Reacción a "A collapse of the AMOC in this century is unlikely, says modelling study"

In this article [the authors] use a wide set of CMIP6 models to predict the future behavior of the AMOC. The CMIP6 models are a very useful tool to understand processes and predict future scenarios. However, they need to undergo a sensitivity analysis using observations to understand the limitations of the results. Here the sensitivity analysis is not shown, and the reader needs to accept the model outputs without having a sound feeling of their reliability. 

To infer the future behavior of the overturning circulation, they use a novel methodology in which they do not only take into the account the vertical transformation (downwelling) taking place in the North Atlantic but also the upwellings taking place at the Southern Ocean, Indian and Pacific Ocean. Consistent with previous results done with CMIP models, they observe a decline of the AMOC in the first 25 years. However, these models do not [predict] a collapse after that, but a steady low state of the AMOC sustained along nearly 100 years. Observations so far do not show an AMOC collapse but they provide signs that suggest that, at least, a weakening of the AMOC is soon to happen. In particular, we observe a warming ocean and atmosphere that contributes to ice, sea-ice and glacier melting, bringing more freshwater into the system and increasing the buoyancy of the upper layers (more buoyancy impedes the vertical transformation from surface to deep layers that occurs when the water mass cools in the North Atlantic and becomes denser).  

In this paper, it is stated that the vertical transformation of the AMOC will keep on taking place as it needs to compensate the upwelling taking place in the Southern Ocean, and the Pacific MOC (PMOC) is not providing enough compensation. Though it is true that the ocean follows the mass balance constraint, the driving mechanisms of the AMOC, PMOC and Southern Ocean upwelling differ and a weaking or collapse of any of the three will impact the others at different timing. If we stop the vertical transformation in the Atlantic, it will reduce the Southern Ocean Upwelling, PMOC and Indian Ocean MOC but with a lag. I missed a detailed explanation on how these vertical processes relate in time. 

Overall is an interesting idea that needs to be further explored with more realistic models that overlap with observations to fully understand the impact of the compensation mechanism described here.