Climatewire (subscription service), from E&E Publishing, reports the surprising conclusion of a study just published in Environmental Research Letters. Some cities, like Dallas, TX, may not be cooled by deployment of white or light-colored roofs and pavements while other cities, like Los Angeles, are. Regional variation is apparent. The study also looked at the effect of desert photovoltaics, with their low albedo (reflectivity), on temperature and found that they can increase an area’s temperature by approximately 0.5° Celsius. White or light-colored roofs and pavements deflect heat, bouncing it back into the atmosphere and creating the cooling effect we desire. But, the study conducted by scientists at the Lawrence Berkeley National Laboratory suggests that there is a feedback effect whereby the bouncing sunlight can disrupt wind and cloud patterns, leading to changes in a region’s hot and cold spots. In humid Dallas, for example, clouds have a cooling effect on a hot day, and deflected heat from white roofs (if deployed widely) could limit cloud formation and therefore raise temperatures according to the study’s model. The researchers conclude that cool roofs are still useful tools, but that the effects might not be as uniform as we may have thought. Regional weather patterns should also be taken into consideration.
The study is available here. Milstein, D. and S. Menon. 2011. Regional climate consequences of large-scale cool roof and photovoltaic array deployment. Environmental Research Letters 6(3).
Praxis in Landscape Architecture 
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