An international team of scientists led by British Antarctic Survey (BAS) has established that warm ocean currents are the dominant cause of recent ice loss from Antarctica. New techniques have been used to differentiate, for the first time, between the two known causes of melting ice shelves -- warm ocean currents attacking the underside, and warm air melting from above. This finding brings scientists a step closer to providing reliable projections（预测） of future sea-level rise. Researchers used 4.5 million measurements made by a laser instrument mounted on NASA's ICESat satellite to map the changing thickness of almost all the floating ice shelves around Antarctica, revealing the pattern of ice-shelf melt across the continent. Of the 54 ice shelves mapped, 20 are being melted by warm ocean currents, most of which are in West Antarctica.

In every case, the inland glaciers that flow down to the coast and feed into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea level rise.

Lead author Dr Hamish Pritchard from British Antarctic Survey, which is funded by the UK's Natural Environment Research Council (NERC), said: "In most places in Antarctica, we can't explain the ice-shelf thinning through melting of snow at the surface, so it has to be driven by warm ocean currents melting them from below.

"We've looked all around the Antarctic coast and we see a clear pattern: in all the cases where ice shelves are being melted by the ocean, the inland glaciers are speeding up. It's this glacier acceleration that's responsible for most of the increase in ice loss from the continent and this is contributing to sea-level rise.

"What's really interesting is just how sensitive these glaciers seem to be. Some ice shelves are thinning by a few metres a year and, in response, the glaciers drain billions of tons of ice into the sea. This supports the idea that ice shelves are important in slowing down the glaciers that feed them, controlling the loss of ice from the Antarctic ice sheet. It means that we can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt -- the oceans can do all the work from below.

"But this does raise the question of why this is happening now. We think that it's linked to changes in wind patterns. Studies have shown that Antarctic winds have changed because of changes in climate, and that this has affected the strength and direction of ocean currents. As a result warm water is funneled beneath the floating ice. These studies and our new results therefore suggest that Antarctica's glaciers are responding rapidly to a changing climate."