Climate Dynamics

, Volume 53, Issue 11, pp 6815–6834 | Cite as

Observable, low-order dynamical controls on thresholds of the Atlantic meridional overturning circulation

  • Richard A. WoodEmail author
  • José M. Rodríguez
  • Robin S. Smith
  • Laura C. Jackson
  • Ed Hawkins


We examine the dynamics of thresholds of the Atlantic Meridional Overturning Circulation (AMOC) in an Atmosphere–Ocean General Circulation Model (AOGCM) and a simple box model. We show that AMOC thresholds in the AOGCM are controlled by low-order dynamics encapsulated in the box model. In both models, AMOC collapse is primarily initiated by the development of a strong salinity advection feedback in the North Atlantic. The box model parameters are potentially observable properties of the unperturbed (present day) ocean state, and when calibrated to a range of AOGCM states predict (within some error bars) the critical rate of fresh water input (Hcrit) needed to turn off the AMOC in the AOGCM. In contrast, the meridional fresh water transport by the MOC (MOV, a widely-used diagnostic of AMOC bi-stability) on its own is a poor predictor of Hcrit. When the AOGCM is run with increased atmospheric carbon dioxide, Hcrit increases. We use the dynamical understanding from the box model to show that this increase is due partly to intensification of the global hydrological cycle and heat penetration into the near-surface ocean, both robust features of climate change projections. However changes in the gyre fresh water transport efficiency (a less robustly modelled process) are also important.


Atlantic meridional overturning circulation Thresholds Climate change Dynamics Fresh water 



RAW, JMR and LCJ were supported by the Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme (GA01101).


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Met Office Hadley CentreExeterUK
  2. 2.National Centre for Atmospheric ScienceUniversity of ReadingReadingUK

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