could have a significant warming effect on the world’s climate. Whether or not this warming would be advantageous or disadvantageous on a global scale is currently unknown. It is generally felt that a decision to curtail fossil fuel combustion to minimize CO2 impacts on climate would have to be made by the year 2000, and the policy to reduce fossil fuel combustion would have to be global to be effective. Unfortunately, at the present time, the state of the art of climate prediction is not developed enough to provide a solid scientific basis that decision makers could use to implement such a policy. 3.1.4 Other Impacts In addition to releasing heat, CO2, primary particles, and precursors of sulfate and nitrate aerosols, coal technologies may affect climate in other ways. The release of water vapor from combustion or from evaporative cooling towers may increase the water vapor content of the atmosphere. Water vapor plays an important role in augmenting the greenhouse effect because it is a strong absorber of several infrared bands. The emission of SO2 and other gases that are also infrared absorbers may contribute to the greenhouse effect as well. 3.2 NUCLEAR TECHNOLOGIES 3.2.1 Waste Heat Impacts The major impact that nuclear energy technologies will have on the climate will occur as a result of heat rejection to the atmosphere. A typical thermal efficiency for a light water reactor (LWR) is of the order of 33%, whereas a liquid metal fast breeder reactor (LMFBR) will have a thermal efficiency of around 40%.^® These efficiencies are similar to those of coal technologies, and thus the waste heat impacts should be similar as well. Global impacts of the heat rejected by nuclear power plants should not be significant. Local impacts will be a function of cooling technology selection and site selection. Presumably, these local climatic impacts will not constrain the use of nuclear technologies but will require selection of sites or selection of cooling methods to fit local meteorological conditions. Impacts of waste heat rejection may be significant on a regional scale if
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