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The Gulf Stream is -NOT- Shutting Down

by Nomad Thu Nov 2nd, 2006 at 07:57:51 AM EST

Remember this diary by Londonbear from last year? It reported a Nature news article that the Atlantic currents were slowing down.

ET readers were quick to point out that there was nothing definitive within this research. In a comment by talos in the same thread, it was flagged that even the RealClimate scientists were cautious. All the more reason to take heed - but the posts on DailyKos claiming that the Gulf Stream is shutting down have gone into the double digits since...

There is just one snag: There is no indication that the Gulf Stream is shutting down.

This made things a lot clearer for me, thanks Nomad -- afew


First things first, and that's the terminology which repeatedly needs attention. When people write "Gulf Stream shutting down!" they don't really mean the Gulf Stream.

There are several mechanisms to get ocean circulation going. First, there is wind stress. Then there are density differences caused by water temperature and salinity changes which both affect water density. And then there are tidal forces.

The Gulf Stream is the descriptor for the heat transport that is generated predominantly by wind. It is an oceanic surface process. The Gulf Stream is consistently mistaken with the whole oceanic Conveyor Belt - which is a far, far larger system. And this mistake is rampant, even to be found in the academic journals. The scathing letter (pdf) from MIT professor Carl Wunsch in Nature is testimony of that.

Next, the Oceanic Conveyor Belt. In popular press, there is no difference between the Gulf Stream and the Oceanic Conveyor Belt, best known in the literature as the Meridional Overturning Circulation (MOC). Yet, the Gulf Stream is just a small limb of the whole conveyor belt. The currents of the deep oceans are believed to be driven mainly by density differences, affected by temperature loss and salinity increase. (But here too Carl Wunsch is not in agreement, which was somewhat revealing to me.)


From: UNEP

Bottom-line in child-speak, the Gulf Stream is a wind-driven limb of the Oceanic Conveyor belt, and the thermo-haline circulation describes the deep oceanic currents.

The report by Bryden et al, published late 2005, dealt with the deep Atlantic currents, and therefore not with the Gulf Stream. The (popular) theory goes that a significant decrease in salinity will prevent the water from getting heavy enough to sink down, hence stop the thermo-haline circulation completely and hell will freeze over Europe. (Likely the Gulf Stream will continue to function but may decrease in its capacity.) So when Bryden and his team announced the results of a thermo-haline slowdown, no wonder this was picked up and reported widely. Perhaps unnecessarily to remind that in news clippings (such as in this one by the BBC) that the decrease was often framed as a 30 percent decrease in the past fifty years, whereas the trend of decrease had began in 1992 and was thus far more recent and shorter spanned - which matters in a subject as oceanography where decadal variations are more rule than exception.


Figure 2 from Bryden et al, 2005, showing a decrease in mass flux since 1992.

We're one year further, and I was wondering how this subject was doing. When I dug through the Geophysical Research Letters last week, I found articles indicating that for the deep water currents before the east coast of the USA no decrease was observed, but surprisingly I found the best update in this very recent post on RealClimate. It reads (emphasis added):

At the meeting this week, Bryden and colleagues gave an update of the work, specifically focusing on the first year of data from the moored array. This is the first time that there has ever been such a continuous set of estimates across the whole Atlantic and so reports of the size and nature of the variability were eagerly anticipated. And they did not disappoint! There were two key observations: first, that the approximations that had been used in the Bryden et al study were actually valid, and secondly, that the variations day by day varied by around 5 Sv (1 Sv is about 10 times the flow of the Amazon). The mean over the year for the MOC was 18 Sv - very close to what was expected and in the middle of recent estimates - and significantly, larger than the value seen in the 2004 snapshot. Given that degree of 'noise', this implies that no conclusions about trends over recent decades can be supported.

Other results presented supported this basic picture: transport estimates at different latitudes were not coherent with the initial results, model variability in the best ocean models was large (suggesting that detectability of a MOC slowdown before 2030-2050 was unlikely), and temperature, salinity and velocity changes in the overflow waters beteen Greenland and Europe showed significant connections to the North Atlantic Oscillation but no obvious trends. A number of records that had seemed to be trending strongly when first looked at, now seem to be simply more variable than first thought. This was something of a theme at the conference - the closer we look at the ocean, the more dynamic it appears.

