Published: March 04, 2006
U.S, German Effort Detects Large Loss of Antarctic Ice Mass
NASA satellites help measure entire ice sheet for the first time
Scientists conducting the first gravity survey of the entire Antarctic ice sheet found the ice sheet's mass decreased significantly from 2002 to 2005.
The scientists based their findings on data from the joint NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE). Isabella Velicogna and John Wahr, both from the University of Colorado, demonstrated for the first time that Antarctica's ice sheet has lost a significant amount of mass since the launch of GRACE in 2002, according to a March 2 NASA press release.
"What is unique about what we've found," Velicogna said, "is that for the first time we're able to get a number for the entire ice sheet ... [and] we're able to say we are sure that the Antarctic ice sheet is losing mass, and at a significant rate."
Because ice sheets are a large source of uncertainty in projections of sea-level change, the GRACE survey is an important step toward more accurate prediction.
The estimated mass loss was enough to raise global sea level about 1.2 millimeters during the survey period - about 13 percent of the overall observed rise in sea level for the same period.
The researchers found Antarctica's ice sheet decreased by about 152 cubic kilometers of ice annually between April 2002 and August 2005. A cubic kilometer is one trillion liters of water - about 264 billion gallons.
This represents a change of about 0.4 millimeters per year in global sea-level rise. Most of the loss in mass came from the West Antarctic ice sheet.
"Antarctica is Earth's largest reservoir of fresh water," Velicogna said. "The GRACE mission is unique in its ability to measure mass changes directly for entire ice sheets, and [it] can determine how Earth's mass distribution changes over time."
Measuring variations in Antarctica's ice sheet mass is difficult because of its size and complexity. GRACE overcomes these issues by surveying the entire ice sheet and tracking the balance between mass changes in the interior and coastal areas.
Previous estimates have used various techniques, each with limitations and uncertainties and an inherent inability to monitor the entire ice sheet mass as a whole.
Even studies that synthesized results from several techniques, such as an assessment by the Intergovernmental Panel on Climate Change, established by the World Meteorological Organization and the United Nations Environment Programme, suffered from a lack of data in critical regions.
The Antarctic mass loss findings were helped by the ability of the identical twin GRACE satellites to track minute changes in Earth's gravity field resulting from regional changes in the distribution off planet mass.
Vast movements of ice, air, water and solid earth reflect weather patterns, climate change and even earthquakes.
To track these changes, GRACE measures micron-scale variations in the 220-kilometer separation between the two satellites, which fly in formation.
Additional information about GRACE is available on the Web sites of the University of Texas and Germany's National Research Centre for Geosciences.
Source: U.S. Department of State
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