Abstract
Abstract. The Parallel Ice Sheet Model (PISM) is applied to the Antarctic Ice Sheet over the last two glacial cycles (≈210 000 years) with a resolution of 16 km. An ensemble of 256 model runs is analyzed in which four relevant model parameters have been systematically varied using full-factorial parameter sampling. Parameters and plausible parameter ranges have been identified in a companion paper (Albrecht et al., 2020) and are associated with ice dynamics, climatic forcing, basal sliding and bed deformation and represent distinct classes of model uncertainties. The model is scored against both modern and geologic data, including reconstructed grounding-line locations, elevation–age data, ice thickness, surface velocities and uplift rates. An aggregated score is computed for each ensemble member that measures the overall model–data misfit, including measurement uncertainty in terms of a Gaussian error model (Briggs and Tarasov, 2013). The statistical method used to analyze the ensemble simulation results follows closely the simple averaging method described in Pollard et al. (2016). This analysis reveals clusters of best-fit parameter combinations, and hence a likely range of relevant model and boundary parameters, rather than individual best-fit parameters. The ensemble of reconstructed histories of Antarctic Ice Sheet volumes provides a score-weighted likely range of sea-level contributions since the Last Glacial Maximum (LGM) of 9.4±4.1 m (or 6.5±2.0×106km3), which is at the upper range of most previous studies. The last deglaciation occurs in all ensemble simulations after around 12 000 years before present and hence after the meltwater pulse 1A (MWP1a). Our ensemble analysis also provides an estimate of parametric uncertainty bounds for the present-day state that can be used for PISM projections of future sea-level contributions from the Antarctic Ice Sheet.
Highlights
Sea-level estimates involve high uncertainty, in particular with regard to the potential instability of marine-based parts of the Antarctic Ice Sheet (e.g., Weertman, 1974; Mercer, 1978; Slangen et al, 2017)
We ran the full ensemble of Parallel Ice Sheet Model (PISM) simulations over the last glacial cycle
Each individual sub-panel shows PPQ vs. VISC, and the sub-panels are arranged from left to right for varying PREC and bottom to top for varying ESIA
Summary
Sea-level estimates involve high uncertainty, in particular with regard to the potential instability of marine-based parts of the Antarctic Ice Sheet (e.g., Weertman, 1974; Mercer, 1978; Slangen et al, 2017). Processed-based models provide the tools to evaluate the currently observed ice sheet changes (Shepherd et al, 2018a, b); to better distinguish between natural drift, variability and anthropogenic drivers (Jenkins et al, 2018); and to estimate future changes for possible climatic boundary conditions (Oppenheimer and Alley, 2016; Shepherd and Nowicki, 2017; Pattyn, 2018). Regarding the involved variety of uncertain parameters and boundary conditions, confidence of future projections from such models is strengthened by systematic validation against modern observations and past reconstructions.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.