Editing IPCC:AR6/WGI/Chapter-4 (section)

==== 4.3.2.2 Global Mean Sea Level ====

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The AR5 assessed from CMIP5 process-based simulations that the rate of GMSL rise during the 21st century will ''very likely'' exceed the rate observed during 1971–2010 for all RCP scenarios due to increases in ocean warming and loss of mass from glaciers and ice sheets ( [[#Church--2013|Church et al., 2013]] ). Further, AR5 concluded that for the period 2081–2100, compared to 1986–2005, GMSL rise is ''likely'' ( ''medium confidence'' ) to be in the 5–95% range of projections from process-based models, which give 0.26–0.55 m for RCP2.6, 0.32–0.63 m for RCP4.5, 0.33–0.63 m for RCP6.0, and 0.45–0.82 m for RCP8.5. For RCP8.5, the rise by 2100 is 0.52–0.98 m with a rate during 2081–2100 of 8–16 mm yr <sup>–1</sup> .

There have been substantial modelling advances since AR5, with most sea level projections corresponding to one of three categories: (i) central-range projections, combining scenario-conditional probability distributions for the different contributions to estimate a central range under different scenarios; (ii) probabilistic projections, which explicitly consider outcomes for a wide range of likelihoods, including low-likelihood, high-impact outcomes; and (iii) semi-empirical projections, based on statistical relationships between past GMSL changes and climate variables, which now calibrate individual contributions and are consistent with physical-model based estimates (Section 9.6.3).

Based on the assessment of the latest modelling information (Figure 4.2d and Section 9.6.3), we conclude that under the SSP3-7.0, the ''likely'' range of GMSL change averaged over 2081–2100 relative to 1995–2014 is 0.46–0.74 m. Under SSP1-2.6, the ''likely'' range over the long-term is 0.30–0.54 m. Further, in SSP2-4.5, SSP3-7.0, and SSP5-8.5, the rise in GMSL is projected to accelerate over the 21st century. A detailed assessment of the processes contributing to these projected rises and accelerations in GMSL, together with a comparison to AR5 and SROCC, can be found in [[IPCC:Wg1:Chapter:Chapter-9|Chapter 9]] (Section 9.6.3). Projected changes in the thermosteric component of GMSL beyond 2300 are assessed in [[#4.7.1|Section 4.7.1]] .

In summary, it is ''virtually certain'' that under any one of the assessed SSPs, there will be continued rise in GMSL through the 21st century.

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