When sweating no longer works 🥵
You're about to hear a lot more about wet-bulb temperatures
Climate solutions // I S S U E # 5 7 // E X T R E M E H E A T
Peter Norton is an associate professor of history at the University of Virginia. Most years, he teaches classes to young engineers eager to invent the next generation of technology. Almost all his students enter his classroom with an unquestioning faith in technological progress.
As climate change rose up Norton’s list of personal concerns, he began to make it a focus of every class. During lectures, Norton challenged his students to think of ways to adapt to a warming world unlike the one they grew up in. Most, he says, only saw solutions in more steel, plastic, and energy, essentially engineering their way out of the problem. “There’s nothing to learn from the past,” he said of his student’s approach. “It’s a very unimaginative way of thinking.”
But it’s one that will have to change.
As our writer shows us today, you’re about to hear a lot more about wet-bulb temperatures, the combined measure of temperature and humidity. As humidity increases, the deadlier heat becomes. Imagine adding steam to a sauna. That’s the danger of hotter wet-bulb temperatures. At 79°Fahrenheit (26°C), health risks rise. Beyond about 95°F (35°C), it’s impossible to dissipate our metabolic heat. The red and black areas below represent a lethal risk.
Fortunately, few places on Earth see conditions like this for long. But that’s changing, fast. Measurements “at or near humans' survivability limit of 35°C (95°F)” are being measured at thousands of places around the world. Killer extremes have extended for up to two hours in California, Arizona, South Asia, and the Middle East. At these temperatures, even healthy people outside cannot survive for long without some respite. By the end of the century, the Intergovernmental Panel on Climate Change expects, these deadly moments will last longer in more places.
“I believe that humid heat is the most underestimated direct, local risk of climate change,” says Radley Horton, a Columbia University professor. “The risk is much larger than most people appreciate.”
Which brings us back to Norton’s classroom at the University of Virginia in Charlottesville. When asking his students how to cool homes and buildings without air conditioning—thousand-year-old technologies deployed in everything from old Florida homes to Bedouin tents in the Middle East—many didn’t know where to start. “Even a mechanical engineer didn’t have a clue of ventilating a building without power,” said Norton. “I’ve learned to expect certain blind spots. The least expensive, most accessible, most proven, and most inclusive solutions are very often low to zero tech. The problems have to be reframed.”
With humanity entering a new climate era, we’ll need to rediscover old technology, and invent new ways to inhabit our planet. Our reporter Dana Smith takes us there.
Welcome to the Extreme Heat series.
Extreme Heat Is Here. Can We Adapt?
By Dana G. Smith
The human body is remarkably effective at cooling itself. Normally as body temperature rises, blood is shunted from the core to the periphery to offload heat through the skin. This is why people flush as they get hot: capillaries at the surface fill with blood, turning the skin red. This process also helps protect critical organs, delaying the time until high temperatures cause cell death.
Next, the body taps into its most effective cooling mechanism: sweating. Millions of glands on the surface of the skin secrete salt water as you heat up. The moisture on the skin evaporates, cooling the temperature of the blood below, which circulates back to the internal organs, cooling them too.
“Our biological mechanisms for dissipating heat are actually really robust and rather impressive,” says Nicole Vargas, a researcher in the Thermal Ergonomics Laboratory at the University of Sydney.
This biological two-step has worked for thousands of years, enabling humans to live in every corner of the globe, including the hottest deserts. But these adaptations have their limits. When the air becomes hotter than our skin temperature, we stop losing heat to the environment and start retaining it. And if the air is too humid, sweating no longer works either. “Rather than the sweat evaporating off into the environment, it drips off onto the floor, just becomes soaked in people's clothing,” says Oliver Gibson, an exercise physiologist at Brunel University London who specializes in heat. “At that point, the body's in quite a difficult position because its best avenue for heat loss is removed.”
