End of the line. The Pine Island Glacier could soon be dumping more of the West Antarctic Ice Sheet into the sea.

Hasty Retreat by Ice Sheet

New radar images hint that the West Antarctic Ice Sheet may be giving way, according to a report in tomorrow's issue of Science. One of the glaciers flowing from the ice sheet into the sea--a glacier that has long been seen as the ice sheet's weak point--is eating into stabler ice at a startling rate. If the deterioration continues, it could accelerate into a wholesale collapse of the ice sheet that would end up flooding any low-lying coast, from all of South Florida to the city of Bangkok This isn't the first unsettling news from West Antarctica. Early this month, researchers sifting through mud drilled from beneath the West Antarctic Ice Sheet reported that the massive pile of ice had disintegrated to next to nothing at least once in the past 1.3 million years (Science, 3 July, p. 17), presumably during a warm interlude between ice ages like today's.

The observations, by radar scientist Eric Rignot of the Jet Propulsion Laboratory in Pasadena, California, show that the "grounding line" of the Pine Island Glacier--where ice resting on its bed gives way to floating ice--has been retreating inland at a rate of more than a kilometer per year, presumably because the glacier is melting at its base. "That's not catastrophic yet," says glaciologist Richard Alley of Pennsylvania State University in State College, "but most models indicate [that the retreat] would speed up if it kept going."

And that, say some glaciologists, might be a first step toward the breakup of the entire West Antarctic Ice Sheet, which covers one-quarter of Antarctica. "It could potentially lead to a collapse" of the ice sheet, says radar glaciologist Mark Fahnestock of the University of Maryland, College Park. The result would be a sea-level rise of more than 5 meters--enough "to back up every sewer in New York City," as one researcher puts it.

But researchers aren't panicking yet. Their primary reservation, which Rignot shares, is that they have only 4 years' worth of observations on the glacier's retreat. That, says Alley, "is a very short interval." To gauge the threat of a continuing retreat, glaciologists will be probing deep within the glacier to see why it might be the ice sheet's "weak underbelly."