Abstract
Abstract. Antarctic ice shelves are vulnerable to warming ocean temperatures, and some 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.
Highlights
1.1 The physical origin of Antarctic sea level rise uncertaintiesMass loss from Antarctica over the past several decades has primarily been a result of melt at the base of ice shelves (Cook et al, 2016; Rintoul et al, 2016; Pritchard et al, 2012; Rignot and Jacobs, 2002). Depoorter et al (2013) found that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front
marine ice shelf instability (MISI) theory suggests that increased basal melt rates beneath some key West Antarctic Ice Sheet (WAIS) ice shelves (e.g., Pine Island and Thwaites) could result in an unstable grounding-line retreat causing runaway ice loss for the entire region
We present results for the Community Ice Sheet Model (CISM) ensemble and show a simple example of using the emulator to generate a probability distribution function (PDF) of sea level rise by propagating prior distributions of basal melt rate parameters based on fits to two ocean models under the A1B emissions scenario
Summary
1.1 The physical origin of Antarctic sea level rise uncertaintiesMass loss from Antarctica over the past several decades has primarily been a result of melt at the base of ice shelves (Cook et al, 2016; Rintoul et al, 2016; Pritchard et al, 2012; Rignot and Jacobs, 2002). Depoorter et al (2013) found that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front. Basal melt weakens the back force on upstream glaciers which causes grounding-line retreat (Konrad et al, 2018; Rignot et al, 2014), increases flow rate (Pattyn, 2018), depresses surface heights of grounded ice (Konrad et al, 2017), and impacts sea level. MISI theory suggests that increased basal melt rates beneath some key West Antarctic Ice Sheet (WAIS) ice shelves (e.g., Pine Island and Thwaites) could result in an unstable grounding-line retreat causing runaway ice loss for the entire region. Forcing due to basal melt is likely to become an increasingly dominant contributor to Antarctic sea level rise (SLR) (Bulthuis et al, 2019).
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call