Consilience and the case for climate science consensus

The refusal of many conservatives and libertarians to confront the reality of climate change has been a repeated subject of my blog posts over the years. The subject is a frustrating one for me because it's clear that many partisans see what they want to see in the available scientific research and close their eyes to the rest. It's even more frustrating because this approach has effectively sidelined the case for more conservative or market-oriented climate-related policies—policies that would pose a much smaller threat to individual liberty than the various regulatory initiatives typically championed by environmentalist activist groups.

Several years ago I explained that it would be ideologically convenient to reject the scientific arguments that human activities are contributing to global climate change. The problem, however, is that the weight of the scientific evidence points overwhelmingly in the other direction. Accepting that some studies have been exaggerated or unduly alarmist, and that the various computer models (which represent just one small part of climate science) are woefully inadequate, the cumulative evidence remains quite strong. And even though the threat of climate change could be used to justify all sorts of policies that I don't like, the evidence that such a threat exists is quite real.

Over at Scientific American, Michael Shermer makes this general point—and makes it better than I did. In an essay titled "Why Climate Skeptics Are Wrong," he explains why it is the cumulative weight of the available scientific evidence—and the convergence of this evidence—that should be particularly persuasive in assessing this sort of question.

Consensus science is a phrase often heard today in conjunction with anthropogenic global warming (AGW). Is there a consensus on AGW? There is. … Why?

It is not because of the sheer number of scientists. After all, science is not conducted by poll. As Albert Einstein said in response to a 1931 book skeptical of relativity theory entitled 100 Authors against Einstein, "Why 100? If I were wrong, one would have been enough." The answer is that there is a convergence of evidence from multiple lines of inquiry-pollen, tree rings, ice cores, corals, glacial and polar ice-cap melt, sea-level rise, ecological shifts, carbon dioxide increases, the unprecedented rate of temperature increase-that all converge to a singular conclusion. AGW doubters point to the occasional anomaly in a particular data set, as if one incongruity gainsays all the other lines of evidence. But that is not how consilience science works. For AGW skeptics to overturn the consensus, they would need to find flaws with all the lines of supportive evidence and show a consistent convergence of evidence toward a different theory that explains the data. . . . This they have not done. . . .

As Shermer explains, while scientists have offered alternative explanations for the available data, these various explanations are not cohesive or consistent. They do not converge. Indeed, they contradict each other. The case that humans are contributing significantly to climate change, on the other hand, is based upon a wide range of studies, employing a wide range of methodologies and looking at a wide range of evidence. The result is that if we throw out one—say, Michael Mann's "hockey stick" or overly sensitive computer models—ample evidence remains.

It is the convergence of the scientific evidence around a set of basic claims that provides the ultimate foundation for the climate "consensus," not the number of scientists who subscribe to one theory or another. It is also what makes the foundation of climate science quite robust. That's the way it is, even if it would be ideologically convenient for it to be another way.