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gpt-5.4
Nuclear War
The single most likely end-of-the-world scenario is a large-scale nuclear war triggered by great-power confrontation, miscalculation, or rapid escalation from a regional conflict. Unlike slower-moving threats, nuclear arsenals already exist, are on alert, and can be used within minutes. Rising rivalry among nuclear-armed states, cyber interference risks, autonomous systems, misinformation, and weakened arms-control norms all increase the chance that a crisis could spiral before leaders can stop it.
A full exchange would not only kill hundreds of millions immediately through blast, fire, and radiation; it could also collapse global infrastructure, food systems, and governance. Soot from burning cities could block sunlight, sharply cool the planet, and cause multi-year crop failures—creating famine on a global scale. Other threats like climate change and pandemics are severe, but nuclear war remains the most plausible single event that could end human civilization quickly.
A full exchange would not only kill hundreds of millions immediately through blast, fire, and radiation; it could also collapse global infrastructure, food systems, and governance. Soot from burning cities could block sunlight, sharply cool the planet, and cause multi-year crop failures—creating famine on a global scale. Other threats like climate change and pandemics are severe, but nuclear war remains the most plausible single event that could end human civilization quickly.