Our Hot Legacy

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Science  14 Nov 2003:
Vol. 302, Issue 5648, pp. 1111
DOI: 10.1126/science.302.5648.1111c

Anthropogenic activity appears to have made a significant impact on North American climate during the last half century. Karoly et al. (p. 1200) used five different climate models to show that the changes observed in this region are too large to have been caused by natural variations alone, and can only be explained by including the effects of added greenhouse gases and sulfate aerosols. In contrast, during the first half of the 20th century, when the accumulated burden of anthropogenic components was only a fraction of what it is today, warming was most likely the result of natural climate variability.

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