The idea that white roofs can both reduce the average temperature of cities and reduce the amount of energy required for cooling buildings received both scientific verification and practical application yesterday.

A report from Lawrence Berkeley National Labs said that if the world’s 100 largest and hottest cities converted to white roofs and lighter colored pavement, they would achieve a one-time offset of 57 gigatons of carbon emissions. That's equivalent to taking all the autos of the world off the road for 11 years, according to Energy Secretary Chu.

The report emerged from the national lab that Chu used to run, and simultaneous with its release, the Department of Energy announced a plan to install “cool roof” technologies on its facilities and buildings. As new buildings are built or as roofs need to be replaced on DOE buildings, cool roofs will be installed. Chu also issued a letter to the heads of other federal agencies encouraging them to follow suit.

“Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change,” Chu said in a statement about the initiative. “By demonstrating the benefits of cool roofs on our facilities, the federal government can lead the nation toward more sustainable building practices, while reducing the federal carbon footprint and saving money for taxpayers.”

Previous studies had shown the method to be effective as well, but the model used in the most recent report is thought to be more accurate; it’s based on a general circulation model that includes measurements for cloud cover in the 100 global cities studied.

The report is a follow-up to a 2008 study, also written by Arthur Rosenfeld, Hashem Akbari and Surabi Menon, and it corroborates the importance of the "albedo effect" -- a measure of how well swaths of territory on the surface of the Earth reflect sunlight and heat.

“Everybody in the climate change business is very aware of albedo cooling,” Rosenfeld told SolveClimate. “We rely on ice in the Arctic ocean, which is disappearing. We rely on glaciers in Iceland and Greenland and so on. So everyone concerned with global warming, and who has access to climate circulation models, will make a run and see how much you can change the albedo of a city by whitening its roofs. And remember we’re getting more urban roofs per year.”

While proving that whitening up roofs really would deliver cooling and emissions reductions is important, the study’s authors are quick to remind policy makers that this is only one small solution of the many necessary to combat climate challenge.

“Two years worth of emissions is huge, but compared to what we need to do, it’s just a dent in the problem,” said Akbari , the former head of the Berkeley Lab Heat Island Group and now Hydro-Quebec Industrial Research Professor at Concordia University in Montreal. “We’ve been dumping CO2 into the atmosphere for the last 200 years as if there’s no future.”

Moreover, the “two years’ worth” is based on changes to pavement as well, which aren’t currently happening. If the roofs alone were to change, according to Rosenfeld, the study predicts an offset of about 31 Gigatons of carbon. Nonetheless, from an adaptation standpoint, white roofs could be fairly critical.