High atop some of the urban jungle's tallest, widest buildings, city residents are laying down soil and planting native vegetation. Modern green roofs, which are typically flat (unlike traditional Scandinavian sod roofs), help to lower heating and cooling costs while reducing air and water pollution. Leaders worldwide are recognizing the benefits of green roofing, and are slowly turning the aerial view of their cities from gray to green.

In Germany, for example, nearly 10 percent of all rooftops are green; in Switzerland, Toronto and Tokyo, laws require certain-sized roofs to be green, and in Chicago, Illinois, a 2005 city grant program helped to finance the planning and installation of more than 200 green roofs.

It's no wonder local and federal governments are interested in encouraging this proliferation. Green roofs and walls catch stormwater runoff, moderate building temperatures, reduce the heat island effect and pull pollution from the air. Another benefit of planting vegetation on the tops and sides of buildings is improved inner city biodiversity. Rooftops lush with native vegetation, like this six-acre roof in Vancouver, Canada, can function as corridors for wildlife, helping birds, bats and bugs "commute" from one green space to the next. This is especially helpful for honeybees, as multiple green pockets throughout a city can quickly become pollinator pathways.

As some governments are already proving, policy can help this growing trend explode. With some legislation or even just some financial support in the form of city grants, green roofs can move from interesting, individual specimens to integral infrastructure. One day soon, native grasses will grow on every rooftop, greening the upper canopy, cleaning the air and providing homes for many creatures. We'll wonder how we ever lived without them.