I think Matt is right that people, even other scientists, agree very readily when a load of experts reach the same set of conclusions. We trust in the process of science, and in our colleagues to spot each other's mistakes, so we take a consensus seriously. I do however wonder if he's overstepped the mark with this one. Predicting the future is tricky, and a lot of effort in IPCC does go into showing the range of possible scenarios and what we are most likely to be on course for. In addition, most of the climate change critics are not professional scientists or experts in climate science. And there's another point he doesn't touch on: the precautionary principle. The potential damage we are on course for is huge. And he doesn't even mention loss of biodiversity in this article: that can never be reversed if it occurs. Sure, mistakes have been made, and wild claims have been withdrawn. But if the news turns out not to be so bad in the end, then we are lucky, not stupid. And we're going to want a sustainable planet eventually anyway.