Evaluation of regional climate features over Antarctica in the PMIP past1000 experiment and implications for 21st-century sea level rise

Abstract

Surface mass balance (SMB) of the Antarctic Ice Sheet (AIS) is an important contributor to global sea level change. We look to the Last Millennium (850-1850 CE) as a period of relative climate stability to understand which processes control natural variability in SMB, distinct from anthropogenic warming. With evidence for large regional differences in climate and SMB trends over the Last Millennium in Antarctic ice core proxy records, model simulations need to be validated over such timescales to assess if they capture those regional variations in order to have confidence in end-of-century SMB projections. In this study, we provide a quantitative evaluation of paleo-simulations in simulating Last Millennium regional climate changes in Antarctica. We evaluate model performance by comparing available Paleoclimate Modelling Intercomparison Project (PMIP) past1000 models and the CESM Last Millennium Ensemble (CESM-LME) to four sets of Last Millennium Antarctic proxy-based reconstructions that are most relevant to the SMB: snow accumulation, surface air temperature (SAT), sea surface temperature (SST) and Niño 3.4 index, using a multi-parameter scoring method. Our results show that no single model performs consistently well across all variables. Models have reasonable strength in capturing SATs and SSTs, while showing strong biases for both snow accumulation and the Niño 3.4 index. The best-performing model, CESM-LME, predicts higher SMB by 2100, which implies stronger mitigation of the projected dynamic ice loss contribution of the AIS to sea level rise.