In this section, we assess available scientific literature on tipping points in ocean and atmosphere circulations. To this end, we focus on the following systems: ocean circulations in the Atlantic and the Southern Ocean; monsoons over West Africa, India and South America; tropical clouds and circulations; El Niño southern oscillation; and mid-latitude atmospheric circulations.
Key: +++ Yes (high confidence), ++ Yes (medium confidence), + Yes (low confidence), – – – No (high confidence), – – No (medium confidence), – No (low confidence)
Primary drivers are bolded, DC: Direct Climate driver (via direct impact of emissions on radiative forcing); CA: Climate-Associated driver (including second-order & related effects of climate change); NC: Non-Climate driver. Drivers can enhance (↗) the tipping process or counter it (↘)
Table 1.4.1: Summary of evidence for tipping dynamics, key drivers, and biophysical impacts in each system considered in this chapter
System | Key drivers | Key biophysical impacts (see S2 for societal impacts) | Key feedbacks | Abrupt / large rate change? | Critical threshold(s)? | Irreversible? (timescale) | Tipping system? |
---|---|---|---|---|---|---|---|
Ocean overturning circulation | |||||||
Atlantic Meridional Overturning Circulation (AMOC) Shutdown/collapse | DC: ocean warming (↗) DC: precipitation increase (↗) CA: Greenland ice sheet meltwater increase (↗) CA: Arctic river discharge increase (↗) CA: sea ice extent & thickness decrease (↗) DC: regional aerosol forcing increase (↘) CA: regional ocean circulation changes (?) | • Cooling over Northern Hemisphere (up to 10°C over W/N Europe) • Change in precipitation and weather patterns over Europe • Change in location and strength of rainfall in all tropical regions • Reduced efficiency of global carbon sink, and ocean acidification • Reduced support for primary production in Atlantic oceans • Deoxygenation in the North Atlantic Change in sea level in the North Atlantic • Modification of sea ice and arctic permafrost distribution • Change in winter storminess • Reduced land productivity in Atlantic bordering regions • Increased wetland in some tropical areas and associated methane emission • Change in rainforest response in drying regions | Salt-advection (↗) Sea ice melting (↗) Heat transport (↘) Temperature (↗) Surface heat flux (↗) Collapse of convection in the Labrador and Irminger Seas (↗) | Feedback-dependent: Century (basin-wide salt advection feedback), Few decades (North Atlantic salt-advection feedback), < few decades (sudden increase in sea-ice cover in all convective regions) | Salinity change/freshwater/AMOC strength Thresholds likely path-dependent (depending on rate and spatial pattern) | ++ (centuries) | ++ |
North Atlantic Subpolar Gyre (SPG) Collapse | • Increase in summer heat waves frequency • Collapse of the North Atlantic spring bloom and the Atlantic marine primary productivity • Increase in regional ocean acidification • Regional long-term oxygen decline • Impact on marine ecosystems in the tropics and subtropics | Years to few decades | Salinity change/freshwater Global warming1.1-3.8°C | ++ (decades) | ++ | ||
Southern Ocean circulation Antarctic Overturning Collapse / Rapid continental shelf warming | DC: ocean warming (↗) CA: Antarctic ice sheet meltwater increase (↗) CA: wind trends (↗) CA: sea ice formation (↗) DC: precipitation increase (↗) | • Modification of Earth’s global energy balance, timing of reaching 2°C global warming • Reduced efficiency of global carbon sink • Change in global heat storage • Reduced support for primary production in world’s oceans • Drying of Southern Hemisphere • Wetting of Northern Hemisphere • Modification of regional albedo, shelf water temperatures • Potential feedbacks to further ice shelf melt | Density-stratification (↗) Meltwater-warming (↗) | ++ (AABW formation & abyssal overturning shutdown within decades) | Salinity change/freshwater | ++ (cavity warming reversion would need 20th-century atmospheric conditions + reduced meltwater input) | ++ |
Atmosphere: Monsoons | |||||||
Indian summer monsoon (ISM) Collapse / Shift to low-precipitation state | NC: increased summer insolation (↘) DC: increased water vapour in atmosphere (↘) CA: Indian Ocean Dipole events (?) CA: ENSO change (?) CA: North Atlantic cold SST (↗) DC: aerosol loading (↗) CA: Indian Ocean warming (↗) CA: low cloud reduction (↘) | Massive change in precipitation Change in tropical and subtropical climates Biodiversity loss and ecosystem degradation | Moisture-advection (↘) | Decades to centuries | Regional AOD level over Indian subcontinent (>0.25) Interhemispheric AOD difference (>0.15) AMOC slowdown (unknown threshold) | Uncertain; likely decades to centuries | unknown |
West African monsoon (WAM) Collapse or abrupt strengthening | DC: increased water vapour in atmosphere (↗) NC: increased summer insolation (↘) NC: land-cover change (↗) CA: desertification (↗) CA: AMOC slowdown (↗) CA: regional SST variations (?) CA: High latitude cooling (↗) CA/NC: regional soil moisture variation (?) CA/NC: regional vegetation variation (?) NC: dust emissions (?) | Massive change in precipitation Change in tropical and subtropical climates Biodiversity loss and ecosystem degradation | Vegetation-albedo (↗) | Decades to centuries | Insolation changes in the Northern Hemisphere summers and surface albedo changes (unknown threshold) Interhemispheric asymmetry in AOD (>0.15) AMOC slowdown (unknown threshold) | Decades to centuries | + |
South American Monsoon (SAM) | DC: increased water vapour in atmosphere (↗) NC: increased summer insolation (↘) CA: AMOC slowdown (↗) NC: Amazon deforestation (↗) | Massive change in precipitation Change in tropical and subtropical climates Biodiversity loss and ecosystem degradation | Vegetation-moisture (?) | Decades | Interhemispheric asymmetry in AOD (>0.15) Extent of Amazon deforestation (30-50%) AMOC slowdown (unknown threshold) | Uncertain; likely decades to centuries | unknown |
Atmosphere: Planetary circulations | |||||||
Tropical clouds, circulation and climate sensitivity Shift to different large-scale configuration | DC: atmospheric warming (↗) DC: ocean warming (↗) | • Massive alteration of hydrology in many regions • Impact on ambient atmospheric-oceanic phenomena such as ENSO • Strong intensification of global climate change | Cloud-moisture-radiation (↗) | Unknown | Unknown | Unknown |
– – |
El Niño Southern Oscillation (ENSO) Shift to more extreme or persistent state | DC: east vs west Pacific warming (↗) DC: increased water vapour in atmosphere (↗) DC: weaker trade winds (↗) CA: MJO strengthening (↗) | • Temporary trade wind collapse during El Niño phase • Increase in global mean surface temperatures during El Niño phase • Modification of global atmospheric circulation • Modification of worldwide patterns of weather variability | Bjerknes (↗) (SST-tradewinds-ocean thermocline) | No evidence (gradual) | No evidence (gradual) | No evidence | – – |
Mid-latitude atmospheric dynamics Shift to wavy-jet state / more frequent or extreme planetary waves or blocks | CA: AMOC slowdown (↗) CA: Midlatitude flow weakening (↗) DC: Arctic amplification (↗) | • More persistent and slower moving weather patterns • Increase in extreme events on Northern hemisphere | Debated: Waviness quasi-resonance (↗) | No evidence | Potentially waviness threshold, beyond which quasi-resonance kicks in | No evidence | – |