Date: April 2, 2001
Contacts: Bill Kearney, Media Relations Associate
Kathi McMullin, Media Relations Assistant
(202) 334-2138; e-mail <>

Impact of Climate Change on Human Health Remains 'Highly Uncertain'

WASHINGTON -- Even though it is understood that changes in climate and weather may factor into some disease outbreaks, it is not yet possible to determine whether global warming will actually cause diseases to spread, says a new report from the National Academies' National Research Council. While some studies have shown an association between short-term climate variability, such as that caused by El Nino, and a higher incidence of certain illnesses, numerous other factors must be considered to fully account for the spread of infectious diseases, said the committee that wrote the report.

"The potential exists for scientists one day to be able to predict the impact of global climate change on disease, but that day is not yet here," said committee chair Donald Burke, professor of international health and epidemiology, Johns Hopkins School of Public Health, Baltimore. "To help scientists and policy-makers gain a better understanding, our committee recommends strong support from the federal government for interdisciplinary efforts to analyze climate-disease relationships. The critical capabilities that must be strengthened and brought together include epidemiological surveillance, field ecology, computer modeling and simulation, and evaluation of public health interventions."

Since the time of Hippocrates, scientists have understood that weather can influence where and when some epidemics occur. For instance, mosquito-borne diseases such as dengue, malaria, and yellow fever are generally associated with warm weather, while influenza epidemics usually occur during cold weather, and outbreaks of intestinal illnesses caused by cryptosporidiosis are linked to heavy rainfall. In recent years, as research has confirmed the likelihood of a long-term global warming trend, questions have been posed as to what effect this might have on infectious disease patterns around the world, prompting numerous studies of climate-disease linkages.

Some of these studies have shown that climate variation from one season or year to the next can affect the life cycle of many pathogens and disease-carrying insects, potentially affecting the timing and intensity of disease outbreaks. A number of computer models have been developed as well to simulate the effects of climate change on disease incidence, but estimates of the extent to which diseases will potentially spread have varied significantly among some of the models. In addition, observational and modeling studies generally are not able to consider complex social factors -- such as sanitation and public health services, population density, and travel patterns -- that also play important roles in disease dynamics. Because of this, the results of such studies must be interpreted with caution, especially when used to develop scenarios of the potential health effects of future climate change, the committee said.

Indeed, the highly uncertain impact of long-term climate change on the spread of disease and on the evolution and emergence of new pathogens stems largely from the confounding influences of human behavioral adaptations and public health interventions. For instance, basic public health protections such as adequate housing and sanitation, as well as the availability of vaccines and drugs, can limit the geographic distribution of diseases regardless of climate. One example of this is along the border between the United States and Mexico, where dengue fever outbreaks are common just south of the Rio Grande river in Mexico, but are rarely seen in neighboring regions just north of the river in the United States, mainly because of differences in socio-economic conditions.

The report also notes that there are potential pitfalls in extrapolating climate and disease relationships from one time scale to another. For example, the ecological effects of short-term climate events, such as El Niño, may be significantly different from the ecological effects and social adaptations expected under long-term climate change.

Research to understand the relationship between climate and infectious disease is in its infancy and needs to be strengthened, the committee said. Interdisciplinary research centers should be established to foster collaboration between scientists in fields such as epidemiology, climatology, and ecology. And federal health agencies such as the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Disease should become actively involved in the U.S. Global Change Research Program, an organization that coordinates climate research among federal agencies.

Recent technological advances, such as gene-sequencing techniques for studying the molecular biology of disease-causing pathogens and satellite-based remote sensing of ecological conditions, should be used to aid research efforts, the committee added. In addition, to overcome the existing lack of high-quality epidemiological data for most diseases, a concerted global effort should be made to collect long-term disease surveillance information, along with the appropriate meteorological and ecological observations, and store it in centralized, accessible databases.

