The amount of ice flowing into the sea from large glaciers in southern Greenland has almost doubled in the last 10 years, possibly requiring scientists to increase estimates of how much the world's oceans could rise under the influence of global warming, according to a study being published today in the journal Science.

The authors said there was evidence that the rise in flows would soon spread to glaciers farther north on the vast island, which is covered with an ancient ice sheet nearly 2 miles thick in places, and which holds enough water to raise global sea levels 20 feet or more should it all flow into the ocean.

The study compared various satellite measurements of the creeping ice in 1996, 2000 and 2005, and was performed by researchers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the University of Kansas.

Sometimes the rate of movement in a particular glacier can change abruptly, but the acceleration in Greenland has been detected simultaneously in many different glaciers, said Eric J. Rignot, the study's author, who has extensively studied glacier flows at both poles of the Earth.

''When you have this widespread behavior of the glaciers, where they all speed up, it's clearly a climate signal,'' he said in an interview. ''The fact that this has been going on now over 10 years in southern Greenland suggests this is not a short-lived phenomenon.''

Richard B. Alley, an expert on Greenland's ice at Pennsylvania State University who did not participate in the study, agreed that the acceleration of glaciers in various places supported the idea that this was an important new trend and not some fluke.