1686Policy-makers and the media, particular-ly in the United States, frequently assertthat climate science is highly uncertain.Some have used this as an argument againstadopting 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 climatechange, then–EPA administrator ChristineWhitman argued, “As [the report] wentthrough review, therewas less consensus onthe science and conclu-sions on climate change”(1). Some corporationswhose revenues mightbe adversely affected by controls on carbondioxide emissions have also alleged majoruncertainties in the science (2). Such state-ments suggest that there might be substantivedisagreement in the scientific communityabout the reality of anthropogenic climatechange. 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 WorldMeteorological Organization and the UnitedNations Environmental Programme, IPCC’spurpose is to evaluate the state of climate sci-ence as a basis for informed policy action,primarily on the basis of peer-reviewed andpublished scientific literature (3). In its mostrecent assessment, IPCC states unequivocal-ly that the consensus of scientific opinion isthat Earth’s climate is being affected by hu-man activities: “Human activities … aremodifying the concentration of atmosphericconstituents … that absorb or scatter radiantenergy. …[M]ost of the observed warmingover the last 50 years is likely to have beendue to the increase in greenhouse gas con-centrations” [p. 21 in (4)].
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