James “the Amazing” Randi is an icon of skepticism. The man has done more — over a span of several decades — to further the cause of critical thinking and to expose flimflammery of all sorts than arguably anyone else in the world, ever. That is why I was struck with incredulity and sadness yesterday when I read Randi’s latest take on global warming.

He begins by stating that, contrary to scientists’ own self-image as almost preternaturally objective human beings, “religious and other emotional convictions drive scientists, despite what they may think their motivations are.” Well, true, to a point. Many philosophers and sociologists of science have said that before (and documented it), but your baloney detector should go up to at least yellow alert when someone starts a commentary on global warming with that particular observation.

The following paragraph is perhaps one of the most astounding I have ever seen penned by a skeptic. It reads in part: “some 32,000 scientists, 9,000 of them PhDs, have signed The Petition Project statement proclaiming that Man is not necessarily the chief cause of warming, that the phenomenon may not exist at all, and that, in any case, warming would not be disastrous.”

Wow, Randi fell for the old “thousands of scientists are against science” trick! First off, I’d like to see the 32,000 signatures (there is no link from the essay). Second, last time I checked, in order to be a career scientist you have to have a PhD, so how come only 9,000 of the signatories did? Did the rest not manage to finish graduate school? But more importantly: were the 32,000 climate scientists? Because if not, then it doesn’t matter how many of them signed the petition. I can easily get thousands of medical doctors (are they “scientists”?) to sign a petition to the effect that evolution doesn’t occur, or an equivalent number of assorted PhDs to express doubts on quantum mechanics, and so on. Having a PhD in a particular field provides no expertise whatsoever in another field, and Randi, of all people, should have known this.

“History supplies us with many examples where scientists were just plain wrong about certain matters, but ultimately discovered the truth through continued research” continues the essay. Another logical fallacy. Yes, the history of science has documented many blunders made by scientists, which usually are redressed by the built-in self-correcting mechanisms of science itself. But to imply that therefore the idea of human-caused global warming is another of these mistakes is like saying “Van Gogh was a great artist and he died penniless; I am penniless, therefore I am a great artist.” It is a non sequitur.

What sort of argument allows Randi to reach his conclusion about global warming? “The myriad of influences that act upon Earth are so many and so variable — though not capricious — that I believe we simply cannot formulate an equation into which we enter variables and come up with an answer.” Really? So Randi doesn’t think climate scientists are aware of the complexities posed by their own discipline? And they should give up building increasingly sophisticated climate models (which, by the way, don’t rely on “an equation”) because he thinks it’s too tough?

And then there is the often lurking ultra-optimism that so many climate skeptics display with no hint of contradiction: “Earth has undergone many serious changes in climate, from the Ice Ages to periods of heavily increased plant growth from their high levels of CO2, yet the biosphere has survived. We're adaptable, stubborn, and persistent — and we have what other life forms don't have: we can manipulate our environment. Show me an Inuit who can survive in his habitat without warm clothing... Humans will continue to infest Earth because we're smart.” So let me get this straight: we are not smart enough to model the changing climate, but whatever problem there is, we are smart enough to solve it. I guess what Walt Whitman used to say is true , great minds are large enough to accommodate contradictions.

But the real damning part of Randi’s essay comes when he says: “I strongly suspect that The Petition Project may be valid. I base this on my admittedly rudimentary knowledge of the facts about planet Earth. ... this my amateur opinion, based on probably insufficient data.” This is essentially saying that although Randi has no expertise whatsoever in a complex scientific field, together with very scant information on the specifics of the problem, he nonetheless “suspects” that the overwhelming majority of (PhD-holding) practitioners in that field have made a colossal mistake. So are we supposed to take his position seriously on authority alone (another logical fallacy)? And where does that authority come from? His undoubted ability to expose real nonsense like hand surgery?

Yesterday was a sad day for skepticism because Randi’s essay will now comfort legions of pseudoscientific “skeptics,” regardless of the fact that I’m sure this was not his intention. But what was his intention, exactly? If Randi were Penn&Teller, I would have a ready answer: it is the libertarian ideological bias of P&T that has led them more than once to talk real bullshit to their audiences about issues like global warming, environmentalism, world politics, and economics. But I do not know Randi’s political leanings, so I will not speculate further. My guess is that this is just classic Randi, who is known for occasionally shooting from the hip just to stir the waters a bit, with the honest intention of stimulating critical thinking. Except that these waters have been quite muddied already by big corporations who have been actively engaged in public deception about this issue for years , so that public opinion and politicians are already confused enough, almost to the point of paralysis. I really think this was an uncharacteristically bad target for Randi to choose.

More broadly, however, we need to pause and think carefully about the entire skeptical movement in light of episodes like this one. “Skepticism” in modern parlance indicates a science- or evidence-based approach to the examination of unusual claims, typically in the realms of the paranormal, astrology, alternative medicine and the like. More recently, skeptics have expanded their aim to include some controversial issues in science, under the reasonable position that science itself should not be exempt from critical analysis. Fair enough, except that science already has a large number of professional critics: scientists themselves (remember the peer review system?), as well as philosophers and sociologists of science. Moreover, while critical analysis of claims of the paranormal does not really require professional scientific expertise (indeed, Randi’s own spectacular career shows that the pertinent expert is more often a magician, since wannabe paranormalists often employ trickery to fool the public), actual science criticism does.

I am not suggesting that critical evaluation of science is a matter to be reserved only to people with PhDs. But I am suggesting that public figures like Randi, Penn&Teller, or Bill Maher (the Dawkins-award winner who thinks that vaccines cause autism and who is generally skeptical of “Western medicine”) are doing a huge disservice to both the skeptical movement and the public at large when they step into territory about which, frankly, they are simply not qualify to talk. The role of skeptics who are not professional scientists is to educate the public about critical thinking (Randi’s Foundation being one of the shiniest examples). This is done most effectively through the kind of public outreach — including spectacular demonstrations, tv shows and comedy sketches — that professional scientists don’t do because they don’t have the time and they are not good at it.

But these same people should remember that the mantle of “skepticism” does not provide one license to shoot from the hip and express a cynical attitude about anything and anyone. When we cross that line from positive skepticism into negative cynicism we do no favors to critical thinking, instead we undermine the whole notion and we make the public equally distrustful of serious scientists as they should be of Deepak Chopra. The public loses, and the Chopra of the world run laughing all the way to the bank.