Americans have made hurricane destruction worse (but not with carbon emissions)

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Appeared in the Financial Post, October 4, 2017

Amidst the epic devastation of this season’s hurricanes, many commentators have demanded a renewed discussion of the hazards of climate change. There was an unseemly opportunism in doing this while the damage was still being cleaned up, but we can’t let the sloganeering go unanswered. The actual event we need to understand is an 11-year absence of landfalling, major hurricanes (Category 3 or higher) followed by a season that is harsh but inside the historical norm. And the human element needing to be discussed is not merely the elusive role greenhouse-gas (GHG) emissions might play in hurricane formation, but the conspicuous desire of people to live in the path of the storms.

The formation of an Atlantic cyclone is a weather event, not a climate event. Hurricanes existed long before humans emitted GHGs. A “climate event” would be a multi-decadal change in their major characteristics. But this has not been observed. According to the U.S. National Hurricane Center, from 1851 to 1960 the U.S. experienced between 15 and 24 landfalling hurricanes per decade, of which between one and 10 were major. From 1960 to 2010 (the period when human GHGs increased sharply) it was 12 to 19 per decade, of which four to seven were major: well within the historical range. It’s same story if we divide the data at 1970.

One recent change is an apparent tendency for fewer landfalling hurricanes. Since 2010 there have only been three, two of which were major. If this season’s numbers repeat through 2019 the decade may end up just inside the normal range. While people are understandably horrified at the 2017 hurricanes, there is a temptation to extrapolate conclusions from the few that formed while ignoring the many that didn’t. Looking at the big picture, the role of GHGs, if any, is currently too subtle to identify.

But there is one pattern in the data impossible to miss, even though it rarely gets discussed. Postwar U.S. migration patterns show that people seem to prefer the kind of weather that includes hurricane risk.

An American can choose just about any climate in which to live, from the Arctic to the tropics, from a rainforest to the desert, and anything in between. We can infer something about peoples’ climatic preferences by looking at where Americans have moved.

From 1950 to 2015 the U.S. population grew at an average rate of 1.2 per cent per year, from 152 million to 321 million. In 1950, the South Atlantic and Gulf states of Texas, Louisiana, Florida, Georgia and South Carolina—the hurricane targets—comprised 12.3 per cent of the U.S. population. For comparison, consider a northern slice covering Massachusetts, Minnesota, Michigan, Wisconsin and Nebraska: states with four seasons and virtually no hurricane risk. This group also comprised 12.3 per cent of the U.S. population in 1950.

Now fast forward to 2015. The Gulf and South Atlantic states grew two per cent per year, almost double the national average, reaching 21 per cent of the U.S. population. The northern slice, by comparison, grew by only 0.7 per cent per year and fell to 9.3 per cent of the population. Taking the rough with the smooth, a large part of the U.S. population decided it prefers a warmer, wetter and more hazardous climate. In other words, Americans paid money to expose themselves to the worst-case warming scenario.

This raises the separate, and thorny, economic issue of disaster relief: If people expect the government to bail them out they will under-insure and over-build in hazard-prone areas. That problem requires addressing, but it is not specifically related to climate change.

U.S. migration patterns show that we cannot single out hurricane damages, call it the “costs of not acting on climate change” and demand new policies. First of all, the storms would likely have happened even without manmade GHGs. Second, many of the people who were in the path arrived there after the risk was known, and accepted it as part of a package that also included the benefits of warm weather. They apparently prefer that package to the colder but less hazardous option up north, and would not appreciate costly (not to mention futile) efforts to reverse their choice through new energy taxes and regulations.

Climate data has a way of upending the simplistic slogans that litter this issue. Historical hurricane records do not reveal a new pattern attributable to GHGs. And market data shows that the so-called social damages of climate change are part of a package of weather conditions perceived as a net benefit by many people experiencing it.

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