The US Midwest could be a hotspot for deadly “moist heat stress” as global temperatures rise

CNN
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Large parts of the world, including China and the Midwestern United States, are on track to become too hot for humans to handle, as accelerating global temperatures expose billions to such heat and humidity that their bodies will no longer be able to adapt, according to For a new study. Stady.

The researchers used temperature and humidity data combined with climate models to analyze humanity's exposure to potentially deadly heat as the world warms, and looked at a range of temperature rises from 1.5°C to 4°C above pre-industrial levels.

They found that if temperatures rise above 2 degrees Celsius, 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 about 1.2 degrees Celsius.

“Heat-moist stress is a particularly challenging problem because it affects the human body directly, causing illness and mortality,” said Matthew Huber, co-author of the study and professor of atmospheric and planetary sciences at Purdue University.

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

The report stated that temperatures exceeding human endurance have only been exceeded a few times in human history, and for several hours at a time in the Middle East and Southeast Asia.

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

Although countries have committed to limiting global warming to no more than 2 degrees Celsius, with a goal of reaching 1.5 degrees Celsius, they are still far from the right track. Even if global climate pledges are met – which the world is not currently on track to do – temperatures are expected to rise by between 2.1 and 2.9 degrees Celsius, according to a recent United Nations report.

More than 2 degrees of warming, the 2.2 billion people living in Pakistan and India's Indus River Valley, 1 billion people in China, and 800 million people in sub-Saharan Africa will face long hours of heat and humidity annually that exceed human tolerance levels. .

The report indicated that people in these areas will be more vulnerable because many of them do not have access to air conditioners or other methods of cooling.

At 3 degrees — which the study authors say is the most likely level for temperatures to rise by 2100 if no action is taken — there is a sharp increase in the number of people exposed to life-threatening heat and humidity. “It's really very disturbing,” Hopper told CNN.

Humid heat waves will affect large areas of the world that are not accustomed to such extreme conditions.

According to the report, the US Midwest will become a “moist heat stress hotspot” when temperatures rise by 3 degrees. The Midwest is vulnerable to this type of heat stress, Hooper explained, in part because its climate walks the line between dry and wet, allowing the region's heat to be pushed into the danger zone on extremely humid days.

Another factor that makes the area vulnerable is its agriculture and the “corn race” phenomenon, Hooper said.

“The plants we eat sweat through evaporation, and this may increase the humidity above what is normal,” he said.

According to the study, so-called “hot hours” — times when heat and humidity are particularly life-threatening — will be concentrated in the Missouri and Mississippi River valleys but also elsewhere in the United States including the Gulf Coast and Atlantic Coast.

At a 4-degree rise in temperatures, the study's worst-case scenario, the researchers found that 1.5 billion people around the world would face a month of humid heat stress each year, and nearly 2.7 billion people would face at least a week of these extreme conditions.

Parts of Yemen can be exposed to heat and humidity beyond human tolerance for more than 300 days a year, making them virtually uninhabitable.

“Around the world, official weather adaptation strategies focus solely on temperature,” Chenqin 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.”

The report found that keeping temperature rise below 2 degrees Celsius by reducing planet-warming pollution would significantly reduce global exposure to life-threatening heat and humidity.

“Every tenth of a degree or something like that after that plays a role, and we want to reduce global warming as quickly as possible,” Daniel Vecellio, the study's lead author and a postdoctoral researcher at George Mason University, told CNN. “If we get to cutting emissions faster, here's all the people we can save, here's all the lifestyles that don't need to change.”

Kim Cobb, a climate scientist at Brown University who was not involved in the study but was the lead author of the latest UN Intergovernmental Panel on Climate Change report, said the study's conclusions 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 an equal opportunity killer. It disproportionately kills people in low-income communities, often communities of color. This is as true here in the United States as it is around the world.” ”