A major portion of one of the ice sheets covering Antarctica is likely to completely melt over the coming centuries, pushing sea levels even higher than has been predicted, NASA scientists say.

In west Antarctica, glaciers that flow into the Amundsen Sea are being melted by a combination of warm currents in the ocean and local geographic peculiarities.

The geography is causing the warm water to melt the glaciers where they are attached to the seabed, causing them to loss mass, which in turn reduces their ability to hold back inland glaciers behind them in their inexorable march to the sea.

The melting is happening more quickly than previously thought and may push the glaciers "past the point of no return," Eric Rignot, a NASA glaciologist says, and the process "appears unstoppable."

Researchers had previously believed the ice sheet, as much as 2 miles thick in places, would be stable for thousands of years, but the observed rate of melting over the past 40 years suggests otherwise, Rignot says.

A complete melting could raise world sea levels as much as 4 feet, he says.

Although that might take a few centuries, some experts say there could be significant impacts felt by 2010.

Latest United Nations climate change assessment predicted sea levels might rise between 1 and 3 feet by the end of this century, driving millions of people from the globe's coastal regions.

But the U.N. prediction was made without taking the melting west Antarctic ice sheet into account says Penn State geosciences Professor Sridhar Anandakrishnan.

"So as this paper and others come out, the (U.N.) numbers for 2100 will almost certainly" be closer to 3 feet, he said.

The ice cover in the Amundsen Sea area represents just a small part of the West Antarctic Ice sheet, and if the entirety of it were to melt, it could raise sea levels around the world by as much as 16 feet, the researchers said.

NASA scientists say the agency will use its satellites, along with others launched by the space agencies of Japan, Canada and Europe, to monitor the ice sheets and track glacier melting.

NASA says it will launch an ICESat-2 satellite in 2017 as a follow-up to ICESat, which was in orbit from 2003 until 2009.

It will use a technology known as laser altimetry for precisely measurements of glacier heights, providing a year-to-year survey capability in one of the world's most remote regions.

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