As the body’s core temperature rises, cooling mechanisms can start to backfire. The heart muscle strains to push more blood to the skin in a vain effort to dump excess heat, causing heart rates to spike. Our blood pressure drops as the same volume of blood flows to a much wider area, which can result in fainting or dizziness—early signs of heat exhaustion. Dehydration from excessive sweating further reduces blood volume, depriving organs of oxygen. Heatstroke sets in after the body reaches 104°F, and cell death and organ failure follow. Many, especially the elderly and those with medical conditions, may die.
Facing Our Biological Limits
Those devastating effects were on full display during an unprecedented heatwave that baked the Pacific Northwest this summer. Temperatures in Oregon and Washington rose into the triple-digits for four days straight, hitting a record 118° Fahrenheit. Hundreds of people, including 67-year-old Portland resident Jollene “Jolly” Brown, did not survive.
Like most people who succumbed during the heatwave, Brown lived alone and was without air conditioning. When her son, Shane, called her the night before she died she shrugged off his urgings to replace her broken window unit or to take up a friend’s offer to stay with them. The next morning when Shane went to check on his mother, the temperature in Brown’s studio apartment was nearly 100°F. She had passed away in her recliner during the night.
It isn’t just the most vulnerable who are at risk. This summer, 37-year-old Phil Kreycik died during a trail run near his home in Berkeley, California. Kreycik was an experienced athlete, but data from his GPS watch show his pace slowed and his movements became erratic an hour into his run as the noon-time temperatures approached 100°F. Officials believe Kreycik died from heatstroke.
This is happening in temperate areas of the richest nation on Earth. There is no question that as the planet warms, stories like this will become more common—and more severe. Heat is already the number one cause of weather-related fatalities. Even if we succeed in slowing global warming, to prevent the deaths of thousands, perhaps millions, more we’ll need to find ways to survive in a hotter world.
The Capacity—and Cap—for Adaptations
Our physiology can adapt. Athletes that train in hot conditions have recorded internal temperatures as high as 107°F without signs of heatstroke. In these people, the body starts to sweat earlier, blood volume and circulation is increased to protect against heart damage, and resting core body temperature is lower, providing them with a greater buffer against the heat.
“I think it's very clear that humans innately have the ability to adapt to heat,” says Vargas. “People do go through the process of acclimatization if they live in a hotter climate for a long period of time, especially if they're outside working regularly or if they're engaging in sports that they're playing outdoors.”
But Vargas is skeptical that many people will go through this adaptation. Because let’s be honest, even in the American South where I live, most people rarely stay out in the heat for more than a few hours (or minutes) during the summer. Instead, we wake up in air-conditioned houses, drive to work in air-conditioned cars, work in air-conditioned office buildings, and exercise in air-conditioned gyms.
What’s more, global warming will go far beyond our ability for biological adaptation. The target set under the Paris climate accords to avoid climate catastrophe is a 2° Celsius (3.6° Fahrenheit) increase. That sounds mild, but that’s just a global average. For locations that are already experiencing regular heatwaves, one scientific paper describes this temperature increase as “the difference between events at the upper limit of present-day natural variability and a new climate regime.”
There are already some places on the planet, such as the southern Persian Gulf and northern South Asia, experiencing heat and humidity “at the edge of and outside the range of natural variability in which our physiology evolved,” according to a study published in the journal Science in 2020. If global warming reaches 2°Celsius, an additional 1.7 billion people could be exposed to potentially deadly temperatures.
Survival in the New Normal
Faced with the limits of our biological adaptation, we’ll need to change our behaviors, our homes, and our cities.
In some places, this means doubling down on technology we already have. Other initiatives, rooted in ancient architecture, passively cool cities and homes. Communities are caring for their most vulnerable by setting up cooling centers and early warning systems.
The extreme heat the world is facing will require more than one solution. This month at Hothouse, we’ve spoken with climate experts, engineers, and urban planners to find out what will it take for all of us to truly adapt to this new future.
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Hothouse is a weekly climate action newsletter written and edited by Mike Coren and Cadence Bambenek. We rely on readers to support us, and everything we publish is free to read.