NASA image by Jesse Allen, using data from AMSR-E

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ScienceShot: Pacific Ocean Keeping Earth Cool—For Now

Earth’s average temperature has remained more or less steady since 2001, despite rising levels of atmospheric carbon dioxide and other greenhouse gases—a trend that has perplexed most climate scientists. A new study suggests that the missing heat has been temporarily stirred into the relatively shallow waters in the western Pacific by stronger-than-normal trade winds. Over the past 20 years or so, trade winds near the equator—which generally blow from east to west—have driven warm waters of the Pacific ahead of them, causing larger-than-normal volumes of cool, deep waters to rise to the surface along the western coasts of Central America and South America. (Cooler-than-average surface waters are depicted in shades of blue, image from late July and early August 2007.) Climate simulations suggest that that upwelling has generally cooled Earth’s climate, stifling about 0.1°C to 0.2°C in warming that would have occurred by 2012 if winds hadn’t been inordinately strong, the researchers reported online yesterday in Nature Climate Change. Both real-world observations and the team’s simulations reveal that the abnormally strong winds—driven by natural variation in a long-term climate cycle called the Interdecadal Pacific Oscillation—have, for the time being, carried the “missing” heat to intermediate depths of the western Pacific Ocean. Eventually, possibly by the end of this decade, the inevitable slackening of the trade winds will bring the energy back to the ocean’s surface to be released to the atmosphere, fueling rapid warming, the scientists contend.

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