KELLY MCEVERS, HOST:
Antarctica is bigger than the U.S. and Mexico combined, and it is covered in thick ice. That ice has been melting recently, most probably because of a warming climate. And as NPR's Christopher Joyce reports, the rate of melting appears to be accelerating.
CHRISTOPHER JOYCE, BYLINE: Antarctica's ice is over a mile deep in some parts. It sits on bedrock, but it flows off the continents' edges slowly, especially along the western edge where giant glaciers creep down toward the sea. Where they meet the ocean, they form ice shelves. They are the specialty of Ala Khazander.
ALA KHAZANDER: You have this floating plate of ice being fed by the glaciers flowing from the interior of the continent while having ocean water underneath it.
JOYCE: Khazander is a polar scientist at NASA's Jet Propulsion Laboratory.
KHAZANDER: I like to think of them as the gates of Antarctica.
JOYCE: Although the shelves float, they're still connected to the mainland. A team from JPL has been using radar to see beneath the ice. They found that the ice is melting faster than they've ever seen, especially at the point where the bedrock ends and the ice shelf floats. They believe the cause is warm water circulating beneath the ice shelf. The melting was most pronounced from 2002 to 2009, and Khazander says the more it melts, the more ice is exposed to warm water.
KHAZANDER: It becomes a runaway process, which makes it unstable.
JOYCE: Where's the warmer water coming from? The team points to global warming that's heating up the oceans. And there's been a spate of research lately showing that Antarctic ice is melting faster than previously thought and raising global sea levels. Khazander says the melting process appears to be irreversible. Polar scientists fear that at some point the shelves will collapse, and Antarctica's glaciers will flow into the sea. As to whether and when that might happen...
KHAZANDER: The simple answer is that we don't know, and that's the scary part.
JOYCE: The research appears in the journal Nature Communications. Christopher Joyce, NPR News.