The Antarctic Ice Sheet
Washington Post, Friday, March 3, 2006;

The Antarctic ice sheet is losing as much as 36 cubic miles of ice a year in a trend that scientists link to global warming, according to a new paper that provides the first evidence that the sheet's total mass is shrinking significantly. "The ice sheet is losing mass at a significant rate," said Isabella Velicogna, the study's lead author and a research scientist at Colorado University at Boulder's Cooperative Institute for Research in Environmental Sciences. "It's a good indicator of how the climate is changing."

Richard Alley, a Pennsylvania State University glaciologist called the study significant and
"a bit surprising" because a major international scientific panel predicted five years ago that the Antarctic ice sheet would gain mass this century as higher temperatures led to increased snowfall. "It looks like the ice sheets are ahead of schedule" in terms of melting, Alley said. "That's a wake-up call."

Scientists have been debating whether the Antarctic ice sheet is expanding or shrinking overall, because the center of the sheet tends to gain mass through snowfall whereas the coastal regions are more vulnerable to melting.

Velicogna and her co-author, University of Colorado at Boulder physics professor John Wahr, based their measurements on data from the two GRACE satellites that circle the world more than a dozen times a day at an altitude of 310 miles. The satellites measure variations in Earth's mass and gravitational pull: Increases or decreases in the Antarctic ice sheet's mass change the distance between the satellites as they fly over the region.
"The strength of GRACE is that we were able to assess the entire Antarctic region in one fell swoop to determine if it was gaining or losing mass," Wahr said.

BBC News, 13 Aug. 2009   Antarctic glacier thinning four times faster than 10 years ago

BBC News, 1 Dec. 2009   Major sea level rise likely as Antarctic ice melts

Geologists measured the chemical composition of rocks collected on seven mountains in the Ford Ranges near the Ross Sea. As the ice began to melt away and the glaciers retreated, rocks where left behind on the freshly uncovered mountains. The rocks were exposed to cosmic rays from deep space and so their chemical make-up changed. By looking at the composition of the rocks, the geologists could calculate how old they were and therefore when the ice melted.
A similar method is used by Swiss geologists on freshly exposed rocks and they found that those rocks were covered with ice for at least the previous 800,000 years. The Swiss glaciers have lost over 50% of their mass since 1850.