Dramatic increase in deadly US heat waves now likely inevitable, but experts say there's still hope

Doyle Rice
  • Heat already kills more Americans each year than any other weather hazard.
  • The record-breaking heat events of recent summers will become much more common in places like North America and Europe.
  • The study looks at the “heat index,” which measures the impact of heat on the human body.

A dramatic increase in deadly heat waves is now probably inevitable, a study published Thursday says.

The authors say there's still hope that global temperature increases resulting from human-caused climate change can be curbed, which would avert even more catastrophic heat in some areas on Earth.

But even if the global temperature goals of the Paris Agreement on climate change are met, study authors warn that heat waves are destined to become more prevalent in coming decades.

"The frequency of extreme heat waves is likely to increase by 3 to 10 times by the end of the century, depending on where you live in the U.S.," study lead author Lucas Vargas Zeppetello told USA TODAY.

The authors say their results highlight the need to reduce future greenhouse gas emissions and to protect populations, especially outdoor workers, against dangerous heat. 

Heat already kills more Americans each year than any other weather hazard, including hurricanes, tornadoes and floods, according to the National Weather Service

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Record-breaking heat to become more common 

The findings suggest carbon dioxide emissions from human activity could drive increases in exposure to extreme temperatures in the coming decades, even if global warming is limited to 2 degrees C, in line with the Paris Agreement. 

“The record-breaking heat events of recent summers will become much more common in places like North America and Europe,” said Vargas Zeppetello, who did the research as a doctoral student at the University of Washington and is now a postdoctoral researcher at Harvard University.

High temperatures pose a threat to public health, with extreme heat contributing to heat cramps, heat exhaustion and chronic illnesses, according to the study. 

"This is especially dangerous for hot and humid places like the South and Eastern Seaboard, but we've seen the consequences of extreme heat on the West Coast as well, so there really is no place in the U.S. where this will not be an issue," Vargas Zeppetello said.

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People in equatorial regions will suffer even more

The forecast is even more ominous in other parts of the world:

“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," Vargas Zeppetello said.

In a worst-case scenario in which emissions remain unchecked until 2100, “extremely dangerous” conditions, in which humans should not be outdoors for any amount of time, could become common in countries closer to the equator – notably in India and sub-Saharan Africa."

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Dangerous heat index possible

The study looks at the “heat index,” which measures the effect of heat on the human body. A “dangerous” heat index is defined by the Weather Service as 103 degrees. An “extremely dangerous” heat index is 124 degrees, which is considered unsafe to humans for any amount of time.

According to study co-author David Battisti, a professor of atmospheric sciences at the University of Washington, the number of days with dangerous levels of heat in the southeastern and central U.S. will more than double by as soon as 2050.

"It’s extremely frightening to think what would happen if 30 to 40 days a year were exceeding the extremely dangerous threshold,” Vargas Zeppetello said. “These are frightening scenarios that we still have the capacity to prevent. This study shows you the abyss, but it also shows you that we have some agency to prevent these scenarios from happening."

The study is published in the British journal Communications Earth and Environment