Climate tipping point

Major identified tipping elements

Polar ice:

• West Antarctic ice sheet collapse — irreversible once initiated; sea-level rise of ~3 meters; threshold possibly 1.5-2.0°C warming
• Greenland ice sheet collapse — slower than WAIS but eventually catastrophic; sea-level rise ~7 meters; threshold ~1.5-2°C
• Arctic sea ice loss — summer sea-ice-free Arctic; threshold ~1.5-2°C; possibly already underway

Ocean circulation:

• AMOC (Atlantic Meridional Overturning Circulation) slowdown or shutdown — major climate consequences for Europe, Africa, Americas; threshold uncertain; possibly 2-4°C; may already be weakening
• Southern Ocean overturning changes

Forests:

• Amazon dieback — possible tipping to savanna; threshold ~3-4°C global warming combined with continued deforestation; may be near
• Boreal forest dieback — particularly Siberian forests; warming-induced drought, fire, pest outbreaks
• Tropical-forest carbon-source transition — some Amazon regions already net carbon sources

Permafrost:

• Abrupt permafrost thaw — rapid release of methane and CO₂; threshold ~1.5-2°C
• Methane hydrate destabilization — possible major release from seabed methane clathrates; threshold and rate uncertain

Coral reefs:

• Coral reef collapse — ~99% loss likely at 2°C warming; substantially underway already
• Coral-algae mutualism breakdown — coral bleaching as the visible expression

Other:

• Indian summer monsoon shifts — potential disruption of monsoon onset, intensity, distribution; affects food production for ~1.5 billion people
• Sahel monsoon shifts — green-vs-arid Sahel oscillation
• Boreal-arctic ecosystem shifts

Recent research

Lenton et al. (2008, 2019, 2023) and McKay et al. (2022) have updated tipping-point analysis with growing concern:

• Some tipping points may be near or already crossed at current ~1.2°C warming
• Multiple tipping points may interact — cascading
• Earlier estimates underestimated risk — IPCC AR6 raised tipping-point concern substantially
• Some tipping is irreversible — cannot be undone by reducing emissions later

The 2022 Science paper by McKay et al. identified five tipping elements potentially crossed at current warming and an additional eight near thresholds at 1.5-2°C.

What tipping points mean for action

• Earlier action is more effective — once tipping points are crossed, the system shifts regardless of subsequent emissions
• Caution outweighs delay — risk-management thinking suggests acting on tipping-point concerns even with substantial uncertainty
• Some loss is irreversible — coral reefs, ice sheets, certain ecosystems can’t be re-built quickly even if conditions return
• Tipping-point dynamics may compound — cascading shifts could accelerate change beyond what gradualist analysis suggests

See also

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• Shares approach with: [[climate-feedback-loop]]

Sources

• McKay et al. (2022) “Exceeding 1.5°C global warming could trigger multiple climate tipping points,” Science
• Lenton et al. (2019) “Climate tipping points — too risky to bet against,” Nature
• IPCC AR6 Working Group I

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