Carl Sagan and Edward Teller: An Uneasy Alliance over Defending the Earth

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CARL SAGAN AND EDWARD TELLER WERE bitter opponents in national security debates about issues such as "Star Wars" and nuclear test bans, but ironically they agreed on defending the Earth against asteroids--an agreement that neither, however, was ready to admit in public. They drew very different conclusions from the impact threat--Sagan saw it is a justification for space exploration, Teller as a reason to build bigger nuclear bombs.

As a consequence of the astounding success of the Cosmos television series, as well as his bestselling books and cover stories in Newsweek and Time, Sagan achieved a celebrity in the 1980s enjoyed by few academics. His fame provided a platform for public opposition to President Reagan's Strategic Defense Initiative (SDD or "Star Wars," and he rallied objections from the academic community that questioned both the technical basis for SDI and its potential destabilizing effect on the balance of nuclear deterrence. In 1982, an additional opportunity presented itself to campaign for nuclear disarmament, thanks to research involving two of his former students, Brian Toon and Jim Pollack.

Toon and Pollack, who had developed atmospheric circulation models to analyze global dust storms on Mars, realized that smoke from petrochemical fires would have a much greater effect on global climate than naturally occurring dust. Sagan joined in a collaboration that generated the now-famous TFAPS paper on nuclear winter published in 1983 (Turco, R.P., Toon, A.B., Ackerman, T.P., Pollack, J.B., Sagan, C. [TTAPS]) 1990. "Climate and Smoke: An Appraisal of Nuclear Winter," Science, volume 247, pp. 167-168, January). The TTAPS authors concluded that even a less-than-full-scale nuclear exchange, especially if directed against cities, could cause global cooling and collapse of agriculture.

Sagan argued that these new findings rendered nuclear war obsolete. But the pro-nuclear forces in the United States counter-attacked vigorously, vilifying Sagan in the process. The National Review called nuclear winter "a fraud" and titled one cover story "Flat-Earth Sagan Falls off the End of the World." Edward Teller, who at age 73 was prehaps the second best known scientist in the U.S., debated Sagan on nuclear winter before a special session of Congress. These confrontations generated deep personal animosity between them. Years later Teller told me about an airport breakfast that he and Sagan shared at this rime, where (to Teller's obvious distaste) three strangers came up to ask Sagan for his autograph, but no one seemed to recognize Teller.

The early 1980s also saw the revolutionary research by Luis and Walter Alvarez that showed the end-Cretaceous mass extinction of 65 million years ago to be the result of an asteroid or comet impact. In addition to its profound effect on geology, paleontology, and evolutionary theory, the impact hypothesis stimulated new thinking about the contemporary hazard from asteroid impacts. Toon used the same basic software developed for nuclear winter to determine the threshold at which the consequences of an impact became global, triggering what is sometimes called an "impact winter."

The impact hazard attracted the interest of the nuclear defense communities in both the U.S. and U.S.S.R., including Edward Teller. In 1994 this shared U.S./U.S.S.R. interest in asteroid defenses provided the occasion for Teller to visit one of the closed "nuclear cities" in Russia--Chelyabinsk 70--an experience that I shared with him. By this time, Teller had become a public advocate for developing and testing asteroid defense systems, including nuclear options. …