect science and operational data. This same U.S./European team is preparing to launch the next satellite in the series, Jason-3, in March 2015.

Contact was lost with the Jason-1 satellite on June 21 when it was out of visibility of ground stations. At the time of the last contact, Jason-1 and its instruments were healthy, with no indications of any alarms or anomalies. Subsequent attempts to re-establish spacecraft communications from U.S. and French ground stations were unsuccessful. Extensive engineering operations undertaken to recover downlink communications also were unsuccessful.

After consultation with the spacecraft and transmitter manufacturers, it was determined a non-recoverable failure with the last remaining transmitter on Jason-1 was the cause of the loss of contact. The spacecraft's other transmitter experienced a permanent failure in September 2005. There now is no remaining capability to retrieve data from the Jason-1 spacecraft.

On July 1, mission controllers commanded Jason-1 into a safe hold state that reinitialized the satellite. After making several more unsuccessful attempts to locate a signal, mission managers at CNES and NASA decided to proceed with decommissioning Jason-1. The satellite was then commanded to turn off its magnetometer and reaction wheels. Without these attitude control systems, Jason-1 and its solar panels will slowly drift away from pointing at the sun and its batteries will discharge, leaving it totally inert within the next 90 days. The spacecraft will not reenter Earth's atmosphere for at least 1,000 years.

"Like its predecessor Topex/Poseidon, Jason-1 provided one of the most comprehensive pictures of changes in the tropical Pacific Ocean, including the comings and goings of El Nino and La Nina events," said Lee-Lueng Fu, Jason-1 project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "These Pacific Ocean climate cycles are responsible for major shifts in sea level, ocean temperatures and rainfall every two to five years and can sometimes be so large that worldwide weather patterns are affected. Jason-1 data have been instrumental in monitoring and predicting these ever-changing cycles."

In the spring of 2012, based on concern over the limited redundancy of Jason-1's aging control systems, NASA and CNES moved the satellite into its planned final "graveyard" orbit, depleted its extra fuel and reconfigured the mission to make observations that will improve our knowledge of Earth's gravity field over the ocean, in addition to delivering its oceanographic data products.

The first full 406-day marine gravity mission was completed on June 17. The resulting data have already led to the discovery of numerous small seamounts, which are underwater mountains that rise above the deep-sea floor. The data also have significantly increased the resolution of Earth's gravity field over the ocean, while increasing our knowledge of ocean bathymetry, which is the underwater depth of the ocean floor.

JPL manages the U.S. portion of the Jason-1 mission for NASA's Science Mission Directorate. CNES manages the French portion of the mission.

Source: NASA/Jet Propulsion Laboratory

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Emergence of modern sea ice in Arctic Ocean, 2.6 million years ago

Field Work in the Arctic sea ice. Credit: Thomas A. Brown and Simon T. Belt

"We have not seen an ice free period in the Arctic Ocean for 2,6 million years. However, we may see it in our lifetime." says marine geologist Jochen Knies. In an international collaborative project, Knies has studied the historic emergence of the ice in the Arctic Ocean. The results are published in Nature Communications.

The extent of sea ice cover in Arctic was much less than it is today between four and five million years ago. The maximum winter extent did not reaching its current location until around 2.6 million years ago. This new knowledge can now be used to improve future climate models.

"We have not seen an ice free period in the Arctic Ocean for 2,6 million years. However, we may see it in our lifetime. The new IPCC report shows that the expanse of the Arctic ice cover has been quickly shrinking since the 70-ies, with 2012 being the year of the sea ice minimum," Jochen Knies.

He is marine geologist at the Geological Survey of Norway (NGU) and Centre for Arctic Gas Hydrate, Climate and Environment, UiT The Arctic Univeristy of Norway.

In an international collaborative project, Jochen Knies has studied the trend in the sea ice extent in the Arctic Ocean from 5.3 to 2.6 million years ago. That was the last time Earth experienced a long period with a climate that, on average, was warm before cold ice ages began to alternate with mild interglacials.

Fossils reveal past sea ice extent

"When we studied molecules from certain plant fossils preserved in sediments at the bottom of the ocean, we found that large expanses of the Arctic Ocean were free of sea ice until four million years ago," Knies tells us.