Which means that the decrease observed in Bryden's work of 2005 falls under a normal variation within the measurements. Meaning: the decrease could simply be part of a natural fluctuation - and not be part of a significant slowdown. As the RealClimate honestly reports, the Guardian reporter missed out on that important bit of nuance. And the myth of an actual slowdown perseveres. Not that a permanent thermo-haline shutdown is inconceivable - it has happened in geologic history - but right now, good old alertness is needed, and not panic stories.

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Should I post this at DailyKos during their political tornadoes? It's not a great diary; written in too much haste.
by Nomad on Wed Nov 1st, 2006 at 12:03:46 PM EST
It's something they need to see, but given the election fever, unless it's a poll or a report on a specific district they won't be listening till the weekend after next (give them time for the hangover to go away)

keep to the Fen Causeway
by Helen (lareinagal at yahoo dot co dot uk) on Wed Nov 1st, 2006 at 12:20:54 PM EST
[ Parent ]
Do you want me to post it under my name? I haven't written yet mt gas tax diary...

In the long run, we're all dead. John Maynard Keynes
by Jerome a Paris (etg@eurotrib.com) on Wed Nov 1st, 2006 at 12:25:16 PM EST
[ Parent ]
You're free to use it if you can squeeze the subject in somewhere. I'm blog exhausted for today. Strike that, computer exhausted. And only 70 e-mails left to answer...
by Nomad on Wed Nov 1st, 2006 at 12:29:31 PM EST
[ Parent ]
There is a piece in the Washinton Post today (Nov 2) regarding a congressionally initiated investigation into allegations that the Bush administration suppressed government scientist research on global warming.  The investigations are being conducted by the Inspector Generals of NASA and the National Oceanic and Atmospheric Administration (NOAA) at the request of N.J. Senator Frank Lautenburg.

Lautenburg said ". "It's extremely important, because the evidence is so obvious that they've tried to block the presentation of information on this in an unbiased fashion.."

Post staff writer Juliet Eilperin states:

The issue of global warming has emerged as one of the most contentious scientific debates within the administration. In the past year, several federal climate scientists, including James Hansen, director of NASA's Goddard Institute for Space Studies, have accused the administration of muzzling them, a charge the White House has denied.

See   http://www.washingtonpost.com/wp-dyn/content/article/2006/11/01/AR2006110103269.html

My guess is that Lautenburg requested an administration IG investigation because its easier than having the General Accounting Office (an arm of the congress) do it. And a GAO probe could require some bipartisan support.  The obvious downside is that all IGs are appointed by the President and serve at his pleasure.  

I can swear there ain't no heaven but I pray there ain't no hell. _ Blood Sweat & Tears

by Gringo (stargazing camel at aoldotcom) on Thu Nov 2nd, 2006 at 03:32:21 PM EST
[ Parent ]
Nomad, I do not agree with you, for me it is a great diary - I appreciate your writing, as you help me this topic better. So, THANKS!
by Fran on Wed Nov 1st, 2006 at 12:50:58 PM EST
[ Parent ]
I agree - the 4 charts tell the entire story (and cut through the related BS coming from a number of sources). You don't need a book's worth of words to convey a strong point.

you are the media you consume.

by MillMan (millguy at gmail) on Wed Nov 1st, 2006 at 01:12:04 PM EST
[ Parent ]
You might want to hold onto it for a week or so.  Right now the frenzy over the elections is consuming everyone's attention over there.  Just saying.

We all bleed the same color.
by budr on Wed Nov 1st, 2006 at 01:16:55 PM EST
[ Parent ]
And I was wrong.  First time that's ever happened.

