Every year, heat takes more lives than floods, hurricanes, and tornadoes combined. The fatalities can sometimes go unnoticed, perhaps because the danger is invisible: There’s no twister that uproots a neighborhood and no flood that sucks it underwater, nor billions of dollars in property damage. Instead, heat’s imprint is seen in empty streets, work slowdowns, cognitive decline, and hospital bills. When autumn arrives and temperatures relent, heat leaves no discernable trace.The Earth is getting hotter. In many places on the planet, summer is already two to three weeks longer than in the 1950s. By the end of the century, the warm season in the United States could last six months, and extreme temperatures could force us to spend much of it indoors. Supercharged heat waves will settle over cities for weeks at a time and cause many people to die. Others will suffer heart attacks, kidney disease, and brain damage. What we now call winter will be a brief, two-month interregnum that feels more like spring.This article was adapted from Sam Bloch’s new book, Shade: The Promise of a Forgotten Natural Resource.Reducing society’s consumption of fossil fuels is necessary for preventing worse-yet climate change. But even if every single power source becomes a renewable one and we stop emitting carbon, the planet’s surface won’t start cooling. The temperature will continue to rise for a few years before gradually leveling off. It will take “many, many centuries,” NASA estimates, to end the global-greenhouse effect. It is a sobering truth that cutting emissions isn’t enough. We also need to figure out how to live on a new Earth.What if the key to that life is older than civilization itself? We need to manage heat to live. And we have an effective and democratic way of doing it: shade.[Read: Shade will make or break American cities]Shade makes long waits for the bus more comfortable. Shade helps keep farmworkers safe when they harvest fruits and vegetables under an unforgiving sun. And shade cools urban environments, improving residents’ chance of surviving blazing summers.“We all know that cities are cooler when we have shade, but we’re not really planning for it,” V. Kelly Turner, an urban-planning and geography professor at UCLA, said on CNN. “In the future, that’s something that cities are going to need to do, is intentionally think about: What does shade infrastructure look like?”Turner believes that shade could be America’s next long-term investment in public health. What safe drinking water and clean air were to the 20th century, shade could be to the climate-changed 21st. Scientific models bear her out. If we can get emissions under control and put the planet on a path to moderate warming, then by 2050, getting out of the sun could be the difference between unsafe heat and a livable environment.One obvious way the planet can get more shade is more trees. We evolved in forests, and some of our oldest myths and stories unfold under their canopies. Hippocrates taught medicine under a plane tree, and Ovid found bittersweet beauty in a laurel’s leaves. The Mesopotamian goddess Inanna slept under a miraculous poplar whose shadow never moved, and Buddha found enlightenment by meditating under a ficus tree. Christian and Muslim heavens alike are cooled by trees’ perpetual shade.Tree shade is where public space was born and civic identities are forged. In hot climates, people naturally prefer to confer, conduct commerce, and gossip out of the sun’s permanent glare. They spend far more time in shady parks or temple courtyards than in sunny ones. They linger and relax, and that engenders more interactions, and possibly even stimulates social cohesion. It’s true in arid cities, humid regions, and even temperate zones with short summers. People want to be in shade. They muse longer, pray more peacefully, and find strength to walk farther.[Read: How climate change is killing cities]Perhaps because we’ve become so adept at cooling inside spaces with air conditioning, we’ve forgotten the importance of cooling outside spaces, too. There is no technology that cools the outdoors as effectively as a tree. These communal parasols are also misting machines that dissipate heat. It’s hard to feel that effect under one or two of them, but get enough trees together and an urban summer can be as fresh as a rural spring, a feat with major implications for energy use and public health.Where tree-planting isn’t viable, cities must invest in other types of public infrastructure that cast shade. Throughout Los Angeles, on streets that are too cramped and paved over to support green canopies, the preferred protections aren’t arboreal but artificial, such as the pop-up tents of taqueros and the cheerful rainbow umbrellas of fruit vendors. In Phoenix, a desert city that struggles to nourish an urban forest, common tools include sidewalk screens, frilly metal filters, and soaring photovoltaic canopies. These interventions are more effective than many might expect. Ariane Middel, an Arizona State University urban-climate researcher who runs the school’s Sensable Heatscapes and Digital Environments (SHaDE) Lab, surveyed students and staff as they strolled through the shadows that solar panels cast on a Tempe campus thoroughfare. More than any change in ambient temperature, humidity, or wind, the mere presence of shade was the only significant predictor of outdoor comfort.Shade’s effectiveness is a function of physics. It depends on the material properties of the sun-blocking objects that cast it—how they reflect, absorb, and transmit different wavelengths of energy in sunlight. It depends on the intensity of that light and the extent of the shade thrown. (A telephone pole that casts a perfect shadow on your body does nothing to stop the solar heating of the surfaces around you.) And it depends on the biology of the person who receives it. Middel has come as close as anyone to adding up all these factors. She praises humble umbrellas and plastic sails, because their shade feels like taking 30 degrees off the afternoon sun, which is about as good as shade cast by a tree. Ultimately, she finds that a city itself can offer the most relief in the shadows of arcaded sidewalks and looming skyscrapers.The Greek philosopher Onesicritus taught that shade stunts growth, a belief that presaged a modern fixation on the healthiness of sunlight. In the 19th and early 20th centuries, doctors and public-health advocates feared that darkness itself caused the poor health of urban slum-dwellers. It was a vector of disease, where contagions bred and spread, and the murkiness also encouraged licentiousness and other urban vices. Some literally believed sunlight was the best disinfectant. Solar codes were written into urban plans, and new materials and technologies allowed architects to design brighter buildings flooded with natural light.[Read: America’s climate boomtowns are waiting]Now we’re beginning to see how a solar fetish may be maladaptive. In New York, a recent summer saw a throng of neighborhood activists protest the construction of a 16-story office tower, with signs to Save Our Light. They did this while huddling in the shadow of another building.As intense heat bears down, we have to see shade as a basic human right. We have forgotten that shade is a natural resource. We don’t grasp its importance, and we don’t appreciate its promise for a better future. Loggers and farmers cut down forests, forcing animals to flee and land to turn fallow. Engineers ignore time-honored methods of keeping out heat, locking us into mechanical cooling systems that fail during blackouts. And urban planners denude shady parks and pave neighborhoods with heat-sucking roads, only to drive us mad with the infernal conditions. But shade is a path to a better future—if we just learn to value it again, and design for it in the places we live.This article was adapted from Sam Bloch’s new book, Shade: The Promise Of A Forgotten Natural Resource.