(NEXSTAR) – A withering July gave a preview of the sustained, dangerously hot temperatures that will become increasingly common in Texas over the next three decades, according to a new study.

In 2023, 8.1 million Americans living in 50 counties will experience temperatures of at least 125 degrees, the highest classification on the National Weather Service’s Heat Index – “Extreme Danger,” according to nonprofit First Street Foundation’s peer-reviewed model.

Three decades later, the same model shows that climate change will cause 1,023 counties – home to 107.6 million people – to see temperatures rise above 125 degrees.

The study found that “dangerous” days with a heat index exceeding 100 degrees occur more often in the southern half of the contiguous U.S., but especially in Florida and Texas. Starr County, Texas, topped all others in 2022 with 109 days above the threshold.

The model takes into account a number of factors including land surface temperatures, tree and other canopy cover, the presence of concrete and other impervious surfaces and the proximity to water. Researchers built the model under an established warming scenario in which greenhouse gas emissions reach their peak around 2040 and then begin to decline.

“Increasing temperatures are broadly discussed as averages, but the focus should be on the extension of the extreme tail events expected in a given year,” said Matthew Eby, founder and CEO of First Street Foundation. “We need to be prepared for the inevitable, that a quarter of the country will soon fall inside the Extreme Heat Belt with temperatures exceeding 125°F and the results will be dire.”

The so-called “extreme heat belt” will include Northern Texas and states bordering the Gulf, stretching north to Illinois, Indiana, and even up to Wisconsin.

Preventing deaths from worsening heat

In July, days after nearly half the country — 154.6 million people — sweated through a blistering heat wave, the Biden Administration unveiled heat.gov, which includes maps, forecasts and health advice. The government can’t lower temperatures in the short-term, but it can shrink heat’s death toll, officials said.

“July 2021 was the hottest month ever recorded on Earth and summers are getting hotter and deadlier,” said National Oceanic and Atmospheric Administration chief Rick Spinrad. “The annual average temperature of the contiguous U.S. has already warmed over the past few decades and is projected to rise by 5 to 9 degrees Fahrenheit (2.8 to 5 degrees Celsius) by the end of this century.”

But officials said even though heat is the No. 1 weather killer, and warming is worsening, deaths can still be prevented. That’s the purpose of the website.

North Carolina state climatologist Kathie Dello said, “extreme heat is one of our greatest challenges as a county and I’m glad to see the interagency cooperation.”

It’s important that the website shows that heat isn’t just a problem for today “but in the future,” Dello said.

Given warming trends, this summer with its widespread heat waves “is likely to be one of the coolest summers of the rest of our lives,” Raimondo said. “That’s a pretty scary thing.”

The Associated Press contributed to this report.