White Roofs Could Raise Global Temperatures
In Effects of Urban Surfaces and White Roofs on Global and Regional Climate, in the Journal of Climate, Mark Z. Jacobson and John E. Ten Hoeve combined land use, vegetation, albedo (reflecting power of the earth’s surface) and soil-type data to model temperatures 20 years into the future, estimating the effects of white roofs on climate.
They found that a worldwide conversion to white roofs, accounting for their albedo effect only, would cool population-weighted temperatures by about 0.02 C but raise overall global temperatures by much more. The researchers said that the extra sunlight reflected by white roofs can increase how much light is absorbed by dark pollutants such as black carbon, according to the Guardian.
They noted that white-roof local cooling may also affect energy use, and therefore emissions – a factor not accounted for by the study. But, Jacobson said, “Cooling your house with white roofs at the expense of warming the planet is not a very desirable trade-off. There are more effective methods of reducing global warming.”
White roofs have been frequently mentioned in media outlets as an easy fix for reducing energy consumption and costs. In the Atlantic in July, president Bill Clinton described them as the single best idea to jumpstart job creation. Clinton, founder of green building funder the Clinton Climate Initiative, pointed to a New York City program that hires young people to paint the city’s roofs white.
In 2008 California scientists said white roofs can cut a building’s energy use by 20 percent, and said they have a formula to calculate how much CO2 can be offset by increasing the reflectivity of rooftops.
Last year, U.S. Department of Energy Secretary Steven Chu announced a series of initiatives to more broadly implement cool roof technologies on DOE facilities and buildings across the federal government.
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