Wet bulb temperatures and human death

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.

5 thoughts on “Wet bulb temperatures and human death”

  1. 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.”

    https://www.economist.com/briefing/2021/07/24/three-degrees-of-global-warming-is-quite-plausible-and-truly-disastrous

  2. “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.”

  3. India’s deadly heatwaves are getting even hotter

    The consequences of climate change will be horrific for the Indo-Gangetic Plain

    Scientists record heat stress as a combination of temperature and humidity, known as a “wet-bulb” measurement. As this combined level approaches body temperature, 37°C, it becomes hard for mammals to shed heat through perspiration. At a wet-bulb temperature of around 31°C, dangerously little sweat can evaporate into the soup-like air. Brain damage and heart and kidney failure become increasingly likely. Sustained exposure to a wet-bulb temperature of 35°C, the level Mr Robinson imagines in his book, is considered fatal. The Indo-Gangetic Plain is one of the few places where such wet-bulb temperatures have been recorded, including on several occasions in the scorched Pakistani town of Jacobabad. A report by the World Bank in November warned that India could become one of the first places where wet-bulb temperatures routinely exceed the 35°C survivability threshold.

    The temperature record provides a horrifying account of the changes afoot. According to the definition of a heatwave used by India’s weather agency, India saw, on average, 23.5 heatwaves every year in the two decades to 2019, more than twice the annual average of 9.9 between 1980 and 1999. Between 2010 and 2019, the incidence of heatwaves in India grew by a quarter compared with the previous decade, with a corresponding increase in heat-related mortality of 27%. During last year’s hot season, India experienced twice as many heatwave days as in the same period in 2012, the previous record year.

    Climate change made last year’s heatwave 30 times likelier than it would otherwise have been, according to World Weather Attribution, a research collaboration. That is both because it has raised India’s average annual temperature—by around 0.7°C between 1900 and 2018—and because it has made heatwaves bigger and more frequent. The magnifying effect of the built urban environment, which can be 2°C hotter than nearby rural areas, is often pronounced in India’s concrete jungles. Those living in slum housing, which offers little air circulation and often uses heat-sucking materials such as tin, suffer the worst of it.

    If the climate warms by 2°C compared with pre-industrial levels, as appears unavoidable, such events would be more likely by an additional factor of 2-20. Even if the world makes more headway towards curbing greenhouse-gas emissions than looks likely, “vast regions of South Asia are projected to experience [wet-bulb temperature] episodes exceeding 31°C, which is considered extremely dangerous for most humans,” according to a paper by Elfatih Eltahir of the Massachusetts Institute of Technology and colleagues.

    They will both increasingly be called on to take much costlier measures, such as designing “cold shelters”, rethinking urban planning and building materials, and bailing out those unable to work in the heat. “We are going to have to learn to live in a warmer world,” says Gabriel Vecchi, a scientist at Princeton University, New Jersey. The question is how orderly, costly or calamitous that learning process will be.

    It is hard to find much comfort in the underlying facts. Year by year, parts of the poor and crowded Indo-Gangetic Plain will become increasingly difficult to live in for days or weeks on end. Even the most capable government would struggle to prevent that leading to catastrophe. And India’s, much less Pakistan’s, is not the most capable.

  4. Despite the work, the numbers of heat-related fatalities have swelled dramatically in recent years, culminating in a record 425 lives lost last year. The climate crisis is upping the stakes, with temperatures only expected to surge further in the coming years. Staying one step ahead has proved a difficult – and deadly – challenge.

    More people are making Phoenix their home even as the risks rise and a growing population is putting strain on housing and water – two resources that help dull the strain of stifling heat – both resources in short supply.

    Heat, a quiet killer and one of the world’s deadliest disasters, takes an unequal toll. Fifty-six percent of those who succumbed to the heat last year in Maricopa county, where Phoenix is located, were unhoused. Of the people who died indoors, all of them were living in homes and buildings that weren’t cooled. In 78% of cases, AC units were present but not functioning.

Leave a Reply

Your email address will not be published. Required fields are marked *