Volume of glaciers and ice caps is estimated.

New topographic data have enabled scientists to estimate the volume of water trapped in glaciers and other icy features that could melt and raise sea levels in a warmer world.

Previously compiled data from field surveys revealed that, excluding Greenland and Antarctica, about 522,000 square kilometers of the world's land are covered by accumulated ice. Most ice atop the two excluded landmasses isn't likely to melt quickly in moderately warmer global temperatures, and the ice surrounding the North Pole won't affect sea levels because it's already floating in the ocean.

The old data alone don't provide insight about how thick the world's icy features are or how much water they hold, says Sarah C.B. Raper of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. So, she and Roger J. Braithwaite of the University of Manchester in England looked at worldwide topographic data, recently assembled by the U.S. Geological Survey, to estimate the volume of ice in regions such as Scandinavia, the Alps, and New Zealand.

The combined data suggest that landbased ice features outside Antarctica and Greenland hold about 87,000 cubic kilometers of ice--enough, if it all melted, to raise sea levels about 24 centimeters, says Raper. She and Braithwaite report their findings in the March 16 Geophysical Research Letters. --S.P.