More Heat Plus More People Equals Deadlier U.S. Summers

A new study shows more Americans will suffer the consequences of extreme heat.

People try to cool off from the heat in Karachi, Pakistan, June 25, 2015. A new study finds the number of people exposed to extreme heat in the U.S. could quadruple by 2070, due to climate change and population changes. Credit: REUTERS/Akhtar Soomro

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The recent heat waves that have scorched Europe, India and Pakistan have served as vivid reminders of the deadliness of heat. Thousands have died so far, and summer has only just begun.

The health toll of heat, unfortunately, is only going to get worse in the United States as well, because not only is climate change bringing more heat, but urbanization is also putting more people in the hottest places, according to a recent study in the peer-reviewed journal Nature Climate Change.

The number of Americans exposed to extreme heat could quadruple by 2070, according to study authored by researchers at the National Center for Atmospheric Research and the City University of New York.

Using a computer model and assuming no significant reductions in greenhouse gas emissions, the researchers calculated exposure to extreme heat based on “person-days.” The formula multiplied the number of days when the temperature was expected to hit at least 95 degrees by the number of people projected to live in the areas beset by extreme heat.

The results show that average yearly exposure to extremely high temperatures would rise from 2.3 billion person-days—the average during the years 1971 to 2000—to between 10 billion and 15 billion person-days during the years 2041 to 2070.

Extreme heat already kills more people in the United States than any other weather-related event, and scientists expect the number of deadly heat waves to increase as the climate warms, according to the study. Urbanization intensifies heat––a phenomenon known as the heat island effect––and in the U.S., people are moving to the hotter parts of the country, not the colder ones.

“Both population change and climate change matter,” NCAR scientist Brian O’Neill, one of the study’s co-authors, said in a prepared statement. “If you want to know how heat waves will affect health in the future, you have to consider both.”

Sharon Harlan, a professor in Arizona States University’s School of Human Evolution and Social Change, said urban areas present the greatest challenges to mitigating the consequences of increasing heat. They’re also home to the most vulnerable class of people––the elderly, sick and poor.  

People in the poorer neighborhoods of big cities find themselves at even greater risk for heat-related health problems, Harlan. These are the people who can’t afford the utility bills that come with air conditioning or whose houses are poorly insulated or ventilated.

Ken Spaeth, a physician and division chief of Occupational and Environmental Medicine at North Shore University Hospital in Manhasset, N.Y., said steadily rising temperatures increase the risks to people’s health.  

“It’s likely that climate change temperature patterns will continue to get worse and the corresponding public health effects will become more demonstrable,” Spaeth said.  

Bryan Jones, a postdoctoral researcher at the City University of New York Institute for Demographic Research and the study’s lead author, said heat waves are also arriving in months not typically associated with extreme heat. Southern California was in the grips of a heat wave in March that sent temperatures soaring 15 to 20 degrees above normal.

Special attention should be paid, Harlan said, to designing cities with heat in mind; the use of tree cover and landscaping around buildings that can reduce temperatures. And buildings themselves must be better designed to repel heat and create comfortable interior environments while controlling energy usage, she said.

The trend toward a warming climate––and the resulting miserable heat that people will have to suffer––should be approached sensibly, Harlan said.

“We need to look toward the future and do the kind of planning to change lifestyles and address climate change issues,” Harlan said.

“A lot of what the future holds involves a public policy discussion and everyone’s recognition of what they need to do to protect themselves.”