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

===== 9.4.2.3.3 Ice-shelf disintegration =====

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Antarctic ice shelves modulate grounded ice flow through buttressing, so their weakening or disintegration is crucial for the timing and magnitude of ice loss and onset of instabilities ( [[#9.4.2.4|Section 9.4.2.4]] ; Box 9.4). Projections of ice-shelf disintegration are uncertain in terms of atmospheric warming and the response of the shelf surface – that is, surface melting, and whether shelves then disintegrate due to hydrofracturing and flexing, or are resilient through refreezing or drainage ( [[#Bell--2018|Bell et al., 2018]] ). The SROCC stated it is not expected that widespread ice-shelf loss will occur before the end of the 21st century, but this was based on only one study, using a regional climate model forced by five GCMs ( [[#Trusel--2015|Trusel et al., 2015]] ), so there was ''low confidence'' in this assessment. The study of [[#DeConto--2016|DeConto and Pollard (2016)]] projected the appearance of extensive surface meltwater several decades earlier than [[#Trusel--2015|Trusel et al. (2015)]] and was therefore assessed to be too uncertain to include in SROCC projections of the AIS.

Since SROCC, further studies have highlighted the modelling uncertainties in this area. Coastal surface air temperature projections in CMIP6 models show large inter-model differences driven by sea ice retreat and exhibit more warming relative to global mean temperature under low emissions than high, due to delayed response of the Southern Ocean to stabilized emissions and stratospheric ozone recovery ( [[#Bracegirdle--2020|Bracegirdle et al., 2020]] ). The updated study of [[#DeConto--2021|DeConto et al. (2021)]] includes improvements to the climate simulations relative to those in [[#DeConto--2016|DeConto and Pollard (2016)]] , and the resulting surface meltwater projections are now consistent with [[#Trusel--2015|Trusel et al. (2015)]] . However, the net effect of meltwater feedbacks on ice shelves is uncertain. Ice discharge is expected to lead to surface ocean and atmosphere cooling: this increases ocean stratification and sub-shelf melting, but also reduces ice-shelf surface melting and delays hydrofracturing ( [[#Golledge--2019|Golledge et al., 2019]] ; [[#Sadai--2020|Sadai et al., 2020]] ; [[#DeConto--2021|DeConto et al., 2021]] ). The new studies are insufficient to change SROCC’s ''low confidence'' assessment on ice-shelf loss. The consequence of this uncertainty on projections is discussed in [[#9.4.2.5|Section 9.4.2.5]] and Box 9.4.

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