Heatwaves are already pushing humans to the brink of survival, with a new study revealing that extreme heat is creating "non-survivable" conditions for humans, even in the absence of the previously thought "absolute limit" of a six-hour exposure to a wet bulb temperature of 35C. This alarming finding highlights the vulnerability of older people, who are more susceptible to rising temperatures than initially assumed.
The research, published in the journal Nature Communications, examined six extreme heatwaves between 2003 and 2024, including events in Mecca, Bangkok, Phoenix, Mount Isa, Larkana, and Seville. Despite none of these heatwaves reaching the wet bulb limit, the study found that older people faced non-survivable periods in full sun, even when they could find shade.
The key to this discovery lies in a new model of human survivability that takes into account the body's ability to function and stay cool depending on age. This model, developed by Prof Sarah Perkins-Kirkpatrick at the Australian National University, challenges the traditional reliance on temperature alone to define heatwaves.
"My first thought was 'oh shit' – I really didn’t expect to see that, especially when you zoom in to individual cities," Perkins-Kirkpatrick said. "If it’s already happening now, then what does a future that is two or three degrees warmer hold?"
The study's findings have profound implications, suggesting that heat-related deaths, particularly in developing and densely populated areas, are "undoubtedly and seriously underreported." Perkins-Kirkpatrick and her colleagues argue that the new model provides a more accurate understanding of how these events can be deadly, moving beyond statistical analysis.
Prof Ollie Jay, a co-author of the study, emphasizes the urgency of the situation: "Conditions that threaten human life are already here and the risk moving forward is almost certainly much greater than we previously thought."
The human body's ability to regulate its core temperature is crucial, relying on sweating and evaporation. However, high temperatures and humidity combine to reduce sweat evaporation, leading to heatstroke. Older people, especially those over 75, are particularly vulnerable due to their reduced ability to sweat.
Prof Steve Sherwood, a climate scientist at the University of New South Wales, underscores the importance of the new research in establishing the true limits of human survivability. He notes that the proximity to physiological limits means that mitigating higher temperatures is essential for humans to thrive in the hottest and most humid regions, including parts of Australia, India, and the Middle East.
"Global warming will really hurt if it goes too much further just due to the extreme temperatures and humidity, even if we manage rainfall, aridity, storm, and sea level changes," Sherwood warns. This highlights the need for urgent action to address the escalating risks posed by heatwaves and extreme temperatures.
