Whiter roofs for a cooler planet - September 10, 2008
Posted on behalf of Amber Dance
Want to save the planet? Grab a can of white paint — and a ladder. At the Global Climate Change Conference this week in Sacramento, California, scientists from the Lawrence Berkeley National Laboratory presented a plan to offset 44 gigatonnes of atmospheric carbon dioxide with a hefty dose of whitewash.
The study is the first to put numbers on what people have known for years — whiter roofs reflect more solar radiation, thus reducing global warming while saving money on air conditioning bills (Los Angeles Times). The research paper is in press at Climate Change.
White-topping the roof of an average family home is like sucking 10 tonnes of carbon dioxide out of the air, says study author Hashem Akbari. It also cuts energy costs by 20 percent, says co-author Art Rosenfeld of the California Energy Commission (East Bay Business Times). If major cities in tropical and temperate zones adopted paler roofs and pavements, the authors estimate, it could offset 44 gigatonnes’ worth of atmospheric carbon dioxide. That’s more than the world emits in a year.
California has required flat-topped, commercial buildings to go white since 2005, and will require new and retrofitted buildings to use cool-color roofing starting in 2009. These shingles and coatings look like their high-absorbing counterparts, but reflect more of the sun’s rays.
However, those white shingles have to be clean to work their magic, and the chore of regular roof-washing could eliminate the appeal of less power use. Akbari’s group reports on its web site that manufacturers have come up with self-washing white shingles.
“I call it win-win-win,” Akbari says. Cities are cooler and more comfortable, home- and business owners save on their summer electricity bills, and everyone feels good about slowing the process of climate change. The scientists hope to persuade the United Nations to help get cities to go white.
Image: Briny Breezes, Boynton Beach by Christopher Dick, via Flickr
Comments
It's encouraging to see estimates of the value of reflective roofs. I've just opted to install a galvanized steel roof on my southern Florida house. I considered white paint, but keeping it clean in the face of materials falling from two oak trees might be a problem. Zinc may perhaps cause modest heavy metal contamination, but the house occupies a bit of an old citrus grove, so the site is possibly already contaminated by copper from fungicides.
Regrettably, the recent fashion in Florida residential roofs has been for rather dark colors.
Posted by: David Martin | September 11, 2008 08:49 PM
1 around 50 percent of sunlight is visible light
2 around 50 percent of sunlight is heat
3 visible light is a frequency of light not absorbed by the atmosphere
4 some heat from the sun is absorbed by the atmosphere directly (greenhouse gasses which makes the atmosphere warmer).
5 heat from the sun also warms the surface of the planet and this heat is then radiated back into the atmosphere again being absorbed by greenhouse gasses.
6 visible light is poorly absorbed by the atmosphere, some of it gets reflected back by the atmosphere.
7 the visible light that doesn't get reflected back by the atmosphere is either reflected by the surface (eg a snow field) or absorbed by the surface (an asphalt carpark/ road). this absorbed light heats the dark surface. this heat is then radiated into the atmosphere and is absorbed by greenhouses gasses makiig the atmosphere warmer.
8 by painting your roof white and other surface you reflect aroud 50 percent of the visible enrgy from the sun, a significant amount of this is reflected back into space without heating the atmosphere.
9 by painting enough roofs you make buildings cooler and cool the atmosphere
great to see someone spreading the message!!
Posted by: wookiemeister | December 30, 2008 06:49 AM