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. Climate Dynamics.

• Published in: Climate Dynamics
• Main Authors: Guemas, Virginie, Salas Y Melia, David
• Other Authors: Groupe d'étude de l'atmosphère météorologique (CNRM-GAME), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: Thermohaline circulation; deep ocean convection; global coupled model; coupled mechanism; climate change; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; [SDE.MCG]Environmental Sciences/Global Changes; [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Arctic; Arctic Ocean; Barents Sea; Climate change; Fram Strait; Global warming; Iceland; North Atlantic; Sea ice; Spitzberg
• Online Access: https://hal-meteofrance.archives-ouvertes.fr/meteo-00187193; https://doi.org/10.1007/s00382-007-0328-8

International audience 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.