At the margins of the ice sheet, marine ice shelves that protrude over the ocean may be susceptible to a warming sea. Some scientists think that if the ice shelves were thinned enough, an important brake on the ice streams that shuttle ice from the interior of Antarctica would be removed, leading to an accelerated discharge of ice into the ocean and a rise in sea level. The West Antarctic is also the only ice sheet on the planet that sits atop slippery marine sediments that are well below sea level. Because of this, some scientists think the ice sheet may slowly collapse into the sea. Scientists disagree about how long such a slow-motion cataclysm might take, Bentley said.
Estimates range from a few hundred to a few thousand years or longer.
Some don't believe the collapse will occur at all. Noticing change may take longer than the projected mission of ICESat, said Bentley. While the satellite can measure new accumulations of ice and snow, annual fluctuations in the amount of new ice and snow could mask any small but telling changes in the ice sheet's mass balance, he said. The ICESat mission may not be long enough to pin down trends in annual precipitation in the Antarctic, he said. Pages will open in a new browser window External sites are not endorsed by CNN Interactive.