Uncertainty and climate change

How confident can we be about the way a system as complex as earth will respond to conditions it has never encountered before? Although greater uncertainty means climate change might be less bad than we fear – for example, an “iris” effect means increases in cloud cover may slow global warming – it also means it might be much worse. While the central predictions of climate change models are arguably not so much worse than many other difficult problems the world faces, the worst possibilities are far, far nastier.

-- from If climate sceptics are right, it is time to worry by Paul Klemperer.