Editing IPCC:AR6/WGI/Chapter-9 (section)

===== 9.6.3.2.4 Low confidence ice-sheet projections =====

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To test the possible effect of additional ice-sheet processes for which there is ''low confidence'' (Sections 9.4.1.3, 9.4.1.4, 9.4.2.5, 9.4.2.6 and 9.6.3.1, and Box 9.4), two additional approaches are considered. For both the Greenland and Antarctic ice sheets, we produce sensitivity cases employing the SEJ projections of [[#Bamber--2019|Bamber et al. (2019)]] , mapping 2°C and 5°C stabilization scenarios to SSP1-2.6 and SSP5-8.5, respectively. For the AIS, we produce an additional sensitivity case using projections, which incorporate MICI ( [[#DeConto--2021|DeConto et al., 2021]] ), mapping projections for RCP2.6 and RCP8.5 to SSP1-2.6 and SSP5-8.5. For the Greenland Ice Sheet, the SEJ projections indicate the potential for outcomes outside the corresponding ''likely'' ranges (Table 9.8). For the AIS, there is no evidence from these studies to suggest an important role under lower-emissions scenarios for processes in whose projections we have ''low confidence'' . By contrast, for SSP5-8.5, the SEJ and MICI projections exhibit 17th–83rd percentile ranges of 0.02–0.56 m and 0.19–0.53 m by 2100, consistent with one another but considerably broader than the ''likely'' contribution for ''medium confidence'' processes of 0.03–0.34 m. This lower level of agreement for higher-emissions scenarios reflects the ''deep uncertainty'' in the AIS contribution to GMSL change under higher-emissions scenarios (Box 9.4). This ''deep uncertainty'' grows after 2100: by 2150, under SSP5-8.5, ''medium confidence'' processes ''likely'' lead to a –0.1–0.7 m AIS contribution, while SEJ- and MICI-based projections indicate 0.0–1.1 m and 1.4–3.7 m, respectively.

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