Stability of the Atlantic meridional overturning circulation: A model intercomparison

Andrew J. Weaver, Jan Sedláček, Michael Eby, Kaitlin Alexander, Elisabeth Crespin, Thierry Fichefet, Gwenaëlle Philippon-Berthier, Fortunat Joos, Michio Kawamiy, Katsumi Matsumoto, Marco Steinacher, Kaoru Tachiiri, Kathy Tokos, Masakazu Yoshimori, Kirsten Zickfeld

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Abstract

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.

Original languageEnglish (US)
Article numberL20709
JournalGeophysical Research Letters
Volume39
Issue number20
DOIs
StatePublished - Oct 28 2012

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