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As arctic ice melts, South Pole ice grows

Scientists are puzzled, but the phenomenon seems to fit the latest global-warming models.

By Peter N. SpottsStaff writer of The Christian Science Monitor / January 10, 2008

Deep freeze: A view through the heads-up display of a US Air Force C-17 cargo plane as it leaves Antarctica.

Ted S. Warren/AP/FILE

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For decades, the vast expanse of sea ice that surrounds Antarctica each winter, and all but vanishes each austral summer, has languished as the Rodney Dangerfield of Earth's cryosphere.

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Antarctic sea ice has gotten little respect, especially compared with its top-of-the-world cousin, or with the enormous ice sheets on Greenland and the Antarctic continent. The sea ice is hard to reach. It has little direct effect on people. And the Southern Ocean was not a cold-war playground for US and Soviet submarines, which amassed a wealth of information on changes in Arctic sea ice before the era of long-term satellite observations.

But as a research target, southern sea ice's stock appears to be rising.

Over the past 20 years, southern sea ice has expanded, in contrast to the Arctic's decline, and researchers want to understand why. Many climate-model experiments show the Arctic responding more rapidly than Antarctica as global warming kicks in. But after looking at the latest projections from the Intergovernmental Panel on Climate Change, "Arctic sea ice is well ahead of the models, and Antarctic sea ice is well behind what the models project," says Stephen Ackley, a polar scientist at the University of Texas, San Antonio.

Moreover, recent studies have shown that in key regions off the Antarctic coast, sea ice shows a strong, coherent response to El Niño-La Niña cycles, decade-scale climate swings in the tropical Pacific whose length, strength, and timing may be affected in uncertain ways by global warming. Indeed, outside the tropics, Antarctica boasts the strongest climate response to El Niño of any region on the planet. This suggests strong climate connections and feedbacks among sea, ice, and air in the Southern Ocean that are poorly understood.

Some scientists say trends in sea ice in key spots around the continent may be bellwethers for worrisome changes that could accelerate the melt of nearby land ice, most notably the West Antarctic Ice Sheet.

The overall growth in Antarctica's sea ice over the past two decades masks significant regional declines in the Bellingshausen and Amundsen Seas – the destination for glaciers flowing from the West Antarctic Ice Sheet. Researchers say these glaciers are losing ice to the sea faster than snow is replenishing the ice. Thus, the large regional drops in sea ice could also signal the presence of "a very big threat to glacier ice" on the continent, says Xiaojun Yuan, a polar scientist at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y. The leading suspect: relatively warm water upwelling near the coast as a result of global warming's effect on wind patterns in the region.

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