This highly unscientific aerial sampling of Los Angeles homes illustrates the city's rooftop problem:
Almost all of the homes here have dark-colored roofs covered in asphalt shingles or black tar, material that we now know is bad for both utility bills and the local climate. Dark-colored roofs absorb more sunlight than lighter colored ones do (in the same way that a black T-shirt ensures you'll bake on a summer day). As a result, a roof like this can perceptibly raise temperatures inside a building (driving up the demand for AC in the hot months) while contributing to the urban heat island effect around it.
