EGU22-2162
https://doi.org/10.5194/egusphere-egu22-2162
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Causal attribution of low AMOC strengths to anthropogenic influence

Eduardo Alastrué de Asenjo1, Armineh Barkhordarian2, Sebastian Brune2, and Johanna Baehr2
Eduardo Alastrué de Asenjo et al.
  • 1School of Integrated Climate System Sciences, Universität Hamburg, Germany (eduardo.alastrue.de.asenjo@studium.uni-hamburg.de)
  • 2Institute of Oceanography, Center for Earth System Research and Sustainability (CEN), Universität Hamburg, Germany

The Atlantic Meridional Overturning Circulation (AMOC) is a crucial feature of Earth’s climate, and the possible recent AMOC weakening in association with anthropogenic emissions is a topic of current scientific discussion. To assess whether anthropogenic emissions affect the circulation, we examine low AMOC strengths with the framework of the causal counterfactual theory.  

We compare the occurrence of low strengths in a factual world with all forcings present against a counterfactual world, equivalent except for anthropogenic forcings. To represent these two worlds, we use past and future 30-member ensembles of simulations from the Max Planck Institute Earth System Model (MPI-ESM1.2-LR), whose AMOC characteristics at 26.5°N are in overall agreement with observations from the RAPID program.

Considering the whole historical period (1850-2020), our results show that causation probabilities for anthropogenic forcings on low AMOC strengths at 26.5 °N are generally low. However, within future projections, we find that anthropogenic forcings will very likely be a necessary cause of any AMOC strength below 16.0 Sv by about 2040. These results are sensitive to the choice of attribution window: if the starting year is chosen closer to the present, all probabilities substantially increase. Within the analyzed simulations, the main attribution results found at 26.5°N are confirmed for other latitudes in the North Atlantic.

How to cite: Alastrué de Asenjo, E., Barkhordarian, A., Brune, S., and Baehr, J.: Causal attribution of low AMOC strengths to anthropogenic influence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2162, https://doi.org/10.5194/egusphere-egu22-2162, 2022.

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