CIESIN Thematic Guides

The Basic Mechanisms Underlying How Global Warming May Influence Health

Weather has an extraordinary influence on human health and well-being. Climatic parameters historically have been a major determinant in the survival and development of human populations. To cope with harsh climatic conditions people have modified their exposure through behavioral changes and adaptations. In some places, such as high altitude regions, people have developed advantageous physiological changes over long periods of time. Whether or how quickly populations might also acclimate to increased temperatures from global warming, however, is unclear. Much of the speculation and documentation of how weather and climate have influenced human diseases over the centuries is part of the vast literature in biometeorology.

Several very good articles review the effects of global warming on health. In the Environmental Protection Agency's 1987 monograph Potential Effects of Future Climate Changes, the chapter "Climate Effects on Human Health" refers to a large body of literature, primarily by medical researchers, on the impact of variable climate and human well-being. Authors Kalkstein and Valimont mention a number of impacts of weather on health but focus primarily on human mortality in terms of temperature-related events.

White and Hertz-Picciotto's section "Human Health" of the Department of Energy's 1985 report Characterization of Information Requirements for Studies of CO2 Effects describes influences of climate, seasons, and weather on human health. The authors cover a wide range of factors: weather variables relevant to human health; changes in the variability of weather; basic human mechanisms (thermoregulation, acclimation, and adaptation); seasonality of morbidity and mortality; and mortality from all causes. The figure "Pathways by which CO2-induced Climate Change May Affect Human Health" illustrates the relationship of direct and indirect effects of climate change on human health, though it does not clarify what specific aspects of climate change induce these effects.

Most research on global warming and health uses mortality statistics as the health outcome due to the widespread availability of such data and the difficulty in obtaining specific morbidity data, except for a few regularly reported diseases. Thus, the relationship examined is the association of mortality with the existing environmental factors at the time of death. In "Human Health," White and Hertz-Picciotto point out that such analyses may miss a more important relationship; that is, how climatic conditions affect the onset and progression of organic diseases. In the article "Atmospheric Change and Temperature-related Health Effects," Kilbourne (1990) examines direct heat-related illnesses and the exacerbation of certain chronic disease processes by heat. In addition, the World Health Organization Task Group report Potential Health Effects of Climatic Change provides a concise description of direct effects (thermal factors, heat disorders) and indirect effects (food and nutrition, communicable diseases, and migration) of global warming (1990a).

Many authors agree that the primary impact of global warming on human health will probably not be direct. In "Anticipated Public Health Consequences of Global Climate Change," Longstreth (1991) says the impacts are "likely to be the result of what the impacts of heat would be on ecosystems such as forests and farmland." In addition to frequently mentioned effects, such as heat stress and vector-borne diseases, Longstreth also briefly discusses allergic diseases, developmental effects, malnutrition and associated infectious diseases, and health problems related to overcrowding.