Too Hot to Live: Coming Sooner Than you Think

At 2° C global warming, most of a billion people will be experiencing periods where it is simply too hot to live unprotected, outside.
But, not too hot to fight, methinks.
No word on what happens to other living things in this scenario.

Washington Post:

Heat waves can already be deadly for the most vulnerable people — but in a warming world, temperatures and humidity will, for growing stretches of every year, surpass a threshold that even young and healthy people could struggle to survive, according to new research published Monday.

Lahore, Pakistan, already an epicenter of human ills linked to climate change, could surpass that survivability threshold for two or three weeks out of the year by the middle of the century, for example, the study in the Proceedings of the National Academy of Sciences found. Under the most dramatic global warming scenarios, it could last for months.

In the Red Sea port of Al Hudaydah, Yemen, such oppressive conditions are expected to last a month or two — or, at the highest levels of global warming projections, would endure for most of the year, scientists found.

The research is the latest to build upon the idea that there is a limit to how much heat and humidity the human body can withstand, that it is likely lower than once thought, and that exposure to it will increase dramatically in the coming decades. The hottest parts of the planet have already surpassed it for brief periods, at least.

That doesn’t mean those places are already “unlivable” for humans, said Daniel Vecellio, the study’s lead author. But they could soon be, if their changing climates mean long stretches without respite from intense heat and humidity, he said.

“It’s when you see these accumulations of weeks or months of this at a time that things become ‘too hot for humans,’” said Vecellio, a postdoctoral researcher at George Mason University’s Virginia Climate Center.

Research has already found increasing likelihood of heat waves that could overwhelm the body’s ability to cool itself. A similar study published in September found that some 200 weather stations around the world have already at times surpassed the threshold. In places like Europe and North America, where people aren’t acclimated to intense heat, temperatures and humidity could surpass the survivability threshold a couple of times a decade even for the most conservative warming estimates.

Greatly enhanced risk to humans as a consequence of empirically determined lower moist heat stress tolerance – Vecellio et al, October 9, 2023, PNAS:

Increased heat and humidity potentially threaten people and societies. Here, we incorporate our laboratory-measured, physiologically based wet-bulb temperature thresholds across a range of air temperatures and relative humidities, to project future heat stress risk from bias-corrected climate model output. These vulnerability thresholds substantially increase the calculated risk of widespread potentially dangerous, uncompensable humid heat stress. Some of the most populated regions, typically lower-middle income countries in the moist tropics and subtropics, violate this threshold well before 3 °C of warming. Further global warming increases the extent of threshold crossing into drier regions, e.g., in North America and the Middle East. These differentiated patterns imply vastly different heat adaption strategies. Limiting warming to under 2 °C nearly eliminates this risk.

Post again:

Past research found that transfer of heat could no longer occur at 35 degrees Celsius (95 Fahrenheit) on what is known as the wet bulb temperature scale, which factors in both temperature and humidity. (Unlike the heat index, which also factors in both heat and humidity, the wet bulb temperature is not designed to be interpreted as a measure of how hot it feels outside.)

But, in a study published last year, the Penn State researchers found that threshold to be closer to a wet bulb temperature of 31 degrees Celsius (88 Fahrenheit) for a sample of young and healthy research subjects who were not accustomed to such muggy conditions. Hours of exposure to such heat could trigger illness or death if people are unable to seek shade or air conditioning, drink water or otherwise find a way to cool themselves down, the researchers found.

Reuters:

While India, Pakistan and the Gulf already have briefly touched dangerous humid heat in recent years, the study found it will afflict major cities from Lagos, Nigeria, to Chicago, Illinois if the world keeps heating up.

“It’s coming up in places that we didn’t think about before,” said Vecellio, highlighting rising risk in South America and Australia.

At 4C of warming, Hodeidah, Yemen, would see around 300 days per year of potentially unsurvivable humid heat.