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Jim Hunt

You're treading on "Snow White's" toes Neven, not to mention Sou's!

Watts seems to have amended the title of his article? Here's an archive of What's original ramblings: https://archive.is/QbErx

Better than a link to the pukka nonsense?

Getting back to the science, here's an ancient article of my own on the North Atlantic THC and the THOR project, including the views of Stefan Rahmstorf on "The Day After Tomorrow"!


The climate of Europe is strongly influenced by the North Atlantic ocean circulation. Variations of the strength of the Thermohaline Circulation (THC) or the Meridional Overturning Circulation (MOC) are in several studies implicated as a main driver for decadal and longer time-scale changes for European and Northern hemisphere climate. Likewise, variations in THC is a commonly attributed mechanism for non-linear and abrupt (i.e., decadal scale) climate changes.

Susan Anderson

Going for OT once again, some of you may be interested in ClimateSight's latest about PETM ocean acidification, particularly the Atlantic, though all of us would be more pleased to "say it ain't so".

If you have not encountered the twisted soup of WUWT, don't even with the best of intentions go there. You can't win, being honest, correct, and grounded in the real world doesn't matter.


I find the other paper in the linked Washington Post story be the more interesting one. It's the first time I've seen a reasonable longer-term reconstruction of either the Atlantic overturning circulation or the SST in the areas most affected by it.

Having what appears to be a reasonably accurate AMOC reconstruction back to 900 A.D., we now have a baseline for unforced noise in the unperturbed natural state to compare with the modern instrumental record. Since 1800, low-frequency variability of the SST in the strongly AMOC-influenced region south of Greenland has been dominated by a single fairly regular oscillation with a period of around 50-70 years. These new data show that this oscillation was basically entirely absent from A.D. 900-1800. There are no other excursions of a remotely comparable amplutide other than two shorter ones during the height Little Ice Age. Furthermore, the SST over the long-term record has been slightly declining in this region, despite warming almost everywhere else. This indicates longer-term strong and accelerating decline in the AMOC.

This is strongly different from what we've been hearing from modellers over the years. Not only is the AMOC declining much more rapidly than expected until recently, and not only does it have much more variability than was believed possible until not that long ago, also now we find that variability of this type and magnitude is clearly new.

Rahmstorf addresses what his data implies for model-based predictions directly in his second-to-last paragraph.

Climate models from the CMIP5 ensamble forced by natural and anthropogenic forcings generally show a much weaker subpolar cooling than the observations and do not capture the observed North Atlantic subpolar cooling during 1970-1990, even though they show a much smaller and more short-lived cooling following the Agung eurption in 1963/1964. The failure of the models to capture the cooling is probably not due to an underestimation of the response to the Agung eruption, as volcaic cooling would if anything strengthen the AMOC, whereas the data indicate an AMOC weakening. Rather, this failure suggests that these models either have an AMOC that is too stable with respect to buoyancy forcing, or are missing an important forcing (and indeed the time history of Greenland meltwater is not included as a forcing in the CMIP5 ensamble).

An increase in random noise amplitude particularly for lower frequencies is characteristic of systems which are approaching a state flip such as an abrupt AMOC shutdown. I still find it more likely than not that there won't be an abrupt shutdown, but this data is not a all reassuring. Whether an abrupt change will occur or not, the system has clearly gotten less stable.

A longer term AMOC record also has important consequences for future climate prediction. The low-frequency summer NAO index is quite closely correlated to the AMOC. Compare, for example figure 3b in that link, with its clear maximum in summer NAO from 1970-1985 with the minimum in AMOC from 1970-1990.

The summer Greenlandic high pressure which so characterized high sea ice melt summers in 2007-2012 was due in significant part to the counter-trend local high of AMOC during that period. This makes trend prediction problematic if done using the endpoints commonly used here of 1979 (start of good satellite data) and 2012 (the minimum). 1979 was in the middle of an unforced low of AMOC variation, while 2012 was a high of unforced AMOC. Clearly the part of the difference in the climate due random AMOC variation should reverse instead of continue to increase.

At least a decade or two of mostly +NAO summers seems probable to me. This should significantly slow summer sea ice declines, at least relative to the same level of global warming forcing and a -NAO state.


That's certainly a very interesting paper. I only read the supplementary stuff they had online. Did they discuss the oxygen deficit, hydrogen sulfide and mass extinction a little more in the main text? It seems that they were pretty much exclusively focused on dissolving of shells. That is what there is the most evidence for, so they need to discuss it, but a little more on the mass extinction would have been welcome.

