I was worried about climate change. Now I worry about climate scientists. (Patreon)

[This is a transcript with links to references.]

A few weeks ago, I made a video on climate sensitivity, explaining why I am worried about it. There have now been a few reactions by climate scientists. I’d like to briefly comment on that, and add something which I took out of the first video.

Just a brief recap of what we’re talking about. The “climate sensitivity” is a model parameter that tells you how much the global average temperature changes

in response to an increase in atmospheric carbon dioxide. It’s the most important number to determine how quickly climate change will get worse.

I should more precisely say that this parameter is called the “equilibrium climate sensitivity” because there are several sensitivities in climate science, and not all of them are model parameters.

The issue I was talking about in my previous video is that this climate sensitivity might be much higher than the IPCC uncertainty range suggests, and therefore also higher than most plans to mitigate climate change assume. And I feel that given the relevance of this possibility, it’s been very underreported.

What’s happened is that a few years ago, some of the world’s best models began to produce a much higher climate sensitivity than the average of the previous models. After that, climate scientists argued that these models are unreliable, and their predictions should be given a lower weight in the IPCC assessments. They dubbed it the “hot models” problem and I’ve found it both funny and concerning that the double meaning didn’t occur to me until a friend pointed it out.

Now the reactions of climate scientists to me saying the problem has been underreported have basically been two. First: Doesn’t matter what the climate sensitivity is, that’s just distraction, we need to stop global warming anyway. And second: Well, there are a lot of papers every year coming out with different climate sensitivities, and one shouldn’t pick one here or there.

About the first point: Doesn’t really matter, it’s bad either way.

I think that climate scientists who say this have totally lost touch with reality. Governments make plans for reaching net zero based on expectation for how fast the situation will get worse. The climate sensitivity is super important for those plans. If you, and I’m talking to you climate scientists, get this number wrong, then all current plans will be grossly off. I really don’t understand how you can just go and say it doesn’t matter. You might as well go and say it doesn’t matter what climate models predict in general.

A particularly crude example comes from Zeke Hausfather and Andrew Dessler. Hausfather was one of the authors of the article in Nature magazine which coined the term “hot models”. In the blog post they write: “Arguments over the Equilibrium Climate Sensitivity

are distractions. Whether it’s 3 or 5 degrees is a bit like whether a firing squad has 6 rifleman or 10.”

Someone’s got to say it, so I will. That’s a really bad comparison. Because the climate sensitivity does not tell you how big the problem is, it tells you how fast it will become worse. Do you have to deal with six riflemen next year, or do you have a century to think about how to deal with them, that’s the question we’re looking at.

Now about the second point: there are always many papers. Yes, but this wasn’t my point. The reason that Hausfather et al were going on about this is that the problem appeared, not in any paper, but in some of the best climate models in the world. Models that are so good that climate scientists had previously decided to include them for the IPCC predictions. It was only after some models produced values that they didn’t want to believe that they looked for a way to do get rid of them. This is the problem I am highlighting.

It worries me because the same thing has happened many times in physics. A particularly stunning example is the lifetime of the neutron. The neutron is one of the constituents of the atomic nucleus. It’s stable so long as it’s inside the nucleus but take it out and it decays in about 10 minutes. That’s interesting in and of itself, but well this is not a video about nuclear physics. The thing is that physicists have been measuring the lifetime of the neutron many times and updated the value. You can see the progression of their measurement results here.

What you see is that the measurement seems be comfortably sitting at some particular value. Then they suddenly make a jump. It’s not like the error bars just get smaller. They jump to outside the previous uncertainty region. Often this happens with new measurement methods, and it means that physicists have systematically underestimated the uncertainty on their measurements.

Even more amazing this didn’t happen for only one quantity, it happened for dozens of them. What is going on? Well, it’s difficult to say exactly what happened there but the explanation that sociologists have come up with is confirmation bias.

A lot of people think confirmation bias means you only look at information that “confirms” your prior beliefs. But this isn’t how it works, because you get information thrown at you whether you like that or not. The way that confirmation bias works is that if a finding doesn’t agree with your prior believes, you think about it very hard and try to find something wrong with it. Whereas when it fits, you just accept it because it’s what you said anyway, so why think about it.

In science this shows up as follows. If you get a measurement result that doesn’t fit with the previous ones, you are much more likely to look for a mistake than if it would fit. And this introduces a bias to confirm the previous finding.

Physicists have learned from their past mistakes and now try to avoid this issue by deciding on a method of analysis before they even look at the data. Then they apply the analysis to the data blindly, crunch the numbers, and only then do they “unblind” the result and look at it. This result then gets published without further changes.

But this is not what climate scientists have done have they. They’ve changed their way of how they interpret the prediction of the models after some of them produced results that didn’t fit their previous narrative.

Clearly the collaborations who work on the models with the high climate sensitivity think that they are the ones who got the physics right, so any such argument will have to weigh one type of evidence over another. It’s a subjective assessment that masquerades as objective. The bottom line is that I believe the uncertainty on the climate sensitivity is much larger than the current IPCC projections make it look.

And yes, I’m not a climate scientist. So you can try to dismiss my concerns by saying that I have a PhD in the wrong field. But I have seen how even large scientific communities reinforce their prior beliefs and arrive at wrong conclusions, like the idea that the large hadron collider would see supersymmetric particles. And I don’t think that the community of climate scientists is immune to such problems.