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1 Summary and Conclusions
Pages 1-9

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From page 1...
... Although there are enormous uncertainties involved in the calculations, the committee believes that long-term climatic effects with severe implications for the biosphere could occur, and these effects should be included in any analysis of the consequences of nuclear war. However, the committee cannot subscribe with confidence to any specific quantitative conclusions drawn from calculations based on current scientific knowledge.
From page 2...
... . The consequences of any such changes in atmospheric state would have to be added to the already sobering list of relatively well-understood consequences of nuclear war, including prompt radiation, blast, and thermal effects, short-term regional radioactive fallout, inadequate medical attention for surviving casualties, and the long-term biological effects of global fallout.
From page 3...
... (Nearly complete consumption of combustible materials is typical of large city-wide fires for which data are available.) Although many of the urban fires would probably spread beyond the 20 cal/cm2 ignition zone, no additional fuel burden from that spreading is assumed in the baseline case.
From page 4...
... , with about one-half of the initial particulates removed from the lower atmosphere in 3 days, and from the upper atmosphere in 30 days.* It is unlikely that the average residence times for postwar smoke would be much less than these values, and quite possible that the mean residence time in the upper troposphere would be longer.
From page 5...
... Obviously, calculations made under these conditions cannot be read as a scientific prediction of the effects of a nuclear exchange; rather, they represent an interim estimate from which the reader can infer something of the potential seriousness of the atmospheric degradation that might occur. Some reviewers of earlier drafts of this report cautioned that even the most qualified numerical results produced under these conditions could be misinterpreted, and some suggested that at present the only scientifically valid conclusion would be that it is not at this time possible to calculate the atmospheric effects of nuclear war.
From page 6...
... In particular, the heights to which smoke is deposited in city-scale fires, the early smoke removal by coagulation and condensation in the fire plume, the extent of continued buoyant rising of sun-heated opaque clouds, and the dynamical response of the atmosphere, first to patchy high-altitude solar absorption and then to the heating of more broadly distributed but still heavy smoke cover, have received only scattered and recent attention. CONCLUSIONS The general conclusion that the committee draws from this study is the following: a major nuclear exchange would insert significant amounts of smoke, fine dust, and undesirable chemical species into the atmosphere.
From page 7...
... During its tenure in the atmosphere, the smoke would gradually spread and become more uniformly distributed over much of the northern hemisphere, although some patchiness would be likely to persist. Light levels could be reduced by a factor of 100 in regions that were covered with the initial hemispheric average smoke load, causing intense cooling beneath the particulate layer and unusually intense heating of the under layer.
From page 8...
... In addition to the large uncertainties in many of the critical physical parameters and the inherent limitations of the models available for computer simulations, the available calculations reflect wide seasonal and geographical differences. Recent general circulation model simulations that incorporate simplifying assumptions indicate that a baseline attack during the summer might decrease mean continental temperatures in the northern temperate zone by as much as 10 to 25C, with temperatures along the coasts of the continents decreasing by much smaller amounts.
From page 9...
... the adequacy of current and projected atmospheric response models to reliably predict changes that are caused by a massive, high-altitude, and irregularly distributed injection of particulate matter. The atmospheric effects of a nuclear exchange depend on all of the foregoing physical processes ((a)


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