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Frank, you've written an impeccable introduction to the subject, and I laud you for it. I actually may copy bits of it, if I get the chance. :)

As for the hesitation if there is a consensus on the thermohaline circulation shutting down: the current consensus is that there is no such thing as a weakening in the thermohaline circulation.

And I'm in a bit of a hurry, so here goes:

  1. the method Bryden used is simply unable to make announcements of a 30% decline, as shown in a Nature publication here;
  2. the first results of the RAPID programme which uses continuous monitoring (unlike Bryden) shows that the variability in the MOC is so large that it invalidates the work of Byrden entirely (and note that Bryden is a co-author), publication abstract here;
  3. I tried to convey that latter message in this diary;
  4. A recent NASA study with different methodologies confirms there is no detected weakening of the conveyor belt, see press release here.

Furthermore, climate models infer, with current projected temperature increases, only an actual slowdown around 2100. And lastly,

RealClimate: Atlantic circulation change summary

Everyone quoted is however agreed on one thing: "the notion that [a future change in the themohaline circulation] may trigger a mini ice age is a myth". The evidence of previous changes for instance at the Younger Dryas or during the 8.2 kyr event is quite strong, and significant coolings were observed particular around the North Atlantic, but even such localised coolings are not predicted to occur if the circulation slows as an effect of global warming.

by Nomad on Thu Dec 9th, 2010 at 06:05:05 AM EST
eurogreen:
The NAO is the dominant mode of atmospheric variability in the north Atlantic throughout the year and particularly prominent in the winter.
Nomad, when people talk about "dominant mode of variability" in this context, is it much more than a statistically derived principal component of the system? In other words, is it just descriptive or is there a real understanding of its dynamics and role?

Of all the ways of organizing banking, the worst is the one we have today — Mervyn King, 25 October 2010
by Migeru (migeru at eurotrib dot com) on Thu Dec 9th, 2010 at 06:17:36 AM EST
[ Parent ]
Hard for me to say - NAO is largely a meteorological phenomenon, which is not my strongest suit. It isn't even sure, I believe, whether the NAO has a coupling effect on oceanic currents. And experts still seem to quibble how to exactly measure it, or define it. So I'm not even sure if it can fully cover "descriptive", as the NAO may include traits that haven't been properly associated to it...

However, if I were to wager, I'd say that the science on NAO is somewhere halfway between describing it and mapping out the dynamics involved.

Does that help?

by Nomad on Thu Dec 9th, 2010 at 07:06:03 PM EST
[ Parent ]
I just remember a turbulence workshop where some people presented a Principal Orthogonal Decomposition of atmospheric data and waxed lyrical about it. "POD modes" are a great way to reduce the hell that is fluid dynamics to a finite-dimensional system of equations, but if you impose the POD modes you obtain for describing past history onto a model to try to predict future behaviour you cannot predict deviations from past history...

Of all the ways of organizing banking, the worst is the one we have today — Mervyn King, 25 October 2010
by Migeru (migeru at eurotrib dot com) on Fri Dec 10th, 2010 at 04:11:45 AM EST
[ Parent ]
In layman's terms - if you try to predict the future based on (complex equations derived from) the past, all you can do is extrapolate the past, not predict new or deviations from past trends?  

But can you not factor in new data - e.g. increased CO2 levels - leading to significantly different results?

Index of Frank's Diaries

by Frank Schnittger (mail Frankschnittger at hot male dotty communists) on Fri Dec 10th, 2010 at 05:09:57 AM EST
[ Parent ]
You can find different amplitudes, speeds, or signs of the oscillations, but if you write something like the NAO into your coordinates you may be unable to see the NAO being replaced by a substantively different pattern of variability.

The problem with dimension reduction (otherwise a very useful technique) is precisely that.

Of all the ways of organizing banking, the worst is the one we have today — Mervyn King, 25 October 2010

by Migeru (migeru at eurotrib dot com) on Fri Dec 10th, 2010 at 05:16:50 AM EST
[ Parent ]
Oops. I hadn't realised this had been discussed on ET before - my time anyway.  The reason I write on topics I don't know much about is that it brings experts like you out of the woodwork who can tell us where things are truly at.  It appears, from your comment, that the Wiki articles I quoted are a bit one-sided and need to be updated, although I deliberately kept my presentation as simple as possible for a general audience to present a hypothesis and am happy to see it rebutted.

Everywhere you go - Malawi, Kwazulu Natal, Ireland - and from the comments, the USA - people are reporting unusual weather patterns - delayed rainy seasons, droughts, excessive rainy seasons, severe winters etc. all of which could be attributed to random variation, but which people and media, being people, are seeking to find rational explanations for, with Climate Change becoming the catch-all bucket explanation when it may have no relevance or at least no provable relevance.

It seems to this non-scientific observer that there is still too great a gulf between global climate models and local weather patterns to enable meaningful connections (explanations/predictions) to be made, although that won't stop people from trying.  People don't like random - hence there has to be a God/cause.

P.S. In your earlier diary you refer to surface currents being wind driven and deep water currents being driven by thermohaline forces. However if both are part of the same interconnected system must there not also be a (reverse) thermohaline component to surface currents to keep overall salt levels within the system in balance? I.e. effectively there is (water borne) salt circulation system at all levels of the system?

