“The results show that the frequency of extreme heat is increasing across the country, both in absolute and relative terms,” ​​the study says. Temperatures in some areas will rise more than others, including the so-called “heat belt of extremes,” which stretches from Texas to the Great Lakes, according to the nonprofit’s study. More than 100 million Americans in this region will experience temperatures above 125 degrees (52 degrees Celsius) during their hottest times of the year, more than 10 times the number currently expected. Using a peer-reviewed extreme heat model, the First Street Foundation used property-level data to find the seven hottest days of the year right now and compared them to the past 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 hottest days will increase to about 30 — meaning what was once the hottest week of the year will become the hottest month by the 2050s, the study found. Miami-Dade County, Florida will see the largest change in temperature extremes, where the hottest seven days of the year in 2023 (heat index of 103 degrees) will increase to 34 days in 2053. Other locations in Florida and along the coast of The Gulf is likely to experience more than 30 additional days with heat indices above 100 degrees by 2053, the study found. Nationally, the number of areas 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 chance of localized heat waves — defined as temperatures well above normal for three consecutive days — will also increase across the country, but is higher along the West Coast, the study found. “Interestingly, exposure to consecutive locally hot days is most likely to occur in West Coast states, while states in the Midwest, Southeast, and East Coast are most at risk of exposure to extremely dangerous temperatures, meaning almost the entire country is subject to in increasing risks associated with heat exposure,” the study found. The study also determined a change forecast for each US state.