Journal
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
Volume 475, Issue 2225, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rspa.2019.0051
Keywords
Atlantic meridional overturning circulation; rate-induced tipping point; ocean heat transport
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Funding
- Higher Committee For Education Development in Iraq (HCED Iraq) [D13436]
- CRITICS Innovative training Network via the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant [643073]
- Met Office Hadley Centre Climate Programme - BEIS
- Defra
- EPSRC [EP/M008363/1, EP/M008495/1]
- EPSRC [EP/M008495/1] Funding Source: UKRI
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The Atlantic meridional overturning circulation (AMOC) transports substantial amounts of heat into the North Atlantic sector, and hence is of very high importance in regional climate projections. The AMOC has been observed to show multi-stability across a range of models of different complexity. The simplest models find a bifurcation associated with the AMOC 'on' state losing stability that is a saddle node. Here, we study a physically derived global oceanic model of Wood et al. with five boxes, that is calibrated to runs of the FAMOUS coupled atmosphere-ocean general circulation model. We find the loss of stability of the 'on' state is due to a subcritical Hopf for parameters from both pre-industrial and doubled CO2 atmospheres. This loss of stability via subcritical Hopf bifurcation has important consequences for the behaviour of the basin of attraction close to bifurcation. We consider various time-dependent profiles of freshwater forcing to the system, and find that rate-induced thresholds for tipping can appear, even for perturbations that do not cross the bifurcation. Understanding how such state transitions occur is important in determining allowable safe climate change mitigation pathways to avoid collapse of the AMOC.
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