Abstract
AbstractThe impact of uncertainties in air‐sea fluxes and ocean model parameters on the ocean circulation and ocean heat uptake (OHU) is assessed in a novel modeling framework. We use an ocean‐only model forced with the simulated sea surface fields of the CMIP5 climate models. The simulations are performed using control and 1% CO2 warming scenarios. The ocean‐only ensemble adequately reproduces the mean Atlantic Meridional Overturning Circulation (AMOC) and the zonally integrated OHU. The ensemble spread in AMOC strength, its weakening, and Atlantic OHU due to different air‐sea fluxes is twice as large as the uncertainty range related to vertical and mesocale eddy diffusivities. The sensitivity of OHU to uncertainties in air‐sea fluxes and model parameters differs vastly across basins, with the Southern Ocean exhibiting strong sensitivity to air‐sea fluxes and model parameters. This study clearly demonstrates that model biases in air‐sea fluxes are one of the key sources of uncertainty in climate simulations.
Highlights
The exchange of momentum, heat, freshwater, and carbon between the atmosphere and the ocean via air-sea fluxes is of fundamental importance for the Earth’s climate
Uncertainty From Air-Sea Fluxes We start by revisiting the spread in air-sea fluxes and variables in the Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble and observation-based products
We presented a new modeling framework to quantify the impact of uncertainty in surface forcing and model parameters on the spread in oceanic circulation and ocean heat uptake (OHU)
Summary
The exchange of momentum, heat, freshwater, and carbon between the atmosphere and the ocean via air-sea fluxes is of fundamental importance for the Earth’s climate. Despite the importance of the air-sea fluxes both in steady state and under transient climate change there are significant long-standing uncertainties and biases in observational estimates and reanalysis products. The extent to which these uncertainties in simulated air-sea fluxes impact the ocean circulation and ocean heat uptake (OHU) in climate models is not fully understood. We refer to this model set as “CMIP5 climate models” in the following for brevity.
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