1.4.2 Current state of knowledge on ocean and atmosphere circulation tipping points

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.

Figure: 1.4.2
Figure: 1.4.2 Potential tipping systems in ocean and atmosphere circulations considered in this chapter. The markers indicate which of the systems are in this report considered a tipping system (+++ high confidence, ++ medium confidence and + low confidence) and which are not (- – – high confidence, – – medium confidence and – low confidence), ▽ indicates systems for which a clear assessment is not possible based on the current level of understanding.

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 driversKey biophysical impacts (see S2 for societal impacts)Key feedbacksAbrupt  /  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 decadesSalinity 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 centuriesRegional AOD level over Indian subcontinent (>0.25)

Interhemispheric AOD difference  (>0.15)

AMOC slowdown (unknown threshold)
Uncertain; likely decades to centuriesunknown
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 centuriesInsolation 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 (?)DecadesInterhemispheric asymmetry in AOD (>0.15)

Extent of Amazon deforestation (30-50%)

AMOC slowdown (unknown threshold)
Uncertain; likely decades to centuriesunknown
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 (↗)UnknownUnknownUnknown
– –
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 evidencePotentially waviness threshold, beyond which quasi-resonance kicks inNo evidence– 
Bezos Earth Fund University of Exeter logo
Earth Commission Systems Change Lab logo Systemiq logo
Global Tipping Points logo
Share this content
Top