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Heat-Related Death Rates Declining Across U.S., Even As Summer Temperatures Rise, Study Says

July 29, 2003-- Heat is the primary cause of weather-related death in the United States. The elderly, young children and people with respiratory and circulatory problems are particularly vulnerable.

But in recent decades the number of heat-related deaths has declined steadily, according to a new University of Virginia study published on-line in the journal Environmental Health Perspectives. (

During the period studied, 1964-1998, average summer temperatures and humidity have steadily increased. Most climatologists attribute increasing temperatures to a global warming trend, possibly caused by industrial society’s increasing use of fossil fuels, which produce carbon dioxide, a “greenhouse” gas. Many scientists have predicted that heat-related deaths will increase as a result.

So why are less people dying from heat stress even as temperatures are increasing? The very technologies that may be altering the climate are also making life better for humans.

“The declining mortality rate can be attributed to various adaptations,” said Robert Davis, associate professor of environmental sciences at U.Va. and the study’s principal investigator. “Air conditioning, improved medical care, better public awareness programs relating to potential dangers of heat stress and both human biophysical and infrastructural adaptations are all factors.”

Davis and his colleagues calculated heat-related mortality rates for 28 U.S. cities from 1964 to 1998 on days each year with high temperature and humidity. They found an average of 41 heat-related deaths per million people per year during the 1960s through ‘70s, and clear indications of significantly higher mortality on high heat and humidity days. But the numbers steadily declined with each decade. By the 1990s, there were only an average of 10.5 deaths per million.

“This decline occurred despite increasingly stressful weather conditions in many urban and suburban areas,” Davis said.

Many cities, particularly in the hot and humid southeastern U.S., experienced no excess mortality during the 1980s, possibly because Southerners are more acclimated to high temperatures. In the 1990s, the effect spread northward.

“In general, over the past 35 years, the U.S. populace has become systematically less impacted by hot and humid weather conditions,” Davis said. “This research suggests that summer heat-related mortality should continue to decline despite increasing temperatures.”

Contact: Robert Davis, (O) (434) 924-0579, (H) 823-1365

FOR ADDITIONAL INFORMATION: Contact the Office of University Relations at (434) 924-7116. Television reporters should contact the TV News Office at (434) 924-7550.

SOURCE: U.Va. News Services


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