Antarctic ice sheet collapse may swamp U.S. coasts

WASHINGTON Thu Feb 5, 2009 8:27pm GMT

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WASHINGTON (Reuters) - North America's coastlines would be hit especially hard by rising sea levels if the huge West Antarctic Ice Sheet collapses and melts in a warming world as some experts fear, scientists said on Thursday.

The loss of that ice sheet alone would inundate some coastal areas, swamping New York, Washington D.C., south Florida, Los Angeles, San Francisco and Seattle, with sea levels in some places higher by 21 feet or more than today, the researchers wrote in the journal Science.

Factors including changes in the Earth's rotation from the loss of the huge ice sheet would make sea level changes highly variable around the globe, they said. The southern Indian Ocean region also would be heavily affected, they added.

"You pay the price in North America," University of Toronto geophysicist Jerry Mitrovica said in a telephone interview.

"The peak sea level rise occurs on the coasts of the United States -- the New York area and down the coast, the eastern seaboard of the United States," Mitrovica added. "On the West coast, it's even just a little bit bigger."

The West Antarctic Ice Sheet covers about 350,000 square miles (900,000 square km), the size of U.S. states Texas and Oklahoma combined. Its volume equals about 100 times the amount of water in all of North America's Great Lakes, said Natalya Gomez of the University of Toronto, another researcher.

Mitrovica said this is not imminent, but rather: "It's a time scale of hundreds of years."

The United Nations Intergovernmental Panel on Climate Change estimates a loss of the ice sheet would raise sea levels around the world on average by about 16.5 feet.

But Mitrovica said the additional ocean volume would not be like adding water to a bath tub and watching the level rise equally, due to other complicated factors.

The researchers said the melting of the ice sheet would cause the Earth's rotation axis to shift about a third of a mile from its current position. This would move water from the southern Atlantic and Pacific oceans northward toward North America and into the southern Indian Ocean.

The loss of the ice sheet also would erase its previous gravitational pull on the surrounding ocean, pushing water away from Antarctica, they said. And the bedrock underneath could rise without the weight of the ice sheet holding it down, pushing some water out into the ocean.

The study did not consider possible melting of other ice sheets in Greenland or Antarctica that could raise sea levels.

(Editing by Maggie Fox and Cynthia Osterman)

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