Emulating Ocean Dynamic Sea Level by Two-Layer Pattern Scaling.

Ocean dynamic sea level (DSL) change is a key driver of relative sea level (RSL) change. Projections of DSL change are generally obtained from simulations using atmosphere-ocean general circulation models (GCMs). Here, we develop a two-layer climate emulator to interpolate between emission scenarios simulated with GCMs and extend projections beyond the time horizon of available simulations. This emulator captures the evolution of DSL changes in corresponding GCMs, especially over middle and low latitudes. Compared with an emulator using univariate pattern scaling, the two-layer emulator more accurately reflects GCM behavior and captures non-linearities and non-stationarity in the relationship between DSL and global-mean warming, with a reduction in global-averaged error during 2271-2290 of 36%, 24%, and 34% in RCP2.6, RCP4.5, and RCP8.5, respectively. Using the emulator, we develop a probabilistic ensemble of DSL projections through 2300 for four scenarios: Representative Concentration Pathway (RCP) 2.6, RCP 4.5, RCP 8.5, and Shared Socioeconomic Pathway (SSP) 3-7.0. The magnitude and uncertainty of projected DSL changes decrease from the high-to the low-emission scenarios, indicating a reduced DSL rise hazard in low- and moderate-emission scenarios (RCP2.6 and RCP4.5) compared to the high-emission scenarios (SSP3-7.0 and RCP8.5).