In their model, the researchers doubled the concentration of atmospheric carbon dioxide and recorded the magnitude and geographic pattern of warming from different factors.

在他们的模型中，这些研究人员加倍关注大气中的二氧化碳量，并记录下有不同原因引起的变暖的多少和覆盖的地理类型。

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Since 1960, the atmospheric concentration of carbon dioxide has risen from 310 to 390 parts per million.

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This measures the amount of warming that can eventually be expected to follow a doubling in the atmospheric concentration of carbon dioxide.

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For the first time, scientists measured an average concentration of atmospheric carbon dioxide of 400 parts per million in Mauna Loa, Hawaii, where the National Oceanic and Atmospheric Administration observatory is located, on Thursday.

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