Dangerous and extremely dangerous heat stress to become more common by 2100

Record-breaking heat waves have occurred recently from Delhi to the Pacific Northwest, and the number of these deadly events is expected to increase. New research from the University of Washington and Harvard University gives a range of heat impacts worldwide by the end of this century, depending on future emissions of greenhouse gases.

The study was published Aug. 25 in the open-access journal Communications Earth & Environment.

“The record-breaking heat events of recent summers will become much more common in places like North America and Europe,” said lead author Lucas Vargas Zeppetello, who did the research as a doctoral student at the UW and is now a postdoctoral researcher at Harvard. “For many places close to the equator, by 2100 more than half the year will be a challenge to work outside, even if we begin to curb emissions.”

“Our study shows a broad range of possible scenarios for 2100,” he added. “This shows that the emissions choices we make now still matter for creating a habitable future.”

The study looks at a combination of air temperature and humidity known as the “heat index” that measures impact on the human body. A “dangerous” heat index is defined by the National Weather Service as 103 F (39.4 C). An “extremely dangerous” heat index is 124 F (51 C), deemed unsafe to humans for any amount of time.

“These standards were first created for people working indoors in places like boiler rooms — they were not thought of as conditions that would happen in outdoor, ambient environments. But we are seeing them now,” Vargas Zeppetello said.

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