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January 6, 2004

Potential Impact of Global Climate Change

As the Earth’s temperature warms, changes in climate and habitat could have a significant effect on human health. In a review article for the Journal of the American Medical Association (JAMA), Andy Haines, MD, MBBS, dean of the London School of Hygiene and Tropical Medicine and Jonathan Patz, MD, MPH, assistant professor in the Department of Environmental Health Sciences at the Johns Hopkins Bloomberg School of Public Health, outline the potential impact of global climate change. The article appears in the January 7 edition of the journal. 

“Humans are making unprecedented changes to the global environment. Much of the warming over last 150 years has taken place in the past three decades,” said Dr. Patz. “Physicians need to be aware of how current climate variability can affect human health. They should also recognize that long-term climate change may exacerbate climate-sensitive health problems.”

Thermal Stresses

In the article, the authors note continued warming may bring an increased frequency in heat waves. Previous research showed that temperate locations tend to experience more heat-related deaths during periods of warm weather. For example, the 1995 heat wave in Chicago, Ill., caused more than 700 heat-related deaths and last summer’s heat wave killed thousands in France.

Floods and Droughts

Continued climate change could also increase the frequency and severity of floods. Developing nations would be particularly vulnerable, because many of their inhabitants live in high-risk flood plains and coastal areas. Many of these nations do not have the public health resources to deal with potential problems. In addition to the injury and economic loss, the authors note that flooding contributes to the spread of diarrheal diseases and contamination of drinking water. Respiratory infections may also increase from crowding of populations and increased growth of molds may cause respiratory symptoms.

Droughts would have a negative impact particularly on developing countries because of the adverse effects on food production and restricted access to and use of clean water.

Infectious Diseases

Changes in temperature, humidity, rainfall, and sea level rise could all affect the incidence of infectious diseases like malaria and dengue fever. With warmer temperatures, rodents and disease-carrying mosquitoes, ticks, and fleas could migrate to higher altitudes, latitudes, or have longer survival periods. However, climate change may render some locations less conducive to disease transmission.

One estimate suggests that 260 to 320 million more people could be at risk for malaria by 2080. In Africa, a recent modeling study suggests a 5 to 7 percent increase in malaria distribution particularly at higher altitudes. The increase in risk of exposure in person months could increase 16 to 28 percent mainly because of a prolonged malaria transmission season.

“Because of the wide ranging potential impacts of global warming, a precautionary approach should be taken that seeks to decrease greenhouse gas emissions substantially, including the introduction of energy efficiency and renewable energy technologies,” said Dr. Haines. --Tim Parsons

Health Effects of Global Climate Change

Public Affairs Media Contacts for the Johns Hopkins Bloomberg School of Public Health: Tim Parsons or Kenna Brigham at 410-955-6878 or Photographs of Jonathan Patz are available upon request.