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the capital cost of the fleet is $2 × 1010. Amortized over 20 years, an annual capital cost of $1 × 109 may be used. The sulfur will cost another $0.6 × 109 per year, and $2 × 106 per ship per year may be allocated for operating costs ($10,000 per operating day), to give a total cost of $2 × 109 annually. Over 40 years (until 2030) this means $8 × 1010, or $1011. This continuously mitigates ˜103 Gt = 1012 t for a cost of $0.10/t of CO2. Of course, this continues to be a yearly cost of $1 × 109/yr.

The SO2 could also be emitted from power plants. These plants could be built in the Pacific Ocean near the equator (hopefully on small deserted islands) and would serve to furnish power for nearby locations (e.g., South America). Transmission or use of the power in the form of refined materials could be considered, or possibly the use of superconducting power transmission systems. It is estimated that eight large power plants using spiked coal would be required (with 4 times the normal amount of sulfur) at a cost of $2 to $2.5 × 106 per plant. Most of the cost would be borne by those buying the power, so the cost might be at most 10 percent per year (the interest on the investment), or a total of $2 × 109 per year (with the above conversion, $2 × 109/3890 × 106 $0.0005/t CO2).

Comparison of the Cloudiness and Proposed Cloud Condensation Nuclei Emissions with Current Estimates in the Real Atmospher

Total U.S. SO2 emissions are 65.7 × 103 t per day, which is roughly 2 times the amount calculated in the previous paragraph. Consequently, there should already be some cloud-enhancing effects evident in the northern hemisphere if Twomey and Wojciechowski's hypothesis, as implemented by Albrecht, is correct. An examination of available CCN data shows that the mean CCN concentration at oceanic locations in the northern Atlantic is about 5 times higher than at remote locations in the southern Pacific (see Schwartz (1988), who, however, concludes that there is no discernible contribution of anthropogenic SO2 emissions to the global cloud cover effect on planetary albedo or temperature). Furthermore, several studies have examined trends in cloudiness in the northern hemisphere and have all come to the same conclusion: The total cloud amount has been increasing in the northern hemisphere (study areas include United States, North America, the North Atlantic, and Europe) since the early 1900s (Henderson-Sellers, 1986, 1989; Changnon, 1981; Angell et al., 1984; Warren et al., 1988). The largest increases in cloudiness in the United States occurred from the 1930s to about 1950 and from the mid-1960s to about 1980. The first period corresponds to a period of rapid growth of U.S. SO2 emissions after the Depression and extends to the end of World War II; the second period corresponds to the proliferation of tall stacks. From 1965 to 1980 the mean effective stack height (physical height of stack plus plume rise) of SO2