As deaths increase, how climate change is making heat more dangerous

: [POST-BROADCAST CORRECTION: An earlier version of this story incorrectly reversed the labels of the parts of the “hockey stick” graph which illustrates the increase in temperatures resulting from climate change. The shaft of the stick represents steady temperatures over decades while the blade of the stick represents the sharp temperature increase in recent years.]

A MARTÍNEZ, HOST:

Heat-related deaths in the U.S. have more than doubled in the last 20 years. That's according to a new analysis in the medical journal JAMA. As Alejandra Borunda with NPR's climate desk reports, human-caused climate change has made heat more dangerous.

ALEJANDRA BORUNDA, BYLINE: Jeff Kulow knows heat. He used to be homeless in Fresno, Calif., in the brutally hot Central Valley.

JEFF KULOW: We tried it outside. We've had plenty of outside we want (laughter).

BORUNDA: He and his partner decided to leave and go someplace cooler. So they went to Portland, Ore., where they got an apartment. And on this day, it's 100 degrees outside.

KULOW: We can - we get the air - it's clean - and two air conditioners. I mean, fans - we're comfortable in here.

BORUNDA: Put Kulow knows people back in Fresno that died from heat. That's a growing risk as human-caused climate change makes hot weather more intense across the country. And the risks are growing quickly. Jeffrey Howard is a public health expert at the University of Texas at San Antonio. He led the analysis. And Howard says something really surprised him.

JEFFREY HOWARD: The dramatic change in the trajectory of the data.

BORUNDA: In the early 2000s, the number of officially reported heat deaths hovered in the hundreds. But by the late 2010s, it shot up. Last year had more than 2,300. That's the most ever recorded. And Howard says there was a clear turning point.

HOWARD: Things really started to change after 2015.

BORUNDA: There's a famous graph in climate science. It's called the hockey stick. It shows Earth's temperatures over hundreds of years. They were steady for a long time. So think of that as the blade of the hockey stick. Then temperatures go way up fast from climate change. That's the handle of the stick. Here's Howard again.

HOWARD: Well, this is a new hockey stick. It has the same shape, but it's measured in human lives lost and not in temperature.

BORUNDA: Climate change is making it hotter for longer in places like Texas, where he lives. The other day, he says...

HOWARD: It was 107, and the heat index was something like 115.

BORUNDA: And it's not just Texas. The last few years have been some of the hottest on record in the U.S., including in Portland, Ore., where Jeff Kulow now lives. Just a few years ago, a heat wave killed dozens of people there. But Kulow says he'd rather be in Portland than outside in Fresno. And for now, his AC is keeping him safe.

Alejandra Borunda, NPR News.

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