Global mean sea level rise will continue in the 21st 
century (virtually certain), with projected regional relative sea level rise 
within 20% of the global mean along two-thirds of the global coastline 
(medium conﬁdence). The magnitude, the rate, the timing of threshold 
exceedances, and the long-term commitment of sea level rise depend 
on emissions, with higher emissions leading to greater and faster rates 
of sea level rise. Due to relative sea level rise, extreme sea level events 
that occurred once per century in the recent past are projected to occur 
at least annually at more than half of all tide gauge locations by 2100 
123 This outcome is characterised by deep uncertainty: Its likelihood defies quantitative assessment but is considered due to its high potential impact. {WGI Box TS.1; 
WGII Cross-Chapter Box DEEP}
and risks for coastal ecosystems, people and infrastructure will continue 
to increase beyond 2100 (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 (limited evidence). The probability and rate of ice mass loss 
increase with higher global surface temperatures (high conﬁdence). 
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).