Nuclear War

The single most likely way the world could end is a large-scale nuclear war, most plausibly triggered by escalation between major powers. Among all global risks, it combines the fastest path from political crisis to civilizational collapse with systems that already exist, are actively maintained, and can be launched within minutes.

Current trends increase this risk: intensifying rivalry among nuclear-armed states, active wars near alliance boundaries, military modernization, cyberattacks that could confuse warning systems, and growing use of AI in surveillance, command, and targeting. As trust declines and decision time shrinks, the chance of miscalculation, false alarms, or uncontrolled escalation rises.

A full nuclear exchange would not only kill hundreds of millions immediately through blast, fire, and radiation; it could also trigger nuclear winter. Smoke from burning cities could cool the planet, collapse agriculture, disrupt trade and infrastructure, and cause global famine. Even if some humans survived, the destruction of states, industry, food systems, and public health could make recovery uncertain enough to count as the effective end of the world as we know it.