As the potential linkages between climate and disease become better understood, it may be possible to provide early warnings to help prevent disease outbreaks, the committee said. To do this, climate forecasts will have to be complemented by ongoing meteorological, ecological, and epidemiological surveillance systems. Together, this information could be used to issue a "watch" for regions at risk and subsequent "warnings" as surveillance data confirm earlier projections.

The committee emphasized, however, that early warning systems should not take the place of proven public health measures since there will always be some element of unpredictability in climate variations and disease outbreaks. Officials should continue to place a high priority on reducing people's overall vulnerability to infectious disease through vaccination programs, mosquito-control efforts, and water-treatment systems, it said.

The report was sponsored by the U.S. Environmental Protection Agency, Centers for Disease Control and Prevention, National Science Foundation, NASA, National Oceanographic and Atmospheric Administration, U.S. Geological Survey, U.S. Global Change Research Program, and the Electric Power Research Institute. The National Research Council is the principal operating arm of the National Academy of Sciences and National Academy of Engineering. It is a private, nonprofit institution that provides scientific and technical advice under a congressional charter.

Read the full text of Under the Weather: Climate, Ecosystems, and Infectious Disease for free on the Web, as well as more than 1,800 other publications from the National Academies. Printed copies are available for purchase from the National Academy Press Web site or by calling (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).

Division on Earth and Life Studies
Board on Atmospheric Sciences and Climate

Committee on Climate, Ecosystems, Infectious Disease, and Human Health

Donald S. Burke, M.D. (chair)
Professor of International Health and Epidemiology
School of Public Health
Johns Hopkins University

Ann G. Carmichael, M.D., Ph.D.
Associate Professor
Department of History
Indiana University

Dana A. Focks, Ph.D.
Senior Research Scientist
Center for Medical, Agricultural, and Veterinary Entomology
U.S. Department of Agriculture
Gainesville, Fla.

Darrell Jay Grimes, Ph.D.
Institute of Marine Sciences, and
Professor of Coastal Sciences
University of Southern Mississippi
Ocean Springs

John Harte, Ph.D.
Energy and Resources Group and Department of Environmental Science, Policy, and Management
University of California

Subhash R. Lele, Ph.D.
Department of Mathematical Sciences
University of Alberta
Edmonton, Alberta

Pim Martens, Ph.D.
Senior Researcher
International Centre for Integrative Studies
Maastricht University

Jonathan D. Mayer, Ph.D.
Professor of Geography
Department of Geography;
Adjunct Professor of Medicine
Division of Infectious Diseases;
Adjunct Professor of Family Medicine; and
Adjunct Professor
School of Public Health
University of Washington

Linda O. Mearns, Ph.D.
Deputy Director
Environmental and Societal Impacts Group
National Center for Atmospheric Research
Boulder, Colo.

Roger Pulwarty, Ph.D.
Research Scientist
Climate Diagnostics Center
Cooperative Institute for Research in Environmental Sciences
University of Colorado, Boulder, and
Program Manager for Regional Integrated Assessments
National Oceanic and Atmospheric Administration Office of Global Programs
Silver Spring, Md.

Leslie A. Real, Ph.D.
Asa G. Candler Professor of Biology
Department of Biology
Emory University

Chester Ropelewski, M.S.
Director of Climate Monitoring and Dissemination
International Research Institute for Climate Prediction
Columbia University
Palisades, N.Y.

Joan B. Rose, Ph.D.
Department of Marine Science
University of South Florida
St. Petersburg

Robert E. Shope, M.D.
Professor of Pathology
Center for Tropical Diseases
University of Texas Medical Branch

Joanne Simpson, Ph.D.*
Chief Scientist for Meteorology
NASA Goddard Space Flight Center
Greenbelt, Md.

Mark L. Wilson, Ph.D.
Associate Professor
Departments of Biology and Epidemiology
University of Michigan
Ann Arbor


Jonathan R. Davis, Ph.D.
Program Officer

Laurie S. Geller, Ph.D.
Study Director

Susan J. Roberts, Ph.D.
Program Officer

* Member, National Academy of Engineering