White roofs could lower global emissions

Changing the color of roofs and pavement worldwide could potentially offset nearly a year’s worth of global CO2 emissions, according to a study released this week at the Conference on Climate Change in Sacramento, Calif.

Painting a single 1,000 square-foot dark roof white would reduce carbon emissions by 10 metric tons, according to Lawrence Berkeley National Laboratory scientists Hashem Akbari and Surabi Menon and California Energy Commissioner Art Rosenfeld. And changing the color of roofs and pavement in 100 of the world’s largest cities could reduce global emissions by 44 billion metric tons, the researchers said.

The world produced 49 billion metric tons of emissions in 2004, according to the Intergovernmental Panel on Climate Change.

Scientists have long known that white roofs leads to lower cooling costs because they reflect, instead of absorb, heat (See New York transit going green and A look at U.C. Davis’ cleantech R&D). But researchers say this is the first study that estimates the actual impact on emissions.

“This simple and effective idea can organize the world into taking measured steps to mitigate global warming,” Akbari said in a news release. “Our findings will help city leaders and urban planners quantify the amount of CO2 they can offset using white roofs and cool pavements.”

White roofs could cut energy use by buildings by 20 percent, the researchers said. The equivalent energy reduction would save the U.S. $1 billion a year in energy costs.

California has already adopted energy-efficient roofing standards. It has mandated since 2005 that flat roofs on commercial buildings must be white.

In 2009, the state will expand the regulation to require cool-colored roofs for flat and sloped roofs on residential and commercial buildings, as well as retrofitted buildings. The state has no similar regulations for the color of pavement.

The research findings came Tuesday at the fifth annual Conference on Climate Change by the California Energy Commission.