Heatwaves in Asia tend to kill millions of people, while the maximum threshold of humid heat that humans can withstand is far exceeded.

HOT WEATHER – “To die of heat” is no longer just a saying in India and Pakistan. The two South Asian countries are experiencing heat wave unprecedented for two months. The temperature there is very hot and reached its peak this Wednesday 11th with over 50°C. The heat, combined with high humidity levels, already exceeded the threshold for survival for people who were outdoors for long periods of time.

This threshold, scientists estimate, is at 35 degrees “wet thermometer” (Tw) for a healthy person. This value takes into account the humidity of the air to measure our resistance to heat. The more humid the air, the more it is saturated with water, and the less efficient our sweat is. If the air humidity is 100%, our sweat no longer cools us down.

Obviously, the human body does not tolerate humid heat well. If humans can withstand temperatures of 100°C as long as the air is dry and the body can sweat, from 25°C in a humid zone, the air becomes unbreathable. This is also why you might tolerate the temperature of the sauna, which is higher, more easily than in the hammam.

Within six hours, the body gives up

Experiments show that a wet bulb temperature well below 35 degrees Celsius is fatal. A study about I’American Physiological Societyreleased in January 2022, measures the ability of healthy young adults to perform simple tasks in six different extreme weather conditions. Several hours of experimentation revealed that none of the participants reached the limit of 35° Tw. Boundary considered “high” by the authors, heat tolerance is much worse in the elderly or susceptible persons. At temperatures less than 35°C, without being able to cool down, in about six hours, the body dies. Under certain climatic conditions, deliquescence is even more rapid. As an example, in FranceDuring the 2003 heat wave, the humidity did not exceed 28° Tw. However, across Europe, with more than 70,000 people dead, this heatwave is historically the deadliest. In Asia, the death threshold has been largely crossed in recent days. The wet bulb temperature was nearly 30° Tw, two degrees above what scientists say the human body can tolerate. The city of Jacobabad, in Pakistan, has recorded six days where wet temperatures have exceeded 35° Tw this year.

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Increasingly deadly temperatures

The extreme heat had already taken its first victim. In the Indian state of Maharashtra, 25 people have died since March from the heat. And mortality associated with heat wave in India, which fell victim to deadly heatwaves in 2015 and 2019, has increased by more than 60% since 1980, according to India’s Minister of Earth Sciences.

The future looks bleaker. In a published study in May 2020 in the magazine ScienceAdvancesBritish and American researchers have found that the frequency of wet bulb temperatures reaching 27°C, 29°C, 31°C and 33°C worldwide doubled between 1979 and 2017. They predict that these lethal values ​​will spread to regions -vulnerable areas of the world as climate change intensifies.

The number of wet ball temperature exceeds that humans can tolerate has doubled in less than 40 years (maximum wet bulb value between 1979 and 2017). (Photo: Raymond et al., 2020, “Existence of heat and humidity is too severe for human tolerance”)

The hotspots to watch out for are South Asia and the Middle East, added the author of this scientific paper. Subtropical and coastal countries, such as California or Mexico, also have to deal with these heat waves more regularly.

“What we are seeing now would be normal, even cold, in a world between +2° and +3°C,” explained Friederike Otto, from Imperial College London. Most of the world’s population has no choice but to leave these places in the most extreme conditions.

See also at The HuffPost: Extreme Heatwave in India, Fire Destroys Garbage Dump in Delhi and Suffocate its Residents

This article was originally published on HuffPost and has been updated.

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