Editing IPCC:AR6/WGII/Chapter-3 (section)

==== 3.2.2.2 Sea Level Rise and Extreme Sea Levels ====

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Global mean sea level (GMSL) (Cross-Chapter Box SLR in Chapter 3) has risen by about 0.20 m since 1901 and continues to accelerate (WGI AR6 [[IPCC:Wg2:Chapter:Chapter-2#2.3.3.3|Section 2.3.3.3]] ; [[#Church--2011|Church and White, 2011]] ; [[#Jevrejeva--2014|Jevrejeva et al., 2014]] ; [[#Hay--2015|Hay et al., 2015]] ; [[#Kopp--2016|Kopp et al., 2016]] ; [[#Dangendorf--2017|Dangendorf et al., 2017]] ; WCRP Global Sea Level Budget Group, 2018; [[#Kemp--2018|Kemp et al., 2018]] ; [[#Ablain--2019|Ablain et al., 2019]] ; [[#Gulev--2021|Gulev et al., 2021]] ).

Most coastal ecosystems (mangroves, seagrasses, salt marshes, shallow coral reefs, rocky shores and sandy beaches) are affected by changes in relative sea level (RSL, the change in the mean sea level relative to the land; [[#3.4.2|Section 3.4.2]] ). Regional rates of RSL rise differ from the global mean due to a range of factors, including local subsidence driven by anthropogenic activities such as groundwater and hydrocarbon extraction (WGI AR6 Box 9.1; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). In many deltaic regions, anthropogenic subsidence is currently the dominant driver of RSL rise (WGI AR6 [[IPCC:Wg2:Chapter:Chapter-9#9.6.3|Section 9.6.3.2]] ; [[#Tessler--2018|Tessler et al., 2018]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). RSL rise is driving a global increase in the frequency of extreme sea levels ( ''high confidence'' ) (WGI AR6 [[IPCC:Wg2:Chapter:Chapter-9#9.6.4.1|Section 9.6.4.1]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ).

GMSL rise through the middle of the 21st century exhibits limited dependence on emissions scenario; between 1995–2014 and 2050, GMSL is ''likely'' to rise by 0.15–0.23 m under SSP1-1.9 and 0.20–0.30 m under SSP5-8.5 (WGI AR6 [[IPCC:Wg2:Chapter:Chapter-9#9.6.3|Section 9.6.3]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). Beyond 2050, GMSL and RSL projections are increasingly sensitive to the differences among emission scenarios. Considering only processes in which there is at least ''medium confidence'' (e.g., thermal expansion, land-water storage, land-ice surface mass balance and some ice-sheet dynamic processes), GMSL between 1995–2014 and 2100 is ''likely'' to rise by 0.28–0.55 m under SSP1-1.9, 0.33–0.61 m under SSP1-2.6, 0.44–0.76 m under SSP2-4.5, 0.55–0.90 m under SSP3-7.0 and 0.63–1.02 m under SSP5-8.5 (Figure 3.5). Under high-emission scenarios, ice-sheet processes in which there is ''low confidence'' and ''deep uncertainty'' might contribute more than one additional metre to GMSL rise by 2100 (WGI AR6 Chapter 9; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ).

Rising mean RSL will continue to drive an increase in the frequency of extreme sea levels ( ''high confidence'' ). The expected frequency of the current 1-in-100-year extreme sea level is projected to increase by a median of 20–30 times across tide-gauge sites by 2050, regardless of emission scenario ( ''medium confidence'' ). In addition, extreme-sea-level frequency may be affected by changes in tropical cyclone climatology ( ''low confidence'' ), wave climatology ( ''low confidence'' ) and tides ( ''high confidence'' ) associated with climate change and sea level change (WGI AR6 [[IPCC:Wg2:Chapter:Chapter-9#9.6.4.2|Section 9.6.4.2]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ).

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