I sometimes post about odd papers which attract my attention, thinking the content or meaning is interesting, only to be put in place by those in the know. However, I think this paper is worth a bit of outreach, and I have some thoughts about it.
Bryden et. al. Impact of a 30 % reduction in Atlantic meridional overturning
during 2009–2010 describes a recent hiccup in the AMOC (not identical to, but can be referred to in connection with the Thermohaline Circulation, or Gulf Stream, which are connected concepts), and goes on to link the event with its effects in Northern Europe and the ITCZ subsequently.
The paper is interesting to me for three main reasons:
There's no surprise to hear that a slowdown of the AMOC in the North Atlantic should result in colder Winter seasons for NW Europe, or enhanced hurricane activity in the ITCZ, since this have been modelled for some time and is, anyway, a reasonably logical inference to make. But it is unusual for a scientific paper to be so clear and unequivocal about its findings, and the paper here leaves little room for alternatives. I find this interesting because, to me, it is a further validation of model output and a clear indicator that a changing climate has real effects down-the-line.
This is also the second reason the paper interests: One frequently heard dialogue of doubt is the argument that, since model output and projections are uncertain, mitigation and adaptation in response to AGW should be put on hold. Whilst the paper is meteorological rather than climatic, to the extent that it deals with a phenomenon which is related to some of the modelled output of GW, it serves as an indicator that messing with the system is a bad idea. This is something some people seem to struggle with; in some ways, the real-and-present effects of GW are too abstract, distant or unclear to get a handle on and really come to terms with. Here is a real case scenario which may or may not be a signal for what is to come down the line in the future: the slowdown of the AMOC has measurable and connectable effects. And so it can serve as a warning; look, the risks from a changing climate are not imagined, they are being played out, and bad things will happen...
The paper does not look for a long-term climate signal in the data or the phenomenon, but neither does it find a causal agency for the slowdown - they know what it did, but not where it came from. Some people might be irritated by the statement in the paper 'The ocean has a mind of its own', as being unconstructive, but this is to ask more of the paper than its authors' set out to do. In other words, it's material for a different piece of work to find any kind of larger signal in the slowdown as it happened at the time.
The third interest is related to the unknown element of the piece; what is the likelihood of the phenomenon being repeated, when might this happen, under what circumstances, and with what effects? Living in the UK, there is a vested interest in me knowing whether to plan for an increasing frequency of cold winters, as there is for those in the USA and Caribbean who are likely to be effected by 'busy' hurricane seasons in the future. One 'Sandy', or 'Katrina' was disastrous and very damaging, and the repair of damage done has still not been completed. What if there were three or four such hurricanes in a single season? What would the impacts and damage look like, and would the effected areas ever be able to recover?
So, finally, this is the message from me, not the paper, about Bryden et. al. and their sterling work: in a world where we continue to destabilise weather patterns through persisting in our emissions patterns, it is rational to expect that such possibilities are actual risks, and we are increasing the risks by inaction on all levels. The paper serves to remind us that we are now past the time where uncertainty is an excuse for inertia; the more time we waste now, the worse it's going to get, and more fool us for not reading the signs.
*Note: in the light of William's comments below, title adjusted...