Consider the case closed on global warming. The assessment released on Feb. 2 by the U.N.'s Intergovernmental Panel on Climate Change (IPCC) concluded for the first time that evidence of the earth's rising temperatures was "unequivocal"—and that this warming was more than 90% likely the result of human activity. We are locked into some amount of climate change: the IPCC reported that even if we managed to end all greenhouse-gas emissions today, the earth would continue to warm through the rest of the century because of the amount of carbon we have already added to the atmosphere. But if the 600...
