Chris Wilson writes:
It appears that Richard Tol is still publishing these data, only now fitting a piecewise linear function to the same data-points.
Also still looks like counting 0 as positive, “Moreover, the 11 estimates for warming of 2.5°C indicate that researchers disagree on the sign of the net impact: 3 estimates are positive and 8 are negative. Thus it is unclear whether climate change will lead to a net welfare gain or loss.”
This is a statistically mistaken thing for Tol to do, to use a distribution of point estimates to make a statement about what might happen. To put it another way: suppose all 11 estimates were negative. That alone would not mean that it would be clear that climate change would lead to a net welfare loss. Even setting aside that “welfare loss” is not, and can’t be, clearly defined, the 11 estimates can—indeed, should—be correlated.
Tol’s statement is also odd if you look at his graph:
As Wilson notes, even if you take that graph at face value (which I don’t think you should, for reasons we’ve discussed before on this blog), what you really have is 1 positive point, several points that are near zero (but one of those points corresponds to a projection of global cooling so it’s not relevant to this discussion), and several more points that are negative. And, as we’ve discussed earlier, all the positivity is being driven by one single point, which is Tol’s own earlier study.
Tol’s paper also says:
This review of estimates in the literature indicates that the impact of climate change on the economy and human welfare is likely to be limited, at least in the twenty-first century. . . . negative impacts will be substantially greater in poorer, hotter, and lower-lying countries . . . climate change would appear to be an important issue primarily for those who are concerned about the distant future, faraway lands, and remote probabilities.
I’m surprised to see this sort of statement in a scientific journal. “Faraway lands”? I looked up the journal description and found this:
The Review of Environmental Economics and Policy is the official journal of the Association of Environmental and Resource Economists and the European Association of Environmental and Resource Economists.
So I guess they are offering a specifically European perspective. Europe is mostly kinda cold, so global warming is mostly about faraway lands. Still seems kinda odd to me.
P.S. Check out the x-axis on the above graph. “Centigrade” . . . Wow—I didn’t know that anyone still used that term!