Preprints
https://doi.org/10.5194/tc-2020-178
https://doi.org/10.5194/tc-2020-178

  17 Aug 2020

17 Aug 2020

Review status: this preprint is currently under review for the journal TC.

Statistical emulation of a perturbed basal melt ensemble of an ice sheet model to better quantify Antarctic sea level rise uncertainties

Mira Berdahl1,3, Gunter Leguy2, William H. Lipscomb2, and Nathan M. Urban3 Mira Berdahl et al.
  • 1Department of Earth and Space Sciences, University of Washington, WA, USA
  • 2Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 3Computational Physics and Methods Group, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Abstract. Antarctic ice shelves are vulnerable to warming ocean temperatures, and have already begun thinning in response to increased basal melt rates. Sea level is therefore expected to rise due to Antarctic contributions, but uncertainties in its amount and timing remain largely unquantified. In particular, there is substantial uncertainty in future basal melt rates arising from multi-model differences in thermal forcing and how melt rates depend on that thermal forcing. To facilitate uncertainty quantification in sea level rise projections, we build, validate, and demonstrate projections from a computationally efficient statistical emulator of a high resolution (4 km) Antarctic ice sheet model, the Community Ice Sheet Model version 2.1. The emulator is trained to a large (500-member) ensemble of 200-year-long 4-km resolution transient ice sheet simulations, whereby regional basal melt rates are perturbed by idealized (yet physically informed) trajectories. The main advantage of our emulation approach is that by sampling a wide range of possible basal melt trajectories, the emulator can be used to (1) produce probabilistic sea level rise projections over much larger Monte Carlo ensembles than are possible by direct numerical simulation alone, thereby providing better statistical characterization of uncertainties, and (2) predict the simulated ice sheet response under differing assumptions about basal melt characteristics as new oceanographic studies are published, without having to run additional numerical ice sheet simulations. As a proof-of-concept, we propagate uncertainties about future basal melt rate trajectories, derived from regional ocean models, to generate probabilistic sea level rise estimates for 100 and 200 years into the future.

Mira Berdahl et al.

 
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Mira Berdahl et al.

Mira Berdahl et al.

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Short summary
Antarctic ice shelves are vulnerable to warming ocean temperatures and have already begun thinning in response to increased basal melt rates. Sea level is expected to rise due to Antarctic contributions, but uncertainties in its amount and timing remain largely unquantified. To facilitate uncertainty quantification, we use a high-resolution ice sheet model to build, test and validate an ice sheet emulator and generate probabilistic sea level rise estimates for 100 and 200 years into the future.