The Paradox of Urban (and Global) Warming

June 10, 2011 • Commentary
This article appeared on Forbes​.com on June 10, 2011.

Ah, summer in our cities, where the climate is woebegone and the temperature is almost always above normal.

Cities tend to get warmer, whether or not there is global or regional warming. Bricks, buildings and pavement absorb more heat during the day than a “natural” vegetated state, and urban structures impede the flow of ventilating winds. The result is that, as cities grow, temperatures rise. In Washington, there is additional warming caused by the waste heat from all the money changing hands.

The official (and silly) definition of “normal” temperature is the average for the past 30 years. In a growing urban environment (which includes suburban sprawl) that number is likely to be lower than what it is now.

As a result, cities are inadvertently testing a dear hypothesis of my greener friends: that global warming will result in increasing heat‐​related mortality.

Those who have read Freakonomics can see this hanging curveball. Global warming should reduce urban mortality as heat waves become more frequent.

I’ve done a bit of work in this area. Robert Davis, a former colleague at the University of Virginia, and I examined three decades of heat‐​related mortality data from the Centers for Disease Control for the 28 largest U.S. cities. We then teamed up with a UVa medical statistician, Wendy Novicoff, who made sure we adjusted for different demographics between cities; we did this because the elderly and infants are most susceptible to heat‐​related mortality, and we wanted to compare disproportionately old cities (like Phoenix) with disproportionally young ones (like Seattle). After all was said and done, we found that heat‐​related mortality is dropping like a stone in almost every major urban area in the nation.

Before you go to the “comments” and blast me with the European heat wave of 2003 or the Chicago disaster in 1995, read on.

The 2003 heat wave in Europe was devastating. In France alone, and very dependent on the way you count things, it appears there were about 35,000 excess deaths. That heat wave was a lulu, with European temperatures about three standard deviations above the average, something that has a 1‐​in‐​333 chance of occurring averaged over your state or province. Given that there are a lot of places of similar size on the planet, such an anomaly can usually be found somewhere. In 2003, that somewhere just happened to be at the epicenter of global warming angst.

Then there was the great French heat wave of 2006.

Whoops. Don’t know about that one? Climatically, it was pretty comparable, but far fewer French fried.

A. Fouillet and his team of researchers wrote this up in a 2008 paper in the International Journal of Epidemiology. They started off with a simple (i.e. logical and testable) model relating temperature to mortality and found that something in addition to the heat killed a lot of people in 2003. While their model predicted about 17 deaths per 100,000, the observed rate was 21 per 100,000, or about nearly 7,000 bodies.

(There’s plenty of speculation on the cause, with fingers pointed at France’s August recess, when everyone — including health care workers — takes to the beach or the hills and leaves the old folks at the non‐​airconditioned home)

In 2006, their model showed nearly 4,500 fewer deaths than expected.

What the French did was (begrudgingly) emulate urban Americans. They adapted. The government bought air conditioning (formerly a crass Yankee invention) for retirement homes. They implemented a National Heat Wave Plan that keeps tabs on the elderly, who were left to swelter in 2003. They set up cooling shelters for those without A/C.

And, of course, adaptation is what’s happening in our cities. Perhaps the most politically incorrect thing an urban administration can do is to be caught flatfooted by the weather. Chicago’s Daley dynasty was (temporarily) swept away by a 1979 snowstorm when it selectively canceled rail service in southside black neighborhoods. And who can forget Washington’s colorful mayor Marion Barry, cavorting at the 1987 Super Bowl during back‐​to‐​back storms. White stuff set him up.

Want proof of our adaptation to heat? Two extremely hot cities, Tampa and Phoenix, have virtually no heat‐​related mortality, despite sporting the oldest populations in our study. In only one city is mortality increasing. That would be young and vibrant Seattle, where summer heat is still very rare.

I am sure many consider it immoral to export heat‐​related mortality to the North, but that won’t last for long. Seattle’s latitude is about 48 degrees north. The vast majority of our hemisphere’s cities are south of there, and by the time you get to 60 degrees, not very far away, you tend to run out of cities. At that point, global warming will have squeezed urban heat‐​related mortality off of the map.

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