TABLE S.1 State of knowledge on potential candidate processes that might undergo abrupt change. These include both abrupt climate changes in the physical climate system and abrupt climate impacts of ongoing changes that, when certain thresholds are crossed, can cause abrupt impacts for society and ecosystems. The near term outlook for this century is highlighted as being of particular relevance for decision makers generally.

Potential Abrupt Climate Change or Impact and Key Examples of Consequences Current Trend Near Term Outlook (for an Abrupt Change within This Century) Long Term Outlook (for a Significant Change1 after 2100) Level of Scientific Understanding Critical Needs (Research, Monitoring, etc.)
Abrupt Changes in the Ocean Disruption to Atlantic Meridional Overturning Circulation (AMOC)

• Up to 80 cm sea level rise in North Atlantic

• Southward shift of tropical rain belts

• Large disruptions to local marine ecosystems

• Ocean and atmospheric temperature and circulation changes

• Changes in ocean’s ability to store heat and carbon

Trend not clearly detected Low High Moderate

• Enhanced understanding of changes at high latitudes in the North Atlantic (e.g., warming and/or freshening of surface waters)

• Monitoring of overturning at other latitudes

• Enhanced understanding of drivers of AMOC variability

Sea level rise (SLR) from ocean thermal expansion

• Coastal inundation

• Storm surges more likely to cause severe impacts

Moderate increase in sea level rise Low2 High High

• Maintenance and expansion of monitoring of sea level (tide gauges and satellite data), ocean temperature at depth, local coastal motions, and dynamic effects on sea level

Sea level rise from destabilization of WAIS ice sheets

• 3-4 m of potential sea level rise

• Coastal inundation

• Storm surges more likely to cause severe impacts

Losing ice to raise sea level Unknown but Probably Low Unknown Low

• Extensive needs, including broad field, remote-sensing, and modeling research

Sea level rise from other ice sheets (including Greenland and all others, but not including WAIS loss)

• As much as 60m of potential sea level rise from all ice sheets

• Coastal inundation

• Storm surges more likely to cause severe impacts

Losing ice to raise sea level Low High High for some aspects, Low for others

• Maintenance and expansion of satellite, airborne, and surface monitoring capacity, process studies, and modeling research



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