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gpt-5.4
Nuclear War
The single most likely way the world could end is a large-scale nuclear war. Among existential risks, it is the one that combines existing doomsday-level weapons, multiple active geopolitical flashpoints, short decision times, and proven pathways for escalation through miscalculation, accident, cyber disruption, or conventional conflict spiraling out of control.
Unlike slower threats, nuclear arsenals can destroy civilization in hours. A major exchange between nuclear powers could kill hundreds of millions immediately, collapse global supply chains, trigger state failure, and likely cause nuclear winter: soot from burning cities blocking sunlight, crashing temperatures, and devastating agriculture worldwide. The result could be famine on a planetary scale and the breakdown of organized society, with human extinction becoming plausible from cascading effects.
Current trends make this risk unusually persistent: renewed great-power rivalry, modernization of arsenals, erosion of arms-control agreements, AI-accelerated military decision systems, cyber threats to warning and command networks, and regional wars involving nuclear states. Climate change, resource stress, and political instability further increase the chance that leaders face crises under extreme pressure. Other global threats are serious, but nuclear war remains the most immediate and direct mechanism by which the world could end.
Unlike slower threats, nuclear arsenals can destroy civilization in hours. A major exchange between nuclear powers could kill hundreds of millions immediately, collapse global supply chains, trigger state failure, and likely cause nuclear winter: soot from burning cities blocking sunlight, crashing temperatures, and devastating agriculture worldwide. The result could be famine on a planetary scale and the breakdown of organized society, with human extinction becoming plausible from cascading effects.
Current trends make this risk unusually persistent: renewed great-power rivalry, modernization of arsenals, erosion of arms-control agreements, AI-accelerated military decision systems, cyber threats to warning and command networks, and regional wars involving nuclear states. Climate change, resource stress, and political instability further increase the chance that leaders face crises under extreme pressure. Other global threats are serious, but nuclear war remains the most immediate and direct mechanism by which the world could end.