On those sweltering summer days—when it’s too hot to play at the playground, it seems like you could fry an egg on the pavement, and your car feels like an oven after a couple hours parked at the mall—it’s not just the beating sun that’s driving up the temperature. It’s our very urban environment, in which most of our paved surfaces are dark, absorbing almost all of the sunlight that shines down on them.

In a typical city, pavements account for 35 to 50 percent of surface area, of which about half is comprised of streets and about 40 percent of exposed parking lots. Most of these streets and parking lots are constructed with dark materials. “It’s amazing how hot these pavements get, and how we’ve let them cover most of our urban surfaces,” says Haley Gilbert, a researcher in the Heat Island Group of Lawrence Berkeley National Laboratory (Berkeley Lab). “Because dark pavements absorb almost all of the sun’s energy, the pavement surface heats up, which in turn also warms the local air and aggravates urban heat islands.”

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