Antarctic Glaciers' Sloughing Of Ice Has Scientists at a Loss

By Marc Kaufman
Washington Post Staff Writer
Friday, March 16, 2007

Some of the largest glaciers in Antarctica and Greenland are moving in unusual ways and are losing increased amounts of ice to the sea, researchers said yesterday.

Although the changes in Greenland appear to be related to global warming, it remains unclear what is causing the glaciers of frigid Antarctica and their "ice streams" to lose ice to the ocean in recent years, the researchers said.

"In Greenland we know there is melting associated with the ice loss, but in Antarctica we don't really know why it's happening," said Duncan Wingham, an author of the review released today in Science magazine. "With so much of the world's ice captured in Antarctica, just the fact that we don't know why this is happening is a cause of some concern."

The Antarctic ice loss, which Wingham said is not caused by melting but rather by the pushing of ice streams into the ocean by several glaciers in the west of the continent, has picked up speed in recent years. But Wingham said that because researchers did not have good measures of the depth of the Antarctic ice shelf until about 10 years ago, scientists do not know whether this is a natural variation or a result of human activity.

Complicating the situation for those studying Antarctica, some parts of the continent are gaining ice depth through snowfall while temperatures on the tip of the Antarctic peninsula, the continent's closest point to South America, are rising faster than almost anywhere else on the planet. The surprisingly fast-moving glaciers are largely on the West Antarctic ice sheet.

Wingham, of University College London, and Andrew Shepherd of the University of Edinburgh said satellite radar readings show that overall, each year the ice loss from Greenland and Antarctica amounts to about 10 percent of the rise in the global sea level, which totals about one-tenth of an inch per year. The net loss of Antarctic ice is estimated to be 25 billion metric tons a year, despite the growth of the ice sheet in East Antarctica.

Because such a large percentage of the world's ice is found in those two locations, scientists are carefully watching for signs of increased ice loss. If that process accelerates, researchers say, it could result in a substantial, and highly disruptive, increase in sea levels worldwide.

In Greenland, glaciers appear to be moving more quickly to sea because melting ice has allowed the sheet to slide more easily over the rock and dirt below. In Antarctica, the loss is believed to be associated with the breaking off into seawater of ice deep under the ice sheet with little-understood internal dynamics that put increased pressure on the massive ice streams.

Wingham said he thinks the final paper of the Intergovernmental Panel on Climate Change will say much the same about the Antarctic. "I believe it will be along the lines of 'Something is happening beneath the ice sheets, but we don't really know what it is yet.' "

The panel, sponsored by the United Nations, concluded last month with more than 90 percent certainty that the burning of fossil fuels and other human activities are causing the planet to warm significantly.

In the same issue of Science, other researchers report that air pollution from industrialized areas is collecting over the Arctic and creating "Arctic haze." The pollution comes from industrial and natural sources -- aerosols, chemicals that can form into ozone and black carbon, which is produced by incomplete burning of fossil fuels. The gradual warming of the large forests below the Arctic has resulted in an increase in forest fires, which produce air pollutants that can increase warming further.

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