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The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t . . .
We will keep them out somehow—even if we have to redefine what the peer-review literature is! . . .
If they ever hear there is a Freedom of Information Act now in the U.K., I think I’ll delete the file rather than send it to anyone . . .

And so on. Since their release last November, the famous hacked emails from scientists in the Climate Research Unit (CRU) at the University of East Anglia have provided a rich source of such incriminating phrases. Participants, including some of the leading figures in the UN Intergovernmental Panel on Climate Change (IPCC), discuss how to prevent skeptics from publishing in peer-reviewed journals, plot to destroy or suppress the raw data underlying their studies, suggest ways to massage the figures for better effect, and generally carry on in a tone more evocative of the “war room” than the common room.

To many, the emails offer disturbing evidence that a number of prominent climatologists have crossed the line, from science into activism. It is clear they view dissenters, not as critics to be engaged, but enemies to be beaten. But in fact there is a more fundamental problem at work: a breakdown of trust between scientists and large sections of the lay public.

Previous ages may have been more prone to error, but not to doubt: whatever foolish things they believed, they believed them together. Ours is a very different era. Science has pushed the boundaries of human knowledge to limits never before imagined. Yet all sorts of anti-scientific, indeed pre-scientific beliefs are flourishing at the same time, from the enduring appeal of naturopathy and other folk cures to the hysterias over childhood vaccines and genetically modified foods, all the way to the dreadful pseudo-science of “intelligent design.”

The science writer Michael Specter has called these examples of denialism, a habit of mind that replaces “the rigorous and open-minded skepticism of science with the inflexible certainty of ideological commitment.” But of course that is exactly what skeptics accuse global warming scientists of: a divine certainty of their own rightness that not only blinds them to legitimate criticism, but gives rise to the sorts of behaviour described in the East Anglia emails.

This is why “Climategate” may prove something of a watershed. In the battle for public opinion, global warming advocates have until now had the singular advantage of claiming that the bulk of respectable scientific opinion was on their side. If at least some of that scientific opinion is discovered to be not so respectable as all that, then it is not only their specific case that is harmed: it is science itself.

So the crisis of trust runs both ways. And, what is more, each has good reason to distrust the other.

Look at it from the climate scientists’ perspective. They have spent many years of their lives immersed in the subject. The data they cite has been drawn from any number of sources, thousands of measuring points, hundreds of studies, all of them submitted to rigorous peer review. Yet they are asked to debate people who in many cases have plainly not read or thought seriously about the issue, and who persist in raising objections that have long since been knocked to the ground. Small wonder that global warming advocates have taken to referring to them as “deniers,” flat-earthers or worse.

But now look at it from the public’s perspective. I don’t mean the already committed, pro or con, most of whom live in the bliss of believing what they want to believe. I mean the honestly confused, trying to puzzle out a complex scientific question they are not remotely qualified to judge, yet which will ask them to make the most profound political choices, with all sorts of potential consequences for their future welfare.

I include myself in this group. I have spent many hours reading as much of the literature on either side as I can, and come away, as it were, serially convinced: first by one side, then the other. Because, contrary to what one would absorb from the CRU emails, not all of the skeptics are yahoos. Though they are in the minority among climatologists, they include many eminent scientists, whose insights, whatever their field, cannot be ignored, raising as they do issues of scientific and statistical methodology that cross all disciplines. It is grotesque to lump nuanced skeptics like Freeman Dyson, perhaps the most celebrated physicist alive, in with creationists and 9/11 “truthers.”

But that does not resolve the dilemma. It is pleasing to lecture global warming advocates, as many have, that “science is never settled,” but it is not quite true. That the earth is round may once have been subject to dispute, but it would be ridiculous to suggest the same today. The issue is not whether scientific questions can ever be settled in principle, but whether the particular thesis of man-made global warming has reached that stage.

It is true there is a fever of unreason abroad. It draws on multiple sources—the relativism of the left, the anti-intellectualism of the right, the absolutism of fanatics of all stripes—and spreads, notoriously, via the Internet, with the illusion of expertise it provides. What is produced often has nothing to do with skepticism. To be a skeptic is to doubt something is true, not—as with many global warming “skeptics”—to declare with ex cathedra certainty that it is not.

But self-professed defenders of science should not fall into the trap of regarding every dissent from orthodoxy in the same light. There are two traps, actually: being too closed-minded, and too open. We are not obliged to give 9/11 truthers and other cranks a respectful hearing. Indeed we are obliged not to: we dishonour our worthy opponents if we treat our unworthy opponents with the same deference. But we do far worse when we dismiss eminent scientists who happen to fall outside the scientific consensus as lunatics or hired guns.

The error here is not only scientific. It is also political. If your desire is to persuade the unpersuaded among the general public, the very worst way to go about it is to advertise your bottomless contempt for your adversaries. That the IPCC scientists reacted in this way shows how unprepared they were, for all their activist enthusiasm, to enter the political arena.

When a new planet is found, its discoverers are treated with appropriate deference, even reverence. The latest theory of the origins of the universe may be the cause of some head-scratching among the general public, but not outright disbelief, even if it displaces what had previously been the prevailing view. Who are we to say?

But the same deference does not apply when science presumes to answer more political questions, though the gap between expert knowledge and the public’s may be no less wide. Who are we to say? Only the voters, that’s who. It is not enough to admonish the public to “listen to the experts.” Experts can get it wrong. Freud was once near-universal dogma. Today his theories have been largely discredited. Perhaps—who knows?—global warming will one day meet a similar fate.

How to distinguish, then, between genuine authority and mere received wisdom? Conversely, how do we tell crankish imperviousness to evidence from legitimate skepticism? Credentials, though hardly infallible, remain a good reference point, a means of weighing the credibility of sources. An impressive CV doesn’t make a bad argument right, of course, but with a problem of such baffling complexity as climate change, it can serve as a proxy for the uninitiated.

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.