Planetary boundaries and Earth-system tipping

Greenhouse gas concentrations and radiative forcing held above the safe range, so the planet keeps accumulating heat and every warming-driven hazard grows more frequent and severe.

Also: carbon dioxide overshoot, radiative forcing excess, carbon budget overshoot, earth energy imbalance

Global mean warming that rises above an agreed goal before any later decline, exposing systems to temporary extremes that can trigger irreversible tipping and losses.

Also: warming overshoot, overshoot pathway

A rise in the rate of global warming beyond earlier trends, from falling aerosol cooling and rising forcing, that shortens the time societies and ecosystems have to adapt.

Also: accelerated warming, warming rate increase

A sustained acceleration of atmospheric methane growth from fossil, agricultural and wetland sources that adds strong near-term warming and ground-level ozone.

Also: methane growth acceleration, methane spike

Species extinction and loss of genetic variety running far above the background rate, permanently narrowing the biological options ecosystems and food systems rely on to adapt.

Also: sixth mass extinction, extinction debt, genetic diversity loss

Human appropriation of so much of the plant growth on land that too little remains to run food webs, regulate climate and sustain wild species.

Also: primary production appropriation, biosphere energy drain

Conversion of the world's forest biomes below the share needed to regulate climate and water cycles, weakening carbon uptake and moisture recycling at continental scale.

Also: forest biome conversion, global forest cover loss

Widespread departure of river flows and groundwater from their natural range through damming, abstraction and climate change, stressing freshwater ecosystems and dependent water supplies.

Also: river flow alteration, streamflow deviation, freshwater boundary

Widespread departure of root-zone soil moisture from its natural range that weakens plant growth, carbon uptake and moisture recycling to downwind rainfall.

Also: soil moisture boundary, root-zone moisture deviation

Fixation of reactive nitrogen far beyond what ecosystems absorb, so surplus leaks to water and air as nitrate, ammonia and nitrous oxide, driving eutrophication, smog and warming.

Also: reactive nitrogen overload, fertiliser nitrogen excess, Nitrogen and phosphorus cycle overload, nitrogen pollution, biogeochemical flow exceedance

Mining and spreading of phosphorus faster than it cycles, so surplus accumulates in soils, rivers and coastal seas and drives algal blooms and oxygen loss.

Also: phosphorus overload, phosphate excess

Uneven loading of light-scattering and absorbing particles between regions or hemispheres that shifts tropical rain belts and monsoons and alters regional warming.

Also: interhemispheric aerosol contrast, aerosol boundary

Extra warming revealed when sulphate pollution that had been reflecting sunlight is removed quickly, for example by cleaner fuels, adding heat faster than forcing alone implies.

Also: aerosol cooling loss, sulphate clean-up warming

Release of synthetic chemicals, plastics and engineered materials faster than they can be assessed or controlled, building a global burden whose combined effects on life are largely unknown.

Also: synthetic chemical overload, chemical pollution boundary, plastics production overload, Novel entities boundary transgression, chemical pollution planetary boundary

Self-reinforcing decline of the Greenland ice sheet as its surface lowers into warmer air and melt outpaces snowfall, committing the world to metres of sea-level rise.

Also: Greenland collapse, melt-elevation feedback

Runaway retreat of ice resting on bedrock below sea level as warm ocean water undercuts its grounding lines, raising global sea level by metres over centuries.

Also: marine ice-sheet instability, Thwaites collapse, marine ice-cliff instability

Irreversible retreat of the marine-based margins of the East Antarctic ice sheet in deep subglacial basins, adding further metres of long-term sea-level rise.

Also: Wilkes basin retreat, Aurora basin retreat

Abrupt loss of Arctic sea ice in winter as well as summer, removing a reflective lid on the ocean and accelerating regional warming, permafrost thaw and ecosystem change.

Also: year-round ice-free Arctic, winter sea-ice tipping

A shift of Antarctic sea ice to a persistently lower state that exposes ice shelves to waves and warm water and disrupts Southern Ocean ecosystems and overturning.

