As climate change leads to rising temperatures around the world, extreme heat is increasingly becoming a threat to health. The human body is re-silient, but it can only withstand to a limited extent. So what is the highest temperature humans can endure?
The answer is simple: a wet bulb temperature of 95 degrees Fahrenheit (35 degrees Celsius), according to a 2020 study in Science Advances journal. The wet bulb temperature is not the same as the air temperature you can see in your local forecaster or your favorite weather app, but the wet bulb temperature is measured with a thermometer covered with a cloth soaked in water and takes into account both heat & Humidity . The latter is important because with more water in the air, it is more difficult for sweat to evaporate from the body and cool a person.
If the humidity is low but the temperature is high, or vice versa, the wet bulb temperature is unlikely to approach the tipping point of the human body, said Colin Raymond, Postdoctoral fellow at NASA’s Jet Propulsion Laboratory studying about extreme heat. But when both humidity and temperature are very high, the wet bulb temperature can drop to dangerous levels. For example, if the air temperature is 115 F (46.1 C) and the relative humidity is 30%, the wet bulb temperature is only 87 F (30.5 C). But when the air temperature is 102 F (38.9 C) and the relative humidity is 77%, the wet bulb temperature is around 95 F (35 C).
The reason people cannot survive high temperatures and humidity is because they can no longer regulate their internal temperature. “If the wet bulb temperature rises above human body temperature, you can still sweat, but you won’t be able to. Cool your body down to the temperature it needs to function physiologically,” Raymond said.
At this point the body becomes hyperthermic above 104 F (40 C). This can lead to symptoms like a rapid pulse, a change in mental state, lack of sweating, fainting, and coma, according to the National Institutes of Health. .
However, a wet bulb temperature of 95 ° C does not lead to immediate death; It probably takes about 3 hours for this heat to be un-survivable, Raymond said. There’s no way to pinpoint the exact time, he said, but studies have attempted to estimate it by submerging human participants in hot water tanks and removing them. when his body temperature began to rise uncontrollably. There is also no way to confirm that 95 F is the exact wet bulb temperature that is un-survivable; Raymond estimated the actual number to be 93.2 ° F to 97.7 ° F (34 ° C to 36.5 ° C).
While no one can live in wet bulb temperatures above about 95 ° F, lower temperatures can also be fatal. Exercise & exposure direct sunlight make it easy to overheat. Old people; People with certain health conditions such as obesity; And people taking antipsychotics also cannot regulate their temperature, making it easier for heat to kill them. For example, people sometimes die in heat that doesn’t reach 95 ° F (35 ° C) wet bulb temperature.
Fortunately, air conditioning can save people from unbearable heat, but of course not everyone has access to it, and even in places where many people have air conditioning, the electrical grid may not be reliable, Raymond said. .
Few places in recorded history have reached 95 ° F wet-bulb temperature, according to the Science Advances study. The Indus Valley in central and northern Pakistan and the southern coast of the Persian Gulf have been hot spots since the late 1980s and 1990s. “There are places that already starting to-experience these conditions for an hour or two,” said Raymond. “And with global warming, that’s only getting more widespread.” Places at risk for these temperatures over the next 30 to 50 years include northwest Mexico, northern India, Southeast Asia, and West Africa, he added.
“Unfortunately, given the already stalled climate change, we will continue to warm up a little even if we no longer emit greenhouse gases today,” said Raymond. “I think it is inevitable that the places I mentioned will deal with this issue for the foreseeable future, and I hope that no more places will be added to this list.