The people who have replied to your question thus far quite frankly haven't a clue what they're talking about. First, 'Six Degrees' uses models of climate change which are imperfect, that much is true. However, so far scientists have found that temperature is increasing at a FASTER rate than their models have predicted, so things look worse and worse than even their models have so far shown. Second, 'Six Degrees' warns that human carbon emissions are extremely unnatural - both more extreme and faster - compared to what has happened at any time in history. Third, it is not just that there will very a linear increase in temperature. There will very likely be positive feedback loops (scientific models show this) and these may result in temperature accelerating out of our control. Positive feedback loops include such events as the melting of the ice caps. They are called positive feedback loops because not only are they the terrible catastrophic effects of climate cjhange so far, but they themselves cause further much worse climate change and so they cause a vicious cycle. Fourth, floods are not the worst outcome from climate change. Irreversible damage to our fragile ecosystem, the death of the Amazon rain forest, desertification of Europe, production of toxic gases by the oceans, complete destruction of the ozone layer through teh release of such gases, destruction of eocsystems and mass extinction events are all predicted by the evidence from scientific models - and remember, that as I have pointed out, so far the scientific models have been shown by the evidence that scientists continue to collect every day to be conservative.