"Later, the sea ice gradually expanded from the very high Arctic before reaching, for the first time, what we now see as the boundary of the winter ice around 2.6 million years ago ," says Jochen Knies, who is also attached to CAGE, the Centre for Arctic Gas Hydrate, 

Environment and Climate at the University of Tromsø, the Arctic University of Norway.

Arctic Ocean likely to be completely free of sea ice

The research is of great interest on the international stage because present-day global warming is strongly tied to a shrinking ice cover in the Arctic Ocean. By the end of the present century, the Arctic Ocean seems likely to be completely free of sea ice, especially in summer.

This may have major significance for the entire planet 's climate system. Polar oceans , their temperature and salinity, are important drivers for world ocean circulation that distributes heat in the oceans. It also affects the heat distribution in the atmosphere. Trying to anticipate future changes in this finely tuned system, is a priority for climate researchers. For that they use climate modeling , which relies on good data.

"Our results can be used as a tool in climate modelling to show us what kind of climate we can expect at the turn of the next century. There is no doubt that this will be one of many tools the UN Climate Panel will make use of, too. The extent of the ice in the Arctic has always been very uncertain but, through this work, we show how the sea ice in the Arctic Ocean developed before all the land-based ice masses in the Northern Hemisphere were established," Jochen Knies explains.

Seabed samples from Spitsbergen

A deep well into the ocean floor northwest of Spitsbergen was the basis for this research. It was drilled as part of the International Ocean Drilling Programme, (IODP), to determine the age of the ocean-floor sediments in the area. Then, by analysing the sediments for chemical fossils made by certain microscopic plants that live in sea ice and the surrounding oceans, Knies and his co-workers were able to fingerprint the environmental conditions as they changed through time.

"One thing these layers of sediment enable us to do is to "read" when the sea ice reached that precise point," Jochen Knies tells us.

The scientists believe that the growth of sea ice until 2.6 million years ago was partly due to the considerable exhumation of the land masses in the circum-Arctic that occurred during this period. "Significant changes in altitudes above sea level in several parts of the Arctic, including Svalbard and Greenland, with build-up of ice on land, stimulated the distribution of the sea ice," Jochen Knies says.

"In addition, the opening of the Bering Strait between America and Russia and the closure of the Panama Cannel in central America at the same time resulted in a huge supply of fresh water to the Arctic, which also led to the formation of more sea ice in the Arctic Ocean," Jochen Knies adds.

All the large ice sheets in the Northern Hemisphere existed around 2.6 million years ago.

Scientists at Norwegian Geological Survey (NGU), CAGE, UiT The Arctic University of Norway,University of Plymouth, Universitat Autònoma de Barcelona, Stellenbosch University in South Africa and Institució Catalana de Recerca i Estudis Avançats in Barcelona have collaborated in this work.

Source:  University of Tromso (Universitetet i Tromsø - UiT)

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'Tipping points' for sea level rise related flooding determined

Annapolis, Maryland, pictured here in 2012, is one of three major East Coast urban areas already being faced with nuisance flooding in excess of 30 days per year. Credit: With permission from Amy McGovern

By 2050, a majority of U.S. coastal areas are likely to be threatened by 30 or more days of flooding each year due to dramatically accelerating impacts from sea level rise, according to a new NOAA study, published today in the American Geophysical Union's online peer-reviewed journal Earth's Future.

The findings appear in the paper "From the Extreme to the Mean: Acceleration and Tipping Points for Coastal Inundation due to Sea Level Rise," and follows the earlier study, Sea Level Rise and Nuisance Flood Frequency Changes around the United States, by the report's co-author, William Sweet, Ph.D., oceanographer at NOAA's Center for Operational Oceanographic Products and Services (CO-OPS). The new analysis was presented at a news conference today at the annual AGU fall meeting in San Francisco.

NOAA scientists Sweet and Joseph Park established a frequency-based benchmark for what they call "tipping points," when so-called nuisance flooding, defined by NOAA's National Weather Service as between one to two feet above local high tide, occurs more than 30 or more times a year.

Based on that standard, the NOAA team found that these tipping points will be met or exceeded by 2050 at most of the U.S. coastal areas studied, regardless of sea level rise likely to occur this century. In their study, Sweet and Park used a 1½ to 4 foot set of recent projections for global sea level rise by year 2100 similar to the rise projections of the Intergovernmental Panel for Climate Change, but also accounting for local factors such as the settlement of land, known as subsidence.

