“Green roofs sprout toward the horizon in Stuttgart, Germany, where since 1989 municipal regulations have required all new, flat-roof buildings to have them. Steven W. Peck, founder of the Canada-based industry association Green Roofs for Healthy Cities, says ‘all you have to do is climb a tall building in Germany, and you’re going to see green roofs all over the place.’”

Photograph by Diane Cook and Len Jenshel, National Geographic