With funding from the California Air Resources Board, Berkeley Lab's Heat Island Group created this map using public data collected in summer 2009. An airplane-mounted sensor measured light-intensity in four spectral bands at 1-meter spatial resolution. These data were originally acquired for the National Agriculture Imagery Program of the U.S. Department of Agriculture.

After various corrections were made (e.g. accounting for light scattering in the atmosphere), individual rooftop pixels were isolated, and the albedo of each roof was estimated. The results were calibrated and “ground-truthed” using laboratory measurements of hundreds of roofing samples and rooftop measurements of albedo using an instrument called a pyranometer. Streets and parking lots were excluded from the analysis.

Note: Rooftop equipment, such as solar panels or HVAC systems, was not distinguished from the roofing material and was included in the albedo estimate for each rooftop. Also note that there is associated uncertainty in the reported albedo for each rooftop, especially for high albedo roofs. For more details on methods, uncertainties, and further analyses and implications, see the CARB report.

Want more science? Check out the Heat Island Group's cool science page.

At noon on a clear summer day in the United States, a flat roof receives about 1000 watts of sunlight per square meter. Traditional dark roofs strongly absorb sunlight and:

Heat up the building.

Increase AC energy use, cost, and associated climate warming greenhouse gas emissions

Heat the air, worsening the urban heat island effect.

Thinking of going cool? Check out our list of resources.