Quantifying the AMOC feedbacks during a 2×CO2 stabilization experiment with land-ice melting

• Published in: Climate dynamics Vol. 29; no. 5; pp. 521 - 534
• Main Authors: SWINGEDOUW, D, BRACONNOT, P, DELECLUSE, P, GUILYARDI, E, MARTI, O
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.10.2007; Berlin Springer Nature B.V; Springer Verlag
• Subjects: Air temperature; Atmosphere; Carbon dioxide; Climate change; Climatology. Bioclimatology. Climate change; Convection; Earth Sciences; Earth, ocean, space; Environmental Sciences; Exact sciences and technology; External geophysics; Geophysics; Global Changes; Global warming; Heat transport; Melting; Meteorology; Ocean-atmosphere interaction; Physics; Physics of the oceans; Salinity; Sciences of the Universe; Sea ice; Temperature gradients; Thermohaline structure and circulation. Turbulence and diffusion; Tropical environments; General circulation models; Atlantic Ocean; Carbon dioxide; Atmosphere cryosphere interaction; melting; digital simulation; ocean-atmosphere interaction; Forecast model; troposphere; Long term; greenhouse gas; Dynamical climatology; Ocean-atmosphere model; feedback; ice sheets; climate modification; global change; sea ice; instability; thermohaline circulation; warming; Forcing; ocean circulation
• ISSN: 0930-7575; 0020-7128; 1432-0894; 1432-1254
• DOI: 10.1007/s00382-007-0250-0

The response of the Atlantic Meridional Overturning Circulation (AMOC) to an increase in atmospheric CO^sub 2^ concentration is analyzed using the IPSL-CM4 coupled ocean-atmosphere model. Two simulations are integrated for 70 years with 1%/year increase in CO^sub 2^ concentration until 2×CO^sub 2^, and are then stabilized for further 430 years. The first simulation takes land-ice melting into account, via a simple parameterization, which results in a strong freshwater input of about 0.13 Sv at high latitudes in a warmer climate. During this scenario, the AMOC shuts down. A second simulation does not include this land-ice melting and herein, the AMOC recovers after 200 years. This behavior shows that this model is close to an AMOC shutdown threshold under global warming conditions, due to continuous input of land-ice melting. The analysis of the origin of density changes in the Northern Hemisphere convection sites allows an identification as to the origin of the changes in the AMOC. The processes that decrease the AMOC are the reduction of surface cooling due to the reduction in the air-sea temperature gradient as the atmosphere warms and the local freshening of convection sites that results from the increase in local freshwater forcing. Two processes also control the recovery of the AMOC: the northward advection of positive salinity anomalies from the tropics and the decrease in sea-ice transport through the Fram Strait toward the convection sites. The quantification of the AMOC related feedbacks shows that the salinity related processes contribute to a strong positive feedback, while feedback related to temperature processes is negative but remains small as there is a compensation between heat transport and surface heat flux in ocean-atmosphere coupled model. We conclude that in our model, AMOC feedbacks amplify land-ice melting perturbation by 2.5.[PUBLICATION ABSTRACT]