These regional tipping points will be surpassed in the coming decades in areas with more frequent storms, the report said. These tipping points will be also be exceeded in areas where local sea levels rise more than the global projection of one and half to four feet. This also includes coastal areas like Louisiana where subsidence, which is not a result of by climate change, is causing land to sink below sea level.

NOAA tide gauges show the annual rate of daily floods reaching these levels has drastically increased -- often accelerating -- and are now five to ten times more likely today than they were 50 years ago.

"Coastal communities are beginning to experience sunny-day nuisance or urban flooding, much more so than in decades past," said Sweet. "This is due to sea level rise. Unfortunately, once impacts are noticed, they will become commonplace rather quickly. We find that in 30 to 40 years, even modest projections of global sea level rise -- 1½ feet by the year 2100 -- will increase instances of daily high tide flooding to a point requiring an active, and potentially costly response, and by the end of this century, our projections show that there will be near-daily nuisance flooding in most of the locations that we reviewed."

"Communities across the country become increasingly vulnerable to water inundation and flooding, effective risk management is going to become more heavily reliant on environmental data and analysis," said Holly Bamford, Ph.D., NOAA acting assistant secretary for conservation and management. "Businesses, coastal managers, federal, state, and local governments, and non-governmental organizations can use research such as this as another tool as they develop plans to reduce vulnerabilities, adapt to change, and ensure they're resilient against future events."

"The importance of this research is that it draws attention to the largely neglected part of the frequency of these events. This frequency distribution includes a hazard level referred to as 'nuisance': occasionally costly to clean up, but never catastrophic or perhaps newsworthy," said Earth's Future editor Michael Ellis in accepting the paper for the online journal.

Ellis also observed that "the authors use observational data to drive home the important point that nuisance floods (from inundating seas) will cross a tipping point over the next several decades and significantly earlier than the 2100 date that is generally regarded as a target date for damaging levels of sea-level. The paper also raises the interesting question of what frequency of 'nuisance' corresponds to a perception of 'this is no longer a nuisance but a serious hazard due to its rapidly growing and cumulative impacts'."

The scientists base the projections on NOAA tidal stations where there is a 50-year or greater continuous record. The study does not include the Miami area, as the NOAA tide stations in the area were destroyed by Hurricane Andrew in 1992 and a continuous 50-year data set for the area does not exist.

Based on that criteria, the NOAA team is projecting that Boston; New York City; Philadelphia; Baltimore; Washington, D.C.; Norfolk, Virginia; and Wilmington, North Carolina; all along the Mid-Atlantic coast, will soon make, or are already being forced to make, decisions on how to mitigate these nuisance floods earlier than planned. In the Gulf, NOAA forecasts earlier than anticipated floods for Galveston Bay and Port Isabel, Texas. Along the Pacific coast the earlier impacts will be most visible in the San Diego/La Jolla and San Francisco Bay areas.

Mitigation decisions could range from retreating further inland to coastal fortification or to a combination of "green" infrastructure using both natural resources such as dunes and wetland, along with "gray" human-made infrastructure such as sea walls and redesigned storm water systems.

Source: National Oceanic and Atmospheric Administration

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Massive study provides first detailed look at how Greenland's ice is vanishing

This NASA visualization shows the change in the surface elevation of the southeast region of the Greenland ice sheet between 2003 and 2012. Thinning ... [show more]
 Credit: NASA's Goddard Space Flight Center Scientific Visualization Studio

The Greenland Ice Sheet is the second-largest body of ice on Earth. It covers an area about five times the size of New York State and Kansas combined, and if it melts completely, oceans could rise by 20 feet. Coastal communities from Florida to Bangladesh would suffer extensive damage.

Now, a new study is revealing just how little we understand this northern behemoth.

Led by geophysicist Beata Csatho, PhD, an associate professor of geology at the University at Buffalo, the research provides what the authors think is the first comprehensive picture of how Greenland's ice is vanishing. It suggests that current ice sheet modeling studies are too simplistic to accurately predict the future contributions of the entire Greenland Ice Sheet to sea level rise, and that Greenland may lose ice more rapidly in the near future than previously thought.

"The great importance of our data is that for the first time, we have a comprehensive picture of how all of Greenland's glaciers have changed over the past decade," Csatho says.

