Not all qualified scientists agree on the existence or size of human-caused global warming, but the evidence for it has improved enough that practical people are starting to prepare for it anyway.

Take General Motors, for instance, one of the “environmental bad guys” if you believe journalists James Ridgeway and Jeffrey St. Clair. GM’s chief economist, G. Mustafa Mohatarem, told a Northwestern University audience last November, “There is sufficient information that some degree of precautionary, prudent, and cost-effective actions are called for….The rational approach for dealing with such uncertainty is to take out an insurance policy.”

The key concept is insurance. “The current debate about detection [of human influence on climate] does not justify inaction,” write MIT professors Henry Jacoby, Ronald Prinn, and Richard Schmalensee in Foreign Affairs (July/August 1998). “It would be irresponsible to ignore such a risk, just as it would be irresponsible to do nothing when you smell smoke at home until and unless you see flames. It would also be irresponsible, of course, to call the fire department and hose down all your belongings at the slightest whiff of what might be smoke.”