By The Associated Press

WASHINGTON (AP) - The huge West Antarctic ice sheet is starting a glacially slow collapse in an unstoppable way, two new studies show. Alarmed scientists say that means even more sea level rise than they figured.

The worrisome outcomes won't be seen soon. Scientists are talking hundreds of years, but over that time the melt that has started could eventually add 4 to 12 feet to current sea levels.

A NASA study looking at 40 years of ground, airplane and satellite data of what researchers call "the weak underbelly of West Antarctica" shows the melt is happening faster than scientists had predicted, crossing a critical threshold that has begun a domino-like process.

"It does seem to be happening quickly," said University of Washington glaciologist Ian Joughin, lead author of one study. "We really are witnessing the beginning stages."

It's likely because of man-made global warming and the ozone hole which have changed the Antarctic winds and warmed the water that eats away at the feet of the ice, researchers said at a NASA news conference Monday.

"The system is in sort of a chain reaction that is unstoppable," said NASA glaciologist Eric Rignot, chief author of the NASA study in the journal Geophysical Research Letters. "Every process in this reaction is feeding the next one."

Curbing emissions from fossil fuels to slow climate change will probably not halt the melting but it could slow the speed of the problem, Rignot said.

Rignot, who also is a scientist at the University of California Irvine, and other scientists said the "grounding line" which could be considered a dam that stops glacier retreat has essentially been breached. The only thing that could stop the retreat in this low-altitude region is a mountain or hill and there is none. Another way to think of it is like wine flowing from a horizontal uncorked bottle, he said.

Rignot looked at six glaciers in the region with special concentration on the Thwaites glacier, about the size of New Mexico and Arizona combined. Thwaites is so connected to the other glaciers that it helps trigger loss elsewhere, said Joughin, whose study was released Monday by the journal Science.

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NASA spots worrisome Antarctic ice sheet melt - NBC40.net