Temperatures above the National Weather Service’s “extreme hazard” threshold, when the heat index is over 125 degrees Fahrenheit, are expected to affect about 8 million people in the US this year. But by 2053, 13 times as many people — 107 million — will experience that extremely dangerous heat, according to the study by the climate research group First Street Foundation.
“The results indicate that the incidence of extreme heat is increasing across the country, both in absolute and relative terms,” the study states.
Temperatures in some areas will rise more than others, including a so-called “extreme heat belt,” stretching from Texas all the way to the Great Lakes, the nonprofit’s study finds.
More than 100 million Americans in this region will experience temperatures of over 125 degrees (52 degrees Celsius) during the hottest parts of the year, more than 10 times the number currently expected.
Using a peer-reviewed model for extreme heat, First Street Foundation used home-level data to find the hottest seven days of the year right now and compare them to the equivalent in 30 years. On average, the seven hottest days will increase to 18 by 2053, the researchers found.
But in the southern half of the country, the number of warmest days will grow to about 30 — meaning what was once the hottest week of the year will become the hottest month by the 2050s, according to the study.
Florida’s Miami-Dade County will see the largest shift in temperature extremes, where the hottest seven days of the year in 2023 (heat index of 103 degrees) will occur on 34 days in 2053. Other locations in Florida and along the Gulf Coast include likely to experience more than 30 extra days with heat indices above 100 degrees by 2053, the study found.
Nationally, the number of counties expected to reach a heat index of 125 degrees at least once a year will increase more than 20-fold from 50 in 2023 to 1,023 in 2053, according to the study.
The likelihood of local heatwaves — defined as temperatures well above normal for three consecutive days — will also increase across the country, but are highest along the west coast, according to the study.
“Interestingly, exposure to consecutive local warm days is most likely to occur in West Coast states, while Midwest, Southeast, and East Coast states are most at risk of exposure to extremely dangerous temperatures, meaning virtually the entire country is subject to increasing dangers associated with heat exposure,” the study finds.
The study also determined a projection of change for each of the US states.