Also: Antarctic sea-ice decline, Southern Ocean ice loss

Near-complete loss of the glaciers of a mountain range, ending their seasonal meltwater buffer and permanently changing river regimes, hazards and cultures downstream.

Also: deglaciation of mountain ranges, glacier disappearance

Gradual slowing of the Atlantic overturning circulation that carries heat northwards, raising sea level on western Atlantic coasts and shifting rainfall and storm tracks.

Also: AMOC slowdown, Gulf Stream system slowdown

A switch of the Atlantic overturning circulation to a weak or collapsed state, cooling north-west Europe sharply, displacing tropical rain belts and disrupting monsoons and fisheries.

Also: AMOC collapse, AMOC shutdown, thermohaline shutdown, Atlantic overturning circulation collapse, Gulf Stream shutdown

Shutdown of deep winter mixing in the North Atlantic subpolar gyre, which can cool the surrounding region within a decade and shift European weather and jet-stream patterns.

Also: Labrador Sea convection shutdown, North Atlantic gyre tipping

Weakening of dense-water sinking around Antarctica as meltwater freshens the surface, reducing deep-ocean ventilation, oxygen supply and the ocean's uptake of heat and carbon.

Also: bottom water formation decline, Southern Ocean overturning collapse

Northward spread of warm, salty Atlantic water and its species into the Arctic Ocean, weakening stratification, thinning sea ice and displacing Arctic food webs.

Also: borealisation of the Arctic, Atlantic water intrusion

System-wide loss of tropical coral reefs as repeated heat stress and acidification outpace recovery, collapsing reef fisheries, shore protection and a large share of marine biodiversity.

Also: global reef collapse, reef ecosystem collapse

Release of methane from frozen hydrates in continental-slope sediments as the deep ocean warms, adding greenhouse gas and possibly weakening slopes; the size of the effect is poorly known.

Also: clathrate release, seabed methane release

Large-scale conversion of Amazon rainforest to degraded forest or savanna as drought, fire and clearing break its moisture recycling, releasing carbon and drying South American rainfall.

Also: Amazon savannisation, Amazon tipping, Tropical rainforest dieback, Amazon dieback, forest-savanna transition

Loss of boreal forest along its warm, dry southern edge through drought, insects and fire, turning carbon-rich forest into grassland or scrub.

Also: boreal forest loss, taiga dieback

Spread of trees and shrubs into the tundra that darkens the snow-covered surface, warming the region and thawing permafrost while displacing tundra species.

Also: tundra shrubification, treeline advance, Arctic greening

Intact tropical forests turning from net absorbers into net emitters of carbon as heat, drought and tree mortality rise, removing a major brake on warming.

Also: tropical forest carbon source, forest sink saturation

A switch of Sahel vegetation and rainfall between wetter and drier states through land-atmosphere feedbacks, with large effects on grazing, crops and migration.

Also: Sahel greening collapse, Sahel drying

Decomposition of carbon frozen in permafrost soils as they thaw, releasing carbon dioxide and methane that add to warming for centuries and cannot be switched off.

Also: permafrost carbon feedback, permafrost methane, methane release, methane burst, clathrate release

Fast carbon release where ice-rich permafrost collapses into lakes and slumps, exposing deep carbon in years rather than decades and emitting relatively more methane.

Also: thermokarst lake methane, abrupt thaw carbon

Thaw of permafrost flooded beneath Arctic continental shelves that lets methane and carbon dioxide bubble to the air; its pace and total are uncertain.

Also: Arctic shelf methane, submarine permafrost thaw

Rising methane emissions from warmer and wetter tropical and northern wetlands that amplify warming and are hard to reduce by direct action.

Also: tropical wetland methane, natural methane feedback

A fall in the share of emitted carbon absorbed by vegetation and soils during heat, drought and fire, leaving more carbon in the air and speeding warming.

Also: land sink collapse, terrestrial sink decline

A fall in the ocean's uptake of carbon dioxide as surface waters warm, stratify and lose buffering capacity, leaving more carbon in the atmosphere.

