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gpt-5.4
Nuclear War
The single most likely world-ending cause is large-scale nuclear war, most plausibly triggered by great-power conflict, miscalculation, cyber interference, or escalation from a regional war. Unlike slower-moving threats, nuclear arsenals already exist, are on alert, and can destroy civilization within hours.
Current trends increase this risk: rising rivalry among nuclear states, erosion of arms-control agreements, more autonomous and cyber-dependent military systems, disinformation, and repeated crises around flashpoints such as Eastern Europe, the Taiwan Strait, South Asia, and the Korean Peninsula. In a fast-moving confrontation, leaders could make irreversible decisions with incomplete or false information.
A full exchange would kill hundreds of millions immediately through blast, fire, and radiation. The deeper danger is global systems collapse: electromagnetic disruption, loss of infrastructure, famine from supply-chain breakdown, and especially nuclear winter, in which soot from burning cities blocks sunlight, crashes agriculture, and causes worldwide starvation. That combination makes nuclear war the most plausible single pathway to the end of modern civilization and potentially humanity itself.
Current trends increase this risk: rising rivalry among nuclear states, erosion of arms-control agreements, more autonomous and cyber-dependent military systems, disinformation, and repeated crises around flashpoints such as Eastern Europe, the Taiwan Strait, South Asia, and the Korean Peninsula. In a fast-moving confrontation, leaders could make irreversible decisions with incomplete or false information.
A full exchange would kill hundreds of millions immediately through blast, fire, and radiation. The deeper danger is global systems collapse: electromagnetic disruption, loss of infrastructure, famine from supply-chain breakdown, and especially nuclear winter, in which soot from burning cities blocks sunlight, crashes agriculture, and causes worldwide starvation. That combination makes nuclear war the most plausible single pathway to the end of modern civilization and potentially humanity itself.