Matthew Kahn’s Climatopolis: How Our Cities Will Thrive in the Hotter Future is a must-read for anyone interested in cities and environmental economics. But it’s also a mighty strange book. The author seems to have committed himself to a marketing strategy as the guy who’s not a climate change denialist but who’s “optimistic” about its consequences. But there’s basically nothing in the book to justify optimism relative to any kind of reasonable baseline:

During one 1980 presidential campaign debate, Ronald Reagan famously asked the American people, “Are you better off than you were four years ago?” The electorate answered with a resounding “no,” and voted Reagan into office over the hapless incumbent, Jimmy Carter. When we ask the same question in 2050, very few of us will want to go back to the bad old days of the twentieth century. Over the next hundred years, the world’s population and per capita income will both continue to grow. Fueled by urbanization, much of this growth will take place in developing countries. This spread of the “American Dream” to more and more people all over the world offers great opportunities that many of us in rich countries take for granted.

Imagine someone telling you in February of 1925 that he’s optimistic about the next 30 years. In 1955, he argues, per capita living standards will be higher than they are in 1925. In reality, the 1925-1955 period saw a Great Depression, Stalin’s Great Terror, the Holocaust & World War II, the partition of India, etc. It sucked. And yet per capita living standards were higher in 1955 than they were in 1925. It’s a very interesting and important fact about the past 200 years of world history that for all N, global GDP per capita is higher in N+30 than in N. But this doesn’t really suffice as an analysis of any particular problem. Avoiding the Depression, or Nazism, or Maoism would have been huge wins for humanity.

Earlier in the book, Kahn observes:

A Berkeley research team who compared long-term impacts of the war in 584 Vietnamese districts that had faced very different bombing intensities found that despite this awesome firepower, there was no robust adverse impact of U.S. bombing on poverty rates, consumption levels, electricity infrastructure, literacy, or population density through 2002; that is, the U.S. bombs had little to no long-term impact on the growth of Vietnamese cities.

That seems to me to be the right way to think about this. Un-mitigated climate change is going to be like Operation Rolling Thunder. A lot of people are going to die. A lot of people are going to be maimed. A lot of existing physical infrastructure will be destroyed. The extent to which pulverizing Vietnam with high explosives didn’t alter the country’s long-term trajectory is fascinating, but obviously constitutes cold comfort to mothers with dead children or people with no legs. As Kahn notes, the negative impact of climate change will fall disproportionately on the global poor and the elderly. If the entire population of Bangladesh dropped dead tomorrow, per capita GDP would go up. A 20 percent increase in the death rate of Americans over the age of 65 would cause our per capita growth rate to accelerate. It’s important to understand these facts, but it’s strange to think of them as optimistic scenarios and I wish Kahn had been a lot more careful in the wording of his qualitative claims since the book presents a lot of interesting research that’s worth understanding.