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US Midwest Could Be Deadly ‘Damp Heat Stress’ Hotspot As Global Temperatures Rise


Large parts of the world, including China and the US Midwest, are on the verge of becoming too hot for humans to cope, as accelerating global temperatures expose billions of people to extreme heat and humidity so extreme that their bodies will no longer be able to cope with it, according to a new study. study.

Researchers used temperature and humidity data as well as climate models to analyze humanity’s exposure to potentially deadly heat as the world warms, looking at a range of temperature increases from 1.5 degrees Celsius to 4 degrees Celsius above pre-industrial levels.

They found that above 2 degrees Celsius of warming, a significant portion of the world’s population will be vulnerable to “moist heat stress” with devastating consequences for human health, according to the study published Monday in the journal Proceedings of the National Academy of Sciences. The world has already warmed by around 1.2 degrees Celsius.

“Damp heat stress is a particularly complex problem because it directly affects the human body and leads to morbidity and mortality,” said Matthew Huber, study co-author and professor of atmospheric and planetary sciences at Earth at Purdue University.

When heat and humidity levels are high, sweat evaporates much more slowly than usual, meaning its cooling effect is lost and the body may become unable to regulate its temperature. This can lead to heat exhaustion and heat stroke, which can cause heart attacks and organ failure. The elderly, the very young, and those with pre-existing health conditions are most vulnerable to heat-related illness.

Temperatures that exceed human tolerance have only been exceeded a few times in human history, and for a few hours in both the Middle East and Southeast Asia, the report said.

But as temperatures continue to rise, more people will be exposed and for much longer periods, the study found.

While countries have committed to limiting global warming to below 2 degrees Celsius, with a target of 1.5 degrees Celsius, they are far from on track. Even if global climate commitments are met – something the world is not currently on track to do – temperatures are expected to rise between 2.1 and 2.9 degrees Celsius, according to a recent report from the UN.

Above 2 degrees of warming, 2.2 billion people living in Pakistan and India’s Indus Valley, 1 billion people in China, and 800 million people in sub-Saharan Africa will experience many hours of heat each year. heat and humidity beyond human tolerance levels. .

Residents in these areas will be even more vulnerable because many do not have access to air conditioning or other means of cooling, the report notes.

At 3 degrees – which the study authors say is the most likely level of warming by 2100 if no action is taken – there is a sharp increase in the number of people exposed to extreme heat and potentially fatal humidity. “It’s really incredibly disturbing,” Huber told CNN.

Humid heatwaves will affect parts of the world that are not used to such extreme conditions.

The US Midwest will become a “humid heat stress hotspot” with 3 degrees of warming, according to the report. The Midwest is susceptible to this type of heat stress in part because its climate falls between dry and humid, Huber explained, allowing the region’s heat to enter the danger zone on very humid days.

Another factor that makes the region vulnerable is its agriculture and the phenomenon called “corn sweat,” Huber said.

“The plants we eat transpire through evapotranspiration, which can increase humidity above what would normally be present,” he said.

So-called “hot hours” – periods when heat and humidity are particularly dangerous to life – will be concentrated in the Missouri and Mississippi valleys, but also elsewhere in the United States, notably on the Gulf Coast Mexico and the Atlantic coast, according to the study.

A man cools off in a mist at Kauffman Stadium as temperatures approach 100 degrees Fahrenheit before a baseball game between the Kansas City Royals and the Cleveland Guardians on June 28, 2023, in Kansas City, Missouri.

With 4 degrees of warming, the study’s worst-case scenario, the researchers found that 1.5 billion people worldwide would face a month of humid heat stress each year, and that about 2.7 billion people would experience at least a week of these extreme conditions.

Parts of Yemen could experience heat and humidity beyond human tolerance for more than 300 days a year, making them virtually uninhabitable.

“Across the world, official weather adaptation strategies focus solely on temperature,” Qinqin Kong of Purdue University and co-author of the study, said in a statement. “But this research shows that moist heat will pose a much greater threat than dry heat.”

Keeping warming below 2 degrees Celsius by reducing pollution from global warming will significantly reduce global exposure to potentially deadly heat and humidity, the report said.

“Every tenth of a degree or something like that then plays a role, and we want to reduce the warming as quickly as possible,” Daniel Vecellio, lead author of the study and a postdoctoral researcher at George Mason University, told CNN. “If we can reduce these emissions faster, here are all the people we can save, here are all the lifestyles that don’t need to be changed.”

Kim Cobb, a climate scientist at Brown University who was not involved in the study but was a lead author of the latest report from the U.N. Intergovernmental Panel on Climate Change, said that the study’s findings are “compelling” but not surprising. “Extreme heat is already responsible for countless deaths around the world every year,” Cobb told CNN.

“It is important to emphasize, as this study does, that heat is not a destructive factor in equality of opportunity. It disproportionately kills people in low-income communities, often communities of color. This is as true here in the United States as it is anywhere in the world.


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