The solution to urban heat is much, much simpler than you think

Johnny Appleseed was ahead of his time. Not because he fed so many people by planting apple trees (really, he got them drunk instead, as his real goal was encouraging the production of cider), but because he created so much shade to enjoy on hot days. More than two centuries later, American cities are wishing they had better followed Appleseed’s lead, as rising temperatures and a lack of tree cover combine to make urban life increasingly stifling. A pair of new studies show how simply planting more trees can provide huge temperature benefits, not to mention how the additional plant life would boost biodiversity and improve mental health for urbanites. The first finds that tree cover can cancel half of the heat island effect, in which the urban jungle gets much hotter than the surrounding countryside. The second compares neighborhoods in 65 American cities, finding that canopy-deprived areas suffer up to 40 percent more excess heat than heavily greened spots. Places like New York and Atlanta and Los Angeles, then, don’t just have to foster and maintain their “gray” infrastructure — roads and sidewalks and such — but their living infrastructure as well. “Heat is already a major public health threat. It kills 350,000 people a year by some estimates, and it’s worse in cities,” said Robert McDonald, the Nature Conservancy’s lead scientist for nature-based solutions and lead scientist for Europe, who spearheaded the first paper. “The urban heat island effect would be about double what it is now if world cities didn’t have trees.” By increasing their canopies, metropolises dress themselves like their more comfortable rural counterparts. A vegetated area cools itself both because plants “sweat” by releasing moisture from their leaves, and because trees provide shade. By contrast, concrete absorbs the sun’s energy, driving temperatures up, and releases it throughout the night. That beats back the cooling typically experienced in the evening, meaning urbanites wit