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However, we first updated the IAM to take account of the extensive research since the 1990s looking at effects on global plant growth from rising CO2 levels. Results from satellite-based surveys and field experiments have shown larger benefits than people predicted in the 1990s, even in a warming climate, especially for the rice crop in Asia.

Also, all the IAMs assume the climate will warm by three degrees Celsius with every CO2 doubling. This is based on simulations with large climate models, but there have been many recent studies in climate journals estimating lower sensitivity based on observed ground- and satellite-measured temperature changes. So we incorporated this information into the IAM as well.

Based on these updates alone, we showed that, even using a low discount rate, the social cost of carbon as of 2020 drops from US$32 per tonne to about 60 cents, and there’s a 50/50 chance it’s below zero. It does grow over time but not by much. By 2050 it’s still under $3 per tonne and has a 46 per cent chance of being less than zero.

Note that we did not say “climate change is a hoax so we shouldn’t do anything.” We relied on scientific studies in mainstream journals, combined with one of the Obama-era EPA’s own preferred economic models, to determine if costly climate policies are justified. The answer is no, at least not for the next few decades.

Our paper was reviewed by three knowledgeable anonymous experts who were surprised by our findings and aggressively challenged them, with one strongly recommending our study be rejected. We had to rebut their extensive counterarguments in detail. We were able to defend our calculations and the journal decided in our favour.

If you don’t believe the science of climate change, then you obviously won’t support carbon taxes and other such policies. But it’s important to note that if you do accept the science, you aren’t obliged to support every policy, no matter how costly or inconvenient, that gets put forward. We should still focus on no-regrets strategies where the benefits outweigh the costs.

Ross McKitrick is a professor of economics at the University of Guelph and a senior fellow at the Fraser Institute.