What's more, the ice sheet shows no signs of halting its inland march, Hall says. At its current pace, it will disappear in 7,000 years regardless of global warming. But that prediction is extrapolated from only four past positions of the ice sheet. Jumps and spurts are especially hard to predict because of the way the continent sheds its icy load. Antarctica may be shrinking, but oddly enough, it is not melting, at least not directly.
Snow falls in the interior, and the streams carry ice to the sea, where it breaks into icebergs.
Until now, no one knew what was happening at the streams' source, but researchers are a giant leap closer to understanding just how these ice streams work, thanks to new images made by a Canadian satellite called Radarsat. On two occasions during the fall of 1997, the satellite measured reflections of cloud-penetrating radar over much of the ice sheet's thick interior upstream from the Ross Ice Shelf. That's what our image does. In times past, a single velocity measurement required that someone go to the spot and plant a stake with a Global Positioning System receiver in the ice, leave for a certain amount of time, then go back and see how far it had moved. In the barren chill of the Antarctic, that's no easy task.