David Sepkoski


On his book Catastrophic Thinking: Extinction and the Value of Diversity from Darwin to the Anthropocene

Cover Interview of September 30, 2020

A close-up

In a case study comes in the book’s fifth chapter, I discuss how paleontological studies of extinction intersected with political debates about nuclear proliferation in the 1970s and 1980s.

A variety of studies had, since the 1950s, attempted to estimate the consequences of a nuclear exchange between the US and the Soviet Union, generally with fairly grim predictions. Nonetheless, by the early 1980s the general public was less concerned about nuclear exchange than it had been in previous decades. While many factors contributed to this—including the overshadowing effect of the cultural and political upheavals of the 1970s and 1980s—a significant component was the persistence of political rhetoric that a nuclear war was “winnable.”

This changed, quite suddenly and dramatically, in the early 1980s, thanks in part to the hypothesis of “nuclear winter.” This scenario, advanced most prominently by the astronomer and television personality Carl Sagan, predicted that even a partial nuclear exchange could set off a cascade of ecological and environmental failures leading, ultimately, to up to a year of near-total darkness from dust kicked into the earth’s atmosphere. The consequence, he and colleagues argued, would be mass extinctions on a scale not seen in 65 million years, potentially including the human species.

Popular films and books like the 1983 television movie The Day After did much to galvanize public opinion by realistically depicting the aftermath of a nuclear war, but it was nuclear winter that provided the unassailable certainty that such a conflict would bring the end of civilization. Moreover, the public’s attention was also directed to a stunning new hypothesis, advanced in 1980, that the dinosaurs’ own extinction was produced by the impact of a gigantic asteroid whose total destructive impact was equivalent, in the estimate of Nobel laureate physicist Luis Alvarez, to “100,000,000 hydrogen bombs.” The connection between the disaster facing humanity and the one that obliterated one of evolution’s most successful groups could not have been clearer.

There is a direct connection between the dinosaur impact hypothesis and changing attitudes towards nuclear proliferation. A striking feature of the impact scenario was that the real damage was done by planet-wide dust clouds that blanketed the atmosphere and cut off photosynthesis for a year or more. Not coincidentally, Sagan and his collaborators had contributed directly to the climate modeling used in the impact hypothesis several years before the nuclear winter scenario was proposed, and explicitly acknowledged that the two hypotheses are essentially identical.

Popular fascination with dinosaurs and their demise therefore reinforced nuclear anxieties—and vice-versa—in a kind of feedback loop that ultimately contributed to the political will to commit to massive disarmament. It also helped shape a new public awareness of extinction that directly informed subsequent debates around climate change and biodiversity loss: if it happened to the dinosaurs, it could happen to us—we are, in a sense, both the dinosaur and the asteroid.