If they adhered to the standards established three centuries ago during the Scientific Revolution, the academies would not be able to make such definitive claims. Nineteenth-century astronomer and philosopher of science John Herschel demanded that the scientist assume the role of antagonist against his own theories; the merits of a theory were proved only by its ability to withstand such attacks. Einstein welcomed attempts to disprove the theory of general relativity. “No amount of experimentation can ever prove me right; a single experiment can prove me wrong,” he is said to have declared. Because in science, the philosopher Karl Popper reasoned, we cannot be sure what is true but we can know what is false, truth is approached by discarding what is shown to be false. Popper articulated the principle of falsifiability, distinguishing scientific theory from the pseudosciences of Marx and Freud, whose followers, he noted, found corroboration wherever they looked.

The IPCC and other leading scientific bodies also appear to follow a prescientific injunction: “Seek and ye shall find.” The formulations “consistent with” and “multiple lines of evidence” recur throughout IPCC reports. The IPCC’s fifth assessment report, published in 2013, retreated slightly from previous certainty on humans’ contributing the totality of increased CO2. Now, the IPCC expressed a “very high level of confidence,” based, it said, on several lines of evidence “consistent with” this claim. Consistency with a proposition is weak-form science—the moon orbiting the Earth is consistent with pre-Copernican astronomy, after all—and a feature of the pseudosciences that Popper had seen in early-twentieth-century Vienna. In addition to seeking confirmatory evidence, AGW’s upholders often adopt the scientific equivalent of Don’t Ask, Don’t Tell when it comes to gaps in scientific knowledge—in particular, those gaps that, if filled in, might conceivably falsify their position. The 2014 National Academy / Royal Society paper ignored entirely the question of interannual variability of net CO2 emission. Rather than acting, as in Herschel’s formulation, as AGW antagonists, the IPCC and the national science academies have become its cheerleaders.

“Climate change is one of the defining issues of our time,” the National Academy / Royal Society paper insists. “It is now more certain than ever, based on many lines of evidence, that humans are changing Earth’s climate. . . . However, due to the nature of science, not every single detail is ever totally settled or completely certain.” With respect to the carbon cycle, this is a serious misrepresentation: it is not a detail but is fundamental to the scientific case for AGW. The implications for AGW of Salby’s analysis, if it holds up, are stark: if AGW means that human CO2 emission significantly modifies global temperatures; or, stronger, that it controls the evolution of global temperatures; or, stronger still, that it forces temperatures to increase catastrophically, then AGW is falsified by the observed behavior.