Oceans' warm water currents are causing Antarctica's ice carpet to melt, scientists say, and as much half of the ice will melt down along the coastline of the Earth's southernmost continent.

It was always believed that calving, the break off of large chunks of ice, was the main factor driving ice-shelf dynamics, but recent research has underscored the role of melting from below, or 'basal' melting. Capitalizing on newly available monitoring data as well as recent modeling, a team of scientists led by Eric Rignot at the University of California, Irvine, has for the first time quantified this effect for the entire continent.

The researchers published their results on the journal Science and they claim that warm ocean currents are melting ice shelves predominantly at certain locations around the continent, to an extent that accounts for 55% of the annual melt water. The findings will help researchers tackle larger questions about how the Antarctic ice sheet might change in future and its contribution to global sea-level rise.

According to Rignot, the ice shelves act like stoppers, stemming the slow flow of continental ice. "If they thin and disappear, then the continental ice will accelerate its movement to the sea," he says.

These results build on a paper published last year in Nature2 suggesting that wind-driven ocean currents are a primary factor in the thinning ice shelves. But Rignot and his colleagues are the first to incorporate a host of recent data into their measurements, including ongoing aerial surveys and a comprehensive analysis of previous data from satellites and other sources.

"This was quite a big gap in our understanding of how the ice sheets interact with their surroundings, and what it shows is that the oceans play a bigger role than we'd previously thought," says Hamish Pritchard, a glaciologist at the British Antarctic Survey in Cambridge who led the Nature study. Other teams are working on similar analyses, Pritchard says, but "Eric won the race".