Paul Krugman nails the dishonest climate change deniers: “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.”

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.”

Read Krugman’s full column here.