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Influence of surface mass balance on the high-end sea-level commitment from the Antarctic Ice Sheet

par Coulon, Violaine ;Ann Kristin, Klose;Kittel, Christoph;Winkelmann, Ricarda;Pattyn, Frank
Référence EGU General Assembly 2022 (23-27 May 2022: Vienna, Austria & Online)
Publication Non publié, 2022-05-26

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Résumé :

Over the last decades, the Antarctic Ice Sheet (AIS) has been losing mass, mainly through icedischarge and sub-shelf melting (Rignot et al., 2019). More specifically, recent observations showthat the AIS is currently losing mass at an accelerating rate in areas subject to strong ocean induced melt. At the same time, no long-term trend in snowfall accumulation changes can bedetected in the interior of the ice sheet. Due to these current trends, basal melting has often beenconsidered as the main driver of future Antarctic mass loss. However, even though stronger basalmelting of ice shelves is projected to drive future AIS mass loss, recent studies (e.g. Seroussi et al.,2020) have shown that surface mass balance (SMB, the balance of accumulation through snowfalland ablation through erosion, sublimation and runoff) has a strong potential in controlling thefuture stability and evolution of the Antarctic Ice Sheet. With increasing temperatures, SMB isexpected to increase in Antarctica in the future as a result of enhanced snowfall. As long as thewarming remains modest, other AIS SMB components (such as runoff) will likely continue to play aminor role in future SMB changes (Lenaerts et al., 2019; Kittel et al., 2021). Under high-emissionscenarios, however, future runoff is likely to significantly compensate for mass gain throughsnowfall (Kittel et al 2021). The balance between these competing processes is still a matter ofdebate and, as of yet, there is no consensus on estimates of the future mass balance of theAntarctic Ice Sheet (Seroussi et al., 2020).Here, we investigate the relative importance of SMB changes and ocean-induced melt on the long-term (multi-centennial to multi-millennial) AIS response as well as their associated uncertainties.To do so, we force two ice sheet models (fETISh and PISM) with atmospheric and oceanicprojections inferred from a subset of models from the sixth phase of the Coupled ModelIntercomparison Project (CMIP6) under the Shared Socioeconomic Pathways (SSP) 5-8.5 andSSP1-2.6. Changes in precipitation rate and air temperature are corrected for elevation changesand used as inputs to a positive degree-day scheme which estimates changes in snowfall, rainfalland surface runoff. Climate projections are used as forcing until the year 2300 and afterwards noclimate trend is applied, allowing to investigate the long-term impacts of early-millennia warming(often called sea-level commitment).Taking into account key uncertainties in both atmospheric and oceanic forcing, our results predictthat atmosphere-ice surface interactions will have an important role on the AIS stability under highend future emission scenarios. We also show the increasingly important role of the melt-elevationfeedback for multi-centennial projections of the AIS. Finally, we find that modelling choicesregarding the atmosphere forcing have a significant influence on the future sea-level contributionfrom the AIS under high-end emission scenarios, leading to a spread from a few centimeters toseveral meters contribution over the coming millennia.