Geoengineering, or manipulation of the planet's climate, can be a dangerous practice—so much so that the UN is attempting to ban it. But there is little downside to painting rooftops white—making them reflect sunlight, cutting down on temperatures in crowded urban areas, and reducing the need for air-conditioning. That's why New York City's Cool Roofs initiative, which just whitewashed its one millionth square foot of rooftop, has become so popular.
The program began this past May and has already whitewashed 105 building roofs, thanks to 1,500 dedicated volunteers. This is just the beginning. If the city can succeed in painting the rest of its 500 million dark roofs white, temperatures could lower by two degrees Fahrenheit. The urban heat island effect (a phenomenon where dark material like asphalt increases the temperature of dense cities) could drop by 33 percent.
Building owners have good reason to celebrate. According to the city, whitewashed roofs lengethen the life expectancy of cooling equipment, cut down on the electrical power used by HVAC equipment, and reduce overall power demand. In a one-story building, for example, a reflective white coating could cut down on air-conditioning by up to 50 percent. White roofs won't halt climate change completely, of course. But it's a safe, surprisingly effective, and relatively cheap start.