Comment on tc-2021-371

doi:10.5194/tc-2021-371-rc1

Abstract

The Antarctic Ice Sheet will play a crucial role in the evolution of global mean sea-level as the climate warms. An interactively coupled climate and ice sheet model is needed to understand the impacts of ice—climate feedbacks during this evolution. Here we use a two-way coupling between the U.K. Earth System Model and the BISICLES dynamic ice sheet model to investigate Antarctic ice—climate interactions under two climate change scenarios. We perform ensembles of SSP1-1.9 and SSP5-8.5 scenario simulations to 2100, which we believe are the first such simulations with a climate model with two-way coupling between both atmosphere and ocean models to dynamic models of the Greenland and Antarctic ice sheets. In SSP1-1.9 simulations, ice shelf basal melting and grounded ice mass loss are generally lower than present rates during the entire simulation period. In contrast, the responses to SSP5-8.5 forcing are strong. By the end of 21st century, these simulations feature order-of-magnitude increases in basal melting of the Ross and Filchner-Ronne ice shelves, caused by intrusions of warm ocean water masses. Due to the slow response of ice sheet drawdown, this strong melting does not cause a substantial increase in ice discharge during the simulations. The surface mass balance in SSP5-8.5 simulations shows a pattern of strong decrease on ice shelves, caused by increased melting, and strong increase on grounded ice, caused by increased snowfall. Despite strong surface and basal melting of the ice shelves, increased snowfall dominates the mass budget of the grounded ice, leading to an ensemble-mean Antarctic contribution to global mean sea level of a fall of 22 mm by 2100 in the SSP5-8.5 scenario. We hypothesise that this signal would revert to sea-level rise on longer timescales, caused by the ice sheet dynamic response to ice shelf thinning. These results demonstrate the need for fully coupled ice—climate models in reducing the substantial uncertainty in sea-level rise from the Antarctic Ice Sheet.

Highlights

The Antarctic Ice Sheet (AIS) is a critically important component of the Earth system (Fyke et al, 2018; Noble et al, 2020)
The Warm Deep Water gains access through the Filchner Trough (Fig. 4f), as found by previous studies (Hellmer et al, 2012; Naughten et al, 2021). As this strong melting only becomes apparent at the end of the 21st century in our simulations, we extend the SSP5-8.5 projections to the year 2115 in order to verify the persistence of this signal, which is confirmed by the drastic increase of melting under this ice shelf during the 15 years of extension (Fig. 5c)
5 Conclusions In this study, we carry out small ensembles of SSP1-1.9 and SSP5-8.5 simulations using the UKESM1.0-ice Earth System Model, which makes these the first simulations with an atmosphere-ocean general circulation model (AOGCM) that has two-way coupling between atmosphere and ocean components to dynamic models of the Greenland and Antarctic ice sheets

Summary

Introduction

The Antarctic Ice Sheet (AIS) is a critically important component of the Earth system (Fyke et al, 2018; Noble et al, 2020). The observed thinning of the grounded AIS, especially in the western sector, is notably associated 45 with strong oceanic melting under ice shelves (Rignot and Jacobs, 2002; Shepherd et al, 2004; Payne et al, 2004; Jacobs et al, 2011; Pritchard et al, 2012) which reduces the ice sheet buttressing force and increases the ice discharge across grounding lines (Schoof, 2007; Fürst et al, 2016). For this reason, it would be concerning if the projected rise of global surface temperature associated with anthropogenic emissions of greenhouse gases (GHGs) were to be replicated in Antarctic ocean properties. None of the current CMIP6 models has included a dynamic AIS model, which makes them unable to simulate the impacts that the ice sheet evolution has on global sea-level rise and the other climate components

Methods

Results

Discussion

Conclusion