Abstract
Abstract. Ice loss from the Antarctic ice sheet (AIS) is expected to become the major contributor to sea level in the next centuries. Projections of the AIS response to climate change based on numerical ice-sheet models remain challenging due to the complexity of physical processes involved in ice-sheet dynamics, including instability mechanisms that can destabilise marine basins with retrograde slopes. Moreover, uncertainties in ice-sheet models limit the ability to provide accurate sea-level rise projections. Here, we apply probabilistic methods to a hybrid ice-sheet model to investigate the influence of several sources of uncertainty, namely sources of uncertainty in atmospheric forcing, basal sliding, grounding-line flux parameterisation, calving, sub-shelf melting, ice-shelf rheology and bedrock relaxation, on the continental response of the Antarctic ice sheet to climate change over the next millennium. We provide probabilistic projections of sea-level rise and grounding-line retreat, and we carry out stochastic sensitivity analysis to determine the most influential sources of uncertainty. We find that all investigated sources of uncertainty, except bedrock relaxation time, contribute to the uncertainty in the projections. We show that the sensitivity of the projections to uncertainties increases and the contribution of the uncertainty in sub-shelf melting to the uncertainty in the projections becomes more and more dominant as atmospheric and oceanic temperatures rise, with a contribution to the uncertainty in sea-level rise projections that goes from 5 % to 25 % in RCP 2.6 to more than 90 % in RCP 8.5. We show that the significance of the AIS contribution to sea level is controlled by the marine ice-sheet instability (MISI) in marine basins, with the biggest contribution stemming from the more vulnerable West Antarctic ice sheet. We find that, irrespective of parametric uncertainty, the strongly mitigated RCP 2.6 scenario prevents the collapse of the West Antarctic ice sheet, that in both the RCP 4.5 and RCP 6.0 scenarios the occurrence of MISI in marine basins is more sensitive to parametric uncertainty, and that, almost irrespective of parametric uncertainty, RCP 8.5 triggers the collapse of the West Antarctic ice sheet.
Highlights
The Antarctic ice sheet (AIS) is the largest reservoir of freshwater on Earth ( ∼ 60 m sea-level equivalent, Fretwell et al, 2013; Vaughan et al, 2013) and has the potential to become one of the largest contributors to sea level in the centuries
We show that the significance of the AIS contribution to sea level is controlled by the marine ice-sheet instability (MISI) in marine basins, with the biggest contribution stemming from the more vulnerable West Antarctic ice sheet
Irrespective of parametric uncertainty, the strongly mitigated representative concentration pathway (RCP) 2.6 scenario prevents the collapse of the West Antarctic ice sheet, that in both the RCP 4.5 and RCP 6.0 scenarios the occurrence of MISI in marine basins is more sensitive to parametric uncertainty, and that, almost irrespective of parametric uncertainty, RCP 8.5 triggers the collapse of the West Antarctic ice sheet
Summary
The Antarctic ice sheet (AIS) is the largest reservoir of freshwater on Earth ( ∼ 60 m sea-level equivalent, Fretwell et al, 2013; Vaughan et al, 2013) and has the potential to become one of the largest contributors to sea level in the centuries. There exist only a limited number of projections (Golledge et al, 2015; Ritz et al, 2015; DeConto and Pollard, 2016; Schlegel et al, 2018) for the whole Antarctic ice sheet on a (multi-)centennial timescale These projections show similar trends for the centuries, but they differ in the magnitude of the mass loss they predict, with differences and uncertainty ranges that can reach several metres for eustatic sea level. Using a numerical ice-sheet model supplemented with a statistical approach for the probability of MISI onset, Ritz et al (2015) have projected a contribution to sea level around 0.1 m by 2100, with a very low probability of exceeding 0.5 m in the A1B scenario Running their simulations with and without sub-grid melt interpolation at the grounding line, Golledge et al (2015) have projected that sea-level rise could range from 0.01 to 0.38 m by 2100 and from 0.21 m to more than 5 m by 2500 considering all RCP scenarios. Coupling an ice-sheet model with a climate model, Golledge et al (2019) have shown that freshwater released by the Antarctic ice sheet can trap warm waters below the sea surface, leading to higher projections by 2100, with a contribution to sea level that could reach 0.05 m in RCP 4.5 and 0.14 m in RCP 8.5
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