Concentrations of dark asphalt roofs, parking lots and roadways in dense areas, especially in large cities, create a negative environmental effect called a "heat island effect" or "urban heat island effect." Heat soaks into these areas because of the dark materials that hold energy throughout the day and night.
Painting rooftops and roads white is one step toward reducing the amount of electricity and time needed to cool these urban hot spots, but another idea is to green the spaces from the tops down. Green or living roofs incorporate a waterproof membrane filled with soil and vegetation intended to cool naturally through soil temperature and growth of greenery. Roofs made of living plants also release oxygen into the air, making it less toxic and harmful than row upon row of petroleum-based shingles atop paved streets. Water runoff also serves to cool the buildings, and the entire system protects the base roofing underneath, adding to roof longevity.
Higher costs and lack of expertise and vision are likely to slow the growth of green roofing. Greenery topped buildings have been keeping buildings cool for decades in modern Europe, and Germany is the first and only country to publish a green roofing guide [source: Miller]. But implementing the techniques on a large scale is years away.