The number of U.S. residents exposed to extreme heat will quadruple by the middle of this century, due to an increase in days that are over 95 degrees in some regions and a shifting population, according to a new study.

The study was conducted by scientists at the National Center for Atmospheric Research  and the City University of New York, and was published Monday in the journal Nature Climate Change. The research combined two distinct factors: the increase in the numbers of days of extreme heat predicted by mid-century, and expected changes in population.

“In the future we know the climate is going to change,” said NCAR climate scientist and study co-author Linda Mearns. “But it’s important to note that many things are going to change. And one of the things that we know will change is the degree of population growth, or declines in population in some other areas.”

The study calculated what it calls “person-days:” the change in the number of extreme heat days, multiplied by the number of people who would be exposed to that heat. It then divided the country into regions. The areas that fare the worst under this prediction are the West South Central region (Texas, Oklahoma, Arkansas, Louisiana) and the South Atlantic (Florida, West Virginia, Georgia, South Carolina, North Carolina, Virginia, Maryland, D.C. and Delaware).

Extreme_Heat_900Erica Peterson | wfpl.org

Mearns estimated that by mid-century, Kentucky will see about 20 more days above 95 degrees. “That’s not nothing, it’s just not as bad as what you see further south,” she said.

The study estimates that because of both climate and population changes between 2041 and 2070, there will be about 500 million more annual “person-days” of exposure to extreme heat in the “East South Central” region, which includes Kentucky, Tennessee, Alabama and Mississippi.

Mearns says this information could prove useful for policymakers considering how regions will adapt to these changes.