He said that as much as 4.5 million square miles of desert may be suitable for covering with a reflective surface for the purpose of offsetting global warming. On the scale required to do so, this would be a Global Albdeo Enhancement Project (GAEP). Gaskill listed the assumptions on which the feasibility of this was based. The additional radiative forcing he projects from 2010-2070 of 2.75 watts/m2 would be the primary target for reduction. This level is reasonable based on emissions forecasts. By 2070, GHG emissions BEGIN to be controlled globally. All additional radiation reflected at the surface is returned to space.
A calculation was presented of net reflected solar radiation from a typical desert vs. one covered with a reflective material. Increasing the surface reflectivity or albedo from 36% to 80% resulted in an additional 136 watts/m2 reflected. This reflected flux was used to calculate the land area coverage required to offset the radiative forcing from various scenarios. All forcing from 1750-2070 would require 7.9 million square miles, more than all available desert land; the forcing from 1750-2000, 3.6 million; the U.S. Kyoto target for 2012 290,000; all U.S. electric power generation from 1750-2070 390,000 and all U.S. forcing from 1750-2000, 2 million.
Of greatest relevance was that 4 million square miles would be required to offset all of the forcing from 2010-2070, almost all of the desert land likely suitable. These numbers point out that the GAEP is not an alternative to emissions reduction, but a delaying tactic until the emissions can be brought under control.
Gaskill noted that averaged over 60 years, the annual coverage would be around 67,000 square miles or about the size of Missouri. However, the coverage in earlier years could be much less since the GHG emissions are expected to increase non-linearly over time. He also noted that 80,000 square miles is planted in wheat annually in the U.S. Thus, the scale of this project is comparable to what is practiced today in modern agriculture.
Gaskill then discussed how the GAEP might be implemented. He said that both global and regional (mesoscale) climate modeling should be done first to detect possible impacts such as changes in temperature, wind flow patterns, precipitation and hydrology. The models could be designed to avoid distortions likely from natural variability. One of these would be that from changing the conditions incrementally as would be the case with the reflective cover. Instead, an instantaneous application of say 60 years of coverage allowed to reach equilibrium, would help define the conditions of importance in applying the cover incrementally. Both Drs. MacCracken and Caldeira helped explain this.
Examples of global climate modeling performed by LLNL were reviewed in which the radiative forcing resulting from a doubling of atmospheric CO2 (280 to 560 ppm or 355 to 710 ppm) levels was completely offset by reducing incoming solar radiation by 1.7% from outside the atmosphere. In these models, there were no temperature increases or decreases observed in the troposphere either globally, regionally, or seasonally, indicating the reduction of solar luminosity compensated for the effects of increased CO2. Gaskill said modeling like this should be done to predict the impact of the GAEP since an uneven reduction in solar radiation absorbed at the surface, like that expected from the GAEP, would be expected to produce uneven heating globally, regionally and seasonally.
