Editing IPCC:AR6/SR15/Chapter-3 (section)

==== Compilation of recent projections for sea level at 2100 (in cm) for Representative Concentration Pathway (RCP)2.6, and 1.5°C and 2°C scenarios. Upper and lower limits are shown for the 17-84% and 5-95% confidence intervals quoted in the original papers. ====

{| class="wikitable"
|-
! rowspan="2"| Study
! rowspan="2"| Baseline
! colspan="2"| RCP2.6
! colspan="2"| 1.5°C
! colspan="2"| 2°C
|-
! 67%
! 90%
! 67%
! 90%
! 67%
! 90%
|-
| AR5
| 1986–2005
| 28–61
|
|-
| Kopp et al. (2014)  <sup>[[#fn:r304|304]]</sup>
| 2000
| 37–65
| 29–82
|
|-
| Jevrejeva et al. (2016) <sup>[[#fn:r305|305]]</sup>
| 1986–2005
|
| 29–58
|
|-
| Kopp et al. (2016) <sup>[[#fn:r306|306]]</sup>
| 2000
| 28–51
| 24–61
|
|-
| Mengel et al. (2016) <sup>[[#fn:r307|307]]</sup>
| 1986–2005
| 28–56
|
|-
| Nauels et al. (2017) <sup>[[#fn:r308|308]]</sup>
| 1986–2005
| 35–56
|
|-
| Goodwin et al. (2017) <sup>[[#fn:r309|309]]</sup>
| 1986–2005
|
| 31–59<br />
45–70<br />
45–72
|
|-
| Schaeffer et al. (2012) <sup>[[#fn:r310|310]]</sup>
| 2000
|
| 52–96
|
| 54–99
|
| 56–105
|-
| Schleussner et al. (2016b) <sup>[[#fn:r311|311]]</sup>
| 2000
|
| 26–53
|
| 36–65
|
|-
| Bittermann et al. (2017) <sup>[[#fn:r312|312]]</sup>
| 2000
|
| 29–46
|
| 39–61
|-
| Jackson et al. (2018) <sup>[[#fn:r313|313]]</sup>
| 1986–2005
|
| 30–58<br />
40–77
| 20–67<br />
28–93
| 35–64<br />
47–93
| 24–74<br />
32–117
|-
| Sanderson et al. (2017) <sup>[[#fn:r314|314]]</sup>
|
| 50–80
|
| 60–90
|-
| Nicholls et al. (2018) <sup>[[#fn:r315|315]]</sup>
| 1986–2005
|
| 24–54
|
| 31–65
|-
| Rasmussen et al. (2018) <sup>[[#fn:r316|316]]</sup>
| 2000
|
| 35–64
| 28–82
| 39–76
| 28–96
|-
| Goodwin et al. (2018) <sup>[[#fn:r317|317]]</sup>
| 1986–2005
|
| 26–62
|
| 30–69
|}

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There is little consensus between the reported ranges of GMSL rise (Table 3.1). Projections vary in the range 0.26–0.77 m and 0.35–0.93 m for 1.5°C and 2°C respectively for the 17–84% confidence interval (0.20–0.99 m and 0.24–1.17 m for the 5–95% confidence interval). There is, however, ''medium agreement'' that GMSL in 2100 would be 0.04–0.16 m higher in a 2°C warmer world compared to a 1.5°C warmer world based on the 17–84% confidence interval (0.00–0.24 m based on 5–95% confidence interval) with a value of around 0.1m. There is ''medium confidence'' in this assessment because of issues associated with projections of the Antarctic contribution to GMSL that are employed in emulation-based studies (see above) and the issues previously identified with SEMs (Church et al., 2013) <sup>[[#fn:r318|318]]</sup> .

Translating projections of GMSL to the scale of coastlines and islands requires two further steps. The first step accounts for regional changes associated with changing water and ice loads (such as Earth’s gravitational field and rotation, and vertical land movement), as well as spatial differences in ocean heat uptake and circulation. The second step maps regional sea level to changes in the return periods of particular flood events to account for effects not included in global climate models, such as tides, storm surges, and wave setup and runup. Kopp et al. (2014) <sup>[[#fn:r319|319]]</sup> presented a framework to do this and gave an example application for nine sites located in the US, Japan, northern Europe and Chile. Of these sites, seven (all except those in northern Europe) were found to experience at least a quadrupling in the number of years in the 21st century with 1-in-100-year floods under RCP2.6 compared to under no future sea level rise. Rasmussen et al. (2018) <sup>[[#fn:r320|320]]</sup> used this approach to investigate the difference between 1.5°C and 2°C warmer worlds up to 2200. They found that the reduction in the frequency of 1-in-100-year floods in a 1.5°C compared to a 2°C warmer world would be greatest in the eastern USA and Europe, with ESL event frequency amplification being reduced by about a half and with smaller reductions for small island developing states (SIDS). This last result contrasts with the finding of Vitousek et al. (2017) <sup>[[#fn:r321|321]]</sup> that regions with low variability in extreme water levels (such as SIDS in the tropics) are particularly sensitive to GMSL rise, such that a doubling of frequency may be expected for even small (0.1–0.2 m) rises. Schleussner et al. (2011) <sup>[[#fn:r322|322]]</sup> emulated the AMOC based on a subset of CMIP-class climate models. When forced using global temperatures appropriate for the CP3-PD scenario (1°C of warming in 2100 relative to 2000 or about 2°C of warming relative to pre-industrial) the emulation suggests an 11% median reduction in AMOC strength at 2100 (relative to 2000) with an associated 0.04 m dynamic sea level rise along the New York City coastline.

In summary, there is ''medium confidence'' that GMSL rise will be about 0.1 m (within a 0.00–0.20 m range based on 17–84% confidence-interval projections) less by the end of the 21st century in a 1.5°C compared to a 2°C warmer world. Projections for 1.5°C and 2°C global warming cover the ranges 0.2–0.8 m and 0.3–1.00 m relative to 1986–2005, respectively ( ''medium confidence'' ). Sea level rise beyond 2100 is discussed in Section 3.6; however, recent literature strongly supports the assessment by Church et al. (2013) <sup>[[#fn:r323|323]]</sup> that sea level rise will continue well beyond 2100 ( ''high confidence'' ).

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