Deadly Effects of Future U.S. Heat Waves Predicted

In 2003, a summer heat wave killed between 22,000 and 35,000 people in five European countries. Temperatures soared to 104 degrees Fahrenheit in Paris, and London recorded its first triple-digit Fahrenheit temperature in history.

If a similar heat wave struck the United States, the results would be disastrous, a new study suggests.

Researchers looked at what would happen if a comparable extreme-heat event settled on five major U.S. cities, learning that not only would the country experience massive blackouts, but thousands of people could die. In New York alone, the number of deaths would increase to nearly 3,000 in a single summer.

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"That would literally double the number of excess deaths over the next hottest summer in the last 40 years in New York," said study leader Laurence Kalkstein, senior research fellow at the University of Delaware's Center for Climatic Research.

Already deadly

History shows that heat waves are deadlier than hurricanes or tornadoes. And studies have indicated that extreme weather events will become more common with global warming.

The warming is underway. With temperatures up to 30 percent higher than the seasonal average over the past few decades in most of Europe, the summer of 2003 was one of the hottest in centuries. Scientists expect 2005 to set a modern record for the warmest average global temperature. Leading computer models show continued warming for at least several decades, even if greenhouse gas emissions are curbed, with only wild schemes proposed to put the brakes on.

Urban areas are particularly vulnerable, because dark asphalt and rooftops absorb more solar radiation than natural landscapes, raising nighttime temperatures by as much as five degrees, according to NASA studies.

In order to see the effects of extreme heat events on the United States, the researchers developed models to simulate scenarios analogous to that of Europe's for heat-sensitive urban areas.

"We tried to take the Paris heat wave in 2003 and transpose it onto the climate of five different cities," Kalkstein said. The cities: Detroit, New York, Philadelphia, St. Louis, and Washington, D.C.

The results were not cool.

In the nation's capital, there were 11 days with temperatures at or above 105 degrees in the virtual scenario.  St. Louis reached an all-time maximum of 116. New York and Philadelphia each broke all-time highs for four days. In Detroit the mercury set all-time records twice.

The total simulated excess deaths were more than five times the historical summer average, with New York and St. Louis showing the highest numbers. This the researchers attribute to size and city structures.

"New York is much bigger and clearly will have more deaths than cities like Washington and Detroit," Kalkstein said. "The second thing is that [a place such as] New York is a very sensitive city with a lot of high-rises and buildings that are sensitive to extreme heat."

Plan for it

Better planning and simple innovations in architecture could effectively reduce mortality rates should things heat up.

There are many things that can be done immediately, Kalkstein told LiveScience.

Cities could provide air-conditioned shelters and cut down on the use of black asphalt in favor of lighter-colored materials. More heat-absorbing trees and gardens could dot urban areas. Cities could work to provide better public transportation, decrease traffic congestion and minimize commutes. Property owners could be encouraged to paint roofs white and build roof gardens.

The study is part of a recently released report titled Climate Change Futures, a project of the Center for Health and the Global Environment at Harvard Medical School.