Of course, warming in Antarctica is a relative concept. West Antarctica remains an exceedingly cold place, with average annual temperatures in the center of the ice sheet that are nearly 50 degrees Fahrenheit below freezing.

But the temperature there does sometimes rise above freezing in the summer, and the new research raises the possibility that it might begin to happen more often, potentially weakening the ice sheet through surface melting. The ice sheet is already under attack at the edges by warmer ocean water, and scientists are on alert for any new threat.

A potential collapse of the West Antarctic ice sheet is one of the long-term hazards that have led experts to worry about global warming. The base of the ice sheet sits below sea level, in a configuration that makes it especially vulnerable. Scientists say a breakup of the ice sheet, over a period that would presumably last at least several hundred years, could raise global sea levels by 10 feet, possibly more.