Posts tagged GRACE
CU study: Melting glaciers are largely responsible for sea level rise
May 16th
While 99 percent of Earth’s land ice is locked up in the Greenland and Antarctic ice sheets, the remaining ice in the world’s glaciers contributed just as much to sea rise as the two ice sheets combined from 2003 to 2009, says a new study led by Clark University and involving the University Colorado Boulder.
The new research found that all glacial regions lost mass from 2003 to 2009, with the biggest ice losses occurring in Arctic Canada, Alaska, coastal Greenland, the southern Andes and the Himalayas. The glaciers outside of the Greenland and Antarctic sheets lost an average of roughly 260 billion metric tons of ice annually during the study period, causing the oceans to rise 0.03 inches, or about 0.7 millimeters per year.
The study compared traditional ground measurements to satellite data from NASA’s Ice, Cloud and Land Elevation Satellite, or ICESat, and the Gravity Recovery and Climate Experiment, or GRACE, missions to estimate ice loss for glaciers in all regions of the planet.
“For the first time, we’ve been able to very precisely constrain how much these glaciers as a whole are contributing to sea rise,” said geography Assistant Professor Alex Gardner of Clark University in Worcester, Mass., lead study author. “These smaller ice bodies are currently losing about as much mass as the ice sheets.”
A paper on the subject is being published in the May 17 issue of the journal Science.
“Because the global glacier ice mass is relatively small in comparison with the huge ice sheets covering Greenland and Antarctica, people tend to not worry about it,” said CU-Boulder Professor Tad Pfeffer, a study co-author. “But it’s like a little bucket with a huge hole in the bottom: it may not last for very long, just a century or two, but while there’s ice in those glaciers, it’s a major contributor to sea level rise,” said Pfeffer, a glaciologist at CU-Boulder’s Institute of Arctic and Alpine Research
ICESat, which ceased operations in 2009, measured glacier changes using laser altimetry, which bounces laser pulses off the ice surface to determine changes in the height of ice cover. The GRACE satellite system, still operational, detects variations in Earth’s gravity field resulting from changes in the planet’s mass distribution, including ice displacements.
GRACE does not have a fine enough resolution and ICESat does not have sufficient sampling density to study small glaciers, but mass change estimates by the two satellite systems for large glaciated regions agree well, the scientists concluded.
“Because the two satellite techniques, ICESat and GRACE, are subject to completely different types of errors, the fact that their results are in such good agreement gives us increased confidence in those results,” said CU-Boulder physics Professor John Wahr, a study co-author and fellow at the university’s Cooperative Institute for Research in Environmental Sciences.
Ground-based estimates of glacier mass changes include measurements along a line from a glacier’s summit to its edge, which are extrapolated over a glacier’s entire area. Such measurements, while fairly accurate for individual glaciers, tend to cause scientists to overestimate ice loss when extrapolated over larger regions, including individual mountain ranges, according to the team.
Current estimates predict if all the glaciers in the world were to melt, they would raise sea level by about two feet. In contrast, an entire Greenland ice sheet melt would raise sea levels by about 20 feet, while if Antarctica lost its ice cover, sea levels would rise nearly 200 feet.
The study involved 16 researchers from 10 countries. In addition to Clark University and CU-Boulder, major research contributions came from the University of Michigan, the Scripps Institution of Oceanography in San Diego, Trent University in Ontario, Canada, and the University of Alaska Fairbanks.
Built by Ball Aerospace & Technologies in Boulder, NASA’s ICESat satellite was successfully operated from the CU-Boulder campus by a team made up primarily of undergraduates from its launch in 2003 to its demise in 2009 when the science payload failed. The students participated in the unusual decommissioning of a functioning satellite in 2010, bringing the craft into Earth re-entry to burn up. ICESat’s successor, ICESat-2, is slated for launch in 2016 by NASA.
-CU media release-
CU study: Glacial ice disappearing at record clip
Feb 8th
CU-Boulder study shows global glaciers, ice
caps shedding billions of tons of mass annually
caps shedding billions of tons of mass annually
Earth’s glaciers and ice caps outside of the regions of Greenland and Antarctica are shedding roughly 150 billion tons of ice annually, according to a new study led by the University of Colorado Boulder.
The research effort is the first comprehensive satellite study of the contribution of the world’s melting glaciers and ice caps to global sea level rise and indicates they are adding roughly 0.4 millimeters annually, said CU-Boulder physics Professor John Wahr, who helped lead the study. The measurements are important because the melting of the world’s glaciers and ice caps, along with Greenland and Antarctica, pose the greatest threat to sea level increases in the future, Wahr said.
