Consensus ? What consensus ?

The notion of a consensus, although it means little in science, is often used in support of the claim of man-made warming. Even quite recently we've seen reports about more than 400 people, mainly highly qualified scientists who "reject the consensus". But what is the history of claims of a consensus and what exactly is the consensus to which these claims refer, and even more importantly, do the claims have much credibility? CLAIMS AND MORE CLAIMS One of the first people to mention a consensus appears to have been Al Gore who, according to Environmental News on 1 April 2000, used this expression prior to his unsuccessful bid of the presidency. "There is overwhelming scientific consensus that human activity is contributing to global warming. .. which can lead to serious public health consequences. .. and extreme weather." [My emphasis] At this time the IPCC's Third Assessment Report was scheduled for release in January of the next year, a full 7 months away, and when Gore made his comment either the second draft was being written or it was in the hands of the reviewers, so he couldn't have based his comments on this report. Perhaps Gore was relying on a 1996 survey by Bray and von Storch 1 that had examined support for the claim as part of gauging the attitude and views of scientists. We'll return to this survey later but for now it should be said that only 40% of over 500 respondents expressed answers that were on the "agree" side of a scale from "disagree" to "agree" on the question of whether climate change was mostly the result of human activity. That's hardly an overwhelming consensus by any stretch of the imagination. Gore had aspirations as an environmentalist so maybe the comment was nothing more than political spin. On 11 October of that same year, 2000, the UK's Guardian newspaper stated: "Hansen and his colleagues accept the scientific consensus that carbon dioxide is responsible for roughly half of all man-made global warming over the last half century." 2 [My emphasis] The "Hansen" in question was James Hansen, the NASA employee who is well recognized for making somewhat extreme claims, and it is not beyond possibility that Hansen mentioned a consensus and The Guardian willingly paraphrased his comments. Where Gore's consensus was about a human contribution to global warming this statement from The Guardian says that the consensus …