Ackerman, Thomas P. (1947- ) American Meteorologist (Scientist)

The theory of nuclear winter, or the catastrophic atmospheric consequences wrought by nuclear war, elicited a sea change in the public perception of the viability of employing nuclear weapons tactically. Thomas Ackerman participated on the team that proposed a scientific model for a nuclear winter scenario in the early 1980s. The theory’s reception varied along political lines: antinuclear activists embraced it as evidence of the insanity of maintaining nuclear arsenals, while the conservative contingent attacked its scientific limitations.

Thomas P. Ackerman attended the University of Washington throughout his academic career, earning his master of science degree in physics in 1971 and his Ph.D. in atmospheric science in 1976. After receiving his doctorate, he went to work as a research scientist at the National Aeronautics and Space Administration (NASA) Ames Research Center.

In 1982, the Swedish environmental journal Ambio published an article in which Paul Crutzen and John W. Birks coined the term nuclear winter to describe the aftereffects of a nuclear war. Interestingly, they theorized that the resulting environmental effects would eclipse the destructiveness of the actual explosions, as carbon soot from the resulting fires would blanket the atmosphere, preventing sunlight from reaching the earth’s surface. When carl edward sagan read this account, he grasped the political implications of such a theory, and he realized that the scientific community could offer the antinuclear movement the ultimate deterrent: a description of mutual assured destruction, or global suicide.

Sagan set out to create a scientific model of nuclear winter, using computer software to extrapolate the effects of a nuclear holocaust. He enlisted Ackerman, along with Richard P. Turco, Owen B. Toon, and James B. Pollack, to form the team later known by the acronym TTAPS. The group developed a one-dimensional model projecting the likely outcomes of significant nuclear events. In their report, "Nuclear Winter: Global Consequences of Multiple Nuclear Explosions," published in the December 23, 1983, issue of Science, they proposed that nuclear weapons exploding over 100 cities, releasing an explosive power totaling as little as 100 megatons, would send so much dust and smoke into the atmosphere that the temperature would drop anywhere from 5 to 15 degrees, an outcome that could have catastrophic environmental consequences.

The nuclear winter theory galvanized the political community: the antinuclear movement used it as an apocalyptic rallying cry to discontinue the stockpiling of nuclear arms, and indeed to reach disarmament treaties. However, the conservative faction seized upon the theory’s limitations, pointing out that it did not take into account the division of the earth’s surface into water and land (which would create heat transfer), the difference between daytime and nighttime sunlight (TTAPS postulated 24-hour sunlight at one-third strength), and the limitations of existing computers to take into account the multiple variables factoring into a realistic scenario. Conservatives further accused the TTPAS team of sacrificing scientific integrity in order to advance a political agenda, a position confirmed by the opinions of leading scientists (including Nobel laureate Richard Feynman) who criticized the study’s methodologies.

The TTAPS team, along with Crutzen and Birks, received the 1985 Leo Szilard Lectureship Award from the American Physical Society, reaffirming their scientific integrity. In 1988, Ackerman joined the faculty of Pennsylvania State University as a professor of meteorology and associate director of Earth System Science Center, and he then held a concurrent position on the NASA’s MISR (Multi-angle Imaging Spectro Radiometer) science team and as a site scientist for the Tropical Western Pacific site in the Department of Energy’s Atmospheric Radiation Measurement Program.

Ackerman also continued to collaborate with the TTAPS team, conducting further research on the nuclear winter question. In 1990, the group published a follow-up article in Science, in which they defended their original theory by offering more sophisticated modeling (available due to more sophisticated computer programs) and taking into account more realistic variables.

Since then, with the demise of the Soviet Union and the melting of the cold war, little research has been applied to the nuclear winter theory. However, the theory lodged itself in the collective conscious, exerting a significant influence on public policy as well as personal angst. The reception of the theory demonstrated the necessity of maintaining impeccable scientific integrity, especially when scientific findings carry political implications. Ultimately, the theory’s influence eclipsed the question of its scientific validity, as it forced a more considered approach to the question of the destructive capacity of nuclear weapons, and the wisdom of maintaining vast nuclear arsenals in a state of readiness.

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