CIESIN Thematic Guides

Models that Predict Potential Increases in Mortality due to Global Warming


To predict potential increases in mortality due to global warming requires 1) identification of the direct and indirect exposures that will be generated; and 2) comprehension of how these exposures will affect the biological systems of individuals with a variety of demographic, socioeconomic, behavioral, and health characteristics who will live and work at different locations around the globe. Unfortunately, our knowledge base is severely limited and more research is needed. (See the essay on Mortality Research Needs and Programs). A few initial attempts have been made, however, to develop models that predict the effects of global warming on heat-related mortality.

In the chapter "Climate Effects on Human Health" of the 1987 Environmental Protection Agency (EPA) monograph Potential Effects of Future Climate Changes, Kalkstein and Valimont (1987) describe some of the general algorithms developed in the early 1970s to predict mortality changes during heat waves. They also discuss the effects on health of other weather variables, such as humidity, precipitation, frontal passages, hours of sunshine, and cloud cover. The impacts of these variables could be modeled independently or together in conjunction with temperature increases.

Since the mid-1980s, Kalkstein and his colleagues have been working on the development of models to estimate heat-related mortality due to global warming. In 1985 Kalkstein and Davis presented a weather-mortality model for environmental impact assessment to the Seventh Conference of Biometeorology and Aerobiology. The following year, Kalkstein et al. (1986) conducted a detailed analysis of the 1980 New York City heat wave that compared deaths among the elderly with total mortality. In "The Impact of Human-Induced Climatic Warming Upon Human Mortality," the authors apply the concept of "threshold temperature," the temperature that, when exceeded by the maximum daily temperature, results in a rapid rise in mortality. They also estimate the average monthly increase in total mortality under different warming scenarios, with and without acclimation, using the concept of "analog" cities. Their model incorporates nine weather elements, including temperature, windspeed, and humidity.

Kalkstein expands the New York City study described above in his 1989 report to the EPA "The Impact of CO2 and Trace Gas-Induced Climate Change upon Human Mortality." The EPA-funded research examines 15 metropolitan areas in terms of total mortality for two Goddard Institute for Space Studies climate scenarios, two future time frames, and two acclimation assumptions. In The Potential Effects of Global Climate Change on the United States, Smith and Tirpak (1989) suggest that, given the sensitivity of the results to the selection of analog cities, Kalkstein's work should be considered as illustrative of possible variations in mortality rather than as reliable for specific predictions. In "Impacts of Global Warming on Human Health," Kalkstein (1992) explains further the difficulties in incorporating acclimation in a weather-mortality model.

Kalkstein (1993) describes more complex models in "Health and Climate Change" as part of The Lancet series on global warming. He delineates the synoptic procedure with its automated index that classifies the air mass over each city daily. Estimates generated for unusually high heat-related mortality associated with offensive summer air masses indicate that increases in mortality are likely even with acclimation. A more detailed application of Kalkstein's model is described in the chapter "Global Warming and Human Health" in The Potential International Impacts of Climate Change. Here, Kalkstein applies his most recent models to cities in Canada, China, and Egypt. By evaluating weather situations rather than individual weather elements, Kalkstein is able to assess the role of extreme events on mortality. The international focus of his research is important given the growing concern among medical and climatological researchers that global warming could generate significant health problems around the world. These problems could be particularly severe in developing countries that lack the resources for effective intervention and treatment.