Also: ocean uptake decline, ocean sink saturation

Faster microbial breakdown of soil organic carbon in a warmer climate that releases carbon dioxide and lowers soil fertility and water holding.

Also: soil carbon loss with warming

A lasting change in the strength, timing or reliability of the South Asian monsoon driven by warming and aerosols, threatening water and food for well over a billion people.

Also: Indian monsoon tipping, monsoon state change

A lasting northward or southward displacement of the West African monsoon rain belt that redistributes drought and flooding across the Sahel and Guinea coast.

Also: Sahel monsoon shift, West African rain belt shift

A lasting weakening or delay of the South American monsoon as forest loss cuts moisture recycling, extending dry seasons over the Amazon and the agricultural south.

Also: South American rainy season shift, flying rivers decline

A lasting change in the position and timing of the East Asian monsoon rain belt that shifts flooding to some basins and drought to others.

Also: East Asian rain belt shift, plum rain shift

Poleward expansion of the tropical circulation that pushes subtropical dry zones and storm tracks towards the poles, drying Mediterranean-type climates.

Also: Hadley cell expansion, subtropical dry zone expansion

A lasting change in the mean state or swing of the tropical Pacific climate, altering the frequency of extreme El Nino and La Nina years worldwide; direction is uncertain.

Also: permanent El Nino-like state, ENSO regime shift

A lasting change in the speed, path or waviness of the mid-latitude jet streams that makes weather patterns stall, prolonging heat, drought and rain extremes; evidence is contested.

Also: wavier jet stream, quasi-resonant amplification, stalled weather patterns

Loss of the bright low cloud decks over subtropical oceans at high greenhouse levels, which would let much more sunlight in and add large extra warming; a deep-uncertainty possibility.

Also: low cloud loss, cloud feedback tipping

A chain in which one tipping element pushes others past their thresholds, such as ice loss weakening ocean circulation and drying forests, locking in a hotter state.

Also: domino tipping, hothouse Earth trajectory, interacting tipping points

An explosive eruption of a vast magma body that buries surrounding regions in ash and loads the stratosphere with sulphate, cooling the planet and failing harvests for years.

Also: caldera-forming eruption, super-volcano eruption

An eruption below supereruption size but large enough to cool hemispheric climate, disrupt aviation and trade, and cause simultaneous crop failures across several regions.

Also: climate-changing eruption, year without a summer

Eruption of enormous lava volumes over millennia that releases carbon and sulphur on a scale linked in the rock record to mass extinctions and ocean anoxia.

Also: large igneous province, flood volcanism

Global darkening and cooling after a large asteroid or comet impact lofts dust, soot and sulphate, collapsing photosynthesis and food production for years.

Also: global impact cooling, impact firestorm soot

A period of greatly raised impact risk when a passing star or galactic tide sends many distant comets into the inner solar system; known only from models and the record.

Also: long-period comet influx, stellar-encounter comet shower

A solar outburst far stronger than any in the instrumental record, whose radiation, particles and geomagnetic storm could disable satellites, grids and communications worldwide at once.

Also: extreme solar particle event, Miyake event, beyond-Carrington event

A beam of high-energy radiation from a distant stellar explosion striking Earth, which could strip much of the ozone layer and raise surface ultraviolet exposure for years.

Also: galactic gamma-ray burst, high-energy transient

A star exploding close enough that its radiation and long-lasting cosmic-ray flux damage the ozone layer and raise radiation doses at the surface.

Also: supernova radiation exposure, cosmic ray surge

A period of greatly weakened or reorganised geomagnetic field during a reversal or excursion, letting more cosmic and solar radiation reach the upper atmosphere and orbiting systems.

Also: magnetic pole reversal, geomagnetic field collapse, dipole weakening

Spread of oxygen-free, sometimes sulphide-rich water through large parts of the ocean after extreme warming and nutrient supply, linked in the rock record to marine mass extinction.

Also: ocean euxinia, hydrogen sulphide ocean