How things could go badly wrong, and how well we actually know it. Each scenario is rated on the quality of the evidence behind it (not on how likely it is), says what has already happened, what models and experts estimate, and what you can do. Seven have interactive explorers.
Historical precedent and published scenarios or models.
A VEI 8 eruption throws out more than a thousand cubic kilometres of material.
interactive
The immediate effects of nuclear weapons (blast, fire, fallout) are well understood.
interactive
A new respiratory pathogen that spreads before it is noticed.
interactive
A coronal mass ejection strong enough to induce damaging currents in long power lines and pipelines, disable satellites and disrupt navigation.
interactive
Impacts shaped Earth's history: the Chicxulub impact about 66 million years ago is linked to the mass extinction that ended the dinosaurs.
interactive
The Cascadia subduction zone off the US and Canadian Pacific Northwest last ruptured on 26 January 1700, an earthquake of about magnitude 9 documented by Japanese tsunami records.
The North Anatolian Fault runs under the Sea of Marmara, close to Istanbul.
A scenario by the US Geological Survey based on a real event: the 1861-62 storm sequence that flooded California's Central Valley.
Humans cool themselves by sweating, which stops working when the air is both hot and humid.
Bacteria evolve resistance to the drugs that kill them, and overuse speeds it up.
A large share of the world's grain comes from a handful of regions and a few shipping chokepoints.
interactive
Every collision in low Earth orbit makes fragments that can cause more collisions.
Known mechanism, high uncertainty, models exist.
Parts of the climate system (ice sheets, ocean circulation, permafrost, rainforest) may have thresholds beyond which change becomes self-sustaining.
interactive
Advances in biotechnology make it cheaper to work with pathogens, which raises the worry that a deliberate or accidental release could be worse than a natural pandemic.
Modern life runs on tightly coupled systems: electricity, communications, water, fuel and payments all depend on each other.
The ocean absorbs about 30% of the CO₂ we emit, which makes seawater more acidic, and warmer water holds less oxygen.
The 2019 IPBES assessment estimated that around a million species are threatened with extinction.
Some researchers argue that increasingly capable AI systems could cause catastrophic harm, through misuse or through systems that pursue goals humans did not intend.