I’ve been lucky enough to live my life in the mountains, where even on the hottest days you can generally find a breeze, and where the temperature drops at night. Happily, I’ve never needed AC; I like my air unconditioned. But this also means that I have a profound appreciation for shade; on a hot day it’s a screened porch or under a sugar maple for me. I’m a shade connoisseur; I know from long experience how the shadows are going to move while I nap, and I’m perfectly willing to turn my baseball cap sideways when demanded. 

I also know that most people lack these luxuries. They’re not in the mountains, they’re in cities. And cities are, of course, hotter than they’ve ever been. That’s what comes from letting our planet go to—well, go in the direction of—hell. Our first job, obviously, is to reverse that descent, and I’ve spent my life fighting for climate action. But in the meantime, as temperatures continue to rise, we have to do what we can to stay cool. Which means, among other things, shade, as a matter of survival and as a matter of justice.

How important is it? Let me tell you a story. In the 1930s, a federal agency, the Home Owners’ Loan Corporation, graded all of America’s neighborhoods and deemed some of them “hazardous” for investment, essentially because they were home to large minority communities. This grading system (from A for “best” and B for “still desirable” to C for “declining” and D for “hazardous”) underlies what came to be known as redlining. The grading system led to chronic disinvestment in the lower-rated neighborhoods, resulting, over time, in less of everything from parks and green spaces to street trees and air-conditioning in homes. Almost a century later, the results of that racism can be measured with a thermometer: in Portland, Oregon, neighborhoods that were graded A in the 1930s now “average 8 degrees Fahrenheit lower than the city’s mean temperature, while D-graded neighborhoods average 4.8 Fahrenheit degrees warmer,” according to the New Yorker. Actually, you don’t need a thermometer—that’s a 13-degree gap that anyone can feel just by walking across town.

The New York Times set out to quantify the difference in its home city a few years ago. At noon one hot August day, with the aid of an infrared thermometer, reporters found that on the “tree-canopied block of West 94th Street near Central Park in Manhattan, the sidewalk temperature was 84. Just across town, at a treeless lot for sanitation trucks on First Avenue in East Harlem, the blacktop registered at 115 degrees, a full 31 degrees hotter.” As the reporter, John Leland, noted: “Plants and trees cool a neighborhood by providing shade, but also by a process called transpiration: as water evaporates from the leaves, its transformation into vapor consumes heat from the atmosphere.” A tree is a cooling machine.

This is not an isolated phenomenon, of course. A recent study in the British medical journal The Lancet, which looked at 530 locations in 51 countries, found that 30 percent more shade could reduce mortality in our new killer heatwaves by remarkable numbers—that would have cut mortality by more than a million human souls so far this century. How do people die from heat? So many ways. Just to give you an example that may not have occurred to you offhand: “Nephrolithiasis” is the technical term for the development of kidney stones, those small formations that, as they pass, can cause excruciating pain. (I’ve never had them, but I know more than one man who has said he came away from the experience with a newfound appreciation for what his wife had undergone during labor.) Doctors have long known that higher temperatures lead to more sweat, which reduces urine volumes and thus increases “the saturation of the insoluble salts that cause kidney stones.” During heat waves in the U.S., it takes just three days before emergency-room visits for kidney stones begin to spike.

If you think it's bad here, imagine what it’s like in truly hot places: a couple of years ago a Washington Post reporter found that a third of the people in the kidney transplant center in Kathmandu were young Nepali men who had worked overseas, mostly in the Gulf. It described, for instance, a young man named Suraj who journeyed to Kuwait in order to send money back to his impoverished family, and to build up enough of a nest egg to someday get married. He “found himself on construction sites where he installed massive, one-ton window frames on skyscrapers rising from the Kuwait desert. Because elevators were not operational, he recounted, he had to walk several stories to access water. But with work schedules so pressing, most workers gathered around the water tank only during their one-hour break. On many days, the water would be gone before the break ended. Often, Suraj didn’t drink anything all day.” When the temperature is well into the triple digits, that’s a bad idea; now he’s back home, living with his sister who wheels him a few times a week to the hospital. “To pay for his kidney transplant and the tests, they’ll sell Suraj’s half-built house with the propane stove. They’ll squeeze back into Panmaya’s mud-and-bamboo hut and cook on the ground with open fire. His dream of getting married was now ‘in ashes,’ Suraj admitted.”

In the ideal world, you’d figure out some ways to provide shade at the same time as you were doing something about the causes of all that heat in the first place. Which, as it turns out, is entirely possible. You’ve seen a solar panel; we’re used to looking at its top, and thinking about the way it faces the sun, turning photons into usable electricity, in the great miracle of our time. Its rapid spread—solar energy is now growing faster than any energy source at any point in human history—is the one scalable hope we have for actually reducing the flow of heat-trapping carbon into the air. 

But solar panels have an underside, and that underside is, by definition, shady. If, say, you built solar panels over California’s irrigation canals, they would cut evaporation in those crucial arteries by 63 billion gallons of water a year.

And on land? A recent survey found that 72 percent of German farmers are considering deploying agrovoltaic arrays on their land, and the French energy giant Total recently set up a “Center for Expertise” in the art of growing food next to PV panels. And no wonder a 2024 study found that solar panels can increase yields for Chardonnay grapes by as much as 60 percent. There are a lot of studies like that, and they serve as a reminder that for many crops, some shade and extra humidity are a blessing, especially as temperatures rise. Near Phoenix, temperatures topped 110 degrees for 31 straight days in the summer of 2024, smashing old records. “The solar arrays help reduce our water use,” a USDA agronomist told a local reporter. “Plants don’t really need as much sun as they get in the West.” Even skipping irrigation every other day, soil moisture under the panels was 15 percent higher than nearby unshaded plots, and black-eyed peas were growing faster because they were less stressed.

Researchers have found much the same in Africa—test plots in Tanzania and Kenya, for instance, revealed that corn, Swiss chard, and beans were thriving under panels. “We created a microclimate that helped certain crops produce more, but they were also better able to survive heat waves and the shade helped conserve water, which is crucial in a region threatened by climate change,” the study’s lead author explained. In Phoenix, which is surrounded by desert, windstorms increasingly blow dust hundreds of feet into the air—that’s because the crust of the desert’s soil is so easily broken, even by a footstep. But this “biocrust” seems to be naturally re-growing under solar panels, which researchers at Arizona State described as “beach umbrellas.” Indeed, they’re now growing these crusts under solar arrays to replant in damaged desert areas; “crustivoltaics,” they’re calling it. In China, where great dust storms have swept off the Gobi into the cities of the country’s north for decades, they’re finding the same thing: the ground under solar arrays had higher plant and microbial diversity than the surrounding desert.

The warmth of the sun was a joy for most of human history; we’re programmed to smile when the sun comes out from behind a cloud and warms our shoulder blades. Thanks to human foolishness, this source of life has become the curse of our age: every tenth of a degree increase in the global temperature now moves another 100 million people out of comfortable climate zones. But now it’s going to have to be our salvation—harnessing the sun is our one way out. And that means luxuriating in the shadows that our planet-saving technology can cast. Some of that technology is coniferous, some of it is deciduous, and some of it is photovoltaic. All of it is delicious. ♦