The major emissions into the atmosphere from SPS activities will occur from rocket launches. Rocket effluents include substantial amounts of CO2, but these emissions are at least 100 times smaller than the CO2 emissions from coal combustion for an equivalent amount of system capacity.153 The possibility exists for some upper-level clouds to be formed by H2O injections into the mesosphere. The impacts of these clouds do not appear to be significant but are not well known at present. A slight depletion of the total ozone column due to emissions of H2O and N0x is possible but is not expected to affect global climate to a noticeable extent.1*1 The ability to reliably predict climatic change resulting from air pollution emissions is currently limited by several factors. There is considerable uncertainty concerning the extremely complex nature of the earthatmosphere system and the interrelations between the various parts of the system. Insufficient knowledge hampers the prediction of how second-order coupled processes or ’’feedback mechanisms” might enhance or suppress a first- order effect on climate such as a surface warming due to CO2. There is also uncertainty about the magnitude of the effect of other greenhouse gases and atmospheric particles compared to the CO2 effect.155 The role of natural climatic fluctuations in enhancing or masking trends due to man-made emissions further contributes to the uncertainty of predictions. It is expected that the ability to predict climatic change will improve with additional research; however, drastic improvements in forecast reliability are probably not to be expected in the near future because of the complexity of the problem. 4.4.5 Thermal Discharges and Resulting Climatic Change Production of electrical energy results in the rejection of waste heat to the environment. A nuclear power plant with an efficiency of 32% releases two units of waste heat for each unit of heat used to produce electrical energy, as do coal- and oil-fired plants that operate on the Rankine cycle. However, with nuclear plants all of this waste heat is rejected to cooling towers. The impacts of this waste heat are local and dependent on the type of cooling technology, the amount of heat released, and the local ambient meteorological conditions. Most existing and all planned nuclear power plants employ cooling towers.141 Most new and planned coal- fired plants also use cooling towers. Mechanical-draft cooling towers can produce an increase in local ground fog a few days per year within a few thousand feet of the towers. Some local icing may occur during the winter when the moist thermal plume contacts the ground. Production or enhancement of cloudiness in the vicinity of large cooling towers has also been observed.156 areas where these problems occur, technology is available at a moderate incremental cost to eliminate the adverse effects. A relatively unlikely, but potentially significant impact could occur in the future if nuclear power plants are clustered into energy ’’parks.” The large release rate of waste heat (e.g., 72,000 MWt from a 36,000 MWe power park) over an area of relatively small radius (10 to 100 km) could produce or enhance severe local weather events such as thunderstorms and hail.157 of the three nuclear options characterized here, the LMFBR has the lowest heat rate and fusion has the highest.
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