Mr. Holman Jenkins, courtesy of the Wall Street Journal:

Mr. Gore’s method is the equivalent of trying to prove that Jack killed Jane by going on and on about how awful it was that Jane was killed….

Suppose the world consisted of exactly one smoker who could be observed only from a distance to test the theory that smoking causes lung cancer. If he died of cancer, it wouldn’t prove smoking causes cancer. If he failed to die of cancer, it wouldn’t prove smoking doesn’t cause cancer.

The link between smoking and cancer is made by observing millions of smokers and nonsmokers. Indeed, what led scientists to seek systematic evidence of a link in the first place was anecdotal evidence that smokers, of whom there have been millions, appeared to die in unusual numbers from lung cancer.

Nothing remotely similar has been involved in developing the hypothesis that carbon dioxide creates warming. The relevant observations are a mess: Measured global temperature has both risen and fallen for considerable periods during the past century, even as CO2 has risen steadily. The geologic record suggests the world was much cooler in the past despite CO2 concentrations higher than today’s. Unlike smoking and cancer, there’s no anecdotal observation for the hypothesis that CO2 causes planetary warming. It may or may not be true, but to believe it is a “scientific truth” is to make a leap of faith, not science.

The consensus that human activities are causing global warming is purely a social invention--there’s no way of showing it to be so, and no self-evident reason for preferring to believe it’s so. The “consensus” is, in truth, a product of itself.