Wet bulb temperatures and human death


in Politics, Science, The environment

The many human impacts of climate change are complex and often indirect, like how warmer winters in the mountains affect downstream agriculture. The most direct possible effects — however — have been on display in the brutal heat waves on the west coast, as well as elsewhere in the world.

CNN recently published an editorial by Ban Ki-moon and Patrick Verkooijen on the most direct imaginable way in which increased global temperatures can bring harm upon people:

Sweltering temperatures have become the norm in Jacobabad, a town of around 200,000 inhabitants in Pakistan’s Indus Valley that has become one of the hottest places on earth. Temperatures can top 126 degrees Fahrenheit and air conditioning is scarce, leaving the streets deserted and forcing farmers to till their fields at night.

The city, along with Ras Al Khaimah in the United Arab Emirates, has temporarily crossed the threshold beyond which the human body cannot sweat enough to cool itself down. A “wet bulb” temperature of 35 degrees Celsius (95 degrees Fahrenheit) — which factors both heat and relative humidity — can be fatal after a few hours, even assuming ideal conditions such as unlimited drinking water, inactivity or shade. In practice, the bar for this wet bulb temperature, which is measured by covering a thermometer with a wet cloth, is much lower — as shown by the deadly heat waves in Europe in 2003 that are estimated to have claimed 70,000 lives.

Our most basic biological function and a prerequisite and definition of life is the ability to maintain stable conditions inside the body compatible with the needs of our physiology and biochemistry; homeostasis is the term for maintaining internal conditions, and if you don’t have it you’re literally dead.

We’re already artificially coping with places which are literally unliveable without air conditioning, from scorching cities around the Persian Gulf to Phoenix and Las Vegas, which are also profoundly threatened by the loss of winter snowpack and lost river volume and reliability.

{ 3 comments… read them below or add one }

. August 20, 2021 at 6:36 pm

Richard Betts, a climatologist in Britain’s Met Office who has led several surveys of the impacts of high-end global warming, says that beyond 2°C small but densely populated regions of the Indian subcontinent start to be at risk of lethal and near-lethal wet-bulb temperatures. Beyond 2.5°C, he says, places in “pretty much all of the tropics start to see these levels of extreme heat stress for many days, weeks or even a few months per year.”


. May 14, 2022 at 1:40 pm

The increasing frequency of fatal wet-bulb temperatures

Unbearable levels of heat and humidity pose an ever greater problem


. May 14, 2022 at 1:42 pm

“A wet-bulb temperature of 35°C is regarded as the theoretical limit of what humans can endure. It would be reached at an actual temperature of 45°C if relative humidity were 50%, or at about 39°C if humidity were 75%. Beyond this point it becomes impossible for sweat to cool the body down, causing people to overheat and in effect cook. Cells swell, proteins are deformed and organ systems fail, resulting in death. At wet-bulb temperatures above 35°C, it is thought that even young healthy people wearing light clothing—regardless of whether they are parked in front of a fan, in the shade or have unlimited water to drink—will die in about six hours.”

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