Abstract
While the world has avoided large-scale nuclear war, questions remain about the role of chance
versus policy choices in preventing such events. This study systematically assesses expert
beliefs about the probability of a nuclear catastrophe by 2045, the centenary of the bombings of
Hiroshima and Nagasaki. We define a nuclear catastrophe as an event where nuclear weapons
cause the death of at least 10 million people. Through a combination of expert interviews and
surveys, 110 domain experts and 41 expert forecasters (“superforecasters”) predicted the
likelihood of nuclear conflict, explained the mechanisms underlying their predictions, and
forecasted the impact of specific tractable policies on the likelihood of nuclear catastrophe.
Experts assigned a median 5% probability of a nuclear catastrophe by 2045, while
superforecasters put the probability at 1%. Factors contributing to higher risk estimates included
ongoing geopolitical tensions, the proliferation of nuclear weapons, and technological
vulnerabilities. Lower risk estimates highlighted the continued effectiveness of nuclear
deterrence. Although Russia and NATO was the adversarial domain thought most likely to
cause a nuclear catastrophe, experts believe that risks are dispersed roughly uniformly across
regional conflict theaters (Russia and NATO, China and the USA, the Korean Peninsula, India
and Pakistan, and Israel and Iran). Participants believe that the implementation of a bundle of
six tractable policies, including the establishment of a crisis communications network and the
implementation of failsafe reviews, would together halve the risk of a nuclear catastrophe.
