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A short history of nearly everythingWhat is most alarming is that we have no idea-none-what natural phenomena could so swiftly rattle EarthБЂ™s thermometer. As Elizabeth Kolbert, writing in the New Yorker, has observed: БЂњNo known external force, or even any that has been hypothesized, seems capable of yanking the temperature back and forth as violently, and as often, as these cores have shown to be the case.БЂ« There seems to be, she adds, БЂњsome vast and terrible feedback loop,БЂ« probably involving the oceans and disruptions of the normal patterns of ocean circulation, but all this is a long way from being understood. One theory is that the heavy inflow of meltwater to the seas at the beginning of the Younger Dryas reduced the saltiness (and thus density) of northern oceans, causing the Gulf Stream to swerve to the south, like a driver trying to avoid a collision. Deprived of the Gulf StreamБЂ™s warmth, the northern latitudes returned to chilly conditions. But this doesnБЂ™t begin to explain why a thousand years later when the Earth warmed once again the Gulf Stream didnБЂ™t veer as before ...» |
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