White roofs have been promoted as a simple, easy, “soft geoengineering” solution to help combat global warming for awhile now. The solution has gotten the strong backing of former president Bill Clinton and current Energy Secretary Steven Chu. I thought this was a rather obvious solution we should adopt — reflect more back into space with lighter roofs. Many thought is was a good idea.
However, new research has flipped this white roofs solution into a potential global warming problem (showing that even the simplest geoengineering solutions may have side-effects we didn’t think up from the start). The study, led by Mark Z. Jacobson, a professor of civil and environmental engineering at Stanford University, found:
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.
Now, one thing Jacobson’s team didn’t include in the study was how much white roofs reduced demand for electricity (and, thus, burning of fossil fuels). Of course, white roofs would also mean a house in a cold climate would need more heating in winter, but it’s not clear which way the benefit is stronger.
Summary points:
- Looks like we shouldn’t go painting everyone’s roof white after all (at least not until more research is done).
- Geoengineering (even “soft” options) will have more than the obvious or targeted effects.
- The best way to address global warming is still to just cut our burning of fossil fuels (vie basic energy efficiency or switching to clean energy options).
In Jacobson’s words: “There does not seem to be a benefit from investing in white roofs…. The most important thing is to reduce emissions of the pollutants that contribute to global warming.”
Solar PV Panels Help (in Multiple Ways)
Now, solar PV panels help address global warming in even more ways now, the study pointed out.
Aside from using sunlight instead of fossil fuels to create electricity, they shade one’s house (helpful in warmer climate, at least), and they don’t reflect sunlight back into the air like white roofs do.
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