Choose white shingles, light or cool metals, or clay or cement roof tiles if you’re building a new house or doing major maintenance on your existing roof. Paint a white coating on flat roofs.

Hey neighbor! Lighten that roof to lower your electric bill. (Turning off some lights would help, too.)

RODALE NEWS, EMMAUS, PA—The color of your roof could save you major money on home-energy costs, and be a major player in offsetting global warming emissions, according to a new study published this month in the journal Climatic Change. While dark-colored roofs absorb sunlight and bake your home, white roofs reflect solar radiation, which helps you keep your air-conditioner turned off.

THE DETAILS: Researchers from the California Energy Commission and the U.S. government’s Heat Island Group used population data to conservatively estimate that 1% of the world’s land in temperate and tropical areas is urban. They used data from sparsely populated and crammed cities to determine that roofs (25%) and pavement (35%) account for 60% of urban surface areas. This is what they came up with: Each house with a 1,000 square-foot area “cool” roof could offset global warming emissions by 10 tons per year by decreasing the need to burn fossil fuels for air-conditioning. If urban dwellers in temperate and tropical regions of the U.S. switched to cool roofs, we’d save more than $1 billion in annual energy bills. Globally, researchers estimate cool roofs and cool (light-colored) pavements in tropical and temperate cities could offset 44 billion metric tons of carbon emissions, worth about $1,100 billion, a relatively easy method for such a huge return.

WHAT IT MEANS: We don’t expect you to grab a ladder and rip out your old, dark, asphalt- shingled roof. But when the time comes to replace it or shell out big money for a major repair, consider cool-roof options. In urban areas, they could actually improve quality of life for everyone—cities often bake 6 to 7 degrees hotter because of all the dark pavement and roofs. And a cool roof won’t cost extra. “White shingles are the same cost as dark shingles, hence no incremental cost. Cool-colored painted metals and light-colored metals are the same cost as dark [metal] ones,” explains study author Hashem Akbari, staff scientist with the Heat Island Group. The same is true for cement or clay tiles. In fact, cool-roofing materials may last longer than the hot ones, and hence the lifetime cost may actually be lower. All the materials needed are already on the market. “Cool roofs and cool pavements are the only measures that I know of that save air conditioning energy use, reduce CO2 emissions, and reduce heat islands that results in improved air quality and citizen comfort, and help to delay global warming,” Akbari explains.