Nuclear Winter

Nuclear Winter. Although there had been earlier antecedents, the widespread public debate about nuclear winter began in 1982 with the suggestion by Paul Crutzen, at the University of Colorado, and John Birks, at the Max Planck Institute, that a large‐scale nuclear war could produce such conflagrations of forests that a smoke pall covering perhaps half the northern hemisphere would develop. This would absorb enough of the light from the Sun that there could be serious and prolonged reductions in photosynthesis and in temperatures over that part of the planet, resulting in catastrophic agricultural failure. The work was quickly picked up by R. P. Turco, O. B. Toon, T. P. Ackerman, J. B. Pollack, and Carl Sagan, who, on the basis of quantitative modeling, concluded that a large‐scale nuclear war could be expected, mainly as a result of the burning of cities rather than forests, to cause temperatures to drop by 36° C. (65° F.) and to remain below freezing for several months. Their work, commonly referred to as the TTAPS study, provided the basis for a number of other publications that appeared in the next three years bearing Sagan's name and the appellation “nuclear winter,” which he and Turco coined to describe the phenomenon.

Not surprisingly, these publications caused a considerable stir, given their wide circulation and some of the apocalyptic visions presented: that a major nuclear exchange would produce “the greatest biological and physical disruption of the planet in its last 65 million years” (a period that included the four great ice ages) and that the number of survivors would be reduced to prehistoric levels (presumably a fraction of 1% of those now alive). All of this was buttressed by claims that the TTAPS results were insensitive to wide variations in assumptions about parameters used in modeling. In fact, the results were anything but robust, as subsequent studies would make clear.

There were basically two kinds of problems. First, TTAPS was based on the simplifying assumption that the burning of cities would produce an instantaneous homogeneous distribution of smoke over the entire northern hemisphere, when in reality it would take some days for such spreading to occur, during which time much of the smoke would likely be removed by natural processes. Moreover, the modeling took no account of the warming effects of the infusion of relatively warm air from oceanic and tropical areas to continental interiors. More refined later modeling that did take account of these phenomena, and used comparable assumptions about amounts and characteristics of the smoke from fires, led to radically smaller temperature effects.

Second, there were a number of uncertainties in key areas which, if resolved, could plausibly lead at one extreme to no significant climatic effects, or at the other, to effects as dire as those discussed in 1983, a range of outcomes largely conceded by Turco and Sagan in a characterization of five different classes of nuclear winter by 1989.

The nuclear winter controversy was perhaps as much about policy as about geophysics. Advocates of enlarged programs for deterrence of nuclear attacks and for defense against them seized on the possibility of nuclear winter to buttress their case for such programs. In contrast, the most vocal proponents of the nuclear winter theory generally argued that it strengthened the case for reducing nuclear stockpiles and foregoing the development and acquisition of new nuclear weapons; and some argued that even if there were doubts about the phenomenon, it would be wise to base policy on “worst‐case analysis.” Others argued that war involving enough nuclear explosions to trigger nuclear winter would likely have consequences so catastrophic, at least for the nuclear weapons states, as to overshadow the possibility of nuclear winter in concerns about policy. (And some of those skeptical about the more dire prognostications warned particularly against worst‐case analysis being used as a basis for mitigative actions by countries not likely to be directly attacked, noting that such actions could well involve the use of scarce resources sorely needed for other purposes.)

By the early 1990s, nuclear winter was no longer a salient issue in geophysics or from a policy perspective, very likely because the geophysical case for it seemed so questionable; because the initiation of massive oil fires in Kuwait during the Persian Gulf War did not lead to significant climatic effects, as some had predicted; and probably most important, because concern about large‐scale nuclear attacks had largely dissipated with the end of the Cold War.
[See also War Plans.]

Bibliography

Paul J. Crutzen and and John W. Birks , The Atmosphere After a Nuclear War: Twilight at Noon, Ambio, Vol. II, no. 2–3 (1982), p. 114.
Paul R. Ehrlich,, Carl Sagan,, Donald Kennedy,, and and Walter Orr Roberts , The Cold and the Dark: The World After Nuclear War, 1984.
National Academy of Sciences , The Effects on the Atmosphere of a Major Nuclear Exchange, 1985.
Nuclear Winter, Vol. 1, no. 2 (1985), p. 112.
A. Barrie Pittock, et al. , The Environmental Consequences of Nuclear War, Vol. I; and Mark A. Harwell and Thomas Hutchinson, Vol. II, 1985.
Stanley L. Thompson and and Stephen H. Schneider , Nuclear Winter Reappraised, Foreign Affairs, Vol. 64, no. 5 (Summer 1986), p. 981.

George W. Rathjens