Projections of Centennial-scale Sea Level Change in an Earth System Model Including Dynamic Ice Sheets

Abstract:

The major contribution to global mean sea level (GMSL) change under contemporary climate conditions involves thermal expansion of the ocean and outflow from the land ice, with the latter increasing more rapidly in percentage as a form of ice sheets. Current earth system models (EMS) can constrain thermal expansion with high confidence in projections; however, few of them have been successfully coupled to an ice sheet model (ISM) to incorporate future evolution of ice sheets. In this study, a coupled EMS - ISM is applied to estimate potential range of their contribution to GMSL change over the next several centuries, by simulating the new emission scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Our results indicate that the thermal contribution to GMSL rise still dominants within this century, with up to 0.4 m in the highest CO₂ case, and continue to increase for many centuries even after stabilization of CO₂. This increase can reach to almost 3.5 m GMSL rise by the end of 25^th century in RCP8.5, when equivalent CO2 concentration exceeds 2500 ppm. Nevertheless, over longer time scales, GMSL contribution from ice sheets enhances more dramatically than linearly with increase in temperature and can eventually overweigh thermal contribution after 24^th century. This contribution mainly results from a negative surface mass balance (SMB) of Greenland ice sheet and can exceed 4 m GMSL rise in RCP8.5. Projection of Antarctic SMB demonstrates a negative contribution to GMSL rise in all scenarios except RCP8.5, in which it can lead to more than 2 m GMSL rise. Moreover, we emphasize that sea level change contribution from these two effects exhibits substantial regional pattern, which requires more comprehensive attention from the policy makers to make their plan against this issue in the future.