In comments at the St. James Palace Nobel Laureate Symposium, U.S. Energy Secretary Steven Chu argues that “if you take all the buildings and make their roofs white and if you make the pavement more of a concrete type of colour rather than a black type of colour, and you do this uniformly . . . it’s the equivalent of reducing the carbon emissions due to all the cars on the road for 11 years.” Chu points to research by Art Rosenfeld, a member of the California Energy Commission, who drove through tough new building rules in California. (also, read an earlier post on this study). According to The Times (UK), “since 2005, California has required all flat roofs on commercial buildings to be white; the measure is being expanded to require cool colours on all residential and pitched roofs.”
If all cities at the global level painted their roofs white, there could be a massive mitigation effect. The Times writes: “Last year Dr Rosenfeld and two colleagues from the laboratory, Hashem Akbari and Surabi Menon, calculated that changing surface colours in 100 of the world’s largest cities could save the equivalent of 44 billion tonnes of carbon dioxide — about as much as global carbon emissions are expected to rise by over the next decade.”
To combat the potential negative effects of white roads on drivers, roads could instead be lightened to a concrete colour so they would not reflect in bright sunlight. Additionally, cars could be added to the list — lighter color cars would, of course, be more reflective.
Climate Progress, a leading climate change policy blog, argues that painting roofs and paved roads white may be one of the few geo-engineering schemes that work. “I would add that by reducing the urban heat island effect (along with shade tree planting), white roofs are also the lowest cost ‘adaptation’ strategy, directly cooling a city. So it is perhaps the one true triple play in climate — mitigation, geo-engineering, and adaptation — that is also both low-cost and scalable.”
While white roofs are more cost-effective than green roofs, simply painting roofs white won’t address stormwater management issues (or water management issues more broadly) or the urban heat island effect in cities. Combinations of green roof elements and lighter-colored roofs may be the best solution for cities facing these inter-connected problems.