June 24, 2004

Baked Big Apple

Filed under: Health Effects, Heat Waves

A new study claims NYC heat deaths will rise dramatically in 21st century. Yet heat deaths have declined in recent decades, proving that humans adapt to climate change.

Will heat-related deaths rise dramatically in 21st-century New York City? That’s the message contained in the interim report of a study originating from Columbia University Earth Institute, to be presented to policymakers and the public on Friday.

Deaths in NYC and its surrounding environs are projected to increase more than 50% above the current baseline by 2025, and to more than triple by the 2080s, according to a report pre-released on Greenwire. Heat is the primary culprit, and climate models project increasingly long and more intense heat waves in the future.

Sounds dire. The problem with that analysis is that it fails to take into account the adaptations to climate changes that are and have been taking place. In truth, excess heat-related deaths in New York City declined significantly between the 1960s and the 1990s, according to conclusive research by University of Virginia researcher Robert Davis (Figure 1).

NYC Mortality

Figure 1. Average annual heat-related mortality (per million people) in New York City, by decade. There has been a significant decline in average heat-related mortality since the mid-1960s (source: Davis et al., 2003).

In the 1960s and 1970s, the NYC metropolitan area experienced an average of 85 excess heat-related deaths per year per million people. By the 1990s, the number had dropped to 28. In other words, the observed trend is exactly opposite to these projections emanating from Columbia. New Yorkers are unlikely to stand by (and then expire) as the Big Apple becomes the Baked Apple. They adapt.

But there’s another component to this: temperature changes. You might say that deaths have declined because hot days and heat waves were worse in the 1960s than the 1990s. In fact, the opposite is true. Summer weather in New York has become more uncomfortable over the same time period. Figure 2 shows New York’s trend in summer daily maximum “apparent temperature”—a measure that combines temperature and relative humidity to approximate how hot a person feels. From 1964 to 1998, apparent temperatures increased by 1.25° C.

NYC Apparent Temperature

Figure 2. Average summer (June, July, August) 4 pm apparent temperature in New York City. There has been a significant rise in apparent temperatures since the mid-1960s.

The bottom line? Fewer people are dying despite increasingly oppressive summer weather.

The reasons why are fairly obvious. More people have access to air-conditioned homes, cars, and offices. Central air, and even window units, were not a common feature in that part of the country a few decades ago, but now are the rule rather than the exception. Medical care has improved also. In general, people are simply more aware of the potential dangers of heat and take better precautions. All these reasons fall under the rubric of adaptations that, apparently, were not at all considered in the Columbia study.

Talk about bad timing. Only a few days ago, the Philadelphia Inquirer reported on all of the lives that have been saved in Philly because of the implementation of low-cost government programs. In a study by Laurence Kalkstein and several coauthors to be released in August, the researchers calculated that at least 270 lives have been saved in Philadelphia since 1995 because of a heat watch/warning system. When a heat warning is issued, hotlines are activated to notify block captains, electric fans are distributed, shelters are opened, and so on. And the total cost of the program is a modest $100,000 per year.

In reality, the number of lives saved according to the Kalkstein study is also probably an overestimate, since heat-related mortality had been declining in Philadelphia long before the heat watch system was implemented. Nevertheless, that kind of system represents a simple adaptation to climate change that is typically ignored by activists with an agenda.

The Columbia study contains a projection of future death rates that run exactly counter to historical observations showing a decline in death rates. And these mortality declines occurred during a period of significant warming, similar to what is projected to happen in the future. Why, exactly, should we believe that society will suddenly stop adapting to a climate change that they, apparently, have largely already adapted to? There is no reason.


Davis, R.E., et al., 2003. Changing heat-related mortality in the United States. Environmental Health Perspectives, 111, 1712-1718.

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