Glaciers give major boost to sea level.

In today's warming climate, the significant melting of the ice sheets capping Greenland and Antarctica garners a lot of attention. However, the ongoing melting of glaciers and other small ice masses worldwide actually makes a larger contribution to the rise in sea level, a new study suggests.

Sea level is now rising about 3 millimeters each year, says W. Tad Pfeffer, a glaciologist at the University of Colorado at Boulder. While some of that increase comes from the expansion of ocean water as it gets warmer, most of the boost is caused by meltwater from land-based ice. The melting of icebergs and of the floating ice shelves that fringe Antarctica doesn't raise sea level.

Net losses of ice from Greenland and Antarctica send about 250 billion tons of water to the sea each year, Pfeffer and his colleagues estimate. However, the team's analysis of satellite and field data also finds that other ice masses, including several hundred thousand glaciers, are losing about 400 billion tons annually. That amount of meltwater is enough to fill Lake Erie. Modest ice masses such as those in Montana's Glacier National Park and atop Tanzania's Mount Kilimanjaro may disappear entirely in the next few decades, scientists estimate (SN: 10/04/03, p. 215).

"We feel that ignoring the contributions of small glaciers and ice caps is dangerous because it affects the accuracy of predictions of sea level rise," says Pfeffer.--S.P.