EGU24-3144, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Overturning Pathways Control AMOC Weakening in CMIP6 Models

Jonathan Baker1, Michael Bell1, Laura Jackson1, Richard Renshaw1, Geoffrey Vallis2, Andrew Watson2, and Richard Wood1
Jonathan Baker et al.
  • 1Met Office, United Kingdom (
  • 2University of Exeter, United Kingdom

Future projections indicate the Atlantic Meridional Overturning Circulation (AMOC) will weaken and shoal in response to global warming, but models disagree widely over the amount of weakening. We analyse projected AMOC weakening in 34 CMIP6 climate models, in terms of changes in three return pathways of the AMOC. The branch of the AMOC that returns through diffusive upwelling in the Indo-Pacific, but does not later upwell in the Southern Ocean (SO), is particularly sensitive to warming, in part, because shallowing of the deep flow of the AMOC prevents it from entering the Indo-Pacific via the SO. In most models, this Indo-Pacific pathway declines to zero by 2100. Thus, the present-day strength of this pathway provides a strong constraint on the projected AMOC weakening. However, estimates of this pathway using four observationally based methods imply a wide range of AMOC weakening under the SSP5-8.5 scenario of 29%–61% by 2100. Our results suggest that improved observational constraints on this pathway would substantially reduce uncertainty in 21st century AMOC decline. We also present new findings that compare the AMOC response in realistic warming scenarios with those found under more extreme climate forcings, including quadrupled CO2 concentrations and large North Atlantic freshwater forcing.

How to cite: Baker, J., Bell, M., Jackson, L., Renshaw, R., Vallis, G., Watson, A., and Wood, R.: Overturning Pathways Control AMOC Weakening in CMIP6 Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3144,, 2024.