Using new evidence that indicates temperatures from earlier centuries, researchers say they have confirmed that surface temperatures in the northern hemisphere have been warmer in the past decade than at any time in the previous 1,300 to 1,700 years. The new findings, published in the Proceedings of the National Academy of Sciences, are the work of Pennsylvania State University researchers who originally came up with the so-called “hockey stick” graph of global warming. That hypothesis said that northern hemisphere temperatures have held relatively steady for more than 1,000 years (the horizontal shaft of the stick) until sharp increases in recent decades (the blade of the stick.) Some scientists criticized the original research, led by meteorologist and geoscientist Michael Mann, for relying on too few “proxy records,” but Mann and his colleagues have bolstered that research with more than 1,200 new records from marine and lake sediment cores, ice cores, coral cores, and tree rings.
New Temperature Data Support ‘Hockey Stick’ Warming Trend
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