OPINION: How long can we afford to keep living in hotboxes like Phoenix?

This summer has been the hottest in recorded human history. It may also be the coolest summer we’ll ever enjoy again. That’s nearly impossible to imagine in places that already are suffering under extreme effects from global warming — places like Phoenix, Arizona.

The broiling desert city has endured 24 consecutive days above 110 degrees Fahrenheit, a record. Sunday morning marked the 14th straight low above 90, also a record. Last Wednesday the low was a miserable 97 F, yet another record. An unbudging heat dome over the southern U.S. kept the city in a pressure cooker and delayed the relief of monsoon season by more than a month. The urban heat-island effect of city development compounded the misery.

Sustained heat at such levels is inhospitable to human life. Homeless people and those living without air conditioning die by the dozens each year in Phoenix. At least a dozen have already perished this year. People passing out from heat stroke get second- and third-degree burns from the pavement. Everyone else is condemned to being trapped inside for months at a time, blasting air-conditioning and straining the electrical grid.

And in the years ahead, a warming planet will make this summer feel comparatively pleasant. The Phoenix area has always been hot, of course. But it can easily get much hotter. Arizona was the third-fastest-warming state in the U.S. between 1970 and 2018, according to a Climate Central study. And a recent ProPublica study suggested the Phoenix region will be among the country’s least-habitable by 2050, with half the year spent at temperatures above 95 F.

Brutal heat isn’t Phoenix’s only challenge. More than a third of its water comes from the Colorado River, which is drying up from climate change and mismanagement. The Salt and Verde rivers, which provide more than half the city’s water, may be in better shape than the Colorado but still depend on melting snow, which will become more scarce. Meanwhile, rising temperatures and increasing droughts also raise the risk of destructive dust storms, the fungal infection known as “valley fever” and other perils.

All of which sound like great reasons to pack up and leave.

“Climate change is revealing how brittle our development is,” said Kristina Dahl, principal climate scientist at the Union of Concerned Scientists. “We’ve put cities and farmland in deserts that have little water and are extremely hot. Increasingly such decisions will be stress-tested.”

Phoenix’s existence has long seemed precarious. The sociologist Andrew Ross in 2013 called it “the world’s least sustainable city.” One decade, megadrought and record-smashing heat wave later, Ross is more convinced of this than ever.

“Nothing about the region’s extreme challenges should surprise long-term residents or Phoenix-watchers,” Ross wrote in an email. “What’s new is that the signals of climate change have now been showing up in other parts of the world, and so Phoenix’s challenges are no longer seen as an anomaly but as the face of the future for large sectors of the world’s population.”

My Bloomberg Opinion colleague David Fickling notes human civilization evolved to thrive within a narrow band of climate conditions. Violent fluctuations in those conditions, as we’re experiencing now, will put particular pressure on Phoenix and other such places at the bleeding edge of that sweet spot of habitability.

“You’ve got to question the viability of living in the lowest parts of the Southwest like Phoenix,” said Jonathan Overpeck, the Samuel A. Graham Dean of the School for Environment and Sustainability at the University of Michigan. He once lived in Tucson but moved away, mainly because of concern about climate change’s effects on the local economy.

Hordes of Americans are making the opposite choice at the moment. More people have moved to Phoenix’s Maricopa County than any other U.S. county since 2010. The pace has only increased since the pandemic. Possibly the biggest draw is the cost of living, which is far lower than that of, say, Southern California, thanks partly to breakneck residential development that keeps housing relatively plentiful.

But that cost of living rises when you need to crank the AC for months on end, not to mention the social cost of burning — mostly — fossil fuels to keep it running. And Phoenix’s sprawl seems finally to be hitting its limits. Arizona’s governor last month told developers there isn’t enough groundwater to support all their plans in the Phoenix area. That will force them to turn to other water sources. But the Colorado River spigot is being tightened. And other, more speculative water sources — desalinization, recycling or pumping water from afar — would be cost-prohibitive, if they’re available or useful at all.

Earlier this year, the city of Scottsdale, part of the Phoenix metro area, cut off water to a neighboring community called Rio Verde Foothills, pleading megadrought. Lawsuits ensued. But building in Rio Verde Foothills continued.

Prehistoric civilizations thrived on the site of present-day Phoenix, and optimists suggest modern humans should have no trouble doing the same. But then those civilizations didn’t face anything like the temperatures Phoenix is about to experience. They also weren’t supporting more than 4.5 million people and counting. And Overpeck notes they appear to have collapsed when rival factions went to war over dwindling water — think Scottsdale vs. Rio Verde, but at apocalyptic scale.

Phoenix may never be completely uninhabited, but its future could be one in which the wealthy spend increasingly shorter winters in the area and flee for cooler haunts when the heat returns. That would leave behind mostly poorer service workers, people who can’t afford to leave and who are often the most vulnerable to extreme heat and other disasters. Wealthy people retreating to climate-controlled fortresses while others suffer isn’t a humane solution.

Humans are amazingly adaptable, but there are limits. At some point state and federal governments will need to pay people to leave the places most exposed to climate change, many of which are already uninsurable, if not uninhabitable. But if we really want to secure Phoenix’s future, the cheapest and sanest way would be to stop burning fossil fuels and contributing to its problems.

Mark Gongloff is a Bloomberg Opinion editor and columnist covering climate change. A former managing editor of Fortune.com, he ran the HuffPost’s business and technology coverage and was a reporter and editor for the Wall Street Journal.

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