Even short-term exposure to high heat and humidity can push the human body past its limits, according to new lab experiments that tested how long people could endure extreme temperatures.
Sachi Kitajima Mulkey reports for Grist.
In short:
- Scientists exposed participants to nine hours of extreme heat and humidity to test when the body can no longer cool itself. The threshold—known as “uncompensable” heat stress—occurred between 26 and 31°C wet bulb temperature, lower than the previously assumed 35°C.
- With global temperatures already breaching 1.5°C of warming, researchers warn that even 2°C of warming could render large parts of the planet dangerous for human health, especially for older adults and those without access to cooling.
- Heat-related deaths have already more than doubled in the U.S. over the past two decades, and in 2023 alone, more than 47,000 Europeans died from extreme heat, particularly in Mediterranean regions.
Key quote:
“People already die from heat waves now. So regardless of what happens to the climate of the future, it’s important to understand, right now, what are these thresholds above which we start to see greater risk of heat related illness and death?”
— Tony Wolf, assistant professor at the University of Georgia
Why this matters:
Once considered survivable, combinations of temperature and moisture now push the human body past its limit faster, particularly in older adults, those with pre-existing health conditions, or people without access to reliable cooling. This means that even modest increases in average temperatures can have devastating effects on public health, especially in urban heat islands and already scorching regions like South Asia and the Middle East. Outdoor workers, the elderly, and communities lacking infrastructure are increasingly vulnerable to heat-related illnesses, kidney failure, and death. These findings shift our understanding of climate change from a future threat to a present emergency.
