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The limits of human adaptability

Scientists and other observers have become alarmed about the increasing frequency of extreme heat paired with high humidity.

In the Middle East, Asaluyeh, Iran, recorded an extremely dangerous maximum wet-bulb temperature of 92.7 F (33.7 C) on July 16, 2023 – above our measured upper limit of human adaptability to humid heat. India and Pakistan have both come close, as well.

People often point to a study published in 2010 that theorized that a wet-bulb temperature of 95 F (35 C) – equal to a temperature of 95 F at 100% humidity, or 115 F at 50% humidity – would be the upper limit of safety, beyond which the human body can no longer cool itself by evaporating sweat from the surface of the body to maintain a stable body core temperature.

It was not until recently that this limit was tested on humans in laboratory settings. The results of these tests show an even greater cause for concern.

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