Hadn't thought about it before, but white or light-colored surfaces reflect sunlight, while dark ones absorb rays and heat up. That's another reason why scientists are concerned about melting polar ice caps (besides the threat of sea level rise) - the white snow and ice help keep the earth cool by reflecting sunlight, while rays beating down on open ocean and land warm it up.
Chu, a Nobel Prize-winning physicist, was quoted in the Telegraph estimating that putting light-colored roofs on all the world's homes and replacing black asphalt with a lighter colored pavement would offset 11 years' worth of climate-warming emissions from all the world's cars.
A study co-authored by a scientist from Lawrence Berkeley National Laboratory in California (which Chu ran before joining the Obama administration) backs up his suggestion that converting a black roof to white would help offset the 10 tons of carbon dioxide emitted annually by the typical US house.
And if fighting climate change isn't reason enough, it also ought to help reduce air conditioning bills in the summer. By one estimate, white roofs everywhere in the US could save $1 billion in energy costs annually.
There's no plan, apparently, to push this bit of geo-engineering on a national level - at least not yet. But California, arguably the greenest of states in the US, already requires white materials on flat roofs, and in July will start requiring "cool-colored substances" on sloped roofs as well.
Anyone doing this in Maryland?