The loss of Antarctic ice is caused mainly by warm ocean currents attacking the underside of ice shelves, a new NASA study has revealed.
Using a combination of measurements from NASA's Ice, Cloud, and land Elevation Satellite (ICESat) and computer models, the team's established that the main reason isn't warm air melting them from above.
The finding should help improve projections of future sea level rise.
Of the 54 ice shelves studied, 20 are being melted by warm ocean currents. Most of these are in West Antarctica, where inland glaciers flowing down to the coast have accelerated, draining more ice into the sea.
And it's this ocean-driven thinning that's responsible for the most widespread and rapid ice losses in West Antarctica and the majority of Antarctic ice sheet loss during the period studied.
"Studies have shown Antarctic winds have changed because of changes in climate," says Hamish Pritchard of the British Antarctic Survey.
"This has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica's glaciers are responding rapidly to a changing climate."
ICESat was the first satellite specifically designed to use laser altimetry to study the Earth's polar regions, and operated from 2003 to 2009. Its successor, ICESat-2, is scheduled for launch in 2016.
Previous studies have used satellite radar data to measure the evolution of ice shelves and glaciers, but ICESat's laser measurements are more precise, particularly in coastal areas.
"This study demonstrates the urgent need for ICESat-2 to get into space," says Jay Zwally, ICESat project scientist at NASA's Goddard Space Flight Center.
"We have limited information on the changes in polar regions caused by climate change. Nothing can look at these changes like satellite measurements do."