Master Thesis Defense by Jakob Skyggebjerg Kjær

Title: Ice sheet model emulation and projection in response to climate change

Abstract:
Realistic ice sheet models are computationally costly to run due to their high complexity, which is why we only have limited ensembles of sea level projections. This gives us a poor insight into the uncertainty of these projections and difficult to explore the full possibility space. In an effort to solve this problem we have in this thesis adjusted and used a simple, physically motivated, temperature-dependent mass balance model (MBM) developed by Fauli and Mikkelsen, 2025 for the Greenland ice sheet (GrIS) as emulator projecting sea level contribution in the period 2015–2100. Here we explore two different MBM-setups, one only having a simple precipitation and melt term and the other adding an explicitly representing the ice discharge. The two models show so similar results in their projections, that we can regard them as identical.

Reusing the data ensemble from Edwards et al., 2021, we calibrate our emulator to the Ice Sheet Model Intercomparison Project 6 (ISMIP6) projections and repeat the sea level estimates conducted for GrIS in Edwards et al., 2021 with the FaIR temperature forcings under Shared Socioeconomic Pathway (SSP) 1-2.6 and SSP5-8.5. Here we project a contribution to the global mean sea level (GMSL) rise of 0.044m ± 0.016m for SSP1-2.6 and 0.083m ± 0.038m for SSP5-8.5, respectively. The projections are within the range of former studies of the GrIS contribution to GMSL, and its uncertainty range, as they are presented in Fox-Kemper et al., 2021. Our results are slightly more moderate and do not show the same outliers as in Edwards et al., 2021, even though we use the same data for fitting the emulator and evaluating the projections. We conclude, that the cause of this limitation probably can be found in the emulator’s lack of self-enhancing mechanisms in the MBM used, or that our fitting procedure favors a regression towards the mean. This show possible pathways for further work and investigation.

Supervisor: Aslak Grinsted
Censor: Sebastian Bjerregaaard Simonsen (DTU)