If the world's 100 biggest cities were to whiten the roofs of all of their buildings and use more reflective pavement, the global cooling effect would be huge, a new study has concluded.
Speaking at the Fifth Annual California Climate Change Research Conference in Sacramento, Hashem Akbari, a physicist with the Lawrence Berkeley National Laboratory, said that he has created a formula to determine how much heat-trapping carbon dioxide would be offset by reflecting the solar radiation back into space. In his presentation [PDF], he said that replacing the dark shingles on a 1,000-square-foot roof – the average size of an American home – with white material would offset 10 metric tons of greenhouse gases.
His paper, "Global Cooling: Increasing Worldwide Urban Albedos to Offset CO2," will be published in the journal Climatic Change.
The benefits of white roofs and reflective pavement extend beyond climate change. White roofs can cut air conditioning costs by 20 percent, according to California's Energy Commissioner. And reflective surfaces would reduce what's known as the urban heat island effect, that is, the capacity of metropolitan areas to absorb more heat than their surrounding areas. According to Mr. Akbari's study, cooler temperatures would slow the rates of chemical reactions that produce smog.
Still, this doesn't have to be an all-or-nothing proposition. If Akbari's numbers are right, then converting 10 percent of the roads and rooftops of the world's 100 largest cities would offset one year of emissions growth. Not too shabby.
That said, I'm not thrilled about the prospect of driving – or crossing a busy street – on a reflective surface. And not all of us get to live in sunny California. Sure, a white rooftop may cut my air-conditioning costs in the summer, but when winter comes, what will it do to my heating bill?