Researchers are trying to determine the maximum temperature at which humans can survive in an increasingly warming world due to extreme heatwaves.
The heatwave in our country is intensifying. This weekend we are facing two days of a red heatwave alert valid in almost the entire country. Everyone is feeling the heat, even though resistance to high temperatures varies depending on several factors.
Climate change fuels extreme heatwaves, and scientists are trying to determine the limits of human survival in heatwave conditions. Recent studies indicate that the threshold for surviving extreme heat is much lower than some scientists knew years ago, as reported by NBC News.
Resistance to heat varies depending on several factors. However, a body temperature of 43 degrees Celsius cannot be tolerated - 99.9% of people who reach this body temperature would die, said Jennifer Vanos, an associate professor at the School of Sustainability at the University of Arizona.
This is the upper limit of survival. However, heat often kills in more subtle ways, by exacerbating pre-existing medical conditions such as cardiovascular or renal diseases, experts say.
Humidity is the key
People regulate their body temperature through sweating. "If the humidity outside is high, sweat does not evaporate, and the skin's surface cannot become cooler than its interior," explained Scott Denning, a climatologist and professor of atmospheric science at Colorado State University.
"Metabolic heat accumulates in the body and leads to very high fever, heatstroke, and death," he added.
Wet-bulb temperature
Scientists use a method called wet-bulb temperature to measure both heat and humidity simultaneously. The thermometer's bulb is covered with a wet material to evaporate heat and approximate the body's cooling through sweating.
"The wet-bulb temperature should be a few degrees lower than the body's internal temperature," Denning said. If the temperature measured by this method is higher than the body's internal temperature, then body heat cannot dissipate.
Based on a 2010 study, climate researchers established a wet-bulb temperature of 35 degrees Celsius as the upper limit for human survival and adaptability without cooling methods.
Even this maximum limit does not take into account other factors such as sun exposure, clothing worn, and physical exertion.
Elderly people are at the highest risk
Recent research suggests that the upper limits of human heat resistance are not realistic.
A 2022 study published in the Journal of Applied Physiology, which used data from tests conducted in a specially heated room, estimated that the wet-bulb temperature threshold could be closer to 30-31 degrees Celsius in young and healthy subjects.
Each person's survival limit is different, and factors such as age are essential, Vanos emphasizes.
Her research, published in Nature Communications, suggests that the physiological thresholds of heatstroke are much lower than previously thought, especially in dry heat conditions.
According to the study, most elderly people who cannot sweat efficiently are at serious risk if they stay continuously for six hours at temperatures above 46 degrees Celsius, even when in the shade and with low humidity.
"There will never be a single threshold for survival, and thinking so is dangerous," the researcher pointed out.
T.D.