Process-based Estimate of Global-mean Sea-level Changes in the Common Era

Though the global-mean sea level (GMSL) rose over the twentieth century with a positive contribution from thermosteric and barystatic (ice sheets and glaciers) sources, driving processes of GMSL changes during the pre-industrial common era (PCE; 1–1850 CE) are largely unknown. Here, the contributions of glacier and ice sheet mass variations and ocean thermal expansion to GMSL in the common era (1–2000 CE) are estimated based on simulations with different physical models. Although the twentieth-century global-mean thermosteric sea level (GMTSL) is mainly associated with temperature variations in the upper 700 meters (86 % in reconstruction and 74±8 % in model), GMTSL in the PCE is equally controlled by temperature changes below 700 meters. GMTSL does not vary more than ±2 cm during the PCE. GMSL contributions from the Antarctic and Greenland ice sheets tend to cancel each other during the PCE owing to their differing response to atmospheric conditions. The uncertainties of sea-level contribution from land-ice mass variations are large, especially over the first millennium. Despite underestimating the twentieth-century model GMSL, there is a general agreement between the model and reconstructed GMSL in the CE. Although the uncertainties remain large over the first millennium, model simulations point to glaciers as the dominant source of GMSL changes during the PCE.