Wired: “The humble tree has long protected humans from sickness and even death—and in the modern city, it’s still doing so. As global temperatures rise, so too does the “urban heat island effect”—the tendency for cities to absorb and hold on to the sun’s energy, which is a growing public-health crisis worldwide. On a small scale, the shade under a single tree is an invaluable refuge on a blisteringly hot day. Scaling that effect up, neighborhoods with more tree cover are measurably cooler. Now research is showing just what an impact this can have on people’s health. A new paper finds that in Los Angeles, planting more trees and deploying more reflective surfaces—something as simple as painting roofs white—could lower temperatures so dramatically, it’d cut the number of heat-related ER visits by up to 66 percent. That research follows a previous study by the same scientists finding that one in four lives lost during heat waves could be avoided with the same techniques. As urban populations are rising around the world, so are temperatures, putting ever more people in ever-hotter environments. “We’re primarily urban dwellers at this point,” says UCLA environmental researcher Edith de Guzman, coauthor of both studies and the cofounder and director of the Los Angeles Urban Cooling Collaborative. “We know that that’s problematic, because there’s a magnification of heat that occurs in those spaces, because of the preponderance of heat-retaining surfaces that then release that heat at night, when the body seeks to cool off.” If a heat wave stretches day after day, the physiological stress builds and builds on residents. Elderly and young people are especially at risk, since their bodies can’t cool themselves as efficiently. Extreme heat also leads to the formation of ozone, which exacerbates asthma…”