Examples of regional modeling performed by Dr. Haider Taha of Altostatus, Inc. were also presented in which impacts of surface albedo enhancement on regional meteorology and tropospheric ozone were studied. The resolution of the regional modeling was 4 km2, while that for the global modeling was around 40,000 square miles, illustrating the need for the mesoscale modeling in predicting impacts over smaller areas.
Gaskill described the characteristics of an ideal surface cover: inexpensive to produce, install, maintain; highly reflective, reflecting >80% of incident sunlight; puncture and tear resistant; stable for years in a field environment; recyclable as cover material and available today or within 5 years. Based on these criteria, he said white polyethylene film is the best choice. The whiteness is due to titanium dioxide pigment. Plastic film used in the field contains additives such as antioxidants, thermal stabilizers and UV inhibitors designed to prolong its life. Such films are often embossed to resist wind fatigue and cracking. However, they are not completely opaque at typical thicknesses (1-6 mil) and may only reflect 60% of sunlight.
For the GAEP cover, he said a composite film consisting of white plastic on the top and aluminized plastic on the bottom may be most effective in reflecting sunlight. The aluminized plastic can reflect as much as 90% of incident sunlight, but only emits 25% of the IR it absorbs, while the white plastic reflects 60% of the sunlight and emits 90% of the IR it absorbs. Combined, they could yield an overall reflectivity of sunlight of 80% and an emissivity of IR of 90%, the best of both worlds.
He showed an example of the use of aluminized surface cover in orchards (slide 96), noting there is still much to be learned about the ideal plastic film for this application.
He said installation would require removal of material that could puncture the plastic and might require grading of the surface. Installation equipment could be patterned after the large installers used for geomembranes. The cover could be kept in place with commercially available mechanical anchors that resemble giant thumbtacks as indicated in slides 98 and 99.
Accurate monitoring of surface albedo would be required for input data for models, to calculate “thermal credits” for emissions trading or in meeting emission reduction targets and to ensure albedo is above its target value. Other radiometric and meteorological parameters would also be determined. Monitoring would be accomplished through a combination of ground stations, unmanned aerial vehicles and satellites.
The cover would be replaced every 3 years and cleaned as necessary using robotic vacuum cleaners to remove dust that would darken the surface. Gaskill said their research found that conventional robotic vacuum cleaners spread fine particles of soil over the surface that could not be removed by vacuuming. Developing vacuum systems that can limit particle adherence to the surface by electrostatic or other means or covering land from which the dust originates are both topics that should be pursued.
Gaskill presented an estimate of the cost of the GAEP, based on the maximum possible coverage of 4 million square miles done equally over 60 years. The following assumptions were made. The plastic is a 3-layer 4-mil polyethylene film costing 1.7-cents/square foot (SF), which can be recycled 3 times at 50% the cost of the original. If aluminized composites are used, they will be more difficult to recycle and may cost more. The cost of installation was 12% the cost of the plastic and the combined cost of monitoring and maintenance were 14%. Maintenance costs were based on 24/7 vacuum operations. [Cost assumptions slide 105 revised to reflect these changes].