From reading the supplementary information, they seem to have a stoppage of deep circulation of 4000 years in the North Atlantic generating a pool of water with enough unfulfilled oxygen demand to make the surface of the South Atlantic and much of the South Pacific and Indian oceans also anoxic for around 4000 years. I find it difficult to understand how that can happen unless the pre-perturbation state was also close to being anoxic. Like I said, I didn't read much discussion of this, so I'm not quite what the explanation for this is in their model.

Bill Fothergill

@ Blaine,

Having just witnessed the astonishing sight of Australian tennis players complaining about the heat at Wimbledon, your comments about the possibility of significant AMOC slowdown (shutdown?) suggests we should enjoy it while it lasts.


Chris Reynolds


The Rahmstorf paper was covered by RC back in March.
With an interesting addendum on cold US winters on the Eastern seaboard.
Not relevant to this discussion.

I find what you write interesting, but suspect that if you're right then there is a modifying role for the AMOC + the post 2007 ice state.

Lindsay & Zhang proposed a trigger point in the mid 1990s for a period of self-accelerated ice loss due to the ice albedo effect.
This would coincide with the AMOC going positive after 1993. So did the AMOC cause the loss of ice?

A key issue here is; to what degree would the AMOC make its effects impact a model like PIOMAS? One route would simply be the incorporation of sea ice concentration. However Lindsay and Zhang find that the post 1990s decline of volume is driven by the ice albedo effect in PIOMAS, and interpreting that decline instead in terms of the AMOC as driver brings the problem that the AMOC was stronger before 1970 than during the 2007 to 2012 period. The AMOC is shown to have substantially reduced over the last century. Would the previously higher AMOC not act against sea ice? A clue here is the emergence of strong Arctic Dipole pattern since summer 2007, and it maintenance until 2012, when the AMOC reduced. This is why I suspect more of a modulating influence on reduced thickness in the 2007 to 2012 period.

However the third year in a row with a failure of the 2007 to 2012 dipole set up seems to me to need an explanation (assuming it doesn't re-assert itself later this year or in years to come. And what you suggest seems to be reasonable.

Have you contacted anyone like James Overland or Stefan Rahmstorf about this?

I ask about Overland because of this paper.

Chris Reynolds


I've been deliberately keeping myself in the lab today, temperature and humidity controlled. :)

No such luxury at home though. :(

Bill Fothergill

No such luxury at home though.

Yep. I went out for a run about 5:30 this evening and thought I was going to melt. The temp wasn't bad, but the humidity was dire.

Jim Hunt


I went surfing yesterday, excited at the prospect of a 17 second swell hitting the North Cornwall coast. I got more than I bargained for!


The longest "hold down" of my career since I tried to take on triple overhead Soup Bowl and lost.


I just read this article in the New Zealand Herald. Maybe some new information:

"What's going on in the big frozen continent below us? Dr Nancy Bertler of GNS Science and Victoria University, a plenary speaker in the 2015 Antarctic Science Conference opening in Christchurch tomorrow, answered these questions." from the NZ Herald.

Q&A: Antarctica - our big icy threat


Bill Fothergill


I presume you also noticed the glaring typo at Q3?


Bill, No, missed it...still don't see it, duh.


Thanks Vaughn, I also posted this over on the Forum (& I missed the typo too!):

Bill Fothergill

Vaughn & Clare

From the NZ Herald...

"3) Despite the melting, we are finding that the extent of sea ice around Antarctica is increasing. How can this be?

In 2013, we observed a strange coincide of extremes - within a few days, the Arctic sea ice extent registered a new record minimum, while in the Antarctic we measured a new record maximum.

The second word of the answer to Q3 is "2013" - it should, of course, be "2012". If it had been preceded by the month - September - it would have been more obvious.


Bill, thanks for pointing out the typo and Clare for posting on the Forum.

Maybe the heat from the Ridiculously Resilient Ridge is getting to me... still 8 - 12 degrees C above normal in Western Oregon & Washington USA.


Chris: No I haven't contacted them.

People tend to just throw up their hands at all the lags between AMOC-linked indicies which have quite different periods of best correlation and lags which aren't even symmetric based on direction of change.

Rahmsdtorf's SST-based AMOC index should be lagged relative to even a northerly measure of the actual AMOC current, but it's pretty close to in phase with the summer NAO, which makes this correlation pretty clear without a lag adjustment. The actual atmosphere has little long-term memory, so the effect of the ocean is pretty much in phase with the atmosphere.

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