The argument about global warming is not whether there is any warming but whether or not and to what extent human activity is responsible for it. My line on that is that we should act as if it is, for this reason, which I borrowed from Jonathan Schell's book on the nuclear question, The Fate of the Earth: We don't have another planet on which to run the experiment. Just as we don't have a right to run an experiment in nuclear exchange on this planet, we have no right to run an experiment in warming it either. So if it turned out to be that there was no severe global warming threat or that it wasn't man-made, then all we would have done would be make a mistake in analysis - which we could correct from. But if it turned out that there was and we didn't do anything about it, then it would be too late to do anything at all. And that would lead to disaster.