Whitewashing Warming

How white paint could help postpone climate crisis

Could the planet's rising temperatures and tides be stemmed by something as simple as white paint? Of course not. But according to a soon to be published study in the journal Climatic Change, a few million buckets could buy the world a few crucial years.Here's the premise: if all the rooftops and paved surfaces in the world's major cities were painted white or replaced by more reflective material (like roads made of concrete rather than asphalt), the global cooling effect would be enormous. Big enough, the study shows, to delay climate change by about 11 years.For centuries, builders have known that a white roof will reflect the sun's rays-rather than absorb them-and keep a building cooler. (Check out this great Christian Science Monitor graphic explaining how different roof colors and materials absorb heat.) That's the reason for the "White Towns" in steamy Andalusia and the white rooftops that pepper the Bermudan landscape. But not until Dr. Hashem Akbari and his colleagues at Lawrence Berkeley National Laboratories ran the numbers did anyone have a sense of how large a collective effect a global "whitewashing" effort could have on climate systems.They started off by calculating that changing a 1,000 square foot roof-the average size on an American home-from black to white would essentially offset the heating effects of 10 metric tons of carbon dioxide emissions. (Conveniently, and coincidentally, 10 metric tons is about the amount that a typical American home emits over the course of a year.) And that's just one building. Collectively, the concentration of hard, dark surfaces causes the "urban heat island" effect, which can make cities an average of 5 degrees Fahrenheit-and up to 20 degrees F-warmer than surrounding areas. And even though cities cover less than 1 percent of the world's land surface, Dr. Akbari and California Energy Commissioner Arthur Rosenfeld, two of the country's leading experts on urban heat island mitigation, emphasize that the collective impact is significant. A global "cool roofs and cool pavement" strategy, they argue, would increase the global albedo (or reflectivity, if you've forgotten your high school physics) enough to reduce planetary warming by the same amount that releasing 44 billion tons of carbon dioxide released to the atmosphere would increase it.

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In a summary of the study, they write, "How can the reader visualize this one time offset of 44 billion tonnes of CO2? … This is equivalent to taking the world's approximately 600 million cars off the road for 18 years."The Los Angeles Times offered another comparison: "That is more than all the countries on Earth emit in a single year. And, with global climate negotiators focused on limiting a rapid increase in emissions, installing cool roofs and pavements would offset more than 10 years of emissions growth, even without slashing industrial pollution."The study doesn't touch upon another dead simple cooling measure that would well complement the whitewash: planting trees, which not only cool the air by "evapotranspiring" water, but also sequester carbon dioxide. Not that Akbari's team is foreign to the concept. In some climatic simulations of Los Angeles, Akbari and Rosenfeld found that "the use of white roofs and shade trees in Los Angeles would lower the need for air conditioning by 18 percent" and that a modest "cool community" strategy could lower the average summer temperatures in the L.A. heat island by 5 degrees Fahrenheit.Thus, climate change aside, the immediate personal and local benefits of lighter roofs and roads-and planting trees-should be incentive enough.

Akbari calls it a win-win-win strategy: "Cool roofs reduce cooling-energy use in air conditioned buildings and increase comfort in unconditioned buildings (win #1). Cool roofs and cool pavements mitigate summer urban heat islands, improving outdoor air quality and comfort (win #2). This latest research shows that cool roofs and cool pavements can cool the entire globe (win #3)."Let's be clear-urban heat island mitigation tactics like cool roofs and pavements and urban tree planting aren't going to solve our climate challenges. But they could buy us some time, slowing planetary warming and polar ice and glacial melt while we transition to a low-carbon energy economy. At a moment when our leaders are searching high and low for productive and environmentally-redeeming ways to spend a stimulus package, projects like painting roofs, repaving roads, and planting trees are shovel (and roller brush) ready.(Photo of Bermuda houses from Flickr user Danny Silverman)