The researchers concluded that glaciers and ice caps are currently contributing about 60 percent of the world's ice to the oceans and the rate has been markedly accelerating in the past decade. The contribution is presently about 100 cubic miles of ice annually -- a volume nearly equal to the water in Lake Erie -- and is rising by about three cubic miles per year.

In contrast, the team estimated Greenland is now contributing about 28 percent of the total global sea rise from ice loss and Antarctica is contributing about 12 percent. Greenland is not expected to catch up to glaciers and ice caps in terms of sea level rise contributions until the end of the century, according to the study.

A paper on the subject appears in the July 19 issue of the journal Science. "One reason for this study is the widely held view that the Greenland and Antarctic ice sheets will be the principal causes of sea-level rise," said Mark Meier, lead study author. "But we show that it is the glaciers and ice caps, not the two large ice sheets, that will be the big players in sea rise for at least the next few generations."

Meier estimated there are several hundred thousand small glaciers and small, pancake-shaped ice caps in polar and temperate regions. They range from modest, high mountain glaciers to huge glaciers like the Bering Glacier in Alaska, which measures about 5, 000 square miles in area and is nearly one-half mile thick in places.

The accelerating contribution of glaciers and ice caps is due in part to rapid changes in the flow of tidewater glaciers that discharge icebergs directly into the ocean, said the study. Many tidewater glaciers are undergoing rapid thinning, stretching and retreat, which causes them to speed up and deliver increased amounts of ice into the world's oceans.

The team estimated accelerating melt of glaciers and ice caps could add from 4 inches to 9.5 inches of additional sea level rise globally by 2100. This does not include the expansion of warming ocean water, which could potentially double those numbers.

"At the very least, our projections indicate that future sea- level rise may be larger than anticipated, and that the component due to glaciers and ice caps will continue to be substantial," wrote the authors.