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 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, the 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,” he said.

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 was able to provide 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,” he said.

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 meltwater
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

The study benefited from ground experiments led jointly by
Centro de Estudios Cientificos; Universidad de Chile;
University of Washington, Seattle, Wash.; and University of
Alaska, Fairbanks, Alaska, 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: