In the climate debate it can be hard to tell the two apart. Over recent days, I've been having some very interesting conversations with Matt Flaherty -- someone who is largely convinced of mainstream climate science. I've been suitably impressed by his open-mindedness. I don't think, however, that I've persuaded him of anything more than that there is a case to answer, but a space for debate has been opened.
When I first came across Matt's blog, the first thing I noticed was the widespread use of the word "denier", which of course is a red rag to a bull for most people here - understandably I would say, when the word was not introduced into the debate for honourable reasons. However, its use is widespread and we should know by now that the mere fact of having used it is not enough to identify the user as a bad person. Those who have been following the debate for a while, which is probably most of us, will remember the jeremiads hurled in Judith Curry's direction when she first started hanging round at Climate Audit. One of the principal objections to her presence was that she had used the d-word. Fortunately she persevered long enough to overcome the distrust and so eventually was elevated to the position of patron saint of lukewarmers. She still uses the d-word though.
I think though that the d-word remains overused. Matt tries to distinguish between deniers, which he defines as people who object to the global warming hypothesis on political grounds, and sceptics - people arguing the science. Obviously, many of the climate bloggers on the other side of the debate would argue that the science has reached a point where anyone arguing against it is a denier. This is pretty obviously a gross overstatement of the case, and not really worth discussing as I think we are all fairly clear that it's an attempt to shut off debate.
Even Matt's more nuanced approach worries me though. Matt has pointed to James Delingpole as a "denier", which he defines as someone who rejects the global warming hypothesis on political grounds. I wonder how he knows this. People come to the opinions they have in all sorts of ways, as regular commenter Nullius in Verba pointed out in the comments on the Simon Singh thread (it's way down at the bottom of the thread at time of writing).
My position is that anybody can hold and express an opinion based in trust in their preferred experts - what is known as Argument from Authority - or any other heuristic they like (correlation implies causation, argument from ignorance, etc.), so long as it is acknowledged that it is not a belief supported by science, and that people who choose different authorities to believe are not thereby any more defective or irrational for doing so.
Essentially, I distinguish ordinary opinions from scientific opinions - only the latter require a detailed personal knowledge of the evidence.
I don't mind people believing in the seas rising 7 metres by 2050 because Al Gore said so, so long as they understand that their belief is based on an unreliable heuristic, and that Science itself utterly rejects all such Argument from Authority. Heuristics are all that non-scientists have, but we must allow them to hold opinions - and Delingpole is at least honest enough to acknowledge his limits. It might make for a more polite and constructive debate if more people showed the same humility.
My guess is that James Delinpole has heard from people he trusts that there are some severe problems with global warming science and that dissenting voices are being suppressed. He concludes that global warming is a scam and, it being his job, he tells everyone so, usually quite loudly. Like Nullius, I see no problems in this and I don't see this as being denialism, any more than all the people in the Skeptic movement [Update: meaning the Skeptic Society, who are , by and large, mainstream on AGW] who accept mainstream global warming views "because the scientists say so".
Human beings seem to like to divide people mentally into "goodies" and "baddies", particularly in matters political. The problem with a politicised science like climatology is that the same mindset can pervade what should be a strictly logical discussion. As one reads the outpourings of the scibloggers about Delingpole, it is clear that this largely left-wing (as far as I can tell) group is that they want to condemn Delingpole largely because he is a man of the right. They scent blood and that has blinded them to the fact that he has reached his opinions on global warming in exactly the same way that, for the most part, they have. To reiterate Nullius's remarks above, it would make for a more constructive debate if they showed more humility.