When the IPCC's Working Group 1 released its section of the Fourth Assessment Report, covering the physical science behind climate change, the Deniers made much of the fact that their estimate for sea-level rise had been narrowed since 2001. Unfortunately, it seems that Working Group 2, which covers impacts, adaptation, and vulnerabilities, disagrees. Their report, due out in April, concludes that there is "medium confidence" (a 50% chance) that we are already committed to seeing the icecaps melt. This would raise sea-levels by four to six metres over several centuries, and gradually inundate low lying countries and cities. If it happens, we can say goodbye to many of the Pacific Islands, much of the Netherlands and Bangladesh, and large areas of New York, London, and Tokyo. In New Zealand, it would put the Wellington and Christchurch CBDs under water, as well as parts of Auckland.
Of course, it's only medium confidence - they could be wrong. But given the enormous damage this would cause, and the uncertainty about how rapidly it could happen, this is not a chance we can afford to take. We may already be committed to seeing this happen, but if we are not, we need to make damn sure that it does not.