The Temperature the Human Body Cannot Survive

One recent case of extreme heat threatening health came at a jamboree in South Korea, where hundreds of scouts fell ill. ANTHONY WALLACE / AFP/File
One recent case of extreme heat threatening health came at a jamboree in South Korea, where hundreds of scouts fell ill. ANTHONY WALLACE / AFP/File
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The Temperature the Human Body Cannot Survive

One recent case of extreme heat threatening health came at a jamboree in South Korea, where hundreds of scouts fell ill. ANTHONY WALLACE / AFP/File
One recent case of extreme heat threatening health came at a jamboree in South Korea, where hundreds of scouts fell ill. ANTHONY WALLACE / AFP/File

Scientists have identified the maximum mix of heat and humidity a human body can survive.

Even a healthy young person will die after enduring six hours of 35-degree Celsius (95 Fahrenheit) warmth when coupled with 100 percent humidity, but new research shows that threshold could be significantly lower.

At this point sweat -- the body's main tool for bringing down its core temperature -- no longer evaporates off the skin, eventually leading to heatstroke, organ failure and death, said AFP.

This critical limit, which occurs at 35 degrees of what is known as "wet bulb temperature", has only been breached around a dozen times, mostly in South Asia and the Arabian Gulf, Colin Raymond of NASA's Jet Propulsion Laboratory told AFP.

None of those instances lasted more than two hours, meaning there have never been any "mass mortality events" linked to this limit of human survival, said Raymond, who led a major study on the subject.

But extreme heat does not need to be anywhere near that level to kill people, and everyone has a different threshold depending on their age, health and other social and economic factors, experts say.

For example, more than 61,000 people are estimated to have died due to the heat last summer in Europe, where there is rarely enough humidity to create dangerous wet bulb temperatures.

But as global temperatures rise -- last month was confirmed on Tuesday as the hottest in recorded history -- scientists warn that dangerous wet bulb events will also become more common.

The frequency of such events has at least doubled over the last 40 years, Raymond said, calling the increase a serious hazard of human-caused climate change.

Raymond's research projected that wet bulb temperatures will "regularly exceed" 35C at several points around the world in the coming decades if the world warms 2.5C degrees above pre industrial levels.

'Really, really dangerous'Though now mostly calculated using heat and humidity readings, wet bulb temperature was originally measured by putting a wet cloth over a thermometer and exposing it to the air.

This allowed it to measure how quickly the water evaporated off the cloth, representing sweat off of skin.

The theorized human survival limit of 35C wet bulb temperature represents 35C of dry heat as well as 100 percent humidity -- or 46C at 50 percent humidity.

To test this limit, researchers at Pennsylvania State University in the United States measured the core temperatures of young, healthy people inside a heat chamber.

They found that participants reached their "critical environmental limit" -- when their body could not stop their core temperature from continuing to rise -- at 30.6C wet bulb temperature, well below the previously theorized 35C.

The team estimated that it would take between five to seven hours before such conditions would reach "really, really dangerous core temperatures," Daniel Vecellio, who worked on the research, told AFP.

The most vulnerableJoy Monteiro, a researcher in India who last month published a study in Nature looking at wet bulb temperatures in South Asia, said that most deadly heat waves in the region were well below the 35C wet bulb threshold.

Any such limits on human endurance are "wildly different for different people," he told AFP.

"We don't live in a vacuum -- especially children," said Ayesha Kadir, a pediatrician in the UK and health advisor at Save the Children.

Small children are less able to regulate their body temperature, putting them at greater risk, she said.

Older people, who have fewer sweat glands, are the most vulnerable. Nearly 90 percent of the heat-related deaths in Europe last summer were among people aged over 65.

People who have to work outside in soaring temperatures are also more at risk.

Whether or not people can occasionally cool their bodies down -- for example in air conditioned spaces -- is also a major factor.

Monteiro pointed out that people without access to toilets often drink less water, leading to 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 shown that El Nino weather phenomena have pushed up wet bulb temperatures in the past. The first El Nino event in four years is expected to peak towards the end of this year.

Wet bulb temperatures are also closely linked to ocean surface temperatures, Raymond said.

The world's oceans hit an all-time high temperature last month, beating the previous 2016 record, according to the European Union's climate observatory.



US Tourist Arrested for Landing on Forbidden Indian Tribal Island

People sit outside medical stores along a street in Varanasi, India, on April 3, 2025. (Photo by Niharika KULKARNI / AFP)
People sit outside medical stores along a street in Varanasi, India, on April 3, 2025. (Photo by Niharika KULKARNI / AFP)
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US Tourist Arrested for Landing on Forbidden Indian Tribal Island

People sit outside medical stores along a street in Varanasi, India, on April 3, 2025. (Photo by Niharika KULKARNI / AFP)
People sit outside medical stores along a street in Varanasi, India, on April 3, 2025. (Photo by Niharika KULKARNI / AFP)

Indian police said on Thursday they had arrested a US tourist who sneaked onto a highly restricted island carrying a coconut and a can of Diet Coke to a tribe untouched by the modern world.

Mykhailo Viktorovych Polyakov, 24, set foot on the restricted territory of North Sentinel -- part of India's Andaman Islands -- in a bid to meet the Sentinelese people, who are believed to number only around 150.

All outsiders, Indians and foreigners alike, are banned from travelling within five kilometers (three miles) of the island to protect the Indigenous people from outside diseases and to preserve their way of life.

"The American citizen was presented before the local court after his arrest and is now on a three-day remand for further interrogation," Andaman and Nicobar Islands police chief HGS Dhaliwal told AFP.

Satellite photographs show a coral reef-fringed island -- stretching to some 10 kilometers (six miles) at its widest point -- with thick forest and white sand beaches.

The Sentinelese last made international headlines in 2018 after they killed John Allen Chau, 27, an American missionary who landed illegally on their beach.

Chau's body was not recovered and there were no investigations over his death because of the Indian law prohibiting anyone from going to the island.

India sees the wider Andaman and Nicobar Islands as strategically sited on key global shipping lanes. They are closer to Myanmar than mainland India.

New Delhi plans to invest at least $9 billion to expand naval and air bases, troop accommodations, the port and the main city in the region.

Dhaliwal said Polyakov kept blowing a whistle off the shore of North Sentinel Island for about an hour to attract the tribe's attention before he went ashore.

"He landed briefly for about five minutes, left the offerings on the shore, collected sand samples, and recorded a video before returning to his boat," Dhaliwal said.

"A review of his GoPro camera footage showed his entry and landing into the restricted North Sentinel Island."

Police said Polyakov was arrested late on Monday, about two days after he went ashore, and had visited the region twice in recent months.

He first used an inflatable kayak in October 2024 but was stopped by hotel staff, police said on Thursday. Polyakov made another unsuccessful attempt during a visit in January 2025.

This time Polyakov used another inflatable boat with a motor to travel the roughly 35 kilometers (22 miles) of open sea from the main archipelago.

The Sentinelese, whose language and customs remain a mystery to outsiders, shun all contact and have a record of hostility to anyone who tries to get close.

A photograph issued by the Indian Coast Guard and Survival International two decades ago showed a Sentinelese man aiming a bow and arrow at a passing helicopter.

Indian authorities have prosecuted any locals who have aided attempts to enter the island and are trying to identify anyone who may have helped Polyakov.

The Andamans are also home to the 400-strong Jarawa tribe, who activists say are also threatened by contact from outsiders. Tourists have previously bribed local officials in a bid to spend time with the Jarawa.