Advocates for doing something expensive about global warming are fond of telling us that the science behind it all is settled, and in one very limited sense they are more-or-less correct. If humans insist on filling the atmosphere with carbon dioxide then we can indeed expect the average temperature of the world to increase slightly. But the scientific consensus on the matter stops right there.

There is no great certainty that the increase will be large enough to be noticeable. There is even less certainty that it will be large enough to make a measurable impact on human affairs. There is virtually no certainty at all that an impact, if and when it occurred, would necessarily be disastrous.

Why then have climate scientists let the whole concept of disastrous global warming get to the stage where it has become the accepted wisdom of nearly all the politically correct people of the western world?

A small part of the answer may be that scientists, like everyone else, have to eat. Big social problems tend to release big dollars. Another part of the answer is that scientists too are human, and can be seduced as easily as anyone else by the pleasures of playing a lead role in well-funded campaigns against the forces of evil. But perhaps the biggest part of the answer is that scientists simply cannot believe that any of their colleagues would deliberately oversell a scientific conclusion for the sake of a political cause. As a consequence they can easily slip into a mode of public support, and indeed into a mode of public advocacy, for a broad scientific theory involving many distinct areas of research about which they personally know very little. They tend to forget how much of their support relies on procedures which have evolved over the years to protect the reputation of science in general. These procedures (peer review is one of them) are far from perfect.

The bottom line is that scientists have allowed themselves to be part of a huge propaganda machine that has developed to such an extent that they can no longer countenance any public expression of doubt about its origins. In particular they have been forced to distance themselves from the scepticism which is the very lifeblood of science as a whole.

The problem with propaganda machines is that the average man in the street has learnt to smell them, recognize them, and be highly sceptical of them. His distrust may be hidden for a while for various reasons of inertia and politics, but given some small encouragement by way of an obvious glitch in the system, he will rather enjoy tearing the thing apart. And such a glitch seems to have occurred in the climate game with the leaking a few months ago of thousands of e-mails and documents from the Climate Research Unit of the University of East Anglia. Among other things, they reveal how researchers may indeed go off the rails when they can no longer distinguish between research and political activism. The blogosphere (and, strangely enough, the main-stream media in the UK) is having a ball with what has become known as the Climategate affair.

The response of prominent scientists within the global warming establishment both to Climategate and to the subsequent emergence of a very obvious and very extensive degree of scepticism about their work is quite extraordinary. They have had control of public opinion concerning the disastrous nature of climate change for so long that they cannot even conceive of the possibility that sceptics may have a point. It seems instead that to return to their place in the sun it will merely be necessary for scientists to engage more powerfully in active promotion of a belief in climatic doom. To build a bigger propaganda machine in other words. It doesn't occur to them that it is exactly this sort of behaviour that got them into trouble in the first place. It is exactly this sort of behaviour that is ultimately likely to lose their battle for them. Perhaps more important in the long term, it is exactly this sort of behaviour that stands a good chance of ruining the hard-won reputation of science as a whole. And that'll learn'em!