Environment

Extreme heat is already creating “non-survivable” conditions for humans in heatwaves that have killed thousands and likely many more, according to new research that warns people are more susceptible to rising temperatures than first thought.

Scientists re-examined six extreme heatwaves between 2003 and 2024 and found that when temperature, humidity and the body’s ability to stay cool were accounted for, all were potentially deadly for older people.

The absolute limit for humans to survive had been assumed to be a six-hour exposure to a wet bulb temperature of 35C – a measure that accounts for temperature and humidity but has rarely been observed on the planet at that level.

Heatwaves in Mecca (Saudi Arabia, 2024), Bangkok (Thailand, 2024), Phoenix (United States, 2023), Mount Isa (Australia, 2019), Larkana (Pakistan, 2015) and Seville (Spain, 2003) had seen thousands of deaths despite none approaching that wet bulb limit, the research found.

But when scientists applied a new model of human survivability that takes into account the body’s ability to function and stay cool depending on age, they found all six events had seen non-survivable periods for older people who could not find shade.