(CNN) — Worsening heat and humidity as a result of climate change will bring extremely dangerous heat indices to much of the United States over the next 30 years, increasing both the intensity and frequency of the hottest days of the year, according to a new study. .

Temperatures above the National Weather Service’s “extreme hazard” category threshold, when the heat index exceeds 51 degrees Celsius, are expected to affect about 8 million people in the United States this year. But by 2053, 13 times as many people — 107 million — will experience such extremely dangerous heat, according to the study by the climate research group First Street Foundation released Monday.

“The results indicate that the incidence of extreme heat is growing throughout the country, both in absolute and relative terms,” ​​the study states.

Temperatures in some areas will rise more than others, including the so-called “extreme heat belt” that stretches from Texas to the Great Lakes, according to the study by the nonprofit organization.

More than 100 million Americans in this region will experience temperatures above 51 degrees Celsius during the hottest parts of the year, more than 10 times the number currently projected.

Using a peer-reviewed extreme heat model, the First Street Foundation used property-level data to find the seven hottest days of the year today and compared them to the equivalent in 30 years. The researchers found that, on average, the seven hottest days will increase to 18 in 2053.

But in the southern half of the country, the number of hottest days will rise to about 30, meaning what was previously the hottest week of the year will become the hottest month in the 2050s, according to the study.

Miami-Dade County, Florida, will see the biggest change in temperature extremes, with the hottest seven days of the year in 2023 (heat index of 39°C) occurring on 34 days in 2053. Other places in Florida and the Gulf Coast will likely experience more than 30 additional days of heat indices above 100°F in 2053, according to the study.

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Nationwide, the number of counties expected to hit a 51C heat index at least once a year will more than multiply by more than 20, from 50 in 2023 to 1,023 in 2053, according to the study.

The likelihood of local heat waves — defined as temperatures well above normal for three consecutive days — will also increase across the country, but is higher on the West Coast, according to the study.

Interestingly, exposure to consecutive local 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 hot temperatures. dangerous, meaning that virtually the entire country is subject to the increased dangers associated with heat exposure,” the study said.

The study also determined a projection of change for each one of the North American states.

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