As more people around the world move from the countryside to cities, the climate effects of urbanization become increasingly important. One of these is the urban heat island effect, where unshaded concrete and asphalt absorb sunlight and radiate heat, warming the surrounding areas by several degrees. Moncef Krarti, a professor at the University of Colorado and an expert on urban heat islands, discusses steps that cities can take to turn down the heat on their microclimates.