We analysed the 1% CO2 idealised run of 30 CMIP6 models and found:
- Globally, open ocean deep convection ceases around 600 ppm. We instead enter a new regime, with large areas of mixed layers not exceeding 500 m;
- Unlike what was found in studies based on individual models, deep convection does not start in the Arctic Ocean;
- Consequently, the flows of North Atlantic Deep Water and Antarctic Bottom Water (AMOC and Southern MOC) fall at half their pre-industrial values;
- The main reason is a global large increase in stratification, which is caused by rising upper ocean temperatures and/or surface freshening. Trends in wind are insignificant; the wind cannot break the stratification.
We submitted this to Nature Climate Change. Twice. The first time in October 2019, the manuscript featured “only” 13 models. We were asked to resubmit once we had more models. The second version, with 30 models and more robust methods, was rejected in October 2020 for not being dramatic enough (my interpretation).
None of us is paid to work on this project. We all need to concentrate on more exciting things (e.g. the MOSAiC data), and, simply, it stopped being fun a long time ago. So sure, we could have played the peer-review game with another journal and forced ourselves through another year of selling this paper. Instead, following advice received from the community, we put the manuscript on EarthArXiv, in hope that it can be useful in its present state.