Editing IPCC:AR6/SYR/SPM (section)

=== Likelihood and Risks of Unavoidable, Irreversible or Abrupt Changes ===

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'''B.3 Some future changes are unavoidable and/or irreversible but can be limited by deep, rapid and sustained global greenhouse gas emissions reduction. The likelihood of abrupt and/or irreversible changes increases with higher global warming levels. Similarly, the probability of low-likelihood outcomes associated with potentially very large adverse impacts increases with higher global warming levels. ''(high confidence)'' Links to longer report3.1'''
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B.3.1 Limiting global surface temperature does not prevent continued changes in climate system components that have multi-decadal or longer timescales of response ''(high confidence).'' Sea level rise is unavoidable for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and sea levels will remain elevated for thousands of years ''(high confidence)'' . However, deep, rapid and sustained GHG emissions reductions would limit further sea level rise acceleration and projected long-term sea level rise commitment. Relative to 1995-2014, the ''likely'' global mean sea level rise under the SSP1-1.9 GHG emissions scenario is 0.15–0.23 m by 2050 and 0.28–0.55 m by 2100; while for the SSP5-8.5 GHG emissions scenario it is 0.20–0.29 m by 2050 and 0.63–1.01 m by 2100 ''(medium confidence)'' . Over the next 2000 years, global mean sea level will rise by about 2–3 m if warming is limited to 1.5°C and 2–6 m if limited to 2°C ''(low confidence)'' . ''[[#box-spm-1|Box SPM.1]] Links to longer report 3.1.3, Figure 3.4''

B.3.2 The likelihood and impacts of abrupt and/or irreversible changes in the climate system, including changes triggered when tipping points are reached, increase with further global warming ''(high confidence)'' . As warming levels increase, so do the risks of species extinction or irreversible loss of biodiversity in ecosystems including forests ''(medium confidence)'' , coral reefs ''(very high confidence)'' and in Arctic regions ''(high confidence)'' . At sustained warming levels between 2°C and 3°C, the Greenland and West Antarctic ice sheets will be lost almost completely and irreversibly over multiple millennia, causing several metres of sea level rise ''(limited evidence)'' . The probability and rate of ice mass loss increase with higher global surface temperatures ''(high confidence)'' . Links to longer report 3.1.2, 3.1.3

B.3.3 The probability of low-likelihood outcomes associated with potentially very large impacts increases with higher global warming levels ''(high confidence)'' . Due to deep uncertainty linked to ice-sheet processes, global mean sea level rise above the ''likely'' range – approaching 2 m by 2100 and in excess of 15 m by 2300 under the very high GHG emissions scenario (SSP5-8.5) ''(low confidence)'' – cannot be excluded. There is ''medium confidence'' that the Atlantic Meridional Overturning Circulation will not collapse abruptly before 2100, but if it were to occur, it would ''very'' ''likely'' cause abrupt shifts in regional weather patterns, and large impacts on ecosystems and human activities. ''[[#box-spm-1|Box SPM.1]] Links to longer report 3.1.3''

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