We all bleed the same color.
by budr on Wed Nov 1st, 2006 at 03:30:23 PM EST
[ Parent ]
under my name: http://www.dailykos.com/story/2006/11/1/145131/710

In the long run, we're all dead. John Maynard Keynes
by Jerome a Paris (etg@eurotrib.com) on Wed Nov 1st, 2006 at 02:52:43 PM EST
[ Parent ]
Considering the overall response, folks desperately needed a diversion. Always surprising how diverse the replies are - and yet how different they are to here. I hope you've gotten used to receiving blunt replies.
by Nomad on Wed Nov 1st, 2006 at 08:31:53 PM EST
[ Parent ]
I hope you've gotten used to receiving blunt replies.

That's why I read and comment here.  Although, my feelings are not easily hurt, I can't tolerate rudeness when combined with ignorance.

Great article!  After watching "The Day After Tomorrow," I snuggled a little closer to my cold weather gear. Guess I can afford to back off a little.

I can swear there ain't no heaven but I pray there ain't no hell. _ Blood Sweat & Tears

by Gringo (stargazing camel at aoldotcom) on Wed Nov 1st, 2006 at 08:49:28 PM EST
[ Parent ]
I think before you entirely dismiss the warning signs you should have investigate Prof. Wunsch some more. From this article quoted by the Royal Society, of which he is an overseas member, he appears to be at least a Climate Change sceptic, if not a denialist. You will see he uses the arguments often put forward by the more considered arguers in the Bush administration that all the effects we are seeing are the result of natural cycles and anyway we do not have enough reliable data to be able to make any claims about the influence of industrialisation.

Rather more relevant to this diary is this critique of Wunsch's letter.


This is essentially a reprint of his letter to Nature that was published in 2004, which stated correctly that the Gulf Stream is basically a wind driven phenomenon and will not stop or reverse while the wind still blows and the Earth still turns.

Gulf Stream SSTThe offending Economist statement was 'The Gulf Stream is driven both by the rotation of the Earth and by a deep water current called the thermohaline circulation' in an article discussing the likelihood of a 'shutdown of the Gulf Stream'. Senso stricto, Wunsch is absolutely correct; the Gulf Stream in oceanographic terms refers to the very strongly intensified current on the western boundary of the Atlantic running from Florida to the Carolinas and which heads off into the mid-Atlantic at Cape Hatteras (see figure). These kinds of currents appear on the western boundaries of basins everywhere in the mid-latitudes and arise from the basic pattern of the winds (easterlies in the tropics, westerlies in the mid latitudes) and the rotation of the Earth


However, the Economist is using the term in a much more colliquial (and common) sense that conflates this current with the Meridional Overturning Circulation (MOC, often conflated with the Thermohaline Circulation) which involves convection in the waters around Greenland and the deep currents that cool the deep ocean. This use of the term is often synomymous with northward ocean heat transport (the North Atlantic Current) that contributes to Europe's warmth and which have often been fingered as a particularly sensitive aspect of the climate. While in one sense the water flow associated with the MOC does contribute to the Gulf Stream, it is definitely the junior partner, and so any changes in the MOC are not going to threaten the Gulf Stream in any existential way. However, a shutdown in the MOC does not make as good a headline as a shutdown in the Gulf Stream, and so this misuse persists in the media and public alike


Since the winds will continue to blow and the Earth continue to turn, does this mean that there can't be any changes to the MOC? Emphatically no. The circulation may well derive it's energy from the winds and tides, but it is heavily steered by density contrasts and the stratification of the ocean (witness the difference between the North Pacific and the North Atlantic). Changes in that modulation can have profound effects on the currents, and in particular, additions of fresh water from massive lake drainages (i.e. the 8.2 kyr event) or ice sheet collapses (the Heinrich events) most likely caused severe slowdowns or shutdowns of the MOC in the past. Wunsch is a little sceptical of this research (he calls fresh water the 'deus ex machina' of climate change), but in this he is probably mistaken - for instance, there is enough information from the 8.2 kyr event to reasonably attribute it to the drainage of Lake Agassiz into Hudson Bay.

