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South American Glaciers Melting Faster, Changing Sea Level



 
 
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Old October 17th 03, 12:24 AM
Ron Baalke
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Default South American Glaciers Melting Faster, Changing Sea Level


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

David E. Steitz (202) 358-1730
NASA Headquarters, Washington D.C.

Claudia Adriasola (011) 56 2 751-7121
Centro de Estudios Cientificos, Valdivia, Chile

News Release: 2003-138
October 16, 2003

South American Glaciers Melting Faster, Changing Sea Level

The Patagonia Icefields of Chile and Argentina, the largest
non-Antarctic ice masses in the Southern Hemisphere, are thinning at
an accelerating pace and now account for nearly 10 percent of global
sea-level change from mountain glaciers, according to a new study by
NASA and Chile's Centro de Estudios Cientificos.

Researchers Dr. Eric Rignot of NASA's Jet Propulsion Laboratory,
Pasadena, Calif.; Andres Rivera of Universidad de Chile, Santiago,
Chile; and Dr. Gino Casassa of Centro de Estudios Cientificos,
Valdivia, Chile, compared conventional topographic data from the 1970s
and 1990s with data from NASA's Shuttle Radar Topography Mission,
flown in February 2000. Their objective was to measure changes over
time in the volumes of the 63 largest glaciers in the region.

Results of the study, published this week in the journal Science,
conclude the Patagonia Icefields lost ice at a rate equivalent to a
sea level rise of 0.04 millimeters (0.0016 inches) per year during the
period 1975 through 2000. This is equal to nine percent of the total
annual global sea-level rise from mountain glaciers, according to the
2001 Intergovernmental Panel on Climate Change Scientific Assessment.
From 1995 through 2000, however, that rate of ice loss from the

icefields more than doubled, to an equivalent sea level rise of 0.1
millimeters (0.004 inches) per year.

In comparison, Alaska's glaciers, which cover an area five times
larger, account for about 30 percent of total annual global sea-level
rise from mountain glaciers. So what's causing the increased
Patagonia thinning?

Rignot and his colleagues concluded the answer is climate change, as
evidenced by increased air temperatures and decreased precipitation
over time. Still, those factors alone are not sufficient to explain
the rapid thinning. The rest of the story appears to lie primarily in
the unique dynamic response of the region's glaciers to climate
change.

"The Patagonia Icefields are dominated by so-called 'calving'
glaciers," Rignot said. "Such glaciers spawn icebergs into the ocean
or lakes and have different dynamics from glaciers that end on land
and melt at their front ends. Calving glaciers are more sensitive to
climate change once pushed out of equilibrium, and make this region
the fastest area of glacial retreat on Earth."

Rignot said the study underscores NASA's unique contributions to
understanding changes in Earth's cryosphere. "From the unique vantage
point of space, the Shuttle Radar Topography Mission provided the
first complete topographic coverage of the Patagonia Icefields," he
explained. "Researchers can now access data on this remote Earth
region in its totality, allowing them to draw conclusions about the
whole system, rather than just focusing on changes on a few glaciers
studied from the ground or by aircraft."

Rignot said scientists are particularly interested in studying how
climate interacts with glaciers because it may be a good barometer of
how the large ice sheets of Greenland and Antarctica will respond to
future climate change. "We know the Antarctic peninsula has been
warming for the past four decades, with ice shelves disappearing
rapidly and glaciers behind them speeding up and raising sea level,"
he noted. "Our Patagonia research is providing unique insights into
how these larger ice masses may evolve over time in a warmer climate,"
he said.

The Northern Patagonia Icefield in Chile and the Southern Patagonia
Icefield in Chile and Argentina, cover 13,000 and 4,200 square
kilometers (5,019 and 1,622 square miles), respectively. The region,
spanning the Andes mountain range, is sparsely inhabited, with rough
terrain and poor weather, restricting ground access by scientists.
Precipitation in the region ranges from 2 to 11 meters (6.6 to 36
feet) of water equivalent per year, a snow equivalent of up to 30
meters (98.4 feet) a year. The icefields discharge ice and mel****er
to the ocean on the west side and to lakes on the east side, via
rapidly flowing glaciers. The fronts of most of these glaciers have
been retreating over the past half- century or more.

The study benefited from ground experiments led jointly by Centro de
Estudios Cientificos; Universidad de Chile; University of Washington,
Seattle; and University of Alaska, Fairbanks, with funding by NASA,
Fondecyt (Chilean National Science Foundation) and the National
Science Foundation International Program.

The Shuttle Radar Topography Mission is a cooperative project of NASA,
the National Imagery and Mapping Agency, and the German and Italian
space agencies. Information about the Shuttle Radar Topography Mission
is available at: http://www.jpl.nasa.gov/srtm/. The California
Institute of Technology in Pasadena manages JPL for NASA.

-end-


 




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