Human Health & Global Climate Change: A Review of Potential Impacts In the United States
Prepared for the Pew Center on Global Climate Change
John M. Balbus, The George Washington University
Mark L. Wilson, The University Of Michigan
Press Release 
The population of the United States is among the healthiest in the world, although there are disparities in life expectancy, infant mortality, and other indices of health among different groups within the U.S. population. The main determinants of disease-related mortality in the United States today are lifestyle factors --- tobacco use, alcohol use, dietary intake of calories and fats, sexual behavior, and physical inactivity. The national level of economic and social development in this country has generally provided resources to address critical health determinants such as nutrition, sanitation, and housing quality. In addition, the United States devotes a large amount of resources to health care and maintains a relatively effective public health infrastructure.
This report on the effects of climate change on human health in the United States finds that the complexity of the pathways by which climate affects health represents a major obstacle to predicting how, when, where, and to what extent global climate change may influence human well-being. Some linkages are strong and clearly defined, whereas other important connections are made difficult to define by being variable, region-specific, or mediated through multiple intervening steps.
Mortality from heat waves has been predicted to increase under most scenarios of climate change. The degree to which heat-related mortality rates increase will be determined by the ability to implement early warning systems and other interventions that focus on at-risk populations, as well as by the frequency of extreme heat waves and the changes in daytime temperature variation under future climate regimes. It is less clear whether warmer winter temperatures will result in a significant decline in wintertime mortality from cardiovascular disease.
If extreme precipitation events become more frequent, and sanitation and water-treatment infrastructure is not maintained or improved, an increase in water-borne infections may result. People are also at risk of injury or death from exposure to extreme climate events such as floods, hurricanes, and tornadoes. The public health burden of such events, however, partly depends on the ability to anticipate them, and the education and emergency response planning that may reduce impacts. In addition, current climate models are not able to confidently predict the future frequency of such events, although there has been a trend toward heavier precipitation events during the twentieth century.
Global climate change may affect human respiratory health by changing levels of air pollutants and pollens. For the United States, impacts of climate change on tropospheric, i.e., ground-level, ozone are both more certain and likely to be more important than impacts on other air pollutants. This is due to the importance of temperature in the formation of ozone as well as the large areas of the country currently affected by ozone levels exceeding national standards. Nonetheless, to date, no published studies have modeled the health impacts in the United States due to climate change effects on air pollutants.
In the United States, improved housing, sanitation, and public health interventions have controlled most of the infectious disease risks that are felt to be most climate sensitive (e.g., dengue, malaria, cholera). Of greatest concern are insect vector-borne infections that may increase as the result of changing climate. However, the multiple determinants of vector-borne disease risk and the complexity of transmission dynamics make estimating future patterns of disease difficult. In addition to climate, the risk of many vector-borne diseases is linked to lifestyle, hygiene, housing construction, trash removal, and a host of other socially- and economically-based factors. Thus, infectious disease risk may increase or decrease with climate change, depending upon the interplay of the above factors within a specific region.
For the United States, the success of public health interventions in eradicating malaria and other vector-borne diseases early in the twentieth century underscores the importance of continued public health surveillance and prevention in protecting the U.S. population from any climate-induced enhancement in vector-borne disease transmission. Maintenance and strengthening of public health infrastructure, especially surveillance and vector control, will be critical to preventing significant outbreaks in the future. Inclusion of public health and climate change experts in planning regarding land-use and utility infrastructure will also help assure maximal protection of public health during this upcoming period of climate change.
It is critical to keep in mind that uncertainty regarding adverse health outcomes is not the same as the certainty of no adverse outcomes. Given the potential scope and irreversibility of ecosystem changes and consequent effects on human health and society, traditional public health values would urge prudent action to prevent such changes. The possibility of relatively sudden but unpredictable consequences further raises the value of climate change mitigation for health concerns.
Dr. John M. Balbus
Dr. John Balbus is the Director of the Center for Risk Science and Public Health and an associate Professor of Environmental and Occupational Health at the George Washington University School of Public Health and Health Services. Board certified in both Internal Medicine and Occupational and Environmental Medicine, Dr. Balbus is also appointed in the Departments of Medicine and International Public Health. He received his MPH degree from the Johns Hopkins School of Hygiene and Public Health, his MD degree from the University of Pennsylvania, and his undergraduate degree in biochemistry from Harvard University. Dr. Balbus is the Principal Investigator on a cooperative agreement with the US Environmental Protection Agency's Office of Water, which focuses on a number of issues related to risk assessment for drinking water contaminants. He is also a co-Principal Investigator on a new Pediatric Environmental Health Specialty Unit. Dr. Balbus' research interests include risk assessment methodologies for health effects of climate change and waterborne pathogens, and variations in susceptibility to microbial and chemical environmental contaminants. He has served as technical consultant and author for the health sector for both the United Nations Environmental Programme project on global climate change and the United States Country Studies program.
Dr. Mark L. Wilson
Mark L. Wilson is currently Associate Professor of Epidemiology and of Biology at the University of Michigan, where his research and teaching cover the broad area of ecology and epidemiology of infectious diseases. After earning his doctoral degree from Harvard University in 1985, he worked at the Pasteur Institute in Dakar Senegal (1986-90), was on the faculty at the Yale University School of Medicine (1991-96), and then joined the University of Michigan. Dr. Wilson's research addresses the environmental determinants of zoonotic and arthropod-borne diseases, the evolution of vector-host-parasite systems, and the analysis of transmission dynamics. He is an author of more than 90 journal articles, book chapters and research reports, and has served on numerous government advisory groups concerned with environmental change and health. He currently is a member of the National Academy of Sciences panel on "Climate, Ecosystems, Infectious Diseases and Human Health."