Thus while density changes don't 'drive' the circulation (in an energetic sense) they can 'drive' (in a modulating sense) changes in that circulation. If this seems complicated, think of the example of greenhouse gases - they don't drive the climate in an energetic sense (the sun does), but they can drive changes in the climate (by modulating radiation flow in the atmosphere).

The author goes on to caution drawing conclusions from one year's data set as there can be considerable variations from year to year. In fact such swings are one predicted effect of climate change brought about by global warming. You only have to compare the mean sea temperature variations observed over the past two years to illustrate this.

by Londonbear on Wed Nov 1st, 2006 at 08:45:18 PM EST
The author goes on to caution drawing conclusions from one year's data set as there can be considerable variations from year to year.

That seems to underline the whole point of the diary and the reported findings on ocean current fluctuation.

Stating that I would "dismiss warning signs" is framing this diary within a wrong context - the previous warning signs seem to be meaningless, that is, if the noise can be louder than the signal.

On the piece by the Royal Society, I wholeheartedly disagree with your assessment on Wunsch; I'd be a denialist by those same terms, but I thank you for the link. I think I've written here at ET that filtering the natural signal from the anthropogenic signal is still one of the toughest contention points and that data collection -is- a major difficulty in practically every climate science field. Denying that does the science no good, it's as simple as that.

Wunsch hits the nail on the head with his final paragraph, bold mine:

it is essential to remember that the inability to prove human-induced change is not the same thing as a demonstration of its absence. It is probably true that most scientists would assign a very high probability that human-induced change is already strongly present in the climate system, while at the same time agreeing that clear-cut proof is not now available and may not be available for a long-time to come, if ever. Public policy has to be made on the basis of probabilities, not firm proof.

(Note: the Stern report uses maximum probabilities of climate change.)

by Nomad on Wed Nov 1st, 2006 at 09:37:50 PM EST
[ Parent ]
The essence of Wunsch's criticisms is that the terms used were not being used properly which is somewhat pedantic but a criticism with which I have some sympathy. Actually if you look at his body of work, he himself seems to use newly collected data in much of his published pieces.

Wunsch seems to want to act a bit like grit in an oyster to get other people to produce pearls. Unfortunately his criticisms are open to misuse. For example, from the piece you quote you can extract

"clear-cut proof is not now available and may not be available for a long-time to come, if ever"

That selective quote - a favaorite trick of the Neocons and their acolytes - can be used to argue that because there is no proof, you need not do anything about it. That again is a distortion of the scientific concept of "proof" and the lay use. Definition creep is well known - look at what "decimation" is taken to mean today. Exactly the same sort of argument is used to claim that creationism is equally valid as evolution.

Whichever view you take of what drives the "Gulf Stream" or what it is, you will agree I hope that there are legitimate scenarios involving the run-off of fresh water from the the melting Arctic ice sheet causing a cooling effect on Northern Europe while there still being a general planetary warming. Elsewhere Wunsch is sceptical that the records show that this was the cause of the increase in ice coverage prior to the last period of glaciation. The problem that his sceptical "Could natural variations have caused this effect" becomes "natural variation caused this effect".

I have not had time to read the Sterm assumptions and compare them to the range. I had understood that there were a range of possible effects taken into account. Frankly though, if complete international cooperation were to result in more reduction in greenhouse gases than is required, would that necessarily be a bad thing? After all, I would rather act on worst case scenarios and be wrong than to be right and no action taken.  

by Londonbear on Wed Nov 1st, 2006 at 10:38:01 PM EST
[ Parent ]
I see your point. But it's not Wunsch's responsibility to phrase every sentence within every twist and turn of legality so it can't be misquoted. Misuse is done by those who misuse - I will join you with shooting at those messengers. The very point to debate about the definitions and philosophy is to attain a clearer and well defined description of a process, and it's a fruitful exercise to my mind. Because definition creep takes place, debate within the scientific field should not be shunned for fear of being misquoted.

There are no different views in oceanography of what the Gulf Stream "is"; it's popular science simplifying the oceanic processes involved and by that way toss edible chunks to the layman. Everyone remembers hearing about the Gulf Stream, who will remember Meridional Ocean Circulation? We can quibble on driving forces; a similar debate rages in earth sciences whether tectonic plates move because of convection or whether convection is generated by plate movements.

