Climate study says summers in Illinois, much of Midwest to feature 'Extreme Heat Belt'

Over a 30-year period from 1991 to 2021, the average number of days with temperatures 90 degrees and above was 14.8.

As of Friday, according to the National Weather Service, Rockford had experienced 19 such days.

A recently released climate study said the number of days with high heat and humidity will continue to increase over the next 30 years.

In fact, the study says Illinois will find itself sitting at the top of an emerging and dangerous heat belt featuring stifling days with a heat index of 125 degrees and hotter.

In mid-August, First Street Foundation released its peer-reviewed extreme heat model along with the implications highlighted in The 6th National Risk Assessment: Hazardous Heat.

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The report identifies the impact of increasing temperatures and how the frequency, duration and intensity of extremely hot days will change over the next 30 years due to a changing climate. As average temperatures increase around the globe, the number of hot days will increase in both frequency and intensity. The study said temperatures across the United States are projected to increase by at least 4.5 degrees Fahrenheit over the course of the next 30 years.

In the study, "Extreme Danger Days" of heat are defined as when heat index exceeds 125 degrees in a given day. A heat index combines the predicted temperature with the predicted humidity.

In the case of extreme heat, the model finds 50 counties, home to 8.1 million residents, are expected to experience heat index or real-feel temperatures above 125 degrees Fahrenheit in 2023, the highest level of the National Weather Services’ heat index.

However, by 2053, 1,023 counties are expected to exceed this temperature, an area that is home to 107.6 million people and covers a quarter of the U.S. land area.

The foundation calls this region the “Extreme Heat Belt,” which stretches from the northern Texas and Louisiana borders to Illinois, Indiana, and even into southern Wisconsin.

Chief Research Officer Jeremy Porter said low lying areas further away from large bodies of water and in areas where humidity is high will generally be more susceptible to extreme heat events over the next 30 years.

"This is true for much of the Midwest, and for Winnebago, Boone, and other counties in Illinois," he said.

According to the study, the Winnebago and Boone counties will each experience at least one day in 2053 with a heat index of 125 degrees or higher.

"Nearer to the coasts, the ocean serves as a kind of physical barrier limiting how high temperatures can get in absolute terms — though dangerously hot days, and the duration of heat waves, are growing in these places as well. In general, distance from water, and growing humidity, make an area more susceptible to increases in absolute and heat indexed temperatures."

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The reason why the heat belt is located in the Midwest is because the Midwest is situated between the two mountain ranges, the Rocky and the Appalachian mountains.

"And the thing that is driving the heat in this area is the humidity," said First Street spokesman Michael Lopes. "Increasing humidity is what creates those real feel temperatures that give the sense that temperatures are hotter than what they really are."

Lopes added the study is not meant to scare people but to prepare them.

"That means more cooling centers and getting people air-conditioning, but getting them air-conditioning that won't make this problem worse. So, that means using green technology as much as possible."

Chris Green: 815-987-1241;; @chrisfgreen

This article originally appeared on Rockford Register Star: Climate study: 125-degree heat index is in Rockford's future