In a provocative post, Joe Romm argues that even “strong climate action” would be well worth the effort. Yet Romm’s claim that stabilizing atmospheric greenhouse gases at 445–535 ppm (CO2-eq) would cost only “one tenth of a penny on the dollar” (through 2050) understates the IPCC’s actual cost estimate by about 95%. In reality, the IPCC’s reported estimate translates into a mitigation cost of about 2.2 cents on the dollar–far far higher than Romm’s figure. Romm’s mistake has nothing to do with climate science: he simply confuses the rate of growth in income, with income itself.
To make matters worse, even when correctly interpreted, the IPCC estimate significantly understates what the cost will be in practice. The IPCC admits that its estimate is a theoretical textbook case, which assumes all participating countries implement their mitigation policies perfectly, and keep them in force throughout the 21st century.…