The sceptical view of Wunsch in relation to the shutdown of the MOC by fresh water input was not at order in this diary. That's a topic for a different day, but suffice to say that I personally have my doubts on his doubts. Other basins, the Red Sea, the Mediterranean, etc show a stratigraphical history which are best explained by changes in water currents because of a new influx of fresh water input. But again, because he is sceptical on that process I see little reason to disparage his arguments because they are easy fodder for misquoting! The world upside down.

On Stern: I agree with you. The point is that for maximal probabilities, Stern gives a number of costs which are well within the boundaries of feasible. In other words: limiting climate change and stopping the carbon output is doable. Let's go, and let's not panic.

by Nomad on Thu Nov 2nd, 2006 at 05:32:08 AM EST
[ Parent ]
I'd bolded the last sentence, too.

Public policy has to be made on the basis of probabilities, not firm proof.


*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Nov 2nd, 2006 at 04:17:27 AM EST
[ Parent ]
Well said.

(I would cheaply quip "peace in our time", but that would mean I'd have to show how ignorant I am of historical details.)

-----
sapere aude

by Number 6 on Fri Nov 3rd, 2006 at 09:47:29 AM EST
[ Parent ]
Thanks, interesting news. In the articles I read at the time, the lack of coherence with similarly strong changes in the atmosphere was noted, and hence also that large-scale fluctuations are a possibility.

BTW, lemme quote this part for you:

This is the first time that there has ever been such a continuous set of estimates across the whole Atlantic and so reports of the size and nature of the variability were eagerly anticipated. And they did not disappoint! There were two key observations: first, that the approximations that had been used in the Bryden et al study were actually valid

Had the mathematics of the approximations used resembled those used in the paleoclimate analyses?

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Nov 2nd, 2006 at 04:08:10 AM EST
That's a very detailed question - I'm out of there... I simply don't know about the degree of ocean current fluctuations put in paleoclimate models; you'd need the experts.
by Nomad on Thu Nov 2nd, 2006 at 08:20:16 AM EST
[ Parent ]
That's not what I mean. Just the mathematics. Paleoclimate temperature reconstructions we discussed months ago work on the basis of extrapolating from a few tree ring series to the whole planet. Last year's ocean current study extrapolated from measurements at a few locations to all of it. (This years', from the short quote, used much more measurement points that were in agreement with the extrapolations.) Was some similar method used to extrapolate from a few points to everywhere?

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Nov 2nd, 2006 at 09:18:49 AM EST
[ Parent ]
The (popular) theory goes that a significant decrease in salinity will prevent the water from getting heavy enough to sink down, hence stop the thermo-haline circulation completely and hell will freeze over Europe.

This is truly the popular version; if I am not mistaken, the actual simulation results do NOT predict a net cooling of Europe, only a smaller-scale or zero temperature rise (and strongly changed precipitation patterns) while the temperature rises globally.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Nov 2nd, 2006 at 04:11:53 AM EST
From memory, I think it depends on the model and what effect the authors of it take into account an effect on the warming of Europe by the transfer of heat accross the northern Atlantic (to avoid using loose definitions). As I understand it, the theory is that the cooler much less saline run off from the Greenland area will cause the warmer but much more saline surface waters to be pushed down to join the westward flow deeper below the surface. This is usually referred to as "short circuiting" the "Gulf Stream".

