Extremely Hot, Humid Weather Could Kill a Person Far More Easily Than We Thought

Theory predicts that the human body won't be able to handle much heat and humidity.

One of the first studies to assess humid heat stress among young people found that the upper limit of human ability is just 31 degrees C.

The threshold is probably even lower for older people.

The wet-bulb temperature is the amount of heat and humidity in the air relative to one another.

The human body can't tolerate hot and humid climates as well. At 100 percent humidity, sweat cannot evaporate as easily as it can at 70 percent.

In a dry environment, the human threshold for survival is around 50 C, but for a humid environment, it's only 31 C.

Death is inevitable when exposed to such conditions.

If we know what the upper temperature and humidity limits are, we can better prepare people for a heat wave.

It could mean setting up an alert to go out to a community when a heatwave is coming, or developing a chart that provides guidance for different temperature and humidity ranges.

The threat of exceeding wet-bulb temperature thresholds becomes more likely as climate change drives excessive global warming and water evaporation. Especially in the tropics.

Climate scientists suspect that by the end of the century, Pakistan, India, and parts of Southeast Asia, the Persian Gulf and Central America will experience max humidity levels at temperatures over 35 degrees.

The cut-off is based on how much heat and humidity the human body can tolerate. Real-word data has been lacking so far.

Researchers recruited 24 young and healthy adults between 18 and 34 years of age to figure out the wet-bulb temperature at which humans are at risk of heat stroke and potential death.

The team started with a young and fit group of humans. Older people, pregnant people and other vulnerable people are not able to tolerate heat and humidity.

Participants swallowed a recording device to measure their core body temperatures before entering a chamber with variable temperature and humidity levels.

As the temperature and humidity of the chamber increased, participants were asked to slowly cycle on a stationary exercise bike.

The experiment was stopped when the participant couldn't maintain a core temperature.

Critical wet-bulb temperatures ranged from 30 to 31 degrees C, although they could be a little higher if the person is not moving a muscle.

The fact that this threshold is so low compared to previous estimates, even for young and fit participants, is worrisome.

In 2020, several cities in Pakistan recorded wet-bulb temperatures.

Statistics show older people are more likely to die from exposure than young people.

In humid parts of the world, we should start to worry about young people, even if they are healthy.

The climate is changing so there will be more heat waves. There are going to be more older adults as the population changes. It is important to study the confluence of those two shifts.

The study was published in a journal.