Dangerous heat predicted to hit 3 times more times in the future

Dangerous heat predicted to hit 3 times more times in the future

What is officially considered “dangerous heat” in the coming decades is likely to hit much of the world at least three times as often as climate change worsens, according to a new study.

In much of Earth’s rich mid-latitudes, temperatures and humidity that look like 103 degrees (39.4 degrees Celsius) or higher — now an occasional summer shock — are statistically expected to happen 20 to 50 times a year by mid-century, he said. a study on Monday. in Communications Earth & Environment magazine.

By 2100, this brutal heat index could last most of the summer in places like the southeastern US, the study’s author said.

And it’s much worse for the sticky tropics. The study said a heat index considered “extremely dangerous” where the heat index appears to exceed 124 degrees (51 degrees Celsius) – now something that rarely happens – is likely to hit a tropical belt that includes India for one to four weeks a year. in the end century.

“So that’s kind of scary about it,” said study author Lucas Zeppetello, a climate scientist at Harvard. “This is something where potentially billions of people will be exposed to extremely dangerous levels of heat very regularly. So something that has practically never happened before will go into something that is happening every year.”

Zeppetello and his colleagues used more than 1,000 computer simulations to analyze the probabilities of two different levels of high heat — heat rates of 103 degrees (39.4 Celsius) and above 124 degrees (51 Celsius), which are dangerous thresholds and extremely dangerous according to the US National Weather Service. They calculated for the years 2050 and 2100 and compared how often this heat happened each year around the world from 1979 to 1998.

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The study found a three- to ten-fold increase in heat from 103 degrees in mid-latitudes, even in the unlikely best-case scenario of global warming limited to just 3.6 degrees (2 degrees Celsius) since pre-industrial times — let alone two international goals.

There’s only a 5% chance that warming is so low and so infrequent, the study found. Most likely, according to the study, heat of 103 degrees will vaporize the tropics “during most days of every typical year” by 2100.

Chicago reached that 103-degree heat index level just four times from 1979 to 1998. But the study’s most likely scenario shows Chicago hitting that hot, sticky threshold 11 times a year by the end of the century.

Heat waves are one of the new four horsemen of apocalyptic climate change, along with rising sea levels, water shortages and changes to the overall ecosystem, said Zeppetello, who did much of the research at the University of Washington during the heat of 2021. wave that broke records and killed thousands.

“Unfortunately, the dire predictions shown in this study are believable,” climate scientist Jennifer Francis of the Woodwell Climate Research Center, who was not part of the study team, said in an email. “The past two summers have provided a window into our steamy future, with lethal heatwaves across Europe, China, Northwest North America, India, South Central US, UK, Central Siberia and even New England. Already hot places will become uninhabitable as heat rates exceed dangerous limits, affecting humans and ecosystems. Areas where extreme heat is now rare will also increasingly suffer as infrastructure and living things are ill-adapted to the crushing heat.”

The study focuses on the heat index, and that’s smart because it’s not just the heat, but the combination with humidity that harms health, said Harvard School of Public Health professor Dr. Renee Salas, ER doctor.

“As the heat index increases, it becomes increasingly difficult to cool our bodies,” Salas, who was not part of the research team, said in an email. “Heat stroke is a potentially deadly form of heat illness that occurs when body temperature rises to dangerous levels.”

The study is based on mathematical probabilities rather than other climate research that looks at what happens at various levels of carbon pollution. Because of this, University of Pennsylvania climate scientist Michael Mann is more skeptical of this research. It also doesn’t take into account US climate legislation that President Joe Biden signed into law earlier this month or new efforts by Australia, he said.

“The obstacles at this point are political and not statistical methods, regardless of how powerful or sophisticated they might predict whether we will muster the political will to overcome them,” Mann said in an email. “But there are reasons for cautious optimism.”

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Follow Seth Borenstein on Twitter at @borenbears

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