1686 P olicy-makers and the media, particular-ly in the United States, frequently assert that climate science is highly uncertain. Some have used this as an argument against adopting strong measures to reduce green-house gas emissions. For example, while dis-cussing a major U.S. Environmental Pro-tection Agency report on the risks of climate change, then–EPA administrator Christine Whitman argued, “As [the report] went through review, there was less consensus on the science and conclu-sions on climate change” ( 1 ). Some corporations whose revenues might be adversely affected by controls on carbon dioxide emissions have also alleged major uncertainties in the science ( 2 ). Such state-ments suggest that there might be substantive disagreement in the scientific community about the reality of anthropogenic climate change. This is not the case. The scientific consensus is clearly ex-pressed in the reports of the Inter-governmental Panel on Climate Change (IPCC). Created in 1988 by the World Meteorological Organization and the United Nations Environmental Programme, IPCC’s purpose is to evaluate the state of climate sci-ence as a basis for informed policy action, primarily on the basis of peer-reviewed and published scientific literature ( 3 ). In its most recent assessment, IPCC states unequivocal-ly that the consensus of scientific opinion is that Earth’s climate is being affected by hu-man activities: “Human activities … are modifying the concentration of atmospheric constituents … that absorb or scatter radiant energy. … [M]ost of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas con-centrations” [p. 21 in ( 4 )]. IPCC is not alone in its conclusions. In
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