Just painting roofs white in warmer climates could decrease air conditioning bills for those buildings by 20%. For the last few years, California law has required all new buildings to have white roofs.

Recent research suggest that if all the roofs in the world were white, enough sunlight would reflect back into the atmosphere to significantly reduce the effects of global warming. This new study says that if the 100 biggest cities painted all their roofs white, and switched their road materials to lighter colors, for example,concrete instead of asphalt, it would reflect enough light and heat back into the atmosphere to almost entirely offset the warming of the last thirty years.