Response to joshcryer (Reply #17)
Fri Jun 8, 2012, 04:37 PM
OKIsItJustMe (13,522 posts)
20. These approaches are also not effective
Last edited Fri Jun 8, 2012, 05:01 PM USA/ET - Edit history (4)
Stanford Report, October 19, 2011
Urban 'heat island' effect is only a small contributor to global warming, and white roofs don't help to solve the problem, say Stanford researchers
Heat emanating from cities – called the "urban heat island" effect – is not a significant contributor to global warming, Stanford researchers have found. They also concluded that if all the roofs in urban areas were painted white, it would increase, not decrease, global warming.
One "geoengineering" proposal for reducing the impact of urban heat islands is to paint roofs worldwide a reflective white. 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.
Jacobson's study did not examine one potential benefit of white roofs – a reduced demand for electricity to run air conditioning in hot weather. But a recent study done at the National Center for Atmospheric Research showed that the decrease in air conditioning use, which occurs mostly in the summer, might be more than offset by increases in heating during winter months.
"There does not seem to be a benefit from investing in white roofs," said Jacobson. "The most important thing is to reduce emissions of the pollutants that contribute to global warming."
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