Over the next 2000 years, global mean sea level will rise by about 
2 to 3 m if warming is limited to 1.5°C and 2 to 6 m if limited to 2°C 
(low conﬁdence). Projections of multi-millennial global mean sea level 
rise are consistent with reconstructed levels during past warm climate 
periods: global mean sea level was very likely 5 to 25 m higher than today 
roughly 3 million years ago, when global temperatures were 2.5°C to 
4°C higher than 1850–1900 (medium conﬁdence). Further examples 
of unavoidable changes in the climate system due to multi-decadal 
or longer response timescales include continued glacier melt (very high 
conﬁdence) and permafrost carbon loss (high conﬁdence). {WGI SPM B.5.2, 
WGI SPM B.5.3, WGI SPM B.5.4, WGI SPM C.2.5, WGI Box TS.4, 
WGI Box TS.9, WGI 9.5.1; WGII TS C.5; SROCC SPM B.3, SROCC SPM B.6, 
SROCC SPM B.9} (Figure 3.4)
The probability of low-likelihood outcomes associated with 
potentially very large impacts increases with higher global 
warming levels (high conﬁdence). Warming substantially above the 
assessed very likely range for a given scenario cannot be ruled out, and 
there is high conﬁdence this would lead to regional changes greater 
than assessed in many aspects of the climate system. Low-likelihood, 
high-impact outcomes could occur at regional scales even for global warming 
within the very likely assessed range for a given GHG emissions scenario. 
Global mean sea level rise above the likely range – approaching 2 m by 
2100 and in excess of 15 m by 2300 under a very high GHG emissions 
scenario (SSP5-8.5) (low confidence) – cannot be ruled out due to 
deep uncertainty in ice-sheet processes123 and would have severe