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APPENDIX: Evolution of Knowledge About Long-Term Nuclear Effects The first nuclear explosion (the Trinity event) near Alamogordo, New Mexico, on July 16, 1945. During development of nuclear weapons, which has spanned four decades, the outcome of nuclear events have repeatedly impressed, and occasionally surprised, nuclear scientists and engineers. The only two nuclear bombs to be used in war time (detonated over occurred in the desert the subsequent Hiroshima and Nagasaki, Japan, in August 1945) each destroyed an entire city, although both were of quite low energy yield by today's standards. The 15-Mt Bravo test on Bikini Atoll in March 1954 underlined the hazard of radioactive fallout. The residents of Rongelap Atoll, more than 150 km downwind of Bikini, were exposed to, and suffered from, serious doses of nuclear fallout radiation even though they were quickly evacuated (Glasstone and Dola-n' 1977~. Following the first successful detonation of a fusion device in 1952, the pace of nuclear testing, the size of individual nuclear warheads, and the total nuclear arsenals of the United States and the USSR expanded rapidly (the USSR detonated the largest weapon, a ~58-Mt device, in the atmosphere in October 19611. Throughout this period and into the early 1960s, a debate developed among nuclear strategists as to whether blast or thermal (fire) effects should be considered the primary destruction mechanism in formulating nuclear strategy. Blast effects were finally settled on because they were certain to occur with each explosion; fire was considered a secondary effect, as was prompt radioactive fallout from surface bursts. With the growth of the arsenals, scientists became concerned that severe global environmental effects might occur if even a fraction of the existing nuclear weapons were detonated. Such concern led, for example, to projects Gabriel and Sunshine--from 1949 through 1959--to evaluate the danger of radioactive fallout. Batten (1966) later assessed the possible climatic impact of dust raised by nuclear surface bursts, while Ayers (1965) undertook a broad analysis of the environmental and biological consequences of nuclear war, including the effects of blast, fires, and fallout. These early studies were hampered by a lack of critical data (some of which are now available) and were based on assumptions that seemed reasonable at the time but in retrospect appear to have been incorrect. They were not quantitative 185

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186 in many important details. Ayers noted that very severe effects were possible in his scenarios, but he could not marshal the data to make a ~ convincing case. During the period of assessment of the global impacts of supersonic flight, Foley and Ruderman (1973) pointed out that the nitrogen oxides (NOX) produced in nuclear fireballs by megaton-size explosions would be carried into the stratosphere. There NOX would react with and deplete the ozone layer, which shields the earth from harmful ultraviolet sunlight. Hampson (1974) suggested that a full-scale superpower nuclear exchange could result in the nearly complete depletion of the ozone shield, possibly subjecting the earth to high levels of ultraviolet radiation for a year or more. The 1975 National Research Council study (NRC, 1975) attempted to resolve some of these questions about the long-term effects of nuclear war. Much of that analysis centered on the recently identified ozone depletion problem. The report concluded that large reductions (about 50 percent) of the global ozone burden could occur. The NRC report judged that the likely climatic impact of nuclear dust from 10,000 Mt of high-yield surface explosions would probably be no more than the slight cooling produced by the great Krakatau eruption of 1883; but it noted a large uncertainty in these findings. The recent renewal of interest in long-term effects arose from two independent activities. One started in a seemingly unrelated field. Analysis of a thin clay layer found widely distributed at the stratigraphic boundary between the Cretaceous and Tertiary periods led Alvarez et al. (1980) to theorize--on the basis of anomalous levels of such noble metals as iridium--that the mass extinction of species that occurred 65 million years ago could be attributed to an asteroid striking the earth. The asteroid, they proposed, had raised a global dust cloud that blocked out sunlight so effectively that the terrestrial and marine food chains supporting the dinosaurs and many other species collapsed. Recognizing a possible parallel between the dust-lofting effect of an asteroid and that of a sizeable exchange of nuclear warheads, William J. Moran, in March 1981, stimulated discussions and preliminary calculations within the NRC. This work led to two meetings of an NRC study panel (December 1981 and April 1982) to further investigate the effects of dust lofted by nuclear detonations. The second key event was the realization of the possible effects of smoke. Prior to this time, assessments of the effects of nuclear war did not include the potential effects of the smoke emitted by fires ignited by nuclear detonation. Attention to fires had focused instead on the immediate damage caused by burning and high temperatures. As part of a study that had been launched in 1980 by the Royal Swedish Academy of Sciences, Crutzen and Birks in early 1982 circulated a draft paper (published in June 1982) that provided the first quantitative evidence of the possible importance of smoke in blocking solar radiation, and suggested consequent alterations of weather and short-term climate in the northern hemisphere. As an input to the April 1982 meeting, Turco, with the assistance of Toon, Pollack, and Ackerman--drawing upon the work in progress of Toon et al. (1982) on the climatic impact of dust lofted by an

