(Continued from page one)

          While Weaver and Hillaire-Marcel reviewed the evidence of ancient climates, others have run computer simulations of future Arctic climates, which also cast doubt on the idea that a new ice sheet could grow under the warmer conditions of the future. Even if the Atlantic Ocean stopped overturning, no permanent snow could exist in Europe or Asia in August, at the levels of carbon dioxide (CO₂) found today. Simulations suggest that ice sheets might get started only at CO₂ levels below 220 parts per million (ppm), but today’s CO₂ level is 380 ppm and is increasing. It will simply be too warm for year-round ice and snow for the foreseeable future.

          The authors find that climate change might indeed disrupt the deep overturning of one susceptible region, the Labrador Sea between Greenland and Canada. But if overturning does cease in the Labrador Sea, it would still continue in the larger expanse of the North Atlantic Ocean between Greenland and Europe; and model simulations of the future oceans support that conclusion.

            Evidence from past climates agrees with model simulations: It is possible though unlikely that the Atlantic Ocean deep water circulation might slow down because of climate change. But even if it does slow down, and even if Europe does cool, ice sheets will not grow under the conditions expected in the next several centuries.

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1. “Global Warming and the Next Ice Age”, by Andrew J. Weaver and Claude Hillaire-Marcel, Science, v. 304, 400-402, 16 April 2004.

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