The new study focused on the first effect. To analyze the impact of a change in the reflectivity of city roofs, scientists with Lawrence Berkeley National Laboratory (LBNL) and the state of California estimated the global number of roofs and asphalt surfaces in cities. They made a conservative estimate that those surfaces make-up 1% of the Earth's surface. Modifying the roofs with light-colored tiles, the team found that using light-colored concrete, or applying white glazes to buildings, could increase the reflectivity of urban surfaces by 10%. That adjustment would negate the warming effects of 44 gigatons of carbon dioxide, the researchers report in an upcoming issue of Climatic Change. (The world currently emits roughly 28 gigatons per year from fossil fuels.) Halting all deforestation of tropical forests could eliminate about seven gigatons of emissions, by comparison.
"We were really surprised. We didn't expect such a big [cooling] effect," says LBNL climate scientist Surabi Menon.
Assuming a global system that would put a price on carbon emissions, the scientists then calculated the value of carbon credits awarded to homeowners and businesses for making their roofs and streets lighter. At $25 per ton, the authors found the market for light-colored roofs would be worth more than $1 billion. It will be up to governments whether to offer such an incentive, says Menon, whose study didn't calculate how much it would cost to make the surfaces more reflective through the various means.
The following might be of interest on the use of highly reflective microcrystals (“micromirrors”) for increasing terrestrial albedo:
This may be a more feasible approach as compared to other proposals.