Understanding the Role of Internal Climate Variability in Future Sea Level Trends

Estimating the magnitude of future sea level rise is among the primary goals of current climate research. Sea level projections contain inherent irreducible uncertainty, which is due to internal climate variability (ICV). This uncertainty is commonly estimated from a spread of sea level projections obtained from Global Climate Models (GCM) under the same forcing but with slightly different initial conditions. Here we analyze the ICV contribution to the sea level variations (1) across the Large Ensembles (LE) of Community Earth System Model (CESM) obtained under different warming scenarios and (2) from an alternative approach based on the power-law statistics theory. The magnitude of the sea level response to ICV is also evaluated by comparison with actual tide gauge data. We show that certain coastal regions of the globe are more sensitive to ICV than others, both in observations and in the GCM results. We identify regions where the sea level change will become significant beyond the ICV, providing useful climate change adaptation guidance.