NASA Mission Detects Significant Antarctic Ice Mass Loss
The first-ever gravity survey of the entire Antarctic ice sheet, conducted
using data from the NASA/German Aerospace Center Gravity Recovery and
Climate Experiment (Grace), concludes the ice sheet's mass has decreased
significantly from 2002 to 2005.
Image right: Antarctica. Image credit: Ben Holt, Sr. + Browse image
Isabella Velicogna and John Wahr, both from the University of Colorado,
Boulder, conducted the study. They demonstrated for the first time that
Antarctica's ice sheet lost a significant amount of mass since 2002. The
estimated mass loss was enough to raise global sea level about 1.2 millimeters
(0.05 inches) during the survey period, or about 13 percent of the overall
observed sea level rise for the same period. The researchers found Antarctica's
ice sheet decreased by 152 (plus or minus 80) cubic kilometers of ice annually
between April 2002 and August 2005.
That is about how much water the United States consumes in three months (a
cubic kilometer is one trillion liters; approximately 264 billion gallons of water).
This represents a change of about 0.4 millimeters (.016 inches) per year to global
sea level rise. Most of the mass loss 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 can determine how Earth's mass distribution changes over time. Because ice sheets
are a large source of uncertainties in projections of sea level change, this represents
a very important step toward more accurate prediction, and has important societal and
economic impacts. As more Grace data become available, it will become feasible to search
for longer-term changes in the rate of Antarctic mass loss," she said.
Measuring variations in Antarctica's ice sheet mass is difficult because of its size and
complexity. Grace is able to overcome these issues, 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 the assessment by the Intergovernmental
Panel on Climate Change, suffered from a lack of data in critical regions.
"Combining Grace data with data from other instruments such as NASA's Ice, Cloud and
Land Elevation Satellite; radar; and altimeters that are more effective for studying
individual glaciers is expected to substantially improve our understanding of the processes
controlling ice sheet mass variations," Velicogna said.
Image left: This figure shows the ice mass loss in Antarctica as observed by Grace over the period 2002-2005 (see browse image) measured in cubic kilometers per year. The ice mass loss observed contributes about 0.4 millimeters (.016 inches) per year to global sea level rise. Image credit: University of Colorado + Browse image
The Antarctic mass loss findings were enabled by the ability of the identical twin Grace
satellites to track minute changes in Earth's gravity field resulting from regional changes
in planet mass distribution. Mass movement 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 (137-mile) separation between the two satellites,
which fly in formation.
Grace is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif. The University of
Texas Center for Space Research has overall mission responsibility. GeoForschungsZentrum Potsdam
(GFZ), Potsdam, Germany, is responsible for German mission elements. Science data processing,
distribution, archiving and product verification are managed jointly by JPL, the University of
Texas and GFZ. The results will appear in this week's issue of Science.
For information about NASA and agency programs on the Web, visit:
For more information about Grace on the Web, visit:
For University of Colorado information call Jim Scott at: (303) 492-3114.
JPL is managed for NASA by the California Institute of Technology in Pasadena.
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Erica Hupp/Dwayne Brown (202) 358-1237/1726
NASA Headquarters, Washington