Atlantic Meridional Overturning Circulation (AMOC)

What is already happening?
  • The AMOC transports heat northwards, contributing to the UK’s mild climate. 
  • Changes in the strength of the AMOC have led to multiple decades of relatively warm or cold sea-surface temperatures in the subpolar North Atlantic. These changes have affected climate in the UK (e.g. drier summers). 
  • There is increasing evidence that the subpolar North Atlantic is entering a cool and fresh phase, associated with a weakened AMOC. It is unclear if this is part of a natural cycle or a long-term response to climate change.

Medium evidence, medium agreement

There is medium confidence that the AMOC is in a weakened state, and also that current AMOC weakening is consitent with multi-decadal variability. There is lower confidence that current AMOC weakening is due to anthropogenic factors.

What could happen in the future?
  • The AMOC is predicted to weaken in the coming century due to climate change, potentially causing large biogeographical and climatic shifts, for example contraction of blue whiting distribution off Rockall.
  • In general, climate models do not project an abrupt shutdown of the AMOC this century

Medium evidence, medium agreement

Predictions of an AMOC slowdown by 2100 are robust, with increased confidence in this statement compared to earlier reporting. There is a still a general consesus that the AMOC is unlikely to collapse this century.

Key Challenges and Emerging Issues
  • Determining whether the ongoing AMOC decline is part of a multidecadal cycle or part of a long-term decline due to climate change. Crucial to understanding this issue is sustaining the direct observations of the AMOC.
  • Resolving model bias issues to improve decadal projections and identify any transition from multi-decadal variability to long term decline.
  • Improving understanding of how individual processes (e.g., wind driven circulation, deep water formation) and the links between them affect Atlantic gyres, and potential effects of climate change.