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Pakistan heatwave

Patients suffering from heat stroke are treated at a hospital in Jacobabad, southern Sindh province, Pakistan on May 11, 2022. (Photo: Aamir Qureshi/AFP via Getty Images)

Heatwaves Rated 'Extremely Dangerous' Could Triple This Century, Warns New Climate Study

"Something that's gone from virtually never happening before," said one Harvard researcher, "will go to something that is happening every year."

Brett Wilkins

As record-breaking high temperatures and historic droughts afflict millions of people around the world, a study published Thursday warned that by the end of the century, dangerous heat driven by the worsening climate emergency will hit much of the Earth at least three times more often than today.

"The kinds of deadly heatwaves that have been rarities in the midlatitudes will become annual occurrences."

The study—conducted by climate researchers at Harvard University and the University of Washington and published in the journal Nature Climate Change—shows how changes in the heat index driven by human carbon dioxide emissions will dramatically increase exposure to "dangerous" and "extremely dangerous" temperatures. The heat index is a measure of how hot it really feels, based on temperature and relative humidity.

The U.S. National Weather Service defines heat index temperatures over 103°F as "dangerous" and over 124°F as "extremely dangerous."

Study co-author David Battisti explained to The Conversation that "'dangerous' in this case refers to the likelihood of heat exhaustion. Heat exhaustion won't kill you if you're able to stop and slow down—it's characterized by fatigue, nausea, a slowed heartbeat, possibly fainting. But you really can't work under these conditions."

"If a person gets to 'extremely dangerous' temperatures, that can lead to heat stroke," he added. "At that level, you have a few hours to get medical attention to cool your body down, or you die."

The study's abstract states that "even if the Paris agreement goal of limiting global warming to 2°C is met, the exposure to dangerous heat index levels will likely increase by 50-100% across much of the tropics and increase by a factor of 3-10 in many regions throughout the midlatitudes."

"Without emissions reductions more aggressive than those considered possible by our statistical projection, it is likely that by 2100, many people living in tropical regions will be exposed to dangerously high heat index values during most days of each typical year, and that the kinds of deadly heatwaves that have been rarities in the midlatitudes will become annual occurrences," the summary continues.

Midlatitude places the study says will experience a 3- to 10-fold increase in heat index levels include the United States, Western Europe, and China. Parts of all three places are currently gripped by either historic drought, record temperatures, or both

Climate scientists stress that the severity of future heatwaves depends on whether humanity can sufficiently reduce greenhouse gas emissions.  

Study lead author Lucas Vargas Zeppetello—whose team conducted much of its research in Washington state during last summer's historic heatwavetold The Guardian that a failure to dramatically slash emissions "is just hugely consequential for billions of people, primarily throughout the Global South."

"So that's kind of the scary thing about this," Zeppetello said in a separate interview with the Associated Press. "Something that's gone from virtually never happening before will go to something that is happening every year."

On Thursday, the Climate Crisis Advisory Group (CCAG) said that "the record-breaking heatwave experienced across Europe this summer will be considered an 'average' summer by 2035, even if countries meet their current climate commitments" under the Paris agreement.

"In the aftermath of the 2003 European heatwave, which is estimated to have killed over 70,000 people, I predicted that such temperatures, so exceptional at the time, would become the norm under continued emissions," Peter Stott, a professor at the U.K. Meteorological Office's Hadley Center, said in response to the new CCAG findings.

"That prediction has now been realized," he added. "The risks of extreme weather, including fires, drought, and flash floods, will keep increasing rapidly unless emissions of greenhouse gases are reduced substantially."

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