Scientists with the British Antarctic Survey say new techniques have allowed them to differentiate between the two known causes of melting ice shelves: warm ocean currents attacking the underside, and warm air melting from above.
The researchers say the findings bring them one step closer to providing reliable projections of future sea-level rise.
Satellite measurements of 54 floating ice shelves around Antarctica found that 20 are being melted by warm ocean currents, mostly in West Antarctica, survey researchers reported Wednesday.
"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," scientist Hamish Pritchard said.
"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," he said.
"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."