Cool buildings and cool communities

Analysis of temperature trends for the last 100 years in several large U. S. cities has indicated that since -1940 there has been a steady increase in downtown temperatures of 0.1-0.5DC per decade (-0.5°C for larger cities like Los Angeles and 0.1°C for smaller cities). Typically, electricity demand in cities increases by 2-4%/°C, hence, about 5-10% of the current urban electricity demand is spent to cool buildings just to compensate for the urban heat island effect. Downtown Los Angeles, for example, is now 3°C warmer than in 1940 leading to an increase in electricity demand of 1500 MW. In L.A., smoggy episodes are absent below about 21°C, but smog becomes unacceptable by 32°C, so a rise of 3°C, because of the heat island effects, can be significant. Urban trees and high-albedo surfaces can offset or reverse the heat island effect, and can potentially reduce the national energy use of air conditioning by 10% and save over $4B per year. The albedo of a city may be increased gradually if high-albedo surfaces are chosen to replace darker materials during routine maintenance of roofs and roads. Incentive programs, product labeling, and standards could promote the use of high-albedo materials for buildings and roads. Similar incentive-based programs need to be developed for urban trees.