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

===== 4.2.2.2.3 Glaciers =====

To assess the mass contribution of glaciers to sea level change, global estimates are required. Recent updates and temporal extensions of estimates obtained by different methods continue to provide ''very high confidence'' in continuing glacier mass loss on the global scale during the past decade (Bamber et al., 2018 <sup>[[#fn:r207|207]]</sup> ; Wouters et al., 2019; Zemp et al., 2019 <sup>[[#fn:r208|208]]</sup> ), see Section 2.2.3 and Appendix 2.A for a detailed discussion also on regional scales). Updates of the reconstructions of Cogley (2009) <sup>[[#fn:r210|210]]</sup> , Leclercq et al. (2011) <sup>[[#fn:r211|211]]</sup> and Marzeion et al. (2012) <sup>[[#fn:r212|212]]</sup> , presented and compared in Marzeion et al. (2015) <sup>[[#fn:r212|212]]</sup> , show increased agreement on rates of mass loss during the entire 20th century (Marzeion et al., 2015 <sup>[[#fn:r213|213]]</sup> ), compared to earlier estimates reported by AR5. The contribution of glaciers that may be missing in inventories or have already melted during the 20th century is hard to constrain (Parkes and Marzeion, 2018 <sup>[[#fn:r215|215]]</sup> ), and there is ''low confidence'' in their estimated contribution. These glaciers are thus neglected in the assessment of the sea level budget (Table 4.1).

While the agreement between the observational estimates of glacier mass changes and the modelled estimates from glacier models forced with climate model simulations has increased since AR5 (Slangen et al., 2017b <sup>[[#fn:r216|216]]</sup> ), there is only ''medium'' ''confidence'' in the use of glacier models to reconstruct sea level change because of the limited number of well-observed glaciers available to evaluate models on long time scales, and because of the small number of model-based global glacier reconstructions.

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