An Icy Tide Rising
Around The World
From Wes Thomas
Sea levels will rise about 50 centimeters by the year 2100 if greenhouse gases continue to increase 1% a year, according to a new computer model. The model, described in the current issue of Nature, predicts glacial melting with greater sophistication than have previous simulations. Such a sea-level rise would threaten countries with low coast lines, such as the Netherlands or the Maldives.
Most scientists say that future greenhouse gas emissions will raise average temperatures on Earth about 2 to 3 degrees Celsius by the end of the next century. This warming, in turn, will heat seawater, increasing the space between molecules and thus raising sea levels by about 25 centimeters. It's trickier, however, to gauge how much additional water will spill into the oceans from melting glaciers and ice sheets, further raising sea levels.
To try to get a better handle on this amount, Jonathan Gregory of the Meteorological Office in Bracknell, U.K., and Johannes Oerlemans of the University of Utrecht in the Netherlands, linked two powerful computer models.
They started with the Atmosphere-Ocean General Circulation Model, which predicts the rates of warming for any point on Earth. These temperatures were fed into another model, developed by Oerlemans and his colleagues, that calculates the extent of glacial melting on mountains. The model incorporates factors such as seasonal variability in melting rate of the ice.
Their calculations suggest that glacial melting will raise the global sea level more than 28 cm. However, the continued industrial production of sulfate aerosols, which reflect sunlight, would lead to a rise of only 21 cm. Experts welcome the refined model. However, scientists are still uncertain about the exact size of many glaciers, which could cloud predictions of how much water would be released, says oceanographer Arnold Gordon of the Lamont-Doherty Earth Observatory in Palisades, New York.

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