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gpt-5.4
Nuclear War
The single most likely way the world could end is a large-scale nuclear war triggered by great-power conflict, miscalculation, or escalation from a regional war. Unlike slower-moving threats, nuclear arsenals already exist, can be launched within minutes, and are controlled under intense political and military pressure. Rising rivalry among nuclear-armed states, more frequent crises, cyber interference risks, autonomous systems, and the weakening of arms-control norms all increase the chance of a catastrophic mistake or rapid escalation.
A full nuclear exchange could kill hundreds of millions immediately through blast, fire, and radiation, then collapse global infrastructure, trade, food systems, and governance. Even beyond the direct destruction, smoke from burning cities could cool the planet, shorten growing seasons, and trigger global famine on a scale that could threaten human civilization itself. Other existential dangers are serious, but nuclear war remains the most immediate, technically feasible, and historically grounded pathway to a world-ending outcome.
A full nuclear exchange could kill hundreds of millions immediately through blast, fire, and radiation, then collapse global infrastructure, trade, food systems, and governance. Even beyond the direct destruction, smoke from burning cities could cool the planet, shorten growing seasons, and trigger global famine on a scale that could threaten human civilization itself. Other existential dangers are serious, but nuclear war remains the most immediate, technically feasible, and historically grounded pathway to a world-ending outcome.