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Patagonian Icefields Melting at Accelerating Rate

The Patagonian icefields, which cover 13,000 square kilometers in Chile and 4,200 square kilometers in Argentina, are a sparsely inhabited world of rough terrain, poor weather and blue glaciers that tumble down from the snow covered mountains of the Andean range. New research shows that these icefields, the largest non-Antarctic ice masses in the Southern Hemisphere, are melting at an accelerating rate.

Melting ice from mountain glaciers is raising sea levels around the world. A new study has found 10 percent of that rise is due to ice melt from Patagonia. That may not seem like much, until you consider that glaciers in Alaska, which cover an area five times larger than Patagonia, account for about 30 percent of that increase.

"So, in effect the Patagonia icefields are contributing more per unit area than the glaciers in Alaska," said Eric Rignot.

Eric Rignot of NASA's Jet Propulsion Laboratory in Pasadena, California is principal scientist for the study. He says so-called calving glaciers, which spawn icebergs into the ocean or lakes, dominate the Patagonian icefields. "And these types of glaciers are known to be more sensitive to climate change," he said. "Once you push them out of equilibrium they can retreat very rapidly, even if climate comes back to normal."

Mr. Rignot says it is the internal dynamics of these icefields that make Patagonia the fastest area of glacial retreat on Earth. "If you warm an icefield, the glaciers can start flowing faster," he explained. "They can produce more icebergs and as a result, they can thin even faster."

Is climate change enough to explain the rapid thinning? "What we found in our study is that climate warming and drier conditions seem to only explain about half of the observed signals," said Mr. Rignot. "And, we believe that the other half is due to the mechanics of ice flow, and in particular some of these glaciers may be flowing faster than they used to be and as a result they thin faster and discharge more ice into the ocean than they used to."

What does the situation in Patagonia tell us about what may be happening elsewhere? "It is showing us an example of interaction of ice and climate warming," said Mr. Rignot. "This is important for our studies of the larger ice sheets in Greenland and Antarctica. It is showing us how rapidly ice can respond to climate warming."

Results of the study are reported in the journal Science. Researchers with the U.S. Space Agency and the Centro de Estudios Cientificos compared data from the NASA space shuttle topography mission in 2000 with historical elevation surveys from aerial photographs, and ground experiments in the 1970s and 1990s.