Report: Heat Waves Increase Across U.S.

June 26 -- For all the terror that tornadoes and hurricanes bring, the real threat this summer may be the slow and steady heat wave, according to a study released today.

Soaring temperatures and high humidity have killed more people in the last decade than other weather phenomenon, including destructive storms, according to National Weather Service data. One reason for the fatalities may be that prolonged periods of excessive heat have become more common.

Analyzing the temperatures from 172 U.S. weather stations over roughly the last 50 years, from 1948-1999, the study found a threefold increase in the number of heat waves across the country. A heat wave is defined as a four-day period when average temperatures are above the 85th percentile for summer temperatures in the area. That means the threshold for a heat wave in Seattle would be lower than the temperature level of a Louisiana heat wave.

The study was released by two nonprofit groups, Ozone Action and Physicians for Social Responsibility. They contend the steady rise in temperatures is a result of global warming caused by human pollution.

“People who have lived Phoenix or Miami for the last 50 years know that it used to be a lot cooler,” says Kert Davies, science policy director for Ozone Action, a 7-year-old group focused on global warming. “It’s not their imagination.”

Honolulu topped the list of cities with the most frequent heat waves. Other cities with frequent heat waves included San Francisco, Lake Charles, La., Tampa, Fla. Tucson, Ariz., Atlanta and Midland, Texas.

Hot Nights and Heart Attacks

Not only are heat waves becoming more frequent, so are sweltering nights, says Davies.

“One of the things that really impacts people’s health during heat waves is that they don’t get a break from the heat,” he says. “They sleep in it and they wake up and face it again.”

The number of deaths caused by heat are higher than reported by medical examiners, says Larry Kalkstein, an independent researcher with the University of Delaware who supports the study’s findings. Heart attack deaths that may be caused largely by excessive heat are labeled only as heart attacks, he says, and therefore the problem does not seem as large as it is.