Christopher Hitchens has for the most part remained silent on the issue of global warming, but he defines it in a rather interesting way here.
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 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.
In other words, even if the science is inconclusive, it would be imprudent and stupid of us to not guard ourselves against the highly plausible (if not dead certain) calamity that our contributions to climate warming may ultimately lead to. Besides, aren't conservatives supposed to be on the side of conservation?
The trouble is, the science isn't uncertain. The evidence for anthropogenic global warming is absolutely overwhelming according to just about every scientific institution known to man, including the United States National Academy of Sciences. I'm hard pressed to find a single one that doesn't staunchly advocate for collective action designed to curb greenhouse gas emissions.
Today, the science for global warming is about as sound as the science for evolution and gravity. Yet, many individuals (particularly in the United States) remain skeptical. The fact that a number of ordinary individuals still doubt the human aspect to climate change doesn't negate the facts in the slightest. It took time for people to come around to the notion that the earth was flat; many willfully denied it until much after the science was made obvious. I suspect that before my generation passes on, global warming will be viewed in the same light.