In this section we assess available scientific literature relating to tipping points in the cryosphere, as summarised in Figure 1.2.2 and Table 1.2.1. We focus on the following systems: the ice sheets on Greenland and Antarctica, sea ice (in the Arctic and Antarctic), mountain glaciers, and permafrost.
Table: 1.2.1 Summary of evidence for tipping dynamics, key drivers and biophysical impacts in each system considered in this chapter
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; CA: Climate-Associated driver (including second-order and related effects of climate change); NC: Non-Climate driver, PF: positive (amplifying) feedback (FB), NF: negative (damping) feedback. Drivers can enhance (↗) the tipping process or counter it (↘)
System (and potential tipping point) | Key drivers | Key biophysical impacts | Selected key feedbacks | Abrupt / large rate change? | Critical threshold(s) (warming > preindustrial) | Irreversible? (decadal / centennial) | Tipping system? |
---|---|---|---|---|---|---|---|
Ice Sheets | |||||||
Greenland Ice Sheet (collapse) | DC: atmospheric warming (↗) DC: precipitation increase (↘) DC: ocean warming and circulation changes (↗/↘) DC: black carbon deposition (↗) CA: sea ice decline (↗) CA: atmospheric circulation changes (↗|↘) | • Sea level rise (up to 7m) over centuries to millennia • Disruption of global ocean circulation • Substantial shifts in atmospheric circulation patterns | • PF: melt-elevation • PF: melt-albedo | +++ | 0.8-3°C | +++ | +++ |
West Antarctic Ice Sheet (collapse) | DC: ocean warming and circulation changes (↗) DC: atmospheric warming (↗) DC: precipitation increase (↘) | • Sea level rise (up to 3m) over centuries to millennia • Disruption of global ocean circulation • Substantial shifts in atmospheric circulation patterns | • PF: marine ice sheet instability • NF: glacial isostatic adjustment ?: melt-stratification | +++ | 1-3°C | +++ | +++ |
Marine basins East Antarctica (collapse) | DC: ocean warming and circulation changes (↗) DC: atmospheric warming (↗) DC: precipitation increase (↘) | • Sea level rise (up to 19m) over centuries to millennia • Disruption of global ocean circulation • Substantial shifts in atmospheric circulation patterns | • PF: marine ice sheet instability • NF: glacial isostatic adjustment ?: melt-stratification | +++ | 2-6°C | +++ | +++ |
Non-marine East Antarctic Ice Sheet (collapse) | DC: atmospheric warming (↗) DC: precipitation increase (↘) | • Sea level rise (up to 34m) over centuries to millennia • Disruption of global ocean circulation • Substantial shifts in atmospheric circulation patterns | • PF: melt-elevation | +++ | 6-10°C | ++ | ++ |
Sea Ice | |||||||
Arctic summer sea ice (loss) | DC: atmospheric warming (↗) DC: atmospheric circulation shifts (↗/↘) DC: ocean warming (↗) DC: ocean circulation shifts (↗/↘) DC: black carbon deposition (↗) DC: storminess increase (↗) CA: ocean stratification increase (↘) | • Regional warming (polar amplification) • Ecosystem disruption • Impacts on ocean circulation • Impacts on atmospheric circulations • Increased evaporation | • PF: Ice-albedo • FBNF: Snow • FBNF: Growth • FBNF: Radiation FB | – – – | N/A | – – – | – – – |
Arctic winter sea ice (loss) | +++ | 3-6 °C | – – | – – (abrupt loss due to Arctic geometry) | |||
Barents sea ice (loss) | – (linear relationship in most models) | unclear | unclear | – | |||
Antarctic sea ice (loss) | unclear | unclear | + (reversible over millennia) | unclear | |||
Glaciers | |||||||
Glaciers (retreat) | DC: atmospheric warming (↗) DC: deposition of dust, black carbon, etc. (albedo) (↗) DC: reduced snow (input and albedo) (↗) DC: local thermokarst (↗) | • Water supply decline • Ecosystem disruption (e.g. wetlands, water chemistry) • Increase in number and size of glacier lakes • Increase in slope instabilities • Transition from glacial to para-glacial landscapes • Sea level rise | • PF: melt-elevation • FBPF: calving front retreat • PF-: ice-dynamic FBs • NF: retreat to higher altitudes | + + (regional) – – (global) | Regionally variable | – – | ++ (regional) – – (global) |
Permafrost | |||||||
Land permafrost (thaw) | DC: atmospheric warming (↗) CA: vegetation increase (increase albedo ↗, increase summer shading ↘, and vice versa for forest die-back) CA: wildfire intensity increase (↗) CA: precipitation increase (rain extremes, snow cover albedo ↗) | • Greenhouse gas emissions • Landscape disruption • Ecosystem disruption | • PF: carbon-climate FB • PF: thermokarst development • PF: summer soil drying •PF-: vegetation interaction | – – (global) ++ (regional) | N/A | +++ (wrt carbon loss) – – – (wrt frozen soil) | ++ (regional) – – (global, on 10s-100s year timescale) |
Subsea permafrost (thaw) | DC: ocean warming (↗) CA: sea ice loss (↗) CA: water pressure reduction (↗) | • Greenhouse gas emissions | • PF: Carbon-climate FB • NF: sediment sink • NF: water column sink | + | N/A | + + (w.r.t. gas hydrate dissociation)+ + (w.r.t. frozen sediment) | – – (global, on 10s-100s year timescale) |