Contact: Dane Konop                          FOR RELEASE:  
                                             12/9/98

In a study showing climate changes that may represent a health threat, particularly to the elderly, two researchers from the National Oceanic and Atmospheric Administration report an increasing frequency of extremely hot and humid days nationwide. Their statistical study of temperature and humidity data for the United States from 1949-95, is published in the current issue of Nature.

In an analysis of hourly temperature and humidity observations at 113 NOAA weather stations nationwide, NOAA scientists Dian J. Gaffen and Rebecca J. Ross found that the frequency of extreme heat stress days is increasing across the United States by about two days a year per decade.

"Meteorologists calculate heat stress using the apparent temperature, or heat index, which is an estimate of human discomfort in sultry weather due to a combination of high temperature and high humidity," said Gaffen, a research meteorologist at NOAA's Air Resources Laboratory in Silver Spring, Md.

"We have found that average summertime temperature and humidity have both increased during the past half century," Gaffen said. "Accompanying these trends in mean conditions, we found that the frequency of extremely high heat stress conditions has also increased, especially at night. We saw the largest and most statistically significant trends in some of the most populated parts of the country, the eastern and western thirds of the conterminous U.S. There has also been a accompanying increase in the frequency of multi-day heat waves, with increases of about 88 percent nationwide during the study period."

According to Gaffen and Ross, it is possible that the trends since 1949 are, in part, associated with increased urbanization. If the spatial extent of urban heat islands has been growing, they report, it is possible that weather stations near large cities might experience more frequent high temperatures, especially at night.

But the NOAA scientists conclude, "The regional consistency of the trends suggests that their origins are not strictly local. Regardless of the root causes, if these climate trends continue they may pose a public health problem, particularly in light of the growing population of elderly people most vulnerable to heat-related sickness and mortality."

For more information about heat waves, visit the following World Wide Web Pages: http://weather.noaa.gov/weather/hwave.html
http://www.ncdc.noaa.gov
http://www.arl.noaa.gov

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