White roofs could cool cities

Jeremy Hance
January 28, 2010

Painting urban roofs white could effectively counteract some of the urban heat-island effect and even lower greenhouse gas emissions in cities, reports a new study in Geophysical Research Letters.

"Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat," says Keith Oleson, the lead author of the study and a scientist at the National Center for Atmospheric Research (NCAR). "It remains to be seen if it's actually feasible for cities to paint their roofs white, but the idea certainly warrants further investigation."

White roofs would act a bit like a mirror in the urban landscape, reflecting some of the heat of the sun back into the atmosphere. Using a computer model simulation, the study found that ideally white roofs could mitigate the heat island effect by 33 percent, cooling cities by 0.4 degrees Celsius (0.7 degrees Fahrenheit). Since the modeling system was not able to recreate all the intricacies of the urban environment, such as dust, weathering, and barriers to painting, the effect would probably be less, but still significant.

The effect would also cool the inside of buildings allowing residents of warmer cities to use less energy in air-conditioning, thereby cutting-down on greenhouse gases. The researchers point out that certain types of cities would benefit more than others, such as those with high roof density, certain roof types, and in warmer climates.

Looking at specific metropolitan areas, the study found that the New York area could receive a cooling benefit of 1.1 degrees Celsius (2 degrees Fahrenheit) for summers in the city by painting the roofs white.

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Jeremy Hance
mongabay.com (January 28, 2010).

White roofs could cool cities.