CIESIN Thematic Guides

The Effects of Ambient Temperature on Mortality

Given the difficulties in predicting the potential future health effects from global warming, many authors emphasize the need to look at past and present examples of the relationship between climate and health. Several studies examine the excess mortality associated with seasonal temperature variations and prolonged periods of high temperatures, referred to as "heat waves." These studies use death as the health outcome due to the availability of mortality data. A more plausible theoretical model might be to consider the effect of temperature on the onset and progression of diseases: however, morbidity data are often very hard to obtain.

Several good articles refer to the range of literature that addresses the impact of ambient temperature on human mortality. In "Human Health," a section of the Department of Energy's 1985 report Characterization of Information Requirements for Studies of CO2 Effects, White and Hertz-Picciotto (1985) summarize a few of the studies that examine death rates due to heat waves. The table "Data from Heat Wave Studies" provides information on heat-wave length, several temperature parameters, and excess mortality for six heat-wave episodes from 1939 to 1978. In addition, the report includes diagrams of temperatures and death rates during a 1936 heat wave for 10 cities in the United States that were included in Gover's (1938) paper "Mortality During Periods of Excessive Temperature."

In the Environmental Protection Agency's (EPA) 1987 monograph Potential Effects of Future Climate Changes, Kalkstein and Valimont discuss several papers related to seasonal variations and heat waves in the chapter "Climate Effects on Human Health." They present a collection of figures from other sources to illustrate the association of heat episodes with mortality.

In "Weather and Human Mortality," Kalkstein and Davis (1989) also refer to the many evaluations of the climate-mortality relationship. They point out, however, that most of these studies have been undertaken by medical researchers who are not trained as geographers or climatologists in the techniques necessary to integrate climate data into a coherent climate-mortality model. Much of this research also neglects interregional variations. The authors present the results of their own research, which evaluates the impact of weather on mortality for 48 cities across the United States. Mortality data are analyzed in terms of death from all causes and weather-sensitive causes by age and race.

In a 1989 EPA report, Kalkstein describes his exploratory research on "The Impact of CO2 and Trace Gas-induced Climate Changes upon Human Mortality." Kalkstein derives historical relationships between mortality and temperature for both summer and winter in New York and 14 other metropolitan areas. He then evaluates the impact of two different climate scenarios.

Kalkstein's 1992 article "Impacts of Global Warming on Human Health" includes a section "Historical Relationships," in which he reviews studies that explore the relationship between various temperature parameters and their effect on mortality. While most researchers seem to agree that hot weather extremes have the greatest impact on mortality, Kalkstein contends that the effect varies with location and month of occurrence. His application of an air mass-based synoptic procedure to 10 U.S. cities indicates interregional mortality/weather sensitivities. Kalkstein classifies days that are meteorologically homogenous into air-mass categories to evaluate simultaneously the effects of various weather components that make up an air mass. "A New Approach to Evaluate the Impact of Climate on Human Mortality" offers a more detailed explanation of the synoptic climatological approach and the reasons for using it (Kalkstein 1991).

While the work by Kalkstein and his colleagues seems to dominate the recent literature on heat-related mortality, several of the references they include are valuable sources of more specific historical information.