John J. Kim/Chicago Tribune/AP
A bicyclist rides past a screen broadcasting a weather report at Daley Plaza in Chicago in August.
CNN
—
Large parts of the world, including China and the Midwestern United States, are on track to become too hot for humans to cope with, as accelerating global temperatures expose billions to heat and humidity so extreme that their bodies will not be able to now cope, according to a new study.
The researchers used temperature and humidity data together with climate models to analyze human exposure potentially lethal 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 “wet heat stresswith devastating consequences for human health, according to the study published on Monday in the journal Proceedings of the National Academy of Sciences. The world has already warmed around 1.2 degrees Celsius.
“Wet heat stress is a particularly challenging problem because it directly affects the human body and causes morbidity and mortality,” said Matthew Haber, study co-author and professor of atmospheric and planetary earth sciences at Purdue University.
When heat and humidity levels are high, sweat evaporates much more slowly than usual, meaning that its cooling effect is lost and the body may not be able to regulate its temperature. This can lead to heat exhaustion and heat stroke, which can cause heart attack and organ failure. The elderly, the very young and those with pre-existing conditions are more vulnerable to heat illness.
Temperatures exceeding human tolerance have only been breached a few times in human history and for a few hours each time in the Middle East and Southeast Asiaaccording to the report.
But as temperatures continue to rise, many more will be exposed for much longer periods, the study found.
While countries have pledged to limit global warming below 2 degrees Celsius, with a target of 1.5 degrees Celsius, way off track. Even if global climate pledges are met – something the world is not currently on track for – temperatures are expected to rise between 2.1 and 2.9 degrees Celsius, according to recent UN report.
Asim Hafeez/Bloomberg/Getty Images
Climate change has made the extreme temperatures that hit northwestern India and Pakistan in April and May more than 100 times more likely, and has also increased the chances that such heatwaves will occur more often by the end of the century.
Above 2 degrees of warming, 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 experience long hours of heat and humidity per year that exceed human levels. tolerance.
People in these areas will be even more vulnerable, as many do not have access to air conditioning or other ways to cool down, 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 people exposed to life-threatening heat and humidity. “It's really incredibly disturbing,” Huber told CNN.
Wet heat waves will affect areas of the world that are not used to such extreme conditions.
The Midwestern United States will turn into a “wet heat stress hotspot” at 3 degrees of warming, according to the report. The Midwest is susceptible to this kind of heat stress in part because its climate straddles the line between dry and wet, Huber explained, allowing the region's heat to push into the danger zone on very humid days.
Another factor that makes the region vulnerable is its agriculture and the phenomenon called “corn sweatHuber said.
“The plants we eat sweat through evapotranspiration and that can add moisture above what would normally be there,” he said.
So-called “hot spots” — periods when heat and humidity are especially life-threatening — will be concentrated in the Missouri and Mississippi River valleys, but also elsewhere in the U.S., including the Gulf and Atlantic coasts. according to the study.
Charlie Riedel/AP
A man cools off in a mister at Kauffman Stadium as temperatures approach 100 degrees Fahrenheit before a baseball game between the Kansas City Royals and Cleveland Guardians on June 28, 2023, in Kansas City, Missouri.
At 4 degrees of warming, the study's worst-case scenario, the researchers found that 1.5 billion people worldwide would experience a month of wet heat stress each year, and 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, rendering it virtually uninhabitable.
“All over the world, official strategies for climate adaptation focus only on temperature,” said Qinqin Kong of Purdue University and a co-author of the study. “But this research shows that humid heat will be a much bigger threat than dry heat.”
Keeping the heating below 2 degrees Celsius Reducing global warming pollution will sharply reduce global exposure to life-threatening heat and humidity, according to the report.
“Every tenth degree or so then plays a role, and we want to reduce the warming as fast as we can,” Daniel Vecellio, the study's lead author and a postdoctoral researcher at George Mason University, told CNN. “If we get to these emissions reductions faster, here are all the people we can save, here are all the lifestyles that don't have to change.”
Kim Cobb, a climate scientist at Brown University who was not involved in the study but was lead author on the latest Report of the UN Intergovernmental Panel on Climate Change, said the study's conclusions are “compelling” but not surprising. “Extreme heat is already responsible for countless deaths worldwide every year,” Cobb told CNN.
“It is important to underline, as this study does, that heat is not an equal opportunity killer. It disproportionately kills people in lower-income communities, often communities of color. This is true both here in the US and around the world.”
