Ocean‐Only FAFMIP: Understanding Regional Patterns of Ocean Heat Content and Dynamic Sea Level Change. (12th August 2020)

• Record Type: Journal Article
• Authors: Todd, Alexander; Zanna, Laure; Couldrey, Matthew; Gregory, Jonathan; Wu, Quran; Church, John A.; Farneti, Riccardo; Navarro‐Labastida, René; Lyu, Kewei; Saenko, Oleg; Yang, Duo; Zhang, Xuebin
• Is Part Of: Journal of advances in modeling earth systems. Volume 12:Number 8(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-12
• Subjects: Dynamic Sea Level -- Ocean Heat Uptake -- Ocean Climate Change; Geological modeling -- Periodicals; Climatology -- Periodicals; Geochemical modeling -- Periodicals; 551.5011
• DOI: 10.1029/2019MS002027
• Languages: English
• ISSNs: 1942-2466

Abstract

Abstract: There is large uncertainty in the future regional sea level change under anthropogenic climate change. Our study presents and uses a novel design of ocean general circulation model (OGCM) experiments to investigate the ocean's response to surface buoyancy and momentum flux perturbations without atmosphere‐ocean feedbacks (e.g., without surface restoring or bulk formulae), as part of the Flux‐Anomaly‐Forced Model Intercomparison Project (FAFMIP). In an ensemble of OGCMs forced with identical surface flux perturbations, simulated dynamic sea level (DSL) and ocean heat content (OHC) change demonstrate considerable disagreement. In the North Atlantic, the disagreement in DSL and OHC change between models is mainly due to differences in the residual (resolved and eddy) circulation change, with a large spread in the Atlantic meridional overturning circulation (AMOC) weakening (20–50%). In the western North Pacific, OHC change is similar among the OGCM ensemble, but the contributing physical processes differ. For the Southern Ocean, isopycnal and diapycnal mixing change dominate the spread in OHC change. In addition, a component of the atmosphere‐ocean feedbacks are quantified by comparing coupled, atmosphere‐ocean GCM (AOGCM) and OGCM FAFMIP experiments with consistent ocean models. We find that there is 10% more AMOC weakening in AOGCMs relative to OGCMs, since the extratropical North Atlantic SST cooling due to heat redistribution amplifies the surface heat flux perturbation. This component of the atmosphere‐ocean feedbacks enhances the pattern of North Atlantic OHC and DSL change, with relatively stronger increases and decreases in the tropics and extratropics, respectively. Plain Language Summary: A rise in sea level, as a result of climate change due to human activity, is a major threat to coastal communities and environments. Sea level rise is partially caused by a warming and expansion of the world's oceans, due to a net heat input from the atmosphere to the ocean. Changes in rainfall patterns and surface winds also affect the sea level, but net heat input changes are the most important factor. State‐of‐the‐art computer models disagree on future projections of local sea level rise. It has been suggested that this disagreement comes from differences in the amount of net heat input, and also the different assumptions going into the computer models. We find a large local sea level rise disagreement in the North Atlantic from giving several different computer models the same net heat input change. These differences are linked to uncertainty in how much Atlantic currents will slow in response to a given amount of warming. We also find that computer models that include an interactive ocean and atmosphere slow the Atlantic currents by more than computer models with an interactive ocean but fixed atmosphere. This finding builds our knowledge of the processes that determine the ocean's role in climate change. Key Points: Ensemble of ocean simulations without atmospheric feedbacks reveal spread in heat content change In the North Atlantic, spread from identical surface flux perturbation is due to circulation change Atmosphere‐ocean feedbacks amplify local surface heat flux, AMOC and dynamic sea level change