As the threat of climate change becomes more pronounced, a number of scientists have proposed supplementing the full range of mitigation efforts with geo-engineering (manipulation of the Earth’s environment) to quickly respond to this threat. Many proposed geo-engineering techniques are novel and unproven. One simple technology has been in practice for thousands of years: changing the solar reflectance (albedo) of the built surface. “Cool roofs” and “cool pavements” should be among the first geo-engineering techniques used to combat global warming. Increasing the solar reflectance of the urban surface reduce its solar heat gain, lowers its temperatures, and decreases its outflow of thermal infrared radiation into the atmosphere. This process of “negative radioactive forcing” can help counter the effects of global warming. It is estimated that resurfacing conventional dark roofs with a cool white material that has a long-term solar reflectance of 0.60 or more increases its solar reflectance by at least 0.40. Retrofitting 100 m2 of roof has an effect on radioactive forcing equivalent to a one-time offset of 10 tonnes of CO2. Similarly, the solar reflectance of pavement can be raised on average by about 0.15, the equivalent of a 4 t reduction in CO2 per 100 m2. Read more..