Still, the ardor of the cool-roof advocates has prompted a bit of a backlash.

Some roofing specialists and architects argue that supporters fail to account for climate differences or the complexities of roof construction. In cooler climates, they say, reflective roofs can mean higher heating bills.

Scientists acknowledge that the extra heating costs may outweigh the air-conditioning savings in cities like Detroit or Minneapolis.

But for most types of construction, they say, light roofs yield significant net benefits as far north as New York or Chicago. Although those cities have cold winters, they are heat islands in the summer, with hundreds of thousands of square feet of roof surface absorbing energy.

The physics behind cool roofs is simple. Solar energy delivers both light and heat, and the heat from sunlight is readily absorbed by dark colors. (An asphalt roof in New York can rise to 180 degrees on a hot summer day.) Lighter colors, however, reflect back a sizable fraction of the radiation, helping to keep a building  and, more broadly, the city and Earth  cooler. They also re-emit some of the heat they absorb.

Image A white roof has helped cool Jon Waldreps Sacramento home. Credit... Jim Wilson/The New York Times

Unlike high-technology solutions to reducing energy use, like light-emitting diodes in lamp fixtures, white roofs have a long and humble history. Houses in hot climates have been whitewashed for centuries.

Before the advent of central air-conditioning in the mid-20th-century, white- and cream-colored houses with reflective tin roofs were the norm in South Florida, for example. Then central air-conditioning arrived, along with dark roofs whose basic ingredients were often asphalt, tar and bitumen, or asphalt-based shingles. These materials absorb as much as 90 percent of the sun’s heat energy  often useful in New England, but less so in Texas. By contrast, a white roof can absorb as little as 10 percent or 15 percent.