Limiting temperatures to 2.7 degrees Fahrenheit above preindustrial levels, as the U.N.’s Intergovernmental Panel on Climate Change urges, is economically and practically impossible—as Mr. Nordhaus’s work shows. The IPCC report significantly underestimates the costs of getting to zero emissions. Fossil fuels provide cheap, efficient power, whereas green energy remains mostly uncompetitive. Switching to more expensive, less efficient technology slows development. In poor nations that means fewer people lifted out of poverty. In rich ones it means the most vulnerable are hit by higher energy bills. The IPCC says carbon emissions need to peak right now and fall rapidly to avert catastrophe. Models actually reveal that to achieve the 2.7-degree goal the world must stop all fossil fuel use in less than four years. Yet the International Energy Agency estimates that in 2040 fossil fuels will still meet three-quarters of world energy needs, even if the Paris agreement is fully […]