By Paul Krugman – The New York Times.

So the joke begins like this: An economist, a lawyer and a professor of marketing walk into a room. What’s the punch line? They were three of the five “expert witnesses” Republicans called for last week’s Congressional hearing on climate science.

But the joke actually ended up being on the Republicans, when one of the two actual scientists they invited to testify went off script.

Prof. Richard Muller of Berkeley, a physicist who has gotten into the climate skeptic game, has been leading the Berkeley Earth Surface Temperature project, an effort partially financed by none other than the Koch foundation. And climate deniers — who claim that researchers at NASA and other groups analyzing climate trends have massaged and distorted the data — had been hoping that the Berkeley project would conclude that global warming is a myth.

Instead, however, Professor Muller reported that his group’s preliminary results find a global warming trend “very similar to that reported by the prior groups.”

The deniers’ response was both predictable and revealing; more on that shortly. But first, let’s talk a bit more about that list of witnesses, which raised the same question I and others have had about a number of committee hearings held since the G.O.P. retook control of the House — namely, where do they find these people?

My favorite, still, was Ron Paul’s first hearing on monetary policy, in which the lead witness was someone best known for writing a book denouncing Abraham Lincoln as a “horrific tyrant” — and for advocating a new secessionist movement as the appropriate response to the “new American fascialistic state.”

The ringers (i.e., nonscientists) at last week’s hearing weren’t of quite the same caliber, but their prepared testimony still had some memorable moments. One was the lawyer’s declaration that the E.P.A. can’t declare that greenhouse gas emissions are a health threat, because these emissions have been rising for a century, but public health has improved over the same period. I am not making this up.

Oh, and the marketing professor, in providing a list of past cases of “analogies to the alarm over dangerous manmade global warming” — presumably intended to show why we should ignore the worriers — included problems such as acid rain and the ozone hole that have been contained precisely thanks to environmental regulation.

But back to Professor Muller. His climate-skeptic credentials are pretty strong: he has denounced both Al Gore and my colleague Tom Friedman as “exaggerators,” and he has participated in a number of attacks on climate research, including the witch hunt over innocuous e-mails from British climate researchers. Not surprisingly, then, climate deniers had high hopes that his new project would support their case.

You can guess what happened when those hopes were dashed.

Just a few weeks ago Anthony Watts, who runs a prominent climate denialist Web site, praised the Berkeley project and piously declared himself “prepared to accept whatever result they produce, even if it proves my premise wrong.” But never mind: once he knew that Professor Muller was going to present those preliminary results, Mr. Watts dismissed the hearing as “post normal science political theater.” And one of the regular contributors on his site dismissed Professor Muller as “a man driven by a very serious agenda.”

Of course, it’s actually the climate deniers who have the agenda, and nobody who’s been following this discussion believed for a moment that they would accept a result confirming global warming. But it’s worth stepping back for a moment and thinking not just about the science here, but about the morality.

For years now, large numbers of prominent scientists have been warning, with increasing urgency, that if we continue with business as usual, the results will be very bad, perhaps catastrophic. They could be wrong. But if you’re going to assert that they are in fact wrong, you have a moral responsibility to approach the topic with high seriousness and an open mind. After all, if the scientists are right, you’ll be doing a great deal of damage.

But what we had, instead of high seriousness, was a farce: a supposedly crucial hearing stacked with people who had no business being there and instant ostracism for a climate skeptic who was actually willing to change his mind in the face of evidence. As I said, no surprise: as Upton Sinclair pointed out long ago, it’s difficult to get a man to understand something when his salary depends on his not understanding it.

But it’s terrifying to realize that this kind of cynical careerism — for that’s what it is — has probably ensured that we won’t do anything about climate change until catastrophe is already upon us.

So on second thought, I was wrong when I said that the joke was on the G.O.P.; actually, the joke is on the human race.