It is also at the center of scientific controversy over its long-term stability. 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 an attendant rise in sea level. It is also the only ice sheet on the planet that sits atop slippery marine sediments well below sea level, setting up what some scientists think may be a scenario where the ice sheet slowly collapses into the sea. Bentley says scientists disagree about how long such a slow-motion cataclysm might take.
Estimates range from a few hundred to a few thousand years or longer.
He explains that while the satellite can measure new accumulations of precipitated 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. An important problem is the fact that you don't get the same amount of snowfall each year. Like Madison, Wis., the West Antarctic Ice Sheet experiences a lot of interannual variability in the amount of precipitation it gets. That is by far the most serious limiting problem in determining changes in the mass of the West Antarctic Ice Sheet. GLAS, the satellite's laser altimeter system, is being developed under the direction of Bob Schutz at the University of Texas at Austin.