Stability of the Atlantic meridional overturning circulation: A model intercomparison

• Published in: Geophysical Research Letters
• Main Authors: Weaver, A.J., Sedláček, J., Eby, M., Alexander, K., Crespin, Elisabeth, Fichefet, Thierry, Philippon, Gwenaëlle, Joos, F., Kawamiy, M., Matsumoto, K., Steinacher, M., Tachiiri, K., Tokos, K., Yoshimori, Masakazu, Zickfeld, K.
• Other Authors: UCL - SST/ELI/ELIC - Earth & Climate
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2012
• Subjects: Atlantic meridional overturning circulations; Intercomparisons; Intermediate complexity; Global warming; Oceanography; Computer simulation; Comparative study; Freshwater input; General circulation model; Ice sheet; Atmosphere ocean general circulation models; Melting; Overturn; Twenty first century; Atlantic Ocean; CECI; CISM; Best estimates; Bistables; Confidence limit; Coupled Model Intercomparison Project; Earth system model; Freshwater fluxes; Ice sheet melting; 1443; Ice Sheet
• Online Access: http://hdl.handle.net/2078.1/119081; https://doi.org/10.1029/2012GL053763

The evolution of the Atlantic Meridional Overturning Circulation (MOC) in 30 models of varying complexity is examined under four distinct Representative Concentration Pathways. The models include 25 Atmosphere-Ocean General Circulation Models (AOGCMs) or Earth System Models (ESMs) that submitted simulations in support of the 5th phase of the Coupled Model Intercomparison Project (CMIP5) and 5 Earth System Models of Intermediate Complexity (EMICs). While none of the models incorporated the additional effects of ice sheet melting, they all projected very similar behaviour during the 21st century. Over this period the strength of MOC reduced by a best estimate of 22% (18%-25%; 5%-95% confidence limits) for RCP2.6, 26% (23%-30%) for RCP4.5, 29% (23%-35%) for RCP6.0 and 40% (36%-44%) for RCP8.5. Two of the models eventually realized a slow shutdown of the MOC under RCP8.5, although no model exhibited an abrupt change of the MOC. Through analysis of the freshwater flux across 30°-32°S into the Atlantic, it was found that 40% of the CMIP5 models were in a bistable regime of the MOC for the duration of their RCP integrations. The results support previous assessments that it is very unlikely that the MOC will undergo an abrupt change to an off state as a consequence of global warming. © 2012. American Geophysical Union. All Rights Reserved.