The role of history and strength of the oceanic forcing in sea level projections from Antarctica with the Parallel Ice Sheet Model

Abstract

Abstract. Mass loss from the Antarctic Ice Sheet constitutes the largest uncertainty in projections of future sea level rise. Ocean-driven melting underneath the floating ice shelves and subsequent acceleration of the inland ice streams are the major reasons for currently observed mass loss from Antarctica and are expected to become more important in the future. Here we show that for projections of future mass loss from the Antarctic Ice Sheet, it is essential (1) to better constrain the sensitivity of sub-shelf melt rates to ocean warming and (2) to include the historic trajectory of the ice sheet. In particular, we find that while the ice sheet response in simulations using the Parallel Ice Sheet Model is comparable to the median response of models in three Antarctic Ice Sheet Intercomparison projects – initMIP, LARMIP-2 and ISMIP6 – conducted with a range of ice sheet models, the projected 21st century sea level contribution differs significantly depending on these two factors. For the highest emission scenario RCP8.5, this leads to projected ice loss ranging from 1.4 to 4.0 cm of sea level equivalent in simulations in which ISMIP6 ocean forcing drives the PICO ocean box model where parameter tuning leads to a comparably low sub-shelf melt sensitivity and in which no surface forcing is applied. This is opposed to a likely range of 9.1 to 35.8 cm using the exact same initial setup, but emulated from the LARMIP-2 experiments with a higher melt sensitivity, even though both projects use forcing from climate models and melt rates are calibrated with previous oceanographic studies. Furthermore, using two initial states, one with a previous historic simulation from 1850 to 2014 and one starting from a steady state, we show that while differences between the ice sheet configurations in 2015 seem marginal at first sight, the historic simulation increases the susceptibility of the ice sheet to ocean warming, thereby increasing mass loss from 2015 to 2100 by 5 % to 50 %. Hindcasting past ice sheet changes with numerical models would thus provide valuable tools to better constrain projections. Our results emphasize that the uncertainty that arises from the forcing is of the same order of magnitude as the ice dynamic response for future sea level projections.

Ocean-induced melt volume directly paces ice loss from Pine Island Glacier

“…The relatively high r 2 values, however, suggest that the spread in the projections from these models is largely driven by differences in the way they each simulate melt, rather than by their respective implementations of the ice dynamics ( 13 ). Our results are also consistent with other studies that find a nearly linear response of ice loss for a doubling or halving of the melt rate using the ISMIP6 models ( 33 , 34 ). Thus, the linear relation between average melt and loss at century scales in both our model and the ISMIP6 models supports a linear response approach to projecting sea-level rise ( 33 ).…”

Comment on tc-2022-105

“…The sensitivity estimate based on the 'best' baseline temperature of 15 ma −1 K −1 for Dotson Ice Shelf fits well with the estimate from Payne et al (2007) for Pine Island Glacier Ice Shelf, which Seroussi et al (2017) for Thwaites Glacier Ice Shelf estimated from ocean simulations with an 0.5 K temperature increase, see Fig. S5 in the Supplement of Reese et al (2020).…”

“…Sub-shelf melt rates are calculated using the Potsdam Ice shelf Cavity mOdel (PICO; Reese et al, 2018a). Observed ongoing retreat in the ASE sector is linked to oceanic forcing (Jenkins et al, 2018) and recent projections underline the importance of the sensitivity of sub-shelf melting to ocean temperature variations (Jourdain et al, 2020;Reese et al, 2020). We thus calibrate the sub-shelf melt module PICO to represent observed (Jenkins et al, 2018) or modelled (Naughten et al, 2021) sensitivities of melt rates to ocean temperature changes.…”

Coupling framework (1.0) for the PISM (1.1.4) ice sheet model and the MOM5 (5.1.0) ocean model via the PICO ice shelf cavity model in an Antarctic domain

“…10k) as root-mean-squared error (RMSE) of modelled grounded ice thickness compared with Bedmap2 data; and surface velocity deviation (Fig. 10l), defined as the RMSE of modelled surface velocities above 100 m yr −1 compared with Ice Velocity Map, v2 (Rignot et al, 2017(Rignot et al, , 2011Mouginot et al, 2012).…”