Gaskill also addressed the potential application of large-scale surface albedo enhancement to the urban heat island problem. This is caused by the absorption and re-emission of solar radiation by the low reflectivity surfaces of building roofs and pavement in urban areas. The low reflectivity plus the lack of trees to carry off heat as transpired water results in higher daytime and nighttime temperatures, higher air conditioning costs and greater tropospheric ozone formation.
Gaskill reviewed some of the work conducted by Lawrence Berkeley National Laboratory (LBNL) and the California Energy Commission (CEC) that have been studying ways to reduce the urban heat island effect for more than 20 years. Their proposals have included whitening of roofs and pavements and the planting of trees. The “whitening” includes the total solar spectrum so some “dark” surfaces can be made “whiter” relative to the total solar spectrum.
LBNL estimates that raising the albedo of the greater Los Angeles area by 7.5% (approximately 4000 square miles) by whitening 1000 square miles of roofs and pavement and planting 11 million trees will reduce the air temperature by 5°F. They estimate this would save almost $500 million annually in electricity and smog costs. Applied nationally to urban areas, nearly $5 billion could be saved.
The CEC takes this a step further and says that raising the albedo of the 100 largest cities on Earth could offset GHG emissions by 2.5% as well as save money from the other benefits noted in the Los Angeles example. This would also serve to lessen the impact of future global warming driven heat waves. It should be noted that although the 100 largest cities include many candidates that might fit a Los Angeles model with lots of paved surfaces and dark rooftops, this list also includes many third world cities like Lagos, Nigeria (7), Karachi, Pakistan (13), Dhaka, Bangladesh (15) and Jakarta, Indonesia (21) that have populations of around 10 million, but probably little in the way of paved streets and roofs amenable to whitening.
Gaskill suggested that the GAEP might be applied to the urban heat island problem by albedo enhancement of areas outside some of these cities by covering land with white plastic. The cooler air produced by this would mix with the hotter air from the city, cooling it. He gave examples of Las Vegas, NV and Phoenix, AZ. The areas mentioned in slide 145 of 5-20 square miles may be too low to be effective.
A more realistic estimate is calculated as follows. Start with the goal of raising the albedo of one fourth the urban area as in the Los Angeles case. Applied to Phoenix, which has an area of around 700 square miles, the land to have its albedo raised by 7.5% would be 175 square miles. However, the albedo in this case is raised by 60% (from 20% to 80%) not 7.5% and no trees are planted, since the albedo increase is outside the city and would not help as much. This would increase the albedo by nearly 4 times and should reduce the land area required to around 45 square miles. At around $500,000/square mile, averaged over 3 years, the plastic cover costs around $8 million per year and should provide savings comparable to roof and pavement whitening. This can also be done much sooner than the whitening of urban surfaces and large scale tree planting, which may take decades to complete. Covering a 45 square mile area around Phoenix could probably be completed in one year.
