Climate Dynamics

, Volume 30, Issue 7, pp 831–844

Simulation of the Atlantic meridional overturning circulation in an atmosphere-ocean global coupled model. Part II: weakening in a climate change experiment: a feedback mechanism

Article

DOI: 10.1007/s00382-007-0328-8

Cite this article as:
Guemas, V. & Salas-Mélia, D. Clim Dyn (2008) 30: 831. doi:10.1007/s00382-007-0328-8

Abstract

Most state-of-the art global coupled models simulate a weakening of the Atlantic meridional overturning circulation (MOC) in climate change scenarios but the mechanisms leading to this weakening are still being debated. The third version of the CNRM (Centre National de Recherches Météorologiques) global atmosphere-ocean-sea ice coupled model (CNRM-CM3) was used to conduct climate change experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). The analysis of the A1B scenario experiment shows that global warming leads to a slowdown of North Atlantic deep ocean convection and thermohaline circulation south of Iceland. This slowdown is triggered by a freshening of the Arctic Ocean and an increase in freshwater outflow through Fram Strait. Sea ice melting in the Barents Sea induces a local amplification of the surface warming, which enhances the cyclonic atmospheric circulation around Spitzberg. This anti-clockwise circulation forces an increase in Fram Strait outflow and a simultaneous increase in ocean transport of warm waters toward the Barents Sea, favouring further sea ice melting and surface warming in the Barents Sea. Additionally, the retreat of sea ice allows more deep water formation north of Iceland and the thermohaline circulation strengthens there. The transport of warm and saline waters toward the Barents Sea is further enhanced, which constitutes a second positive feedback.

Keywords

Thermohaline circulation Deep ocean convection Global coupled model Coupled mechanism Climate change 

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Centre National de Recherches Météorologiques/Groupe d’Etude de l’Atmosphère Météorologique (CNRM/GMGEC)Météo-France, CNRSToulouse CedexFrance
  2. 2.Laboratoire des Sciences du Climat et de l’Environnement, UMR 1572CEA-CNRS-UVSQGif-sur-YvetteFrance