Replacing roofs and pavements with more reflective versions could lower global temperatures by up to 0.07 °C, equivalent to a reduction in carbon-dioxide emissions of about 150 billion tonnes. That is according to researchers in Canada who used a global climate model to look at the effects of such albedo changes in urban areas.
I almost don't want to post the next paragraph:
"Scientists have been proposing novel ideas – mostly untested – for the geoengineering of global climate," says Hashem Akbari of Concordia University. "But humans have had experience with white buildings and reflective pavements for thousands of years without any unknown negative side effects. Hence, cool urban surfaces should be our geoengineering 101."
The problem isn't geoengineering...it's political will.
Physics World: Reflective roofs and pavements could fight climate change