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All scenarios / Human-made

Nuclear War

The classic. Never goes out of style.

Evidence baseline34%
Snapshot rank#1 of 32
See the live number →

What it is

Nuclear war means two or more states exchanging nuclear weapons. The immediate blasts, fires and radiation would kill tens of millions of people. The bigger threat to civilization comes after that: soot from burning cities rises into the stratosphere, blocks sunlight and cools the planet for years. Scientists call this nuclear winter.

Nine countries hold nuclear weapons, and the arsenals of the United States and Russia together still number in the thousands of warheads. You don't need a deliberate decision to start a war for one to begin. Accidents, false alarms and escalation from a conventional conflict have all brought the world close before.

Why it ranks where it does

Nuclear war sits at the top of our board because the main risk factors are all elevated at the same time. The Bulletin of the Atomic Scientists moved its Doomsday Clock to 85 seconds to midnight, the closest it has ever been. A US–Israeli war with Iran is now in its eighth month and has closed the Strait of Hormuz. Prediction markets are also pricing real odds on new nuclear states and a direct NATO–Russia clash.

Evidence on the board

What the experts say

Researcher Toby Ord estimates the chance that nuclear war causes an existential catastrophe this century at about 1 in 1,000. The odds of a nuclear war that kills a large share of humanity without wiping us out are much higher. A 2022 study in Nature Food modelled a full US–Russia exchange and found it could cut global calorie production by about 90% and lead to more than 5 billion deaths from famine. Even a regional India–Pakistan war could put around 2 billion people at risk.

What would move the number

Up

  • A nuclear test or a declared weapon by a new state, such as Iran
  • Direct combat between NATO and Russian forces
  • Collapse of the remaining arms-control treaties
  • Leaders openly threatening first use

Down

  • A ceasefire in the Middle East and reopening of the Strait of Hormuz
  • New US–Russia arms-control talks
  • The Doomsday Clock moving away from midnight

Live signals we track

The baseline above is set from the evidence as of October 13, 2026. On the live board, your browser adjusts it in real time using these feeds. Chatter can only nudge a score in proportion to its evidence, so attention alone can't make an unlikely scenario look likely.

Sources

  1. Xia et al. 2022, Nature Food: nuclear war and global famine
    https://www.nature.com/articles/s43016-022-00573-0
  2. Science: Nuclear war would cause a yearslong global famine
    https://www.science.org/content/article/nuclear-war-would-cause-yearslong-global-famine
  3. 80,000 Hours: Toby Ord's existential risk estimates
    https://80000hours.org/articles/existential-risks/
  4. Wikipedia: Nuclear winter
    https://en.wikipedia.org/wiki/Nuclear_winter
  5. UChicago News
    https://news.uchicago.edu/story/doomsday-clock-ticks-down-85-seconds-midnight-2026-closest-ever-apocalypse
  6. Reuters
    https://www.internazionale.it/ultime-notizie-reuters/2026/10/11/middle-east-war-high-debt-levels-to-dominate-imf-world-bank-meetings-in-bangkok
  7. Polymarket: Iran nuke before 2027
    https://polymarket.com/event/iran-nuke-before-2027
  8. Polymarket: A US ally gets a nuke before 2027
    https://polymarket.com/event/will-a-us-ally-get-a-nuke-before-2027
  9. Polymarket: NATO × Russia military clash in 2026
    https://polymarket.com/event/nato-x-russia-military-clash-in-2025

Baseline scores are an editorial threat index from 0 to 100 that combines current reporting with published expert estimates. They're meant for comparing risks, not as actuarial forecasts. See how the numbers work.