ORONO, Maine - Scientists who study the health of our planet are raising alarm flags about the unstable condition of Antarctica, which is shedding its icy mantle at a disturbing rate.
They warn that the shrinking of the enormous southern ice cap - half again as big as the United States - could raise sea levels dramatically in coming centuries, flooding coastal areas and significantly altering Earth's climate.
The peril is not immediate, scientists say, but it is serious enough to warrant a major research effort. The first effects could be felt within our grandchildren's lifetimes.
The latest observations from space satellites, ocean vessels and holes bored into Antarctic ice were aired at an international conference of experts earlier this month at the University of Maine.
Their focus is the West Antarctic Ice Sheet, a mile-thick slab of partly rotting ice stretching for more than 2,000 miles across the bottom of the South Pacific.
Glacier expert Terence Hughes of the University of Maine called it the "weak underbelly" of the continent.
"An ice sheet like the one over West Antarctica is a subject of much concern today because of its possible instability and the effect a rapid disintegration could have on global sea level," researcher Richard Hindmarsh of the British Antarctic Survey noted.
An average of 212 square miles of West Antarctic ice tumbles into the sea each year, according to Jane Ferrigno, a researcher at the U.S. Geological Survey in Reston, Va. During the past 20 years, that has been enough to make an ice cube almost 600 miles on a side, she said.
The ice loss has speeded up in the past decade and might be an "early warning for imminent accelerated collapse of the ice sheet," Hughes said.
Scientists aren't sure what is causing the melting of the southern ice cap, but they assume global warming - partly the result of human activity - bears some of the responsibility.
Other factors are long-range ups and downs in the world's temperature, related to the fact that our planet wobbles on its axis, like a spinning top, as it revolves around the sun, as well as to periodic changes in the radiation Earth receives from the sun.
Antarctica is constantly gaining new ice as snow falls and freezes, and losing it as glaciers slide toward the sea. Their slide accelerates when the glacier bottom warms, melts and turns slippery.
West Antarctica has lost two-thirds of its mass since the last Ice Age, 18,000 years ago. After thousands of relatively warm years, punctuated by occasional cold spells, the ice sheet is now "just a remnant of its former self," said Robert Bindschadler, a NASA glaciologist.
If the rest of West Antarctica's ice slipped into the ocean, it would raise global sea levels by 20 feet, glaciologists say. If the entire continent lost its ice - an awesome but unlikely catastrophe - there would be a 200-foot sea rise that would drown most of Delaware, New Jersey, Florida and Louisiana and swamp low-lying coastal areas from Maine to California and all over the world.
The most likely scenario, according to Michael Oppenheimer, a scientist with the Environmental Defense Fund in New York City, is that the oceans will start rising gradually about 100 years from now, leading to disintegration of the West Antarctic Ice Sheet during the next 500 to 700 years. That's a long time to humans but the blink of an eye to a geologist.
Thomas Kellogg, a University of Maine glaciologist, said the evidence suggests the ice cap could break up in what he called "a frighteningly short interval measured in hundreds, rather than thousands, of years."
A major concern is the Pine Island Glacier, which drains a basin the size of Florida and is sliding toward the ocean at 1.5 miles per year. One chunk of the glacier, 100 miles wide and 30 miles long, broke off and disappeared in 1990, Kellogg said.
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