New research has found that humans are less able to tolerate hot and humid weather than previously thought. Even a temperature of 31 degrees Celsius can be potentially deadly for a healthy young person in high humidity. The human body is able to maintain its core temperature of 37 degrees Celsius through sweating and evaporative cooling, but when humidity is high, sweat cannot evaporate and cooling is ineffective. This can lead to heatstroke and even death. Previous medical understanding was that a healthy person could tolerate a cooling limit temperature of 35 degrees Celsius for around six hours, but this has now been shown to be too high.
Researchers from Pennsylvania State University conducted experiments on 24 healthy participants aged between 18 and 34, exposing them to different combinations of heat and humidity in climate chambers while monitoring their core and skin temperatures and sweat production. The results showed that the previous cooling limit temperature of 35 degrees Celsius was too high, with critical values being reached at much lower temperatures. At 100% humidity, the limit was 31 degrees Celsius. The study also found that a slight decrease in humidity did not increase heat tolerance, with critical cooling limit temperatures being reached at 25-28 degrees Celsius in hot, dry environments.
The implications of these findings are significant, particularly as climate change is expected to bring more frequent and intense heatwaves. The study suggests that regions with a cooling limit temperature above 31 degrees Celsius should be cause for concern, and that even young people may be at risk of heat exhaustion. The study also highlights the potential for large numbers of people to be affected by life-threatening heatwaves, with 1.2 billion people already living in regions where this is a risk. The critical cooling limit temperature is dependent on regional climate conditions, and therefore cannot be universally applied.
