Ocean Heat Storage Rate Unaffected by MOC Weakening in an Idealized Climate Model

Peter Shatwell,David Ferreira,Arnaud Czaja

doi:10.1029/2020gl089849

Peter Shatwell, David Ferreira + Show 1 more

Open Access

https://doi.org/10.1029/2020gl089849

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Abstract

AbstractTo study the role of the Atlantic meridional overturning circulation (AMOC) in transient climate change, we perform an abrupt CO2‐doubling experiment using a coupled atmosphere‐ocean‐ice model with a simple geometry that separates the ocean into small and large basins. The small basin exhibits an overturning circulation akin to the AMOC. Over the simulated 200 years of change, it stores heat at a faster rate than the large basin by 0.6 ± 0.2 W m−2. We argue that this is due to the small basin MOC. However, we find that as the MOC weakens significantly, it has little impact on the small basin's heat storage rate. We suggest this is due to the effects of both compensating warming patterns and interbasin heat transports. Thus, although the presence of a MOC is important for enhanced heat storage, MOC weakening is surprisingly unimportant.

Highlights

Due to anthropogenic carbon emissions, there is greater absorbed solar radiation than outgoing longwave radiation over the surface of the Earth, leading to an imbalance, designated Earth's energy imbalance (EEI) (Hansen et al, 2011; Trenberth et al, 2014; Von Schuckmann et al, 2016)
By considering areal proportions of the total global ocean heat content (OHC) increase, we find that this is due to a combination of the SB taking up more heat than expected for its size, and the large basins (LB) taking up less than expected
We find that the SB experiences an enhanced heat storage rate due to a rapid advection of surface temperature anomalies into its interior

Summary

Introduction

Due to anthropogenic carbon emissions, there is greater absorbed solar radiation than outgoing longwave radiation over the surface of the Earth, leading to an imbalance, designated Earth's energy imbalance (EEI) (Hansen et al, 2011; Trenberth et al, 2014; Von Schuckmann et al, 2016). Given the importance of constraining and monitoring EEI through OHC observations, and the possibility that the AMOC may continue to weaken into the future, it is imperative to better understand the AMOC's role in ocean heat uptake and storage as the world continues to warm. To this end, we examine the response of a coupled atmosphere‐ocean‐ice general circulation model under an abrupt doubling of atmospheric CO2.

Model Description and Setup

SB and LB Heat Storage Rates

Role of the SB MOC

Heat Storage Response to MOC Weakening

Parallels With CMIP5 Models

Conclusion