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187 asteroidal impact--presented preliminary calculations on the climatic impact of nuclear dust emissions. The work of Crutzen and Birks on smoke was also reported by Turco and Eric Jones, and its potential importance was immediately recognized by the NRC study panel. A letter report (Moran, 1982) concluded that sufficient scientific data were available to warrant a thorough examination of the environmental effects of a nuclear exchange. Discussions then began between the NBC and the Department of Defense that culminated in the request for the present study. Meanwhile, Turco and his colleagues continued their studies presented at the April meeting and soon made the first quantitative estimates of the climatic effects of smoke and dust mixtures (Turco et al., 1982, 1983a,b). Related work by Crutzen et al. (1984), scientists at the Lawrence Livermore National Laboratory (e.g., MacCracken, 1983), and climatologists at the National Center for Atmospheric Research (Covey et al., 1984) underscored the potential seriousness of the problem. Thus, nearly four decades after the introduction of nuclear weapons technology, a series of unplanned, separate scientific developments has led to a reevaluation of our understanding of the global effects of nuclear war. One can ask whether even now the full range of physical consequences--let alone the biological effects--of nuclear warfare is within our comprehension. REFERENCES Alvarez, L.W., W. Alvarez, F. Asaro, and H.W. Michel (1980) Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208:1095-1108. Ayers, R.U. (1965) Environmental Effects of Nuclear Weapons. Vols. 1-3. Report HI-518-RR. Harmon-on-Hudson, N.Y.: Hudson Institute. Batten, E.S. (1966) The Effects of Nuclear War on the Weather and Climate. Memorandum RM-4989-TAB. Santa Monica, Calif.: RAND Corp. 50 pp. Bethe, H. (1976) Ultimate catastrophe? Bull. At. Sci. 32:36-37. Covey, C., S.H. Schneider, and S.L. Thompson (1984) Global atmospheric effects of massive smoke injections from a nuclear war: Results from general circulation model simulations. Nature 308:21-31. Crutzen, P.J., and J.W. Birks (1982) The atmosphere after a nuclear war: Twilight at noon. Ambio 11:114-125. Crutzen, P.J., C. Brahl, and I.E. Galbally (1984) Atmospheric effects from post-nuclear fires. Climatic Change, in press. Foley, H.M., and M.A. Ruderman (1973) Stratospheric NO production from past nuclear explosions. J. Geophys. Res. 78:4441-4450. Glasstone, S., and P.J. Dolan (eds.) (1977) The Effects of Nuclear Weapons. Washington, D.C.: U.S. Department of Defense. 653 pp. Hampson, J. (1974) Photochemical war on the atmosphere. Nature 250:189-191.

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188 MacCracken, M.C. (1983) Nuclear war: Preliminary estimates of the climatic effects of a nuclear exchange. Paper presented at the International Seminar on Nuclear War, 3rd Session: The Technical Basis for Peace. Ettore Majorana Centre for Scientific Culture, Erice, Sicily, Aug. 19-24, 1983. Moran, W.J. (1982) Letter report to Frank Press, chairman of the National Research Council, April 20, 1982. National Research Council (1975) Long-Term Worldwide Effects of Multiple Nuclear Weapons Detonations. Washington, D.C.: National Academy of Sciences. Silver, L.T., and P.H. Schultz (eds.) (1982) Geological implications of impacts of large asteroids and comets on the earth. Geol. Soc. Am. Spec. Pap. 190. 328 pp. Toon, O.B., J.B. Pollack, T.P. Ackerman, R.P. Turco, C.P. McKay, and M.S. Liu (1982) Evolution of an impact generated dust cloud and its effects on the atmosphere. Geol. Soc. Am. Spec. Pap. 190:187-200. Tur co, R.P., O.B. Toon, J.B. Pollack, and C. Sagan (1982) Global consequences of nuclear warfare. Eos Trans. AGU 63:1018. Turco, R.P., O.B. Toon, T.P. Ackerman, J.B. Pollack, and C. Sagan (1983a) Nuclear winter: Global consequences of multiple nuclear explosions. Science 222:1283-1292. Turco, R.P., O.B. Toon, T.P. Ackerman, J.B. Pollack, and C. Sagan (1983b) Global Atmospheric Consequences of Nuclear War. Interim Report. Marina del Rey, Calif.: R&D Associates. 144 pp.