Heat Waves: Exposure to Increase 4-Fold by 2050

With climate change causing much of the world's hot extremes, heat waves are likely to become more common. Well, now new research shows that, at least in the United States, exposure to extreme heat could increase four- to six-fold by 2050, due to both a warming climate and a population that's growing especially fast in the hottest regions of the country.

Surprisingly, extreme heat kills more people in the United States than any other weather-related event. And with blazing heat becoming the new norm, the number of deadly heat waves, and therefore fatalities, are expected to increase as the climate warms.

This latest study, conducted by researchers at the National Center for Atmospheric Research (NCAR) and the City University of New York (CUNY), highlights the importance of considering societal changes when trying to determine future climate impacts.

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

According to the new findings, overall exposure of Americans to these future heat waves would be vastly underestimated if the role of population changes were ignored.

That said, the total number of people exposed to extreme heat is expected to increase the most in cities across the country's southern reaches, including Atlanta, Charlotte, Dallas, Houston, Oklahoma City, Phoenix, Tampa, and San Antonio.  (Scroll to read on...)

For the study, the research team used 11 different high-resolution simulations of future temperatures across the United States between 2041 and 2070. This is assuming that we don't achieve any significant reductions in greenhouse gas emissions - after all, our goal of limiting warming an additional two degrees Celsius (3.6 °F) is likely utterly unattainable.

The simulations were produced with a suite of global and regional climate models as part of the North American Regional Climate Change Assessment Program.

Using a newly developed demographic model, the scientists also studied how the US population is expected to grow and shift regionally during the same time period, assuming current migration trends within the country continue.

Then, they calculated the total exposure to extreme heat in "person-days," by multiplying the number of heat waves - days when temperatures reach at least 95 degrees - by the number of people who are projected to live in the areas where extreme heat is occurring.

This way, the team could determine how many Americans will experience extreme heat in the future.

What they found was that the average annual exposure to extreme heat during the study period is expected to be between 10 and 14 billion person-days, compared to an annual average of 2.3 billion person-days between 1971 and 2000.

That's due to three factors: the warming climate, population change, and a combination of the two, which all roughly contributed a third to increased exposure to heat waves.

"We asked, 'Where are the people moving? Where are the climate hot spots? How do those two things interact?'" explained NCAR scientist and co-author Linda Mearns. "When we looked at the country as a whole, we found that each factor had relatively equal effect."

Although at a regional scale some areas of the country will be more affected by climate change (i.e. urban areas) than population growth, and vice versa, the bottom line is that some increase in total exposure to extreme heat is expected in every region of the continental United States.

It's really no surprise that climate change is bringing heat waves with it, but the research team hopes that their study will inspire other researchers to incorporate social factors as well, such as population change, into studies of climate change impacts.

"There has been so much written regarding the potential impacts of climate change, particularly as they relate to physical climate extremes," added Bryan Jones, a postdoctoral researcher at the CUNY Institute for Demographic Research and lead author of the study. "However, it is how people experience these extremes that will ultimately shape the broader public perception of climate change."

Their findings were published in the journal Nature Climate Change.

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