One can understand Mr. Mann’s irritation. His hockey stick, which purported to demonstrate the link between man-made carbon emissions and catastrophic global warming, was the central pillar of the IPCC’s 2001 Third Assessment Report, and it brought him near-legendary status in his community. Naturally he wanted to put Mr. McIntyre in his place.

The sensible way to do so is to prove Mr. McIntyre wrong using facts and evidence and improved data. Instead the email reveals Mr. Mann casting about for a way to smear him. If the case for man-made global warming is really as strong as the so-called consensus claims it is, why do the climategate emails show scientists attempting to stamp out dissenting points of view? Why must they manipulate data, such as Mr. Jones’s infamous effort (revealed in the first batch of climategate emails) to “hide the decline,” deliberately concealing an inconvenient divergence, post-1960, between real-world, observed temperature data and scientists’ preferred proxies derived from analyzing tree rings?

This is the real significance of the climategate emails. They show that major scientists who inform the IPCC can’t be trusted to stick to the science and avoid political activism. This, in turn, has very worrying implications for the major international policy decisions adopted on the basis of their research.