Painting urban roofs white is perhaps the simplest and most benign of the various schemes that have been proposed to fight climate change through geo-engineering.
Steven Chu, the US energy secretary, advocated white roofs last year but some experts doubted whether the idea would make enough impact to be worth pursuing.
Now the first computer modelling study to simulate the impact of white roofs on cities worldwide, carried out at the US National Center for Atmospheric Research, has confirmed that they could significantly cool urban areas and mitigate some effects of global warming. The study will be published in Geophysical Research Letters.
“Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat,” says NCAR scientist Keith Oleson. “It remains to be seen if it’s actually feasible for cities to paint their roofs white, but the idea certainly warrants further investigation.”
The study team used a new computer model to simulate the amount of solar radiation absorbed or reflected by urban surfaces. The simulations, which provide an idealized view of different types of cities around the world, indicate that, if every roof were entirely painted white, the urban heat island effect could be reduced by 33 percent.
While the model did not have enough detail to capture individual cities, it did show the change in temperatures in larger metropolitan regions. The New York area, for example, would cool in summer afternoons by around 1 degree centigrade.
White roofs are evidently not going to save the planet on their own but it does sound as though we should be considering a painting programme.