Process-based estimate of global-mean sea-level changes in the Common Era

Abstract

Abstract. Although the global-mean sea level (GMSL) rose over the twentieth century with a positive contribution from thermosteric and barystatic (ice sheets and glaciers) sources, the 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 m (86 % in reconstruction and 74 ± 8 % in model), GMTSL in the PCE is equally controlled by temperature changes below 700 m. The 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 out during the PCE owing to the differing response of the two ice sheets 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 proxy-based GMSL reconstructions 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.

Global mean sea level higher than present during the Holocene

“…The mountain glacier ensemble produced here accords within uncertainties with quantitative estimates of Holocene mountain glacier contribution to Common Era sea level, which suggest -0.9±2.1 cm of glacier contribution to GMSL from 1800 to 1850 49 and a maximum of 8±1.5 cm of glacier contribution at ∼900 CE relative to 1850 CE 48 . It also agrees with more qualitative assessments of minimal mountain glacier volumes in the early-mid Holocene followed by a readvance to the Little Ice Age maximum 35;68 .…”

Glacier projections sensitivity to temperature-index model choices and calibration strategies

“…We use the open-source numerical modelling framework OGGM (Maussion and others, 2019), which has been applied in several global and regional studies (e.g. Furian and others, 2022;Gangadharan and others, 2022;Li and others, 2022;Yang and others, 2022;Malles and others, 2023, for most recent examples) and is well suited for our model intercomparison thanks to its modular structure. Here, we focus on the changes made to OGGM's default configuration as of version 1.5.3.…”