Against a backdrop of increased tension among the world’s major powers, the risks and effects of nuclear war have received growing interest in recent years. These topics were discussed at the highest political and scientific levels during the Cold War. They are now back front and center, even though the world and the type of nuclear risks it faces have changed in many ways since.
Last year, the US National Academies of Sciences, Engineering, and Medicine published its long-awaited report on the environmental impacts of nuclear war. The last time it did such a comprehensive study was in … 1985. Also, an independent scientific panel mandated by the United Nations is preparing to submit a report on the effects of nuclear war to the UN General Assembly next year. The UN never had a scientific panel dedicated to the issue. Meanwhile, new research based on the most advanced climate models is bringing new insights into the understanding of the global effects of nuclear war. And nuclear war scenarios are evolving, beyond the all-out nuclear exchange between the two Cold War superpowers to include more complex scenarios of limited nuclear exchange involving smaller arsenals—but with the inherent risk of escalation.
These recent developments raise uncomfortable questions: Are scenarios of limited nuclear exchange—scenarios that might not trigger irreversible nuclear winter—making the use of nuclear weapons more likely? Is it morally acceptable for scientists to work on scenarios of nuclear war below the “threshold” for nuclear winter? And do such scenarios even exist, given the irreducible risk of escalation and uncertainty in human behavior involved?
To address these questions, the Bulletin asked experts in nuclear winter and associated scientific areas about what they know of the global effects of nuclear war and what decision-makers should do to reduce the risk of self-destruction.
In the first piece of the series, atmospheric chemist John W. Birks tells the fascinating yet little-known history of how he and his colleague Paul Crutzen first discovered the global climatic effect of nuclear war, later known as “nuclear winter.”
In an interview, Earth scientists Brian Toon and Alan Robock discuss their latest book, Earth in Flames (Oxford University Press, 2025), which draws parallels between the extinction of dinosaurs and potential human extinction from nuclear war. Nuclear war is much more unpredictable than asteroids, but, Toon and Robock emphasize, unlike the dinosaurs of 66 million years ago, humans can avoid causing their own extinction.
In a second interview, atmospheric chemist and climate scientist Susan Solomon describes her role as a co-author of the study, published last summer by the National Academies of Sciences, Engineering, and Medicine, on the environmental impacts of nuclear war. Solomon explains how the study made her realize the importance of the science of rising smoke and fuel loads at nuclear detonation sites in nuclear winter scenarios and discusses a major limitation of the study: not including the radiation fallout effects.
Finally, in the last piece of the series, food security expert Florian Ulrich Jehn explains how nuclear war would impact the global food trade, arguing that it is not morally misplaced for countries that do not possess nuclear weapons—and therefore have no say on whether they will ever be used—to prepare for the possibility of a nuclear winter.
A weeklong look at nuclear winter
Come back every two days from May 12 to May 18 for the next piece in the Bulletin's series on nuclear winter.
