Nuclear War

The most likely existential risk remains deliberate or accidental nuclear escalation among major powers. Current geopolitical tensions, eroding arms control frameworks, and modernization of nuclear arsenals create a permissive environment for catastrophic miscalculation. A single crisis—whether in Eastern Europe, the Taiwan Strait, or the Korean Peninsula—could trigger rapid escalation, leading to a full-scale exchange.

Such a war would not only cause immediate mass casualties and destruction but also trigger a "nuclear winter," where soot and debris block sunlight, collapsing global agriculture and leading to widespread famine. The resulting societal collapse, failure of critical infrastructure, and long-term environmental damage would render modern civilization unsalvageable on a planetary scale.