Gaskill noted that this could also lead to economic costs for planting trees! Countries would be penalized for having too much forestland vs. a baseline. Irrespective of any tree planting schemes, it is likely that the boreal forest will expand into the tundra anyway as the Arctic warms in this century.

Caldeira said that since albedo changes can be measured from space, they would be easy to quantify and verify. He suggested that in the future, people might pay an albedo tax if they install a black asphalt driveway and get credit for installing a reflective one. This isn’t the case now, but recent California building regulations do give credits to pay for white roofs and require new ones to be highly reflective.

Dr. Akbari from LBNL submitted written comments on proposed Urban Heat Island Mitigation research. He provided further details of how the increases in surface albedo for the Los Angeles basin were calculated. They estimated that if the albedo of roofs were increased by 30% and pavements by 15%, then the albedo for all such surfaces in the Los Angeles basin (totaling 1000 square miles) would be increased by 22.5% and the albedo of the entire basin (4000 square miles) by 5.6%, not 7.5% as indicated in the text of this report.

Applying such a strategy aggressively, by changing the albedo of roofs by 60% (applying white roofs and keeping them clean) and pavements by 25%, then the average albedo of these surfaces is increased by 42.5% and that of the entire basin by 10.6%.

For Phoenix, he estimates that half of the surface areas are amenable to having their albedo increased or around 350 square miles. Using the first Los Angeles example, the albedo of 350 square miles could be increased by 22.5%. It’s not clear if the massive tree planting included in the assumptions for Los Angeles would apply to Phoenix or could be applied, given the scarcity of water. It is also unclear what the effect on air temperatures a 22.5% whitening of 350 square miles of urban Phoenix would have vs. that of a 60% whitening of a 45 square mile area just outside Phoenix. Clearly, these are calculations that require a detailed analysis.

Akbari says that increasing the albedo inside the city should be the first priority, since it saves energy, reduces GHG emissions and improves air quality. After taking care of the largest 100 heat islands around the globe (assumed to be 100 largest cities by population), if we were going to increase the albedo of the desert adjacent to Phoenix (as an experiment to see how it could be done for the Sahara), we should also design its implementation such that it would reduce the ambient air temperature in Phoenix.

Dr. Taha from Altostratus noted that each city has be considered separately, pointing out that although Los Angeles and Houston are about the same size geographically, only 5 million trees would be required to achieve the same degree of cooling there as 11 million in Los Angeles.