If weather trends continue as they have since scientists have tracked climate change, each year billions of people will be exposed to heat and humidity so extreme they will be unable to naturally cool themselves.

Since the Industrial Revolution, when humans began to burn fossil fuels to power machines and factories, global temperatures have risen about 1 degree Celsius, or 1.8 degrees Fahrenheit.

A new study from university researchers at Penn State and Purdue finds that if global temperatures climb above that level to 1.5 degrees Celsius or beyond, life across the planet will be intolerably hot, a lot more often.

The Penn State researchers found in 2022 that the extreme heat our bodies can stand is lower than previously believed. The more accurate limit is closer to 87 degrees Fahrenheit and 100% humidity. Those are wet-bulb temperatures, or the temperature air will cool to when water evaporates into unsaturated air.

If you’ve spent any time in the South, you may have felt humidity so high that the sweat on your skin won’t evaporate. The air feels heavy and wet.

The newer study suggests that at current warming levels, the U.S. will experience more heatwaves, although they likely won’t surpass human limits as often as in other parts of the world.

However, if more pessimistic global warming predictions pan out, the researchers said heat and humidity beyond our tolerance would begin to affect the Eastern Seaboard and the middle of the United States — from Florida to New York and Houston to Chicago.

While less dire predictions may save us, it’s enough to make one long for all things cold and frosty.