Concerns about global warming shifting disease patterns are misplaced, declares physicist Hadi Dowlatabadi of the Department of Engineering and Public Policy at Carnegie Mellon University in Pittsburgh, Pa., and director of the Center for Integrated Study of the Human Dimensions of Global Change. Speaking at the International Conference on Emerging Diseases, held in Atlanta, Ga., last summer, Dowlatabadi asserted that "demographics, socioeconomics, technology, and political factors are more important than climate in public health outcomes."
Climate determines the potential range of disease vectors but is only one factor among many human-induced changes than can influence those vectors.
"The pursuit of climate policy, though laudable, cannot be justified on public health grounds," he says. "If we pursue climate change as a major objective, we are taking away potential income growth from those (others) on the curve."
Some experts fear that climate change will lead to a spread of tropical diseases, such as malaria, into temperate regions, Dowlatabadi says. However, history shows that malaria was endemic in the 18th century in temperate regions of North America, such as southern Ontario in Canada, and it did not disappear from Europe until after the end of World War II - yet climate change is not implicated in those shifts of malaria away from temperate zones. Meanwhile, malaria prevalence remains greatest in very poor areas of the world. Concerning the relationship between disease prevalence and per capita income, "if you have a (per capita) income over $3,100 per year, you are able to control malaria," he says. "Where people prosper, they will devote resources to fighting malaria."
He cites statistics on dengue fever in Texas and in Mexican border states that lead him to draw a similar conclusion about this other disease of the tropics. For the period 1980-1996, there were approximately 50,000 cases of dengue fever in Mexican states along the U.S.-Mexican border, but only 43 cases in Texas, he notes. "If climate were the only factor, there should be a gradual gradient of disease. We find very large gradients at political boundaries, not those set by climate."
Forced migrations, which have increased by 50 percent in the past 10 years, can act as disease vectors by restricting access to health care. Moving from a rural to an urban area can also be deleterious to human health. Nonclimatic factors, including changes in land use patterns and the capacity of sewage systems, can determine whether the runoff from a torrential rain will promote the development of cryptosporidiosis. Yet other nonclimatic factors, such as political stability and access to health care, change more rapidly than does climate, and they are easier to manipulate.
"A poorly designed climate policy will do more harm than good, and we are ill-equipped to face the public health challenges in the years ahead," he says.