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Friday, July 24, 2009

Richard A. Kerr, Science, 325 (24 July 2009), Clouds Appear to Be Big, Bad Player in Global Warming

Science, Vol. 325, No. 5939, 376 (24 July 2009); DOI: 10.1126/science.325_376

News of the Week

Climate Change:

Clouds Appear to Be Big, Bad Player in Global Warming

Richard A. Kerr

The first reliable analysis of cloud behavior over past decades suggests—but falls short of proving—that clouds are strongly amplifying global warming. If that's true, then almost all climate models have got it wrong. On page 460, climate researchers consider the two best, long-term records of cloud behavior over a rectangle of ocean that nearly spans the subtropics between Hawaii and Mexico. In a warming episode that started around 1976, ship-based data showed that cloud cover—especially low-altitude cloud layers—decreased in the study area as ocean temperatures rose and atmospheric pressure fell. One interpretation, the researchers say, is that the warming ocean was transferring heat to the overlying atmosphere, thinning out the low-lying clouds to let in more sunlight that further warmed the ocean. That's a positive or amplifying feedback. During a cooling event in the late 1990s, both data sets recorded just the opposite changes—exactly what would happen if the same amplifying process were operating in reverse.

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