Heat Wave Report Clouded by Global Warming Agenda

Published October 1, 2000

This sounds bad: “Over the past 50 years, the number of [high heat index] days has doubled. The incidence of extended heat waves (four consecutive days of high heat stress) has nearly tripled. Adding to human health concerns, high heat stress nights have also doubled in frequency nationwide.”

Two organizations that are prime purveyors of global warming hysteria, Physicians for Social Responsibility (PSR) and Ozone Action (OA) (whose “hit list” targets Environment & Climate News contributing editor Patrick Michaels), have combined their intellectual firepower to produce a major heat wave report. Rather than simply surf the ‘Net Walter Mitty-style for quotations about the coming apocalypse, as they have done in the past, they’ve embarked on a real adventure: they’ve actually attempted to do science by gathering and analyzing real data.

In 1998, NOAA scientists Gaffen and Ross computed trends in apparent temperature across the United States. Apparent temperature, a combination of air temperature and humidity, is related to how comfortable a person “feels” on a hot day. It is similar to the “heat index” the National Weather Service uses and commonly broadcast by the weather media throughout the summer. You know, “hot and dry in Phoenix, sweltering in New Orleans,” and so on.

Using data from 1949 to 1995, Gaffen and Ross found heat waves were increasing across much of the United States. So PSR/OA decided to extend the study through 1999 by gathering recent NOAA weather records. Following the approach of Gaffen and Ross, they identified high heat stress days (or nights) as those exceeding the 85th percentile of apparent temperatures for any given weather station. Ironically, the choice of the 85th percentile was based on a 1989 paper Larry Kalkstein and I prepared as an approximate temperature above which deaths tend to rise above the baseline. PSR/OA should have read our paper more carefully.

Yet Kalkstein and I demonstrated that heat waves have their greatest impact in the North and Interior, where the populace is unaccustomed and unadapted to unusually stressful summer conditions. Even if the PSR/OA analysis is correct, this result would not have the (political) impact they really desire: more deaths from heat across the South from “global warming.”

The PSR/OA report concludes: “The health implications of this ongoing trend are significant. The human health toll of the increased heat stress documented here remains to be quantified.” Well, let’s help them out a little. We’ve already done the quantifying, and the quantity is zero!

Take Tampa, Florida, for instance. The number of heat stress days each summer in Tampa since 1948 show essentially no change until 1970, but since then, the trend has been markedly upward. Their inference? Tampa residents must be dropping like flies from summer heat and humidity.

Fortunately, reality comes to the rescue like a banana popsicle on a July afternoon. Consider the relationship between daily deaths (corrected for population changes) and afternoon apparent temperatures sorted by decade. In the 1960s (when apparent temperatures were steady), warm and humid days did indeed generate more deaths. But since 1970, there have been no excess deaths at high apparent temperatures. And in the 1990s, the death rate actually drops the more uncomfortable it gets. Very similar results have been found for nearly every southern city we’ve studied thus far.

Our astute readers already know things like improved medical technology and air-conditioning have played a major role in keeping people alive. Wouldn’t Ozone Action and Physicians for Social Responsibility (whom you would think, by definition, are in favor of lower death rates) know about those very things? But how do you think they feel about air-conditioning? Back to the report:

Higher humidity, higher average heat indexes and extended heat waves mean elevated air conditioning demand and therefore higher utility bills. Extended heat waves push our electricity grid to its limits year after year, causing brownouts and power failures. A major power failure in an urban center during a severe heat wave could have devastating health impacts. Ironically, greater electricity demand causes the price of electricity on the open market to soar. The result is every available power plant is turned on full throttle–including aging and less efficient plants–burning more coal, oil and natural gas and pumping more carbon dioxide global warming pollution into the atmosphere as well as other air pollutants.

Sounds like OA and PSR should be at the front of the line demanding we build more power plants to meet the increasing demand and keep electricity prices low. Yet those are the very same groups that oppose every petition to build new, efficient, high-tech power plants because they will contribute to global warming.

On the summer heat and mortality issue, there is one simple and pervasive truth: Technology, driven by the consumption of fossil fuels, saves lives. And while we hope that Physicians for Social Responsibility, Ozone Action, and like-minded groups will come to that realization, we somehow doubt it fits their global warming agenda.

Robert E. Davis, Ph.D., is an associate professor of environmental science at the University of Virginia.


Davies, K., et al., 2000. Heat waves and hot nights. Ozone Action and Physicians for Social Responsibility, July 26, 18 pp. Web site: (http://www.ozone.org/heatstress/report.html)

Gaffen, D., and R. Ross, 1998. Increased summertime heat stress in the U.S. Nature, 396, 529-530.

Kalkstein, L.S., and R.E. Davis, 1989. Weather and human mortality: An evaluation of demographic and interregional responses in the United States. Annals of the Association of American Geographers, 79, 44-64.