On Monday, Washington Post columnist Michael Gerson took a tilt at climate skeptics. “The assumption that the vast majority in a scientific field is engaged in fraud or corruption is frankly conspiratorial,” Gerson wrote. As a non-scientist, he decided that the answer to the question of whether humans had warmed the planet was to trust scientists.

The article’s timing was unfortunate. Three weeks ago, Lennart Bengtsson, a leading Swedish meteorologist approaching his 80s, announced that he was joining the avowedly skeptical Global Warming Policy Foundation think tank. In an interview with Spiegel Online, Bengtsson spoke of the need for climate-model predictions to be validated against observations. “Since the end of the 20th century, the warming of the Earth has been much weaker than what climate models show,” he said.

Hadn’t the IPCC covered this in its recent report? “Yes,” Bengtsson replied,

the scientific report does this but, at least in my view, not critically enough. It does not bring up the large difference between observational results and model simulations. I have full respect for the scientific work behind the IPCC reports but I do not appreciate the need for consensus. It is important, and I will say essential, that society and the political community is also made aware of areas where consensus does not exist.

One of the most telling features of climate science is just how few climate scientists changed their minds as the evidence changed. The pause in global temperature in the last 15 years or so has been unexpected. Now we know why: Yesterday, Bengtsson dropped a bombshell. He was resigning from the think tank. In his resignation letter, Bengtsson wrote:

I have been put under such an enormous group pressure in recent days from all over the world that has become virtually unbearable to me. If this is going to continue I will be unable to conduct my normal work and will even start to worry about my health and safety. . . . Colleagues are withdrawing their support, other colleagues are withdrawing from joint authorship etc. I see no limit and end to what will happen. It is a situation that reminds me about the time of McCarthy.

Especially significant was a tweet from Gavin Schmidt, a leading climate modeler at the NASA Goddard Institute, who for many years worked alongside James Hansen. “Groups perceived to be acting in bad faith should not be surprised that they are toxic within the science community,” Schmidt tweeted. “Changing that requires that they not act in bad faith and not be seen to be acting in bad faith.”

Evidently the right to practice and discuss climate science should be subject to a faith test. It is an extraordinarily revealing development. Fears about unbelievers’ polluting the discourse, as some academics put it, illustrate the weakness of climate science: The evidence for harmful anthropogenic global warming is not strong enough to stand up for itself.

Inadvertently Schmidt’s tweet demonstrates how far climate science has crossed the boundary deep into pseudo-science. Karl Popper observed of the trio of pseudo-sciences prevalent in 1920s Vienna that their followers could explain why non-believers rejected their manifest truths. For Marxists, it was because of their class interests. For subscribers to Freudian psychoanalysis and Alfred Adler’s psychology, non-belief was evidence of unanalyzed repressions crying out for treatment. So it is with climate science. Only the pure of heart should be allowed an opinion on it.

Science regresses if it becomes intolerant of criticism. At the beginning of her reign, Queen Elizabeth I of England spoke words of tolerance in an age of religious strife, declaring that she had no intention of making windows into men’s souls. Unlike religion, science is not a matter of the heart or of belief. It exists only in what can be demonstrated. In their persecution of an aged colleague who stepped out of line and their call for scientists to be subject to a faith test, 21st-century climate scientists have shown less tolerance than a 16th-century monarch.

There is something rotten in the state of climate science.

— Rupert Darwall is the author of The Age of Global Warming: A History.