And not only them. When an aspiring academic writes a paper, the first thing he does is lard it with quotations from other, more established academics, in hopes that their credibility will buttress his own. And why are these academics so well regarded? Because earlier in their careers they wrote papers citing still weightier names. The whole of human knowledge is constructed in this way, as a kind of pyramid of confidence.
A second rough guide: how new is the thesis? Has it stood the test of time? Or is it more or less fresh out of the box? To advocate creationism today rightly invites ridicule. Yet when Darwin first proposed his theory of natural selection, he faced opposition not only from church leaders, but some of the finest scientific minds of the age. It would be anachronistic to call them cranks: they did not have the benefit, as we do, of 150 years of observation confirming Darwin’s insight.
To believe, or pretend to believe, that man-made global warming is as well established as evolution is a sure sign of hubris, and sows doubts not about the skeptics but their antagonists. Humility is especially in order in the face of a problem as knotty as global warming, with so many interdependent variables, and such degree of “human contingency,” as the climatologist Mike Hulme has written. Where the consensus claims to be able to predict the course of events far into the future—average temperatures a century from now—there is naturally more room for skepticism than in the interpretation of past events.
A third test: what sorts of long-established scientific axioms would have to be overturned in order to reject the orthodox view? That’s always possible: every now and then a radical “paradigm shift” occurs that requires us to throw out much of what we thought we knew about a subject. But is it plausible? To doubt that concentrations of carbon dioxide in the air create a greenhouse effect, for example, would require us to renounce much elementary physics and chemistry. Unlikely. But in fact the mainstream of climate skeptics do not doubt this at all. Rather, it is the relative shares of greenhouse gases, as opposed to other “forcing agents,” in causing the warming we have observed that is at issue.
Reasonable people can differ, in other words, but so can unreasonable people. Between “the science is settled” and “global warming is a hoax,” the experts and the public must grope their way to a common understanding.
