Appendix A

Comparison of Emission Offsets to Number of Emission Sources

Another way of evaluating the potential effectiveness of the surface albedo cover in reducing the impact of global warming is to calculate this impact in terms of how many emission sources a given degree of coverage will offset during their lifetime.

For example, one SUV with a fuel economy of 12 mpg driven 12,000 miles per year emits 22,000 lbs of carbon dioxide as a result of the 1000 gallons of gasoline it burns, each gallon of gasoline producing 22 lbs of carbon dioxide. This is roughly equivalent to the weight of the vehicle every 4-6 months (172). An average passenger car with a fuel efficiency of 22.5 mpg driven 12,500 miles produces 10,000 lbs of carbon dioxide, while an SUV with a fuel efficiency of 15.3 mpg driven 14,000 miles produces 14,000 lbs of carbon dioxide (173).

The SUV with a 12-mpg fuel efficiency produces 10 metric tons of carbon dioxide per year or 2.7 tons of carbon (carbon dioxide is 27% carbon). Assuming a 15-year lifetime for the vehicle, a total of 41 tons of carbon are emitted during this period. The plastic cover applied to 4 million square miles will offset the emissions from 1170 GtC or 293,000 tons/sq. mi. Thus, 293,000 tons/sq. mi divided by 41 tons from the SUV yields the never before calculated statistic of 7000 SUVs/sq. mi.

Similarly, the emissions from electric power stations can be related to the area covered. Assuming that all U.S. emissions are around 500 million tons of carbon annually and that there are 5000 such power stations, then each station emits 100,000 metric tons annually or 3.5 million over a 35 year operating lifetime. Dividing this into the 293,000 tons/sq. mi. offset by the plastic cover yields the figure 0.0837 power stations /sq. mi. or roughly 1 power station/12 sq. mi. This compares rather favorably with typical estimates of how much forest is required to offset power station emissions. One such estimate is that 766 sq. mi. is required to absorb the carbon dioxide produced during the operating life of a 500 MW coal fired station (174).