A few weeks ago, a study by Copenhagen University researchers Peter and Susanne Ditlevsen concluded that the Atlantic Meridional Overturning Circulation (AMOC) is likely to pass a tipping point already this century, most probably around mid-century. Given the catastrophic consequences of an AMOC breakdown, the study made quite a few headlines but also met some skepticism. Now that the dust has settled, here some thoughts on the criticisms that have been raised about this study. ...
Tipping this decade?
I wouldn’t be surprised. There is some expectation that the circulation state change will occur very quickly once it gets started, and there are already multiple indications that we’re approaching the tipping point. Also this ENSO cycle is doing a lot of damage; I’m having trouble imagining what the other side of it is going to look like.
I’m fairly convinced at the moment that it will happen before 2050, but there’s not enough data and too much noise in what we’ve got to be certain of anything very specific. New data could change the picture. So could El Niño. Until then, my gut says no later than 2035. For clarity I do stand by the centennial vs interdecadal predictions and the researchers making them, I’m just trying to interpret the missing data and its likely implications. The state change is almost certainly going to occur FTE compared to models, so this is me exploring the question what is that FTE likely to actually look like? If each year this decade gets progressively worse, then 10 years out or so doesn’t sound all that unlikely to me.
It seems impossible to prepare for. Do you know if other variables will accelerate once this happens?
Yeah… that’s my impression, too. We can make life easier for ourselves, but I’m not sure we can really be “prepared.”
After a change to the AMOC slow state? I know that it has a direct effect, such as reduced temperatures and rainfall in much of Europe. Combined with other changes, that probably will look like a lowered average temperature but with an increase in volatility - periods of extreme heat intermixed with periods of extreme cold - at least in the shorter term. I can’t recall any tipping points that it might provoke though. If there is one my guess would be that it would be along the lines of ocean currents, acidity, and/or temperature. This will also affect the atmospheric currents like the changes in regional ocean temperatures cause during ENSO cycles, but again I’m not aware of any trends that would necessarily accelerate because of the AMOC state change. The data for modeling the AMOC is not at all ideal, even though there have been significant advances, so there are a lot of unknowns.
They say century not decade. Mid century is 2 decades away.
But scientists are the most conservative people I have ever met or worked with. They are almost certainly underplaying the timeline so as to make their conclusion more solid and defensible.