White roofs were getting a lot of press for their ability to help fight global warming. Heck, we wrote about the virtues of a white roof right here! Last summer, the U.S. Energy secretary had the Department of Energy install a white roof to lead by example. Now, new research is showing that white roofs may not be all they're cracked up to be. In fact, they could be making things worse.
Our pals at CleanTechnica point us to a study by Mark Z. Jacobson, a professor of civil and environmental engineering at Stanford University that looked at white roofs' net effects and tells a different story:
Jacobson’s computer modeling concluded that white roofs did indeed cool urban surfaces. However, they caused a net global warming, largely because they reduced cloudiness slightly by increasing the stability of the air, thereby reducing the vertical transport of moisture and energy to clouds. In Jacobson’s modeling, the reduction in cloudiness allowed more sunlight to reach the surface.
The increased sunlight reflected back into the atmosphere by white roofs in turn increased absorption of light by dark pollutants such as black carbon, which further increased heating of the atmosphere.
A Grain of Salt
Before you go painting your white roof black, though, there's an added benefit to a light roof: lower air conditioning bills. As Zach at CleanTechnica points out, this study didn't take into account the reduced emissions from relying less on coal-fired power to cool these structures.
I'd definitely like to see some more research on this topic that does take that difference into account. Heating and cooling make up a huge portion of our energy bills, so including energy use to cool these building might just change everything.
Do any of you guys have a white roof? How did it impact your cooling bills? What about heating in the winter?
Photo credit: NNSANews via flickr