Multimodel analysis on the response of the AMOC under an increase of radiative forcing and its symmetrical reversal

Sgubin, Giovanni; Swingedouw, Didier; Drijfhout, Sybren; Hagemann, Stefan; Robertson, Eddy

doi:10.1007/s00382-014-2391-2

Cited by 20 publications

(21 citation statements)

References 47 publications

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“…It is mainly due to a large-scale advective feedback causing a long-lasting reduction of the ocean’s northward heat transport, which drives a more regular but persistent temperature decrease over the entire northern NA, that is, up to 4 °C in 50 years. This confirms the large inertia of the AMOC in CMIP5 models 56 , for which a shutdown has been previously shown to occur through a gradual decline 57 rather than in an abrupt fashion as suggested in conceptual models 22 24 and models of intermediate complexity 58 .…”

Section: Discussionsupporting

confidence: 86%

Abrupt cooling over the North Atlantic in modern climate models

et al. 2017

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Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models’ varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy.

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Section: Discussionsupporting

confidence: 86%

Abrupt cooling over the North Atlantic in modern climate models

et al. 2017

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“…Good et al (2015) attribute the red Atlantic and European sectors to the nonlinear weakening of the Atlantic meridional overturning circulation (AMOC) affecting regional air temperature. This behavior will be GCM-dependent, though Sgubin et al (2015) find that HadGEM2-ES AMOC changes are similar to other CMIP5 GCMs during transiently increasing forcing, and that model dependence arises principally after a switch to decreasing forcing. High-latitude features with doubling ratios below one (blue) are related to changes in snow or sea ice that are rapid under the first doubling but then stabilize (thus weakening feedbacks) in the second doubling.…”

Section: Assessing the Influence Of Climate System Nonlinearitiesmentioning

confidence: 69%

Performance of Pattern-Scaled Climate Projections under High-End Warming. Part I: Surface Air Temperature over Land

et al. 2018

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Pattern scaling is widely used to create climate change projections to investigate future impacts. We consider the performance of pattern scaling for emulating the HadGEM2-ES general circulation model (GCM) paying particular attention to “high end” warming scenarios and to different choices of GCM simulations used to diagnose the climate change patterns. We demonstrate that evaluating pattern-scaling projections by comparing them with GCM simulations containing unforced variability gives a significantly less favorable view of the actual performance of pattern scaling. Using a four-member initial-condition ensemble of HadGEM2-ES simulations, we infer that the root-mean-square errors of pattern-scaled monthly temperature changes over land are less than 0.25°C for global warming up to approximately 3.5°C. Some regional errors are larger than this and, for this GCM, there is a tendency for pattern scaling to underestimate warming over land. For warming above 3.5°C, the pattern-scaled projection errors grow but remain small relative to the climate change signal. We investigate whether patterns diagnosed by pooling GCM experiments from several scenarios are suitable for emulating the GCM under a high-end warming scenario. For global warming up to 3.5°C, pattern scaling using this pooled pattern closely emulates GCM simulations. For warming beyond 3.5°C, pattern-scaling performance is notably improved by using patterns diagnosed only from the high-forcing representative concentration pathway 8.5 (RCP8.5) scenario. Assessments of climate change impacts under high-end warming using pattern-scaling projections could be improved by using change patterns diagnosed from pooled scenarios for projections up to 3.5°C above preindustrial levels and patterns diagnosed from only strong forcing simulations for projecting beyond that. Similar findings are obtained for five other GCMs.

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“…The high-density water mass reaching downwelling regions has been used to explain strong recovery and overshoot, (Wu et al 2011;Jackson 2013;Bouttes et al 2015). The way in which models disperse this density anomaly defines the recovery process within each model (Sgubin et al 2015). Our results indicate that the progress of the high-density water mass through the North Atlantic plays a crucial role in the recovery, and gives the high-frequency variability within the overshoot.…”

Section: Discussionmentioning

confidence: 79%

Explaining asymmetry between weakening and recovery of the AMOC in a coupled climate model

et al. 2018

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The Atlantic meridional overturning circulation (AMOC) is projected to weaken in the coming century due to anthropogenic climate change. Various studies have considered AMOC weakening and collapse, with less research focusing on the processes and timescales of the recovery phase. This study uses a coupled climate model to explore the roles of salinity and temperature in AMOC recovery after a weakening. The North Atlantic and Arctic region was hosed with freshwater for 200 years. The mean Atlantic salinity increased strongly during recovery, and remained elevated for ~ 600 years post hosing. The behaviour of the AMOC was well reconstructed by applying "rotated geostrophy" to meridional density gradient profiles between 50°N and 30°S. This makes it possible to determine the role of overturning, gyre, and surface fluxes in the North and South Atlantic. Changes at 50°N dominate the weakening and early recovery. The magnitude of the overshoot to high AMOC transports in the recovery phase was related to density changes in the South Atlantic.

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Multimodel analysis on the response of the AMOC under an increase of radiative forcing and its symmetrical reversal

Cited by 20 publications

References 47 publications

Abrupt cooling over the North Atlantic in modern climate models

Abrupt cooling over the North Atlantic in modern climate models

Performance of Pattern-Scaled Climate Projections under High-End Warming. Part I: Surface Air Temperature over Land

Explaining asymmetry between weakening and recovery of the AMOC in a coupled climate model

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