This is a great article! I’ve learned a bunch of things, not least of which is that the AMOC (the circulation the Gulf Stream is part of) starts way farther south than I realized. Also, the South Atlantic is anomalous in that it has surface currents that transport heat from the pole to the equator (the opposite of every other major current), which not only contributes to Europe and the northern hemisphere being warmer but also Antarctica being colder.

I’ve also learned that the AMOC’s resistance to being cut off by too much melt water has a bistable regime in its relationship, which means that once it stops it becomes much harder to restart. (It also gave me the ‘interesting’ idea – which is definitely not in the article – that maybe if we had nuked Greenland to melt the ice all at once decades ago when the global-warming-induced meltwater was still in the monostable regime, we could’ve saved the current in the long run because it would’ve restarted. But now it’s too late for that.)

I also find myself wondering if cutting off the AMOC will help make the Sahara cooler/wetter in addition to freezing Europe (a silver lining?), or if it’ll just compress the temperate band smaller and thus just be completely awful with no upside at all. I’m only halfway through the article while writing this, so maybe it mentions it further down.

Edit: continuing to read, I found this doozy:

There is in fact a substantial body of research suggesting that the AMOC is generally too stable in climate models. One reason might be what the IPCC has called “tuning towards stability.” If a model has a too unstable AMOC that already collapses for the present climate, as has happened in a number of models (e.g., Manabe and Stouffer, 1988), the model will be “repaired” (i.e., improved to better reflect reality). But if the AMOC is too stable, that model will not look wrong because the present-day climate is correctly reproduced.

Having now finished the article, I get the distinct impression that its conclusion, as alarming as it is…

A full AMOC collapse would be a massive, planetary-scale disaster. We really want to prevent this from happening.

In other words: we are talking about risk analysis and disaster prevention. This is not about being 100% or even just 50% sure that the AMOC will pass its tipping point this century; the issue is that we’d like to be 100% sure that it won’t. That the IPCC only has “medium confidence” that it will not happen this century is anything but reassuring, and the studies discussed here, which came after the 2021 IPCC report, point to a much larger risk than previously thought.

…is still perhaps not alarming enough because of the way it (as a scientist typically should) resists speculating too much about the unknown effects of things like Greenland icecap melt affecting the salinity models that still can’t be modeled all that well. Reading between the lines, it sounds to me like the author suspects the AMOC shutdown could be imminent – as in, on the order of years, not decades – but the accumulating evidence is too circumstantial to make that claim explicitly.