"This information is crucial for developing and validating numerical models that predict how the ice sheet may change and contribute to global sea level over the next few hundred years," says Cornelis J. van der Veen, PhD, professor in the Department of Geography at the University of Kansas, who played a key role in interpreting glaciological changes.

The project was a massive undertaking, using satellite and aerial data from NASA's ICESat spacecraft and Operation IceBridge field campaign to reconstruct how the height of the Greenland Ice Sheet changed at nearly 100,000 locations from 1993 to 2012.

Ice loss takes place in a complex manner, with the ice sheet both melting and calving ice into the ocean.

The study had two major findings:

• First, the scientists were able to provide new estimates of annual ice loss at high spatial resolution.

• Second, the research revealed that current models fail to accurately capture how the entire Greenland Ice Sheet is changing and contributing to rising oceans.

The second point is crucial to climate change modelers.

Today's simulations use the activity of four well-studied glaciers -- Jakobshavn, Helheim, Kangerlussuaq and Petermann -- to forecast how the entire ice sheet will dump ice into the oceans.

But the new research shows that activity at these four locations may not be representative of what is happening with glaciers across the ice sheet. In fact, glaciers undergo patterns of thinning and thickening that current climate change simulations fail to address, Csatho says.

"There are 242 outlet glaciers wider than 1.5 km on the Greenland Ice Sheet, and what we see is that their behavior is complex in space and time," Csatho says. "The local climate and geological conditions, the local hydrology -- all of these factors have an effect. The current models do not address this complexity."

The team identified areas of rapid shrinkage in southeast Greenland that today's models don't acknowledge. This leads Csatho to believe that the ice sheet could lose ice faster in the future than today's simulations would suggest.

The results will be published on Dec. 15 in the Proceedings of the National Academy of Sciences.

How much ice is the Greenland Ice Sheet losing?

To analyze how the height of the ice sheet was changing, Csatho and UB research professor and photogrammetrist Anton Schenk, PhD, developed a computational technique called Surface Elevation Reconstruction And Change detection to fuse together data from NASA satellite and aerial missions.

The analysis found that the Greenland Ice Sheet lost about 243 metric gigatons of ice annually -- equivalent to about 277 cubic kilometers of ice per year -- from 2003-09, the period for which the team had the most comprehensive data. This loss is estimated to have added about 0.68 millimeters of water to the oceans annually.

The figures are averages, and ice loss varied from year to year, and from region to region.

Why are today's projections of sea level rise flawed, and how can we fix them?

Glaciers don't just gradually lose mass when the temperature rises. That's one reason it's difficult to predict their response to global warming.

In the study, scientists found that some of Greenland's glaciers thickened even when the temperature rose. Others exhibited accelerated thinning. Some displayed both thinning and thickening, with sudden reversals.

As a step toward building better models of sea level rise, the research team divided Greenland's 242 glaciers into 7 major groups based on their behavior from 2003-09.

"Understanding the groupings will help us pick out examples of glaciers that are representative of the whole," Csatho says. "We can then use data from these representative glaciers in models to provide a more complete picture of what is happening."

In a new project, she and colleagues are investigating why different glaciers respond differently to warming. Factors could include the temperature of the surrounding ocean; the level of friction between a glacier and the bedrock below; the amount of water under a glacier; and the geometry of the fjord.

"The physics of these processes are not well understood," Csatho says.

The NASA missions: A colossal undertaking

The study combined data from various NASA missions, including:

• NASA's Ice, Cloud and Land Elevation Satellite (ICESat), which measured the ice sheet's elevation multiple times a year at each of the nearly 100,000 locations from 2003-09.

• NASA's, massive aerial survey that employs highly specialized research aircrafts to collect data at less frequent intervals than ICESat. These missions began measuring the Greenland Ice Sheet's elevation in 1993. Operation IceBridge was started in 2009 to bridge the time between ICESat-1 and ICESat-2, and will continue until at least 2017, when NASA's next generation ICESat-2 satellite is expected to come online.

Csatho says the new study shows why careful monitoring is critical: Given the complex nature of glacier behavior, good data is crucial to building better models.

Collaborators

Besides Csatho, Schenk and van der Veen, the project included additional researchers from the University at Buffalo, Utrecht University in The Netherlands, the Technical University of Denmark and Florida Atlantic University.

Source:  University at Buffalo

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