Mapping the summer from hell: Extreme heat was widespread across the U.S. this season — and it will get worse

A Grid analysis shows how heat advisories spared few Americans this summer.

The most direct and obvious climate change impact is the heat. As global average temperatures rise, the potential for extreme heat rises along with it — and this summer has demonstrated just how widespread the consequences will be. A Grid analysis of Census Bureau and National Oceanic and Atmospheric Administration data has found that an estimated 170 million Americans, more than half the population, were under an extreme heat watch or warning at some point this summer.

Heat wave creep

Grid also analyzed the number of excessive heat warnings and watches issued by the National Weather Service and found a few extreme heat — ahem — hot spots around the country, including parts of Southern California, Oklahoma and the Pacific Northwest. But heat advisories were issued at least once this summer across much of Texas; in or near the Mississippi River in Missouri, Tennessee and other states; in both of the Dakotas and the Carolinas; and elsewhere. Even northern Minnesota was not spared.


A look back across the last 15 years indicates a rising prominence of these heat warnings and watches, though as with all climate phenomena, there is plenty of year-on-year variability. And importantly, Swain pointed out that one reason for the rising number of advisories is policy changes at the NOAA’s National Weather Service that have altered the parameters for when such advisories are issued.

“It’s a combination of the fact that climate change is making dangerous extreme heat more common, more frequent and more widespread, and, also, there’s more widespread recognition of the societal and ecological impacts of that heat,” he said.


“We have taken heat less seriously as a hazard than we have for flooding, wildfires, sea level rise,” Keith said. The last few years have been an improvement, though, with major events like last year’s deadly Pacific Northwest heat wave contributing to an increased awareness. “I think the big lesson is that there’s no place that’s safe from heat anymore. Every community will experience it a little bit differently, but no community is heat resilient yet,” he said.

Hot future

More and more communities will need to get to improved levels of such resiliency in the coming years. To understand how extreme heat might change in the future, Grid analyzed data released by the National Integrated Heat Health Information System that predicts how temperatures are expected to rise by 2050 over historical averages.

The data project that an extreme temperature belt is expected to emerge along the southern and central parts of the country, under a higher emissions model the federal government used in the last National Climate Assessment.

The analysis shows that about 2,500 counties in the United States have historically experienced at least one day a year above 95 degrees. But that’s expected to increase to more than 3,000 counties by 2050. Those additional areas are home to roughly 45 million Americans, or 17 million households, according to the Census Bureau.

About a third of the counties in the U.S. — roughly 1,100 — could experience more than 50 days with temperatures above 95 degrees by 2050, about seven times as many as the historical average. About 100 million people live in those counties today.

Scorched California

“September is increasingly becoming like a summer month” in parts of California, Swain said.

“The climate of the future is actually going to be worse than what we’re experiencing today,” Keith said, warning that it is problematic to look outside and try to adapt to the current situation, “because 2030 will be worse than what we’re experiencing today if we don’t get greenhouse gas emissions under control.”

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