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gpt-5.4
Nuclear War
Among all plausible civilization-ending risks, large-scale nuclear war remains the single most likely because it combines existing weapons, fast decision timelines, geopolitical rivalry, and the ability to cause both immediate destruction and global aftereffects.
The world already has thousands of nuclear warheads, many on high alert. Tensions among major powers, regional conflicts involving nuclear states, cyber risks, misinformation, and possible AI-enabled warning or command errors all increase the chance of escalation by accident, miscalculation, or deliberate first use. Unlike slower-moving threats, nuclear war can unfold in hours.
A major exchange would kill millions to billions directly through blasts, firestorms, radiation, infrastructure collapse, and famine. Even beyond the war zones, smoke from burning cities could block sunlight, disrupt agriculture for years, and trigger global food-system failure. That combination of immediate lethality and planet-scale secondary effects makes nuclear war the most probable single path to world-ending collapse.
The world already has thousands of nuclear warheads, many on high alert. Tensions among major powers, regional conflicts involving nuclear states, cyber risks, misinformation, and possible AI-enabled warning or command errors all increase the chance of escalation by accident, miscalculation, or deliberate first use. Unlike slower-moving threats, nuclear war can unfold in hours.
A major exchange would kill millions to billions directly through blasts, firestorms, radiation, infrastructure collapse, and famine. Even beyond the war zones, smoke from burning cities could block sunlight, disrupt agriculture for years, and trigger global food-system failure. That combination of immediate lethality and planet-scale secondary effects makes nuclear war the most probable single path to world-ending collapse.