In this installment in our review of Bjorn Lomborg’s massive analysis of 21st century climate policy, we come to his assessment of the costs and benefits of the Paris treaty. Or rather, his review of what others have said, namely the IPCC, government agencies and mainstream economists. Lomborg keeps getting into trouble with alarmists and many climate scientists for not screaming and gluing himself to the road and instead reading through the reports and calmly explaining that they debunk activist claims about the necessity of expensive climate policy. Boiling it down, he shows that Paris will cost a lot and accomplish little. At best, every dollar spent on meeting the Paris targets will deliver less than ten cents of benefits. And how often does government policy manage a best-case outcome?

Indeed, Lomborg begins by noting two iron rules of climate policy: i) governments always under-estimate the costs and ii) they always choose the least efficient options. So when he looks at government projections of the costs of their latest climate policy he checks it against either independent estimates from peer-reviewed sources or their own estimates of past policies.

By this route, he finds the more likely costs are double what the government estimates, which frankly is still probably too optimistic. But even so, going with a few credible, published estimates he finds that over the life of the Paris treaty, which ends in 2030, global compliance will cost between $945 billion (best case) and $1,890 billion (most likely case).

Still, what price to save the climate, right? Except here he can pull numbers straight from the IPCC’s own reports, plus standard climate modeling studies, to show that if Paris treaty measures were fully implemented from 2016 to 2030 it would reduce global emissions by only about 0.45% from the business-as-usual total. Or, under the most optimistic scenario, a reduction of 0.9%. And, again using the IPCC’s own models, this reduction will translate into a reduction in global temperatures of about 0.03 (as in zero-point-zero-three, or three one-hundredths) degrees C as of 2030.

Not much to show for a trillion bucks or more, is it? Still, some studies ask what happens if countries maintain the Paris reductions right through to 2100? Well then, the costs go up to about $70 trillion and the temperature reduction as of 2100 rises to a whopping... 0.17 degrees C. Which is within the range of month-to-month variations in global average temperatures, a.k.a. too small to notice. (For instance it’s less than the cooling from November 2022 to January 2023 in the global lower troposphere. Did it feel like the world was saved? Did the alarmists even admit it happened?)

Lomborg notes that other studies claim Paris will reduce temperatures by much more. But when he digs into those ones he discovers that they fudge the numbers by assuming that the Paris treaty will magically translate into 50 times more emission reductions free of charge through the rest of the century. He dismisses this as wishful thinking:

“It would be similar to an overweight dieter promising to eat a single salad and then suggesting this constitutes success for a decades-long future diet and a rock-hard beach body.”

Besides which, Lomborg notes, it’s already evident that rather than exceeding the Paris target, countries around the world are already falling short so even the pessimistic scenarios are rose-coloured or worse.

Probably worse, because Lomborg then looks at recent mainstream estimates of the Social Cost of Carbon from the economics literature. These calculations attempt to estimate the dollar value of the economic and social harm done by each tonne of carbon emitted through burning fossil fuels, so as to figure out the appropriate cost we should be willing to pay to prevent that tonne. And yes, they fail to take proper account of the benefits to plants of CO2 fertilization, and depend on models within models within models to put numbers to vague alarmist worries. But even with all those weaknesses, all tending to increase the result, the numbers come out pretty small. Much smaller than the cost of trying to reduce emissions.

Tallying it all up, Lomborg shows that, at best, every dollar spent on Paris compliance yields only 25 cents of social benefits, and more likely only 6 cents of social benefit. It’s an investment scheme about as good as choosing to throw in with Bernie Madoff. Except that in this case governments are choosing for you and forcing you to lose your money.