Ocean model resolution dependence of Caribbean sea-level projections

Abstract

Sea-level rise poses severe threats to coastal and low-lying regions around the world, by exacerbating coastal erosion and flooding. Adequate sea-level projections over the next decades are important for both decision making and for the development of successful adaptation strategies in these coastal and low-lying regions to climate change. ocean components of climate models used in the most recent sea-level projections do not explicitly resolve ocean mesoscale processes. Only a few effects of these mesoscale processes are represented in these models, which leads to errors in the simulated properties of the ocean circulation that affect sea-level projections. Using the Caribbean Sea as an example region, we demonstrate a strong dependence of future sea-level change on ocean model resolution in simulations with a global climate model. the results indicate that, at least for the Caribbean Sea, adequate regional projections of sea-level change can only be obtained with ocean models which capture mesoscale processes. The ongoing increase of global sea level threatens both coastal and low-lying regions. The combination of future sea-level rise with increasing storm occurrence and intensity may exacerbate beach erosion 1. This can have severe consequences for areas which are highly dependent on their beaches, either for flood safety or economically for local tourism 2,3. Higher sea levels can also lead to changes in coastal ecosystems, and permanent submergence of land and human settlements 4. For making adequate decisions on the development of successful adaptation strategies to sea-level rise, skillful projections over the next decades are crucially important 5. By decomposing the components contributing to the satellite-observed global mean sea-level (GMSL) rise between 1993 and 2014, it was shown that the dominant contributor to GMSL is thermal expansion of the ocean 6. Over the same period, the contribution of mass loss of both glaciers and large ice sheets to GMSL rise became more important over time 6,7. On a regional scale, sea-level rise may deviate from GMSL rise 8 and can be caused by other processes than thermal expansion. For example, the dominant contributor to sea-level rise in the Caribbean is thermal expansion (40% = 0.8 mm year −1) while east of the Caribbean 9 this is ocean mass redistribution (50% = 1.7 mm year −1). Regional sea-level change induced by variations in the gravitational contribution due to large ice sheets and glacial isostatic adjustment is very homogeneous over these two regions 9. Hence, the difference in magnitude of sea-level rise in the different regions is caused by ocean sterodynamic effects (i.e. mass redistribution and thermal expansion) 10. Ocean volume conserving climate models, such as those used in the sixth coupled model inter-comparison projects (CMIP) of the Intergovernmental Panel on Climate Change (IPCC) Assessment Report, provide projections of the dynamic sea level (DSL) and sterodynamic sea level (SDSL) 22. Due to their low spatial resolution, the ocean component ...

Emulating Ocean Dynamic Sea Level by Two‐Layer Pattern Scaling

“…The ensemble spread of the 5th-95th range of DSL projections are relatively large over the Southern Ocean, Arctic and Subpolar Atlantic than other areas. The large uncertainties over these areas, consistent with previous literatures (M. D. Palmer et al, 2020;Perrette et al, 2013;Yin, 2012), may be interpreted by the diverse characteristics simulated by GCMs that do not explicitly resolve non-linear mesoscale processes of the ocean current over these areas (van Westen et al, 2020).…”

Emulating ocean dynamic sea level by two-layer pattern scaling

“…The ensemble spread of the 5 th -95 th range of DSL projections are relatively large over the Southern Ocean, Arctic and Subpolar Atlantic than other areas. The large uncertainties over these areas, consistent with previous literatures (Palmer et al, 2020;Perrette et al, 2013;Yin, 2012), may be interpreted by the diverse characteristics simulated by GCMs that do not explicitly resolve non-linear mesoscale processes of the ocean current over these areas (van Westen et al, 2020).…”

“…Near the eastern coast of North America, DSL is closely related to AMOC (Goddard et al, 2015), which is expected to weaken in a warming climate (Caesar et al, 2018). Low skill in capturing AMOC behavior can affect the DSL projections in the Atlantic basin as well as its coasts (van Westen et al, 2020). As the coefficients of pattern scaling depend on the simulations…”

Ocean eddies strongly affect global mean sea-level projections

“…Most of the monthly averaged quantities are converted to yearly averages unless stated otherwise. Two additional LR-CESM simulations (not used) were branched off after a spin-up period of 200 and 1200 years, the latter is used in (21). The shorter spin-up period has an initial sea-ice distribution similar to the HR-CESM control.…”