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Nuclear Escalation
Of the plausible ways the world could end, a nuclear exchange is the most likely. It is the only one that could do catastrophic, civilization-scale damage within hours, using weapons that already exist.
Geopolitical trends point the same way. The last major U.S.–Russia arms control treaty, New START, expired in early 2026, which removed verification and limits on deployed warheads. China is expanding its arsenal quickly. Wars in Ukraine and the Middle East, and tensions over Taiwan and the Korean Peninsula, keep several nuclear-armed states in close confrontation. Nuclear rhetoric has become normal, and more states are considering their own weapons.
Technology adds to the risk. Hypersonic missiles, cyber operations against command-and-control systems, anti-satellite weapons, and AI-assisted decision tools all shorten decision times. Deepfakes and disinformation can distort a leader's picture of a crisis. These pressures make a miscalculation, false alarm, or rapid escalation more likely.
Environmental and social stress make the risk worse. Resource scarcity, climate migration, polarization, and weakened international institutions reduce the ability to defuse crises. A limited regional strike could escalate into a wider exchange. Smoke from burning cities could cause "nuclear winter," collapsing global agriculture and leaving billions to starve.
The absolute probability in any given year is low. But it is higher than for the other threats, which are slower or less certain: climate change, engineered pandemics, and unaligned AI.
Geopolitical trends point the same way. The last major U.S.–Russia arms control treaty, New START, expired in early 2026, which removed verification and limits on deployed warheads. China is expanding its arsenal quickly. Wars in Ukraine and the Middle East, and tensions over Taiwan and the Korean Peninsula, keep several nuclear-armed states in close confrontation. Nuclear rhetoric has become normal, and more states are considering their own weapons.
Technology adds to the risk. Hypersonic missiles, cyber operations against command-and-control systems, anti-satellite weapons, and AI-assisted decision tools all shorten decision times. Deepfakes and disinformation can distort a leader's picture of a crisis. These pressures make a miscalculation, false alarm, or rapid escalation more likely.
Environmental and social stress make the risk worse. Resource scarcity, climate migration, polarization, and weakened international institutions reduce the ability to defuse crises. A limited regional strike could escalate into a wider exchange. Smoke from burning cities could cause "nuclear winter," collapsing global agriculture and leaving billions to starve.
The absolute probability in any given year is low. But it is higher than for the other threats, which are slower or less certain: climate change, engineered pandemics, and unaligned AI.