One of the familiar cries of the people who want us to doubt AGW is ‘There is no scientific consensus’. The arguments are summed up well on Skeptical Science.

The other side of the coin is also sometimes spread; ‘the idea of consensus is nonsense; it has no meaning’. This one came up a couple of days ago.

The much-over-discussed Schulte paper-which-is-a-draft-and-not-yet published is, on the face of it, another attempt to use this line of argument. But it is fruitless.

First of all, what do those national academies of science mean (or think they mean) when they say ‘there is a consensus among climate scientists that…X’? As their comments are aimed at the politicians and the public, their meaning is the commonly understood one; ‘Consensus’ = ‘general agreement’. So; ‘consensus’ does have at least one meaningful use.

Any statement that there is not a general agreement amongst climate scientists that ‘most of recent global warming is anthropogenic in origin’, is false.

Being sneaky, slimy types, though, the disinformationists then try to imply; ‘there is no consensus that global warming will be catastrophic’. As SS points out, this is a straw man argument; it is a proposition set up in advance to be knocked down ( a tradition as old as Socrates, at least). It should be noted, though, that there at least some climate scientists who believe that there is a real risk that the effects of global warming will, eventually, be catastrophic, if the warming goes up enough. Two notable exponents of this view (not climate scientists) are James Lovelock and Mark Lynas. Indeed, Lovelock believes that, thanks to political inertia and public ignorance, this is already inevitable. James Hansen’s position (he is a climate scientist), on the other hand, appears to be that the risk is real enough to take immediate preventative action, and that the ‘window of opportunity’ to act may be as short as ten years.

Many bloggers and scientists try to defuse this version by pointing out that this isn’t what they are (generally) claiming, but the danger of this approach is that it can too easily be read to mean, ‘There is unlikely to be enough ‘effect’ of GW to make action worthwhile’. This is dangerous, because it is also wrong. If climate scientists as a whole were asked, ‘Do you think that, unchecked by mitigation, GW will seriously damage the environment?’, a good proportion might well answer ‘Yes.’

The third attempt to claim a lack of consensus is the claim that ‘there is no unanimous agreement among climate scientists’. This is a trick of switching the usage of ‘consensus’ from its’ everyday meaning, to the special and specific meaning attached to it in Consensus Theory, a branch of social studies which attempts to give a precise definition of the term to allow for robust analysis. And even in Consensus Theory, universality is not a necessary condition for stating that a consensus exists; there are several acceptable alternatives which are used as the circumstance demands. The way in which these people are using the universality excluder is not even acceptable in consensus theory, never mind everyday English.

So if anyone tries to tell you that there is still a debate about the causes of global warming, or that ‘there is no consensus’, the answer is simple;

‘No consensus? Nonsensus!’