Extreme heat waves show the ultimate climate impact may arrive sooner than we thought

Dave Levitan

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The road to an unlivable climate isn’t exactly a scenic route.

In parts of Iraq right now, temperatures have soared to 125 degrees Fahrenheit, sending people who live on parched farmland in toward the baking cities — and many to hospitals. Elsewhere in this summer from hell, thousands of excess deaths have been recorded during the U.K.’s unprecedented heat wave, hundreds of millions of Americans have been in and out of heat advisories and warnings for days or weeks at a time, and an extended heat wave in India and Pakistan sent temperatures well into the triple digits in one of the more densely populated and impoverished parts of the world.

It is a preview of some of the most dire of climate impacts: that with unchecked warming, some parts of the globe will literally become uninhabitable, as heat overwhelms the body’s ability to cool itself. Climate modeling and studies of human physiology have suggested we could be decades away from such unthinkable outcomes in places like the Middle East, South Asia, and elsewhere — but recent research and this year of extremes is demonstrating that such a future may be arriving faster than anticipated. And it certainly won’t be fun along the way.

Without dramatically increased action on climate change, U.N. Secretary-General António Guterres has said, humans are “firmly on track toward an unlivable world.” With extreme temperatures popping up all over the planet, this was not, it appears, an exaggeration.

Wet bulbs and hot humans

A widely publicized paper in 2010 suggested a sort of upper limit to human habitability. Focusing on the “wet-bulb” temperature, a combined measure of heat and humidity that can indicate when humans can no longer cool themselves effectively by sweating, researchers from the University of New South Wales in Australia and Purdue University pinpointed a wet-bulb mark of 35 degrees Celsius (95 degrees Fahrenheit equivalent) as the threshold beyond which people can’t survive. Under high-warming scenarios, they wrote, certain parts of the world would eventually become uninhabitable.

That paper, though, was more theoretical than practical. Newer research, published in January of this year, actually tested wet-bulb thresholds in young, healthy people. The researchers had volunteers perform tasks inside a heat chamber at a rate that mimicked “basic activities of daily life.” They found that the wet-bulb threshold is likely more on the order of 30 or 31 degrees C (86 to 88 degrees F) — meaning unlivable temperatures are potentially a lot closer than they seem.

Importantly, study lead author and Penn State University postdoctoral fellow Daniel Vecellio said the wet-bulb threshold is better thought of as a gradient, where one’s overall health, acclimatization to extreme temperatures, and other factors all add up to a wet-bulb danger zone. And even when these gradated thresholds are reached or approached for a given area, it is not a matter of flipping a switch.

“It doesn’t mean everyone’s going to die just like that, in an instant,” he told Grid. “The biggest thing that this is going to cause is a change in lifestyle.” That may mean changes to work patterns, such as being more active in the early morning or at night; more time spent in air conditioning where it is available; and so on. “It’s going to change the way we live; it may not, you know, kill us all.”

What the heat waves this year are demonstrating, though, is that those thresholds may be crossed on a more consistent basis in certain places. A given area — Baghdad, say, where this week’s 125-degree heat has led to widespread power outages, forcing people into their cars just for the brief relief of air conditioning — won’t suddenly flip from livable to unlivable from one day to the next. But the increasing extremes, which Vecellio pointed out may be underestimated in global climate modeling, will see humans dipping into that unhealthy, potentially fatal range of temperatures more and more often. And a place that is temporarily unlivable more and more often isn’t all that far off from becoming permanently unlivable.

Outdoor workers, vulnerable people

“We see those events happening with more frequency and more intensity,” said Rachel Bezner Kerr, a professor of global development at Cornell University, and a co-author of one of the huge U.N. climate reports released earlier this year. Kerr focuses her research on food systems and agriculture, one of the sectors where the idea of an unlivable climate will likely rear its head first.

“It’s a risk for outdoor labor, and agriculture, of course, is a key kind of outdoor labor,” she said. “Some crops require manual labor and will continue to require manual labor for the foreseeable future.”

Kerr suggested that certain areas will become “unworkable” before they are literally unlivable — places where, as the extreme heat waves increase in frequency, people simply cannot survive outside for as long as the crops require them to. She stressed that while that sort of burden will likely fall on the most vulnerable and marginalized people, it will not be restricted to the developing world.

“I think it’s sometimes easy, if you’re if you’re living in the Global North, if you’re living in a high-income country, to think, ‘Oh, this is really a problem for out there, where places will become unlivable. Good thing I live here,’” she said. But agricultural workers in parts of the U.S. may see those unworkable temperatures in a similar time frame to poorer parts of the world.

California, which produces more than a tenth of the entire country’s agricultural output by value, implemented the first workplace standards for farmworkers after a heat wave almost two decades ago. But critics say the protections, involving requirements for breaks, shade, and water, haven’t kept pace with the warming climate. In fact, over the past decade, dozens of farmworkers have died from heat-related illness.

“Everyday living becomes more challenging for all of us, and vulnerable groups being at greater risk,” Kerr said.

Other sectors are at risk as well. Construction workers often have to be outside for long days without shade or air conditioning; drivers for UPS have suffered heat-related illnesses in several states this summer, prompting the union to push for better working conditions. “When you start to think about that the kinds of activities that do take place outdoors, it quickly does shift from unworkable to unlivable,” Kerr said.

Global hot spots

While even rich countries like the U.S. may start to see some areas tip toward unworkable or unlivable for some, it remains the case that certain parts of the world are most vulnerable to heat extremes that will push human boundaries. The Middle East will see its already-extreme heat pushed even further: one 2021 study found that by the second half of this century the area will start to see “super-” and “ultra-extreme” heat wave events, with temperatures pushing 56 degrees C (133 degrees F). By 2100, the study found, 600 million people in the Middle East and North Africa could see such extremes every single year.

Detouring off this road to unlivability will require massive reductions in greenhouse gas emissions in short order — a project that saw some of its first truly good news in years when the Senate passed the Inflation Reduction Act this weekend, which is projected to bring U.S. emissions down by around 40 percent below 2005 levels by 2030. But even with those needed reductions, many impacts are baked into the system already, meaning “unlivable” and “unworkable” are increasingly a fact of life with climate change.

“There probably already are people that are living in conditions that for days or weeks during the warm season, that are just not conducive to healthy living,” Vecellio said. “You’re not going to be able to go outside if it’s above this threshold for six hours a day.”