Nuclear War

The single most likely way the world could end is a large-scale nuclear war that escalates beyond human control. Among global catastrophic risks, it combines high destructive power with persistent real-world triggers: great-power rivalry, regional wars involving nuclear states, military automation, cyber interference, misinformation, and very short decision times during crises.

Unlike slower threats, nuclear war can unfold in hours. A conflict between major powers—or a regional nuclear exchange that draws alliances in—could cause immediate mass death, collapse of infrastructure, electromagnetic and cyber disruptions, and failure of global supply chains. If enough weapons are used, smoke from burning cities could cool the planet, shorten growing seasons, and trigger famine on a worldwide scale, potentially causing civilizational collapse and human extinction.

This risk is reinforced by current trends: eroding arms-control frameworks, modernization of arsenals, AI-assisted command systems, hypersonic delivery systems that compress response windows, and increasingly unstable geopolitics. Many existential threats are serious, but nuclear war remains the most plausible single pathway to a rapid global end because the weapons already exist, the command structures are under stress, and a single miscalculation could be irreversible.