Index of Frank's Diaries

by Frank Schnittger (mail Frankschnittger at hot male dotty communists) on Thu Dec 9th, 2010 at 09:25:08 AM EST
[ Parent ]
Frank Schnittger:
In your earlier diary you refer to surface currents being wind driven and deep water currents being driven by thermohaline forces. However if both are part of the same interconnected system must there not also be a (reverse) thermohaline component to surface currents to keep overall salt levels within the system in balance? I.e. effectively there is (water borne) salt circulation system at all levels of the system?
The answer is in the caption to the picture you lifted from Wikipedia for the diary body.

Wikipedia: Thermohaline Circulation


Blue paths represent deep-water currents, while red paths represent surface currents
You can see there are at least five points on the globe where the "grat ocean conveyor" current turns from surface to deep water or vice-versa.

Of all the ways of organizing banking, the worst is the one we have today — Mervyn King, 25 October 2010
by Migeru (migeru at eurotrib dot com) on Thu Dec 9th, 2010 at 10:27:37 AM EST
[ Parent ]
My query was whether haline forcing (due to increased water density caused by evaporation) was one of the engines driving surface currents as well as deepwater ones..

Index of Frank's Diaries
by Frank Schnittger (mail Frankschnittger at hot male dotty communists) on Thu Dec 9th, 2010 at 11:42:09 AM EST
[ Parent ]
I have updated the diary to reflect your more recent evidence and conclusions. Damn.  You've spoiled a good story.  However we must be responsible and not confuse the ET masses!

Index of Frank's Diaries
by Frank Schnittger (mail Frankschnittger at hot male dotty communists) on Thu Dec 9th, 2010 at 10:06:38 AM EST
[ Parent ]
I have no trouble understanding that a tiny event can cause a great change.

Say you're standing next to someone, and a cop is swinging a water cannon in your direction. You shout "Hey, Pig!" and the sound of your voice causes him to twitch the hose in your direction.

I've also worked with fluid amplifiers, which work just like transistor amplifiers. Eerily similar.

BUT, you can't back-predict, because you don't know enough. All we really know is that change is increasing, which is a bad sign. We're delicate creatures, balanced on the hope of good growing seasons, and the return of the salmon...

Align culture with our nature. Ot else!

by ormondotvos (ormond.otvosnospamgmialcon) on Sat Dec 11th, 2010 at 03:14:27 AM EST
[ Parent ]
As I understand it catastrophe and chaos theories in maths are all about modelling "unstable" systems where small changes can give rise to dramatic and otherwise counter-intuitive consequences - the mathematical equivalent of walking off the edge of a cliff you didn't realise was there.

The problem is that predicting climate changes - particularly as they apply to particular regions requires such a monstrous amount of data - which we currently are only beginning to gather - that the degree of uncertainty around such climate models is huge.

However, as you say, human societies, and particularly those in NW Europe, are highly optimised to particular climatic patterns and any significant changes are therefore almost always problematic - e.g. rising sea levels, extreme weather events, droughts, harvest failures etc..

It seems to me that human adaptation becomes problematic and expensive at those extremes - e.g. persistent temperatures outside the 0-40 centigrade range, wind velocities above storm force, precipitation levels much above/below the long/short term average.

Global climate change thus poses huge adaptation challenges for societies as well as for the biosphere, where a further increase is mass extinction events can be expected.

Index of Frank's Diaries

by Frank Schnittger (mail Frankschnittger at hot male dotty communists) on Sat Dec 11th, 2010 at 07:46:20 AM EST
[ Parent ]
ormondotvos:
All we really know is that change is increasing, which is a bad sign. We're delicate creatures,

yes we are, sometimes too much so, spoiled and pampered by the gimme lifestyle.

supposing peoples' thoughts have power, how many people suffering have been aching and praying for change for so long?

we are comfortable, for some it has taken years of careful choices to become so, and yes we want things to stay as stable as possible, natch.

but for the vast majority of humans on earth right now, i'd venture a guess that they are fed up to the molars with the status quo, and are entreating every deity imaginable to end their pain, and, most importantly, can't afford the compassion to care very much what has to come tumbling down in our cosy world, if it holds any promise of things changing on the ground for them... that's not envying our freedoms, except the one that lets us continue to look away from the problem, and even if we grok it, we can't help be conditioned by our own survival fears, and worry that social justice/equality might take what we have gathered and have it swept away in a flood of change.

that's why it's hard not to be pessimistic, seeing the lack of action on climate change, the continued bad banking practices left unchecked, etc etc.

the ignorance of a few is holding back the betterment of many, and the fact that some of us have carved little niches of relative health in a fundamentally sick host system is entirely moot, unless we find a model of living that allows for scaling up, maybe not to infinity, lol, but a hell of a way more so than the ones most westerners model, and which the new bric richsters are falling over themselves aping and even parodying in their rabid envy and lust for the rotten apple of consumerschlockism, premature planned obsolescence, and fashionista-ism.

i say this not to counter what you have said, but to riff further on it...

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty

by melo (melometa4(at)gmail.com) on Sat Dec 11th, 2010 at 10:55:33 AM EST
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