theory holding that the smoke and dust produced by a large nuclear war would result in a prolonged period of cold on the earth. The earliest version of the theory, which was put forward in the early 1980s in the so-called TTAPS report (named for last initials of its authors, Richard P. Turco, Owen B. Toon, Thomas P. Ackerman, James B. Pollack, and Carl Sagan), held that the ensuing low temperatures and prolonged periods of darkness would obliterate plant life and seriously threaten the existence of the human species. Later models, which took into account additional variables, confirmed the basic conclusions of the TTAPS report and suggested that the detonation of 100 megatons (the explosive power of 100 million tons of TNT) over 100 cities could produce temperature drops ranging from 5 to 15 degrees.

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