The researchers used satellite measurements taken with the Gravity Recovery and Climate Experiment, or GRACE, a joint effort of NASA and Germany, to calculate that the world’s glaciers and ice caps had lost about 148 billion tons, or about 39 cubic miles of ice annually from 2003 to 2010. The total does not count the mass from individual glacier and ice caps on the fringes of the Greenland and Antarctic ice sheets — roughly an additional 80 billion tons.
“This is the first time anyone has looked at all of the mass loss from all of Earth’s glaciers and ice caps with GRACE,” said Wahr. “The Earth is losing an incredible amount of ice to the oceans annually, and these new results will help us answer important questions in terms of both sea rise and how the planet’s cold regions are responding to global change.”
A paper on the subject is being published in the Feb. 9 online edition of the journal Nature. The first author, Thomas Jacob, did his research at CU-Boulder and is now at the Bureau de Recherches Géologiques et Minières, in Orléans, France. Other paper co-authors include Professor Tad Pfeffer of CU-Boulder’s Institute of Arctic and Alpine Research and Sean Swenson, a former CU-Boulder physics doctoral student who is now a researcher at the National Center for Atmospheric Research in Boulder.
“The strength of GRACE is that it sees everything in the system,” said Wahr. “Even though we don’t have the resolution to look at individual glaciers, GRACE has proven to be an exceptional tool.” Traditional estimates of Earth’s ice caps and glaciers have been made using ground-based measurements from relatively few glaciers to infer what all of the unmonitored glaciers around the world were doing, he said. Only a few hundred of the roughly 200,000 glaciers worldwide have been monitored for a decade or more.
Launched in 2002, two GRACE satellites whip around Earth in tandem 16 times a day at an altitude of about 300 miles, sensing subtle variations in Earth’s mass and gravitational pull. Separated by roughly 135 miles, the satellites measure changes in Earth’s gravity field caused by regional changes in the planet’s mass, including ice sheets, oceans and water stored in the soil and in underground aquifers.
A positive change in gravity during a satellite approach over Greenland, for example, tugs the lead GRACE satellite away from the trailing satellite, speeding it up and increasing the distance between the two. As the satellites straddle Greenland, the front satellite slows down and the trailing satellite speeds up. A sensitive ranging system allows researchers to measure the distance of the two satellites down to as small as 1 micron — about 1/100 the width of a human hair — and to calculate ice and water amounts from particular regions of interest around the globe using their gravity fields.
For the global glaciers and ice cap measurements, the study authors created separate “mascons,” large, ice-covered regions of Earth of various ovate-type shapes. Jacob and Wahr blanketed 20 regions of Earth with 175 mascons and calculated the estimated mass balance for each mascon.
The CU-led team also used GRACE data to calculate that the ice loss from both Greenland and Antarctica, including their peripheral ice caps and glaciers, was roughly 385 billion tons of ice annually. The total mass ice loss from Greenland, Antarctica and all Earth’s glaciers and ice caps from 2003 to 2010 was about 1,000 cubic miles, about eight times the water volume of Lake Erie, said Wahr.
“The total amount of ice lost to Earth’s oceans from 2003 to 2010 would cover the entire United States in about 1 and one-half feet of water,” said Wahr, also a fellow at the CU-headquartered Cooperative Institute for Research in Environmental Sciences.
The vast majority of climate scientists agree that human activities like pumping huge amounts of greenhouse gases in the atmosphere is warming the planet, an effect that is most pronounced in the polar regions.
One unexpected study result from GRACE was that the estimated ice loss from high Asia mountains — including ranges like the Himalaya, the Pamir and the Tien Shan — was only about 4 billion tons of ice annually. Some previous ground-based estimates of ice loss in the high Asia mountains have ranged up to 50 billion tons annually, Wahr said.
“The GRACE results in this region really were a surprise,” said Wahr. “One possible explanation is that previous estimates were based on measurements taken primarily from some of the lower, more accessible glaciers in Asia and were extrapolated to infer the behavior of higher glaciers. But unlike the lower glaciers, many of the high glaciers would still be too cold to lose mass even in the presence of atmospheric warming.”
“What is still not clear is how these rates of melt may increase and how rapidly glaciers may shrink in the coming decades,” said Pfeffer, also a professor in CU-Boulder’s civil, environmental and architectural engineering department. “That makes it hard to project into the future.”
According to the GRACE data, total sea level rise from all land-based ice on Earth including Greenland and Antarctica was roughly 1.5 millimeters per year annually or about 12 millimeters, or one-half inch, from 2003 to 2010, said Wahr. The sea rise amount does include the expansion of water due to warming, which is the second key sea-rise component and is roughly equal to melt totals, he said.
“One big question is how sea level rise is going to change in this century,” said Pfeffer. “If we could understand the physics more completely and perfect numerical models to simulate all of the processes controlling sea level — especially glacier and ice sheet changes — we would have a much better means to make predictions. But we are not quite there yet.”
