(This was originally a comment in this metafilter thread about the University of East Anglia's email leak)
I'm an environmentalist, and I'm a big supporter of looking at rationalism and science as opposed to ideological hand waving. And I think the 'scientific method' is one of the best tools we have in this world.
But the scientific method as applied to, say, early 20th century physicists exploring properties of sub-atomic particles - with easily repeatable experiments - is very different to the 'scientific method' as applied to climate science - which basically boils down to peer review of papers that deal with large complex data sets from many different sources.
A lot of the 'climate denier' stuff does seem to be just shrill finger-pointing that doesn't look at the bigger picture. But if you look at some of the more reasonable analysis by sceptics, there are some valid points to consider. (Nigel Lawson's Appeal to Reason is a good short summary - I wouldn't agree with all his points, but some are reasonable).
It seems feasible that there is bias in the way the IPCC puts together its reports. It seems feasible that scientists might cherry-pick their data or their analysis of the data in a way that could be biased, and that such distortions could easily pass through peer review. Although fantastically complex, our climate models have significant holes in them - e.g. how to treat clouds, or the heat-storing properties of oceans - that are big enough that the resulting uncertainty probably offsets most of the data we get out of them.
As Anthropological Climate Change becomes more accepted politically, it seems to me that the scientific debate has entered a new phase. As the likelihood of real political action grows, people are going to look back over the climate science in fine-combed detail. That a lot of problems with data and methodology are apparently coming to light now, just when it was all supposed to be 'settled' should be no surprise. The stakes are very high in both directions, and everything is going to be scrutinised like never before.
I say problems apparently coming to light, because for me personally, it is very hard to validate the scientific arguments being made on either side. Take, for example, the Hockey Stick controversy - RealClimate's handling of it (see articles from Dec 2004 and Aug 2006) has the feel and tone of a solid rebuttal. But the defence, inevitably, always has to consist of defending one paper of fantastically complex climate science by pointing to another one that is equally complex.
Without taking a degree in climate science, a masters in statistical analysis, building my own supercomputer climate model, and personally visiting all of the data gathering stations to see if they are working right, there is no way for me personally to validate any of this.
So it just comes down to which side you believe in. And to me, both sides have the smell of bias and the feel of higher political beliefs that are interfering with clear thinking. Which isn't that surprising given the stakes.
As an environmentalist, I feel that even if Anthropological Climate Change doesn't turn out to be happening (on balance, the ACC theory being wrong is unlikely but definitely possible, in my view), some sort of environmental limit or feedback is definitely going to get us eventually. You can't just endlessly expand resource usage without hitting some sort of crisis point in a closed system.
So I think we definitely do need to change our large-scale behaviour as a species. But proving whether Anthropological Climate Change is happening or not is way beyond us at the moment. We are not experiencing the last frail complaints of a minority against an overwhelming consensus - the scientific debate here is so complex that it is going to run and run and run and run.