CMIP6 Models Predict Significant 21st Century Decline of the Atlantic Meridional Overturning Circulation
The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate system, so an accurate representation of the AMOC in climate models is essential for building confidence in their projections. In this study we evaluate the present-day AMOC in the latest generation of climate models, and compare the projected changes in the AMOC in the 21st century under different scenarios of socio-economic development.
The study shows that the AMOC decline projected by CMIP6 models is stronger than in previous model generations (CMIP3, CMIP5), in particular for the most aggressive mitigation scenarios. In fact, AMOC decline in CMIP6 models is insensitive to the specific scenario through at least 2060, suggesting that much of the AMOC decline has already been committed by historical emissions.
In this study, we investigate the AMOC in 27 climate models that contributed simulations to the Coupled Model Intercomparison Project phase 6 (CMIP6). In general, the model ensemble reproduces the present-day AMOC quite well, but there are still several models in which the AMOC is much too weak or too strong. Simulations representing different scenarios for future socioeconomic development suggest a stronger AMOC decline compared to previous assessments, in particular for the scenarios that reflect aggressive mitigation. Using direct measurements of the AMOC since 2004 and an emerging across‐model relationship between AMOC decline in the 21st century and their present‐day mean state, we find that the majority of CMIP6 models point to an end of century AMOC weakening of 34%‐45% of its present‐day strength. A smaller group of models projects much less weakening of only up to 30% of its present state.