NASA mission detects significant antarctic ice mass loss (Forwarded)

Erica Hupp/Dwayne Brown
Headquarters, Washington March 2, 2006
(202) 358-1237/1726

Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
(818) 354-0474

RELEASE: 06-085

NASA MISSION DETECTS SIGNIFICANT ANTARCTIC ICE MASS LOSS

Scientists were able to conduct the first-ever gravity survey of the
entire Antarctic ice sheet using data from the joint NASA/German
Aerospace Center Gravity Recovery and Climate Experiment (GRACE).
This comprehensive study found the ice sheet's mass has decreased
significantly from 2002 to 2005.

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 the launch of GRACE in 2002. The estimated mass loss was
enough to raise global sea level about 1.2 millimeters (0.05 inches)
during the survey period; 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.

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 (JPL),
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:
http://www.nasa.gov/home

For more information about Grace on the Web, visit:
http://www.csr.utexas.edu/grace
http://www.gfz-potsdam.de/grace

For University of Colorado information call Jim Scott at:
(303) 492-3114.