Climate: Two Metapoints

This post is about why you should have little confidence in your beliefs about the effects of climate change.

Round One

The reason to believe that climate change is a serious threat is not, for most people, that they have evaluated the evidence for themselves. The reason is that they have been told by multiple respectable sources that everyone competent to hold an opinion on the subject agrees it is a threat, that that is not a matter of serious debate.

Fifty years ago, population growth had the same status. Not all respectable opinion agreed with the Ehrlichs’ prediction of unstoppable mass famine in the 1970’s with hundred of millions dying but almost everyone agreed that unless something substantial was done to slow or stop population growth the future would be grim, especially for poor countries.

In the fifty years since then population continued to grow. The rate of extreme poverty declined sharply. Calorie consumption per capita in poor countries went up. What happened was the precise opposite of what had been confidently predicted.

That does not tell us whether climate change is a serious problem but it is evidence that the status of that belief as orthodoxy is at most weak evidence that it is true.

We have been here before.

A broken system

Rennert et. al. 2022 is an article recently published in Nature that attempts to estimate the cost due to an additional ton of CO2 summed from now to 2300. About half the total cost they calculate comes from increased mortality due to temperature change. Mortality due to temperature change depends, among other things, on income, since richer people are more likely to have air conditioning, less likely to have to go out in bad weather. The figures the article uses for the relation between temperature and mortality ignore that relation — although Rennert projects per capita GNP to triple by the end of this century, increase more than ten-fold by 2300.

Temperature-related mortality also depends on medical technology, how likely a bad health effect is to kill someone. Rennert’s figures are based entirely on past experience. The implicit assumption is technological stasis — no progress in medicine for the next three centuries. There are other problems with the article — you may want to look at a detailed critique that I have webbed — but those are the two clearest ones.

My point is not that Rennert’s figure for the cost of carbon is too high; although the authors exaggerate the costs they look at there are other costs that they do not include in their calculations, possibly because they had no way of putting numbers on them. My point is that an article whose calculation of cost assumed no relation between income and vulnerability to temperature and no change in medical technology for three centuries ought not to have been published, even written. The fact that it was written by serious scholars in the field, accepted by a top scientific journal, considered by the EPA as a possible basis for regulatory decisions, implies that the mechanisms for discovering what is true in this part of climate science, the subfield of estimating the cost of climate change, are badly broken.