The key to the scientific method is re-examining one's hypothesis as evidence changes. For a decade, James Hansen, the researcher with NASA who kicked off the debate in the 1980s, has done just that.

Hansen's reputation has been on a roller coaster ever since he announced with "99 per cent confidence" that global warming had arrived. Initially, many of his peers criticized him for taking such a public role on a scientific issue. Yet, partly because he was so concerned about the issue and made it a political one, computers have been humming, scholars have circled the globe to examine bore holes and sea ice, and temperature records have been scrutinized and reviewed. Hundreds of scientific articles have been published since Hansen's announcement, as researchers try to figure out what is really happening to the climate.

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