If the 100 largest cities in the world replaced their dark roofs with white shingles and their asphalt-based roads with concrete or other light-colored material, it could offset 44 metric gigatons (billion tons) of greenhouse gases, a study by Lawrence Berkeley National Laboratory and UC Berkeley shows.

White surfaces would also lower the cost of air conditioning by up to 20% in hot months and cool a city by a few degrees, which dramatically reduces smog.