Is climate change dangerous?

Yes, it is. There is a long debate in the literature about the extent of the impacts of climate change but no one doubts that people will get hurt. The uncertainty about climate change impacts is large, which in itself is a reason to worry, and most would say the uncertainty is skewed the wrong way: Negative surprises are more likely than positive surprises (of equal size). It is easy to see how things can go very wrong if climate changes, hard to see how things would get a lot better. If President Obama had asked me to write his Endangerment Finding I would have given him two words: “well duh”. (There is a reason I don’t work in government.)

The Trump Administration wants to overturn this. The EPA published a legal document. The EPA argues that “GHGs […] impact[] public health and welfare only indirectly and not by its mere presence in the ambient air’’. That is true. Carbon dioxide (CO2) is not toxic. Your lungs are full of it. We worry about CO2 because it changes the climate, an indirect effect.

We often worry about indirect effects. As Einstein noted, it is not the fall that kills you, it is the sudden stop. Pushing someone off a building only indirectly kills them.

The EPA does not take issue with characterizing nitrogen dioxide (NO2) and sulphur dioxide (SO2) as air pollutants, even though these gases too affect public health and welfare only indirectly, after being transformed into nitric acid (HNO3) and sulphuric acid (H2SO4), respectively.

My legally trained friends tell me that the law is impartial. If a line of argument holds for two substances (NO2 and SO2) then it also holds for a third (CO2).

The DoE published a scientific report in support of the EPA’s legal argument. I am cited 3 times, incorrectly all three times. I am not the only one, as reported by Science and Wired.

First, the authors write that “Tol (2017) estimates that the private benefit of carbon is large relative to the social cost.” This paper was never published in a peer-reviewed journal and is therefore not admissible by the rules of the US government. The paper was peer-reviewed and rejected, because my private benefit is an average whereas the social cost is a marginal. The two cannot be compared (unless you make a ridiculous assumption about linearity). I still hope to fix the paper one day. As it stands, however, the comparison is wrong.

The authors further write that “[a]n influential study in 2012 suggested that global warming would harm growth in poor countries but the finding has subsequently been found not to be robust (Tol 2024). Studies that take full account of modeling uncertainties either find no evidence of a negative effect on global growth from CO2 emissions or find poor countries as likely to benefit from it as rich countries.” The authors did not read my paper carefully. The Dell/Jones/Olken result is indeed not robust: Later studies found that the differentiation is between hot and cold countries rather than rich and poor ones; or that everyone is affected equally. But the DJO result is indistinguishable from the pooled estimates of all later studies with a comparable specification. If there is one robust paper in this part of the literature, it is Melissa’s.

The second sentence is wrong. The authors refer to “studies” but without references. Tol (2024) finds that the then available studies jointly point to a negative impact of climate change on global economic growth. My less systematic reading of the literature since has not led me to change my mind.

Their conclusion that “poor countries” are “likely to benefit” is again not backed up with references. Tol (2024), the only reference in the paragraph, concludes the opposite.

The third citation is to FUND in the section on the social cost of carbon. The literature is vast. I counted 446 papers with estimates. There are numerous commentaries; and two handfuls of meta-analyses (e.g. Tol (2023) and Moore et al. (2024)). Instead, the authors wrote their own review, which omits the most influential papers and misses key insights. Cherry-picking may be a better term than review.

Strikingly, in all three examples of twisting the literature on the economic impact of climate change, the authors do not argue that there would be no effect, or a positive one. Even their “poor countries [are] as likely to benefit from it as rich countries” is best read as “not likely at all” if “it” refers to climate change and the sentence is based on Kahn et al. (2021).

If, instead, “it” refers to carbon dioxide emissions then indeed cost-benefit analysis of climate policy calls for a gradual decarbonisation. That is, in the short run — but not in the long run — the benefits of fossil fuel combustion outweigh its costs. More importantly, we should reduce emissions now.* Complete decarbonisation in the long run requires partial decarbonisation in the short run.

In other words, this attempt by the DoE to undermine the economic case for climate policy fails — and thus inadvertently strengthens said case.

*Actually, we should have started cutting emissions in the 1970s and did. Reagan was wrong to reverse Carter’s policies.