Ed Dolan posted at the Niskanen Center blog on the question of what GDPs would be in 2099 with and without climate change. His graph of GDPs "with" climate change was based on the work of Burke et al. (Nature, 2015), and data published on their website. However, the data published on their website was based on the SSP5 scenario, which is similar to the RCP 8.5 scenario, which has extremely unrealistic (incredibly high) projections of coal usage in the 21st century. Anyway, Ed Dolan's figure looked like the one I recreated below (Ed Dolan's figure appears as an insert in the top-right of my graph).
The question is, what would the graph look like for a more realistic scenario, like RCP 4.5? To find out, I performed the following analysis:
1) I obtained the global average temperature increase for the RCP 8.5 scenario and the RCP 4.5 scenario from wonderful Wikipedia. The mean temperature increase is 3.7 degrees Celsius for RCP 8.5 and 1.8 degrees Celsius for RCP 4.5. So the increase in temperature is about half as much for RCP 4.5 as for RCP 8.5. The response of GDP to temperature, from the Burke et al. analysis, indicates an inverted "U" shape, peaking at about 15 degrees Celsius, and sloping away more and more quickly farther from the peak. I therefore assumed that a temperature change of half as much for RCP 4.5 versus RCP 8.5 would have about one-quarter of the effect on GDP for each country as the RCP 8.5 (/SSP5) scenario. The resultant graph looks like this (once again, the original Ed Dolan graph is in the top-right):
I welcome any more-refined analysis based on the work of Burke et al. (Nature, 2015). However, I think my analysis is probably pretty close to what they'd get. Unsurprisingly there is much less effect on GDPs for a global average temperature increase of 1.8 degrees Celsius than a global average temperature increase of 3.7 degrees Celsius.
JULY 27TH UPDATE
I realized I made errors in how I should translate the idea that half the temperature change results in one-quarter of the effect. Here is my new graph for what the GDPs would look like without and with climate change of the magnitude in the RCP 4.5 scenario.
I realized I was still making errors in my July 27th analysis and that the "one-quarter effect for one-half temperature change" rule was a bit crude. So I did a more sophisticated analysis. If anyone is interested in the details, contact me. Here are the results of the more sophisticated analysis:
Here's a table for some selected countries, spanning varying initial temperatures, initial GDPs, and growth rates without climate change.
The "money" columns here are the "Ratio 2099/2010 without CC (climate change)" and the column that shows the ratio of 2099/2010 GDPs for the RCP 4.5 scenario (as calculated by me, based on "more sophisticated analysis." For example, for the United Arab Emirates (one of the hottest countries in the world, and already rich) the ratio of GDP in 2099 to GDP in 2010 is 4.6 without climate change, and 0.3 with climate change at the RCP 8.5 level (both per Burke et al. in Nature 2015). My calculated ratio with climate change at the RCP 4.5 ratio is 2.6. In contrast, for the Russian Federation (a cold relatively poor country) the ratio is 10 without climate change, 50 with climate change at the RCP 8.5 level, and 32 with climate change at the RCP 4.5 level.
Overall, according to my analysis, climate change at the RCP 4.5 level has very little effect on GDPs when compared to no climate change (see the figure directly above).
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