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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, most plausibly through escalation between nuclear-armed states. Unlike slower global threats, nuclear arsenals already exist, can be launched within minutes, and are embedded in military doctrines, warning systems, and geopolitical crises.
Current trends make this especially dangerous: renewed rivalry among major powers, wars near alliance boundaries, modernization of nuclear forces, cyber risks to command-and-control systems, misinformation, and reduced trust between governments. A conventional conflict, false alarm, unauthorized launch, or misread cyberattack could escalate rapidly before diplomacy can catch up.
A full exchange would likely kill hundreds of millions directly, collapse global infrastructure, and trigger nuclear winter severe enough to destroy food systems worldwide. Even societies not hit by bombs could face famine, state failure, disease, and cascading technological collapse. Among existential risks, it is the one that combines high destructive power with a mechanism for sudden, irreversible global failure that already exists today.
Current trends make this especially dangerous: renewed rivalry among major powers, wars near alliance boundaries, modernization of nuclear forces, cyber risks to command-and-control systems, misinformation, and reduced trust between governments. A conventional conflict, false alarm, unauthorized launch, or misread cyberattack could escalate rapidly before diplomacy can catch up.
A full exchange would likely kill hundreds of millions directly, collapse global infrastructure, and trigger nuclear winter severe enough to destroy food systems worldwide. Even societies not hit by bombs could face famine, state failure, disease, and cascading technological collapse. Among existential risks, it is the one that combines high destructive power with a mechanism for sudden, irreversible global failure that already exists today.