The long-term effect of increasing the albedo of urban areas
Solar reflective urban surfaces (white rooftops and light-colored pavements) can increase the albedo of an urban area by about 0.1. Increasing the albedo of urban and human settlement areas can in turn decrease atmospheric temperature and could potentially offset some of the anticipated temperature increase caused by global warming. We have simulated the long-term (decadal to centennial) effect of increasing urban surface albedos using a spatially explicit global climate model of intermediate complexity. We first carried out two sets of simulations in which we increased the albedo of all land areas between ±20° and ±45° latitude respectively. The results of these simulations indicate a long-term global cooling effect of 3 × 10 −15 K for each 1 m 2 of a surface with an albedo increase of 0.01. This temperature reduction corresponds to an equivalent CO 2 emission reduction of about 7 kg, based on recent estimates of the amount of global warming per unit CO 2 emission. In a series of additional simulations, we increased the albedo of urban locations only, on the basis of two independent estimates of the spatial extent of urban areas. In these simulations, global cooling ranged from 0.01 to 0.07 K, which corresponds to a CO 2 equivalent emission reduction of 25–150 billion tonnes of CO 2 .