Scientists identify mix of heat, humidity a human body can survive
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When combined with 100% humidity, even a healthy young individual would die after surviving six hours of heat of 35 degrees Celsius; however, new research suggests that threshold may be far lower.
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A man puts on his shirt in Madrid, Spain, on June 24, 2023, where temperatures rose to 35C with the weather that was expected to become hotter in the coming months. (AP)
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.
Sweat, the body's primary cooling mechanism, can no longer drain from the skin at this stage, which finally results in heatstroke, organ failure, and death.
Only about a dozen times had this critical limit -- which is violated at 35 degrees of what is known as "wet bulb temperature" -- been exceeded, largely in South Asia and the Persian Gulf, 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.
However, excessive heat does not need to reach that level in order to cause death, and experts claim that everyone has a varied threshold depending on their age, health, and other social and economic circumstances.
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 2.5C over preindustrial levels, wet bulb temperatures will "regularly exceed" 35C in various locations throughout the world in the ensuing decades.
'Really, really dangerous'
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 measured 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 theorized human survival limit of 35C wet bulb temperature shows 35C of dry heat and 100 percent humidity -- or 46C at 50% humidity.
Researchers from Pennsylvania State University in the United States monitored the core temperatures of young, healthy individuals within a heat chamber to test this limit.
They discovered that participants achieved their "critical environmental limit" -- the point at which their bodies could no longer prevent their core temperatures from rising -- at 30.6C wet bulb temperature, significantly below the previously theorized 35C.
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.
Risky for young children and over 65s
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 occurred considerably below the wet bulb threshold of 35C.
There are "wildly different limits on human endurance for different people," he told AFP.
"We don't live in a vacuum -- especially children," said Ayesha Kadir, a health advisor at Save the Children and paediatrician in the UK.
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 individuals since they have fewer sweat glands. Over 65s accounted for almost 90% of the heat-related deaths in Europe last summer.
Additionally, those who must work outside in sweltering weather are particularly vulnerable.
Another important consideration is whether or not people can occasionally chill off, as in air-conditioned environments.
As Monteiro noted, those without access to restrooms frequently consume less water, which can cause dehydration.
"Like a lot of impacts of climate change, it is the people who are least able to insulate themselves from these extremes who will be suffering the most," Raymond said.
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.
He added that the temperatures of wet bulbs are closely related to those of the ocean's surface.
According to the EU's climate observatory, the temperature of the world's oceans reached a record high last month, breaking the previous record set in 2016.
