Science Express: Glacier Melt Impact on Sea-Level is Underestimated

Global sea level has been climbing steadily over the past 80 years—and the contribution from melting ice has been more substantial than previously estimated, according to new research in Science Express.

The missing factor in earlier calculations: how much of the Earth's water is impounded in artificial reservoirs, say Benjamin Chao and colleagues at National Central University in Chung-Li, Taiwan.

The total rise in sea level over the past century is due mostly to ocean water expanding in volume as it warms up, and ice melt from mountain glaciers and Greenland and Antarctic ice sheets. Subtracting the effect of thermal expansion from the observed rate of sea level rise should give a reasonable estimate of the rate of ice melting, the researchers say, but the equation leaves out the amount of water locked up in reservoirs.

They estimate that trapping the reservoir waters has artificially dropped sea levels by 30 millimeters over the past half-century. Add that water back in, they say, and the contribution of ice melt must be higher than previously thought.

The paper was published in the 13 March issue of Science Express ("Impact of Artificial Reservoir Water Impoundment on Global Sea Level"). The Web site provides electronic publication of selected Science papers in advance of print; some editorial changes may occur between the online version and the final printed version.

Becky Ham

14 March 2008