The highest temperature and humidity levels that a human body can withstand have been determined by scientists.
When combined with 100% humidity, even a healthy young individual will die after surviving six hours of heat of 35 degrees Celsius (95 degrees Fahrenheit), but new research indicates that threshold may be far lower.
When perspiration, the body’s primary mechanism for lowering its internal temperature, reaches this point, it can no longer evaporate off the skin, which finally results in heatstroke, organ failure, and death.
Only a handful of times—mostly in South Asia and the Persian Gulf—has this critical limit—which is reached at 35 degrees of what is known as “wet bulb temperature”—been exceeded, according to Colin Raymond of NASA’s Jet Propulsion Laboratory.
According to Raymond, who oversaw a significant study on the subject, none of those occurrences lasted longer than two hours, indicating that there have never been any “mass mortality events” connected to this limit of human existence.
According to specialists, everyone has a varied threshold for excessive heat depending on their age, health, and other social and economic circumstances. excessive heat does not even need to reach that level to cause death.
In Europe, for instance, where there is rarely enough humidity to produce deadly wet bulb temperatures, more than 61,000 people are reported to have perished as a result of the heat last summer.
The warmest month ever recorded was last month, which was confirmed on Tuesday, but scientists warn that dangerous wet bulb events will also grow more frequent as global temperatures rise.
In the previous 40 years, the frequency of these occurrences has at least doubled, according to Raymond, who called the growth a severe risk of human-caused climate change.
According to Raymond’s research, if global temperatures rise by 2.5°C over preindustrial levels, wet bulb temperatures will “regularly exceed” 35°C at a number of locations around the world in the ensuing decades.
Wet bulb temperature was once determined by placing a wet cloth over a thermometer and exposing it to the air, despite the fact that it is now mostly computed using heat and humidity readings.
This made it possible to gauge how rapidly sweat from the skin dissipated after being soaked into the cloth.
The theoretical threshold for human survival is 35°C wet bulb temperature, which corresponds to 46°C at 50% humidity or 35°C of dry heat.
Researchers from Pennsylvania State University in the US examined the core temperatures of young, healthy individuals within a heat chamber to test this limit.
They discovered that participants’ bodies could no longer prevent their core temperatures from rising over their “critical environmental limit” at 30.6°C wet bulb temperature, much below the previously hypothesized 35°C.
Before such conditions would reach “really, really dangerous core temperatures,” the team predicted it would take five to seven hours, according to Daniel Vecellio, a researcher on the project, who spoke to AFP.
The most vulnerable
According to Joy Monteiro, an Indian scientist who published a paper in Nature last month on wet bulb temperatures in South Asia, the majority of dangerous heatwaves in the area were considerably below the wet bulb threshold of 35°C.
There are “wildly different limits on human endurance for different people,” he told AFP.
Children in particular do not live in a vacuum, according to Ayesha Kadir, a pediatrician in the UK and health advisor for Save the Children.
She claimed that young children are more at risk since they are less able to control their body temperature.
The most at risk are older persons, who have fewer sweat glands. Last summer, over 65s accounted for over 90% of the heat-related deaths in Europe.
Additionally, those who must work outside in sweltering weather are particularly vulnerable.
Another important consideration is whether or if individuals can occasionally chill off, such in air-conditioned areas.
As Monteiro noted, those without access to restrooms frequently consume less water, which can cause dehydration.
The people who are least able to protect themselves from these extremes would suffer the most, as is true of many climate change effects, according to Raymond.
His research has demonstrated that in the past, wet bulb temperatures have been driven upward by El Nino weather occurrences. The climax of this year’s first El Nino event in four years is anticipated.
According to Raymond, the temperatures of wet bulbs are closely related to those of the ocean’s surface.
According to the climate observatory of the European Union, the temperature of the world’s oceans reached a record high last month, breaking the previous record set in 2016.