On top of this, Jamieson argues, there is a second problem in the models economists use to discus climate change. Because the payoff from carbon-dioxide reduction will occur many decades from now, Nordhausian analysis suggests that we should do the bare minimum today, even if that means saddling our descendants with a warmer world. Doing the minimum is expensive enough already, economists say. Because people tomorrow will be richer than we are, as we are richer than our grandparents were, they will be better able to pay to clean up our emissions. Unfortunately, this is an ethically problematic stance. How can we weigh the interests of someone born in 2050 against those of someone born in 1950? In this kind of trade-off between generations, Jamieson argues, “there is no plausible value” for how much we owe the future.

Given their moral problems, he concludes, economic models are much less useful as guides than their proponents believe. For all their ostensible practicality—for all their attempts to skirt the paralysis-inducing specter of the apocalypse—economists, too, don’t have a good way to talk about climate change.

Years ago, a colleague and I spoke with the physicist Richard Feynman, later a national symbol of puckish wit and brash truth-telling. At the frontiers of science, he told us, hosts of unclear, mutually contradictory ideas are always swarming about. Researchers can never agree on how to proceed or even on what is important. In these circumstances, Feynman said, he always tried to figure out what would take him forward no matter which theory eventually turned out to be correct. In this agnostic spirit, let’s assume that rising carbon-dioxide levels will become a problem of some magnitude at some time and that we will want to do something practical about it. Is there something we should do, no matter what technical arcanae underlie the cost-benefit analyses, no matter when we guess the bad effects from climate change will kick in, no matter how we value future generations, no matter what we think of global capitalism? Indeed, is there some course of action that makes sense even if we think that climate change isn’t much of a problem at all?

As my high-school math teacher used to say, let’s do the numbers. Roughly three-quarters of the world’s carbon-dioxide emissions come from burning fossil fuels, and roughly three-quarters of that comes from just two sources: coal in its various forms, and oil in its various forms, including gasoline. Different studies produce slightly different estimates, but they all agree that coal is responsible for more carbon dioxide than oil is—about 25 percent more. That number is likely to increase, because coal consumption is growing much faster than oil consumption.

Although coal and oil are both fossil fuels, they are used differently. In this country, for example, the great majority of oil—about three-quarters—is consumed by individuals, as they heat their homes and drive their cars. Almost all U.S. coal (93 percent) is burned not in homes but by electric-power plants; the rest is mainly used by industry, notably for making cement and steel. Cutting oil use, in other words, requires huge numbers of people to change their houses and automobiles—the United States alone has 254 million vehicles on the road. Reducing U.S. coal emissions, by contrast, means regulating 557 big power plants and 227 steel and cement factories. (Surprisingly, many smaller coal plants exist, some at hospitals and schools, but their contributions are negligible.) I’ve been whacking poor old Nordhaus for his ideas about who should pay for climate change, but he does make this point, and precisely: “The most cost-effective way to reduce CO2 emissions is to reduce the use of coal first and most sharply.” Note, too, that this policy comes with a public-health bonus: reining in coal pollution could ultimately avoid as many as 6,600 premature deaths and 150,000 children’s asthma attacks per year in the United States alone.