Apart from in the deeper bunkers of the White House, there seems to be an agreement that there has been a change in weather patterns and that a significant contribution to this has been the effect of increased emmissions of greenhouse gases. I have anectdoctal evidence of this in the block I live. It was orginally built in 1795 as a naval warehouse. It still has the original layout of internal guttering to take rain water away from the double pitched roof and most of the original rainwater features. When the landlord repaired the leaks in the slate roofs to make those watertight, they do not appear to have changed any of the internal systems of removing the water to the outside. A very high percentage of the flats have been affected by ceilings collapsing from water penetration in the last few months. Now these buildings were designed by naval architects, people who understood the way in which rain could be dealt with. What has changed is the pattern of rainfall from sustained moderate rainfall to intense short periods of downpours which the systems were not designed to deal with. Similar things are happening to the roof of the 100 year old or so school building where I am a governor.

by Londonbear on Thu Nov 2nd, 2006 at 06:57:06 AM EST
[ Parent ]
From memory, I think it depends on the model and what effect the authors of it take into account an effect on the warming of Europe by the transfer of heat accross the northern Atlantic (to avoid using loose definitions).

I'm not sure I can parse the above. Do you meant that the result depends on which effect of the Transatlantic heat transfer is taken into account, or whether it is taken into account?

If it is the latter, then I have to make myself more clear: what I read is NOT that the stopping of the heat transfer would have negligible effect, but that it would be of the same order (indeed smaller) than overall global warming, and thus the net result would still be warming or at least no cooling in Europe (but there would be a much stronger change in rain patterns as you already have anecdotal evidence for).

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Nov 2nd, 2006 at 07:29:39 AM EST
[ Parent ]
You may know by now my main preference lies not with numerical climate models; I'm more interested in the measurement branch.

By head, I've seen an indication of a 2 degrees C decrease in Europe shortly after shutdown in one model.

From my bookmarks the following articles:
Jacob: Decrease of temperatures.

KNMI: Increase of temperatures.

Ruhlemann (pdf!)
: Increase of temperatures.

Rind: Decrease of temperature.

I'll leave it at that...

by Nomad on Thu Nov 2nd, 2006 at 08:06:16 AM EST
[ Parent ]
Hmmm... upon reading the abstracts, I see no contradiction here. The two articles that speak of decrease simulated only the slowdown (either parametrically or as the result of sweetwater input into the oceans), without considering simultaneous greenhouse gas-induced global atmospheric warming, both with an eye on past, natural cycles of THC slowdown/coolings.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Nov 2nd, 2006 at 09:26:10 AM EST
[ Parent ]
see this article:

http://www.americanscientist.org/template/AssetDetail/assetid/51963?fulltext=true

which fairly convincingly argues that the Gulf Stream is overrated. In other words its contribution to the warming of Europe is minor.

So why is western Europe warmer than eastern USA (for example)? Because the prevailing winds around the globe at this latitude are from the west. For Europe that means the air has been warmed by the Atlantic (Gulf Stream or no Gulf Stream, the sea is a heat-store that remains warmer in winter than the land). For the eastern USA it means the air has been cooled in winter across the whole continent. Notice that Seattle and Vancouver on the north-west coast have a similarly mild climate to western Europe, but no Gulf Stream.

Another effect which is stronger than the Gulf Stream is that the European prevailing wind is actually from the south west. The article explains why. Surprisingly it is because of the Rocky Mountains.

by Inselaffe on Fri Nov 3rd, 2006 at 11:47:54 AM EST
Thanks for bringing the attention to the AS article! I knew of Seager's results when I wrote this diary - but I've learned a lesson: it does no good if you put everything to question immediately. The response at DailyKos on Jerome's posting shows that even erecting fairly reasonable questionmarks leads to short-tempered responses. Step by step seems to work better.

Regarding Seager: the only true way to find out whether his premise is correct or not would be diverting the Gulf Stream or stopping the winds - all clearly impossible... Numerical modelling only take you so far... Like my reply to DoDo's second question in this thread, there seems a long way yet to get a consensus view on this topic.

But thank you for bringing this up!! Appreciated!

by Nomad on Fri Nov 3rd, 2006 at 12:57:15 PM EST
[ Parent ]
Well I can understand some scepticism I suppose. There are a lot of vested interests deliberately muddying the waters (pardon the pun).

I do accept that if the Gulf Stream were stopped it may have other serious implications, and I am in no way implying that man-induced global warming is not a very serious fact.

by Inselaffe on Fri Nov 3rd, 2006 at 01:17:25 PM EST
[ Parent ]


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