Judith Curry’s Climate etc website gets my top billing, as I’ve said before, and one of its great virtues lies in the Comments section that follows the essay. The reason is that the Comments section is a live and continuing debate, not just on the supposed topic of the day, but on aspects of it, or on something that comes in almost by accident, strikes a chord, and becomes itself a new argument.
As with all websites, hers has a retinue of regulars, plus some of the big names in climate science who drop in from time to time to disagree with the hostess or one of the commenters. Yes, there is a fair bit of name-calling, but you can scroll past that and watch for the real learning. And there are hundreds of comments, so reading them all requires dedication and time. Before I established my own website I wrote a few essays for her, and one of them attracted more than 700 comments. I’d love to say they were all complimentary. It wasn’t so.
I was prompted to write this essay because of a post of hers that I noted with a nod and at first let go. It was about the recruitment of a top Swedish climate scientist, Lennart Bengtsson, to the Academic Advisory Council of the Global Warming Policy Foundation in London. I passed the comments by, but a few days later, about to dismiss the post from my system, I had a quick look at them, which lasted for a couple of hours. It was well worth the time.
At one point the disputation began to centre around what was a theory. Was AGW a theory, a real theory, or just a hypothesis? How was a hypothesis different from a theory? Do all theories have to be tested against a body of observations? If so, what about the theory of evolution? I began wrestling with that stuff when I was an honours undergraduate student, and it was more or less familiar territory. Then out of the blue came the following crisp summary of the situation by Matthew R. Marler, a statistician. This is what he wrote.
There is a prima facie case, very simple, that human CO2 might warm the Earth. It has been presented many places, but for now I shall reference a relatively readable book: “Atmosphere, Clouds, and Climate” by David Randall, pp 45-49. Basically, an increase in atmospheric CO2 should lead to an increase in the absorption of upward long-wave infrared radiation from the Earth surface, so there could somewhere be an increase in heat accumulated in the Earth climate system, other things being equal. Whether you call that a hypothesis or a theory does not matter very much, and those words do not have exact enough definitions, but it certainly is at least a hypothesis.
However, there is almost no “body of evidence” that the accumulation of human-sourced CO2 is actually having any such effect. That the Earth has warmed since the end of the Little Ice Age has at least two different explanations, one of which says all of the increase is independent of human-sourced CO2, and the IPCC version which says that the increase up to 1945 or so is independent of human-sourced CO2. At least one theory says that the most prominent effect of the heat accumulation ought to be in the upper troposphere, but that effect has not been found in the most relevant (satellite) records of troposphere temperature.
At least one theory specifies “polar amplification”, a stronger warming at the poles than at the Equator and in mid-latitudes; if that is happening, it is only in the Arctic region not the Antarctic region. The computational models, known as GCMs (for global circulation models, or general climate models), incorporate a great deal of known physics over small regions, but their model runs produce modeled temperature increases greater than what has been observed since they were run, and miss the recent near 17-year “pause” aka the “hiatus” in surface and troposphere warming that has been observed. And so on: addressing the predictions of the diverse AGW theories point-by-point one finds little to no evidence that they have made any accurate predictions, where their predictions can even be calculated.
There it is, in a very few hundred words. Why couldn’t I have written that myself? Well, I didn’t, and Matthew Marler did. He is one of those whose comments I always read, in part because he is a statistician, and climate science is pretty weak when it comes to statistics. There are others there whose comments are also worth reading, and there are some whose very name causes me to scroll quickly by: I have read enough to know that they are there to be difficult, to hi-jack the post, to stop the flow of useful debate.
Yes, I know that is a value judgment, but you have to make them all the time, especially when you are reading the Comments sections!