Ocean Conveyor Belt Dismissed

After nearly 50 years of acceptance, the theory that a great ocean “conveyor belt” continuously circulates water around the globe in an orderly fashion has been dismissed by a leading oceanographer. According to a review article in the journal Science, a number of studies conducted over the past few years have challenged this paradigm. Oceanographers have discovered the vital role of ocean eddy currents and the wind in establishing the structure and variability of the ocean’s overturning. In light of these new discoveries, the demise of the conveyor belt model has been become the new majority opinion among the world's oceanographers. According to M. Susan Lozier, of Duke University, “the conveyor-belt model no longer serves the community well.”

The idea that the ocean conveyor belt transports cold, dense water from the subpolar North Atlantic along the “lower limb” of the conveyor belt to the rest of the global ocean, where the waters are upwelled and then transported along the “upper limb” back to deepwater formation sites, has been supported by the majority of oceanographers for decades. This circulating flow was assumed to operate along western boundary currents in the deep ocean and provide a continuous supply of relatively warm surface waters to deepwater formation sites. While it was thought to be vulnerable to changes in deepwater production at high latitudes, with significant injections of fresh water capable of disrupting the smooth operation of the system, under normal conditions the conveyor belt was thought to function constantly and consistently. Now it seems that opinions within the oceanographic community have shifted, and the great ocean conveyor belt model has fallen from grace.

As detailed in an eye opening article by Dr. Lozier, the conveyor belt has been found wanting and dismissed as the dominant ocean overturning paradigm. Lozier is Professor of Physical Oceanography and Chair of the Earth and Ocean Sciences Division at Duke, and is an expert in large-scale ocean circulation, water mass distribution and variability. The article, “Deconstructing the Conveyor Belt,” begins with a short history of the conveyor belt theory's development. According to Lozier, our modern idea of the ocean’s overturning, and our understanding of its importance to Earth's climate, developed as a result of the work of two prominent oceanographers:

Fifty years ago, Henry Stommel theorized that recently ventilated waters of high-latitude origin must be transported equatorward at depth along western-intensified boundary currents. Assuming that water masses formed via deep convection in isolated regions in the northern North Atlantic and near Antarctica essentially fill the abyssal ocean, Stommel surmised that the deep ocean exports these waters via a distributed upwelling to the surface. Furthermore, he suggested that because such upwelling produces a stretching of the water column that induces a loss of angular momentum, the deep interior waters must compensate by flowing poleward toward regions of higher angular momentum. Thus, the equatorward transport of deep water masses was confined to the western boundaries of the basins. Stommel’s theory gave the ocean’s overturning, previously amorphous in its third dimension, a structure: Deep waters are transported equatorward in a steady, continuous deep western-intensified boundary current from their formation sites at high latitudes.


The abyssal flow field, as theorized by Stommel in 1958.

The second important oceanographer was the eminent Wallace S. “Wally” Broecker, Newberry Professor in the Department of Earth and Environmental Sciences at Columbia University and a scientist at Columbia's Lamont-Doherty Earth Observatory. Arguably one of the world’s greatest living geoscientists, for more than half a century, Broecker has investigated the ocean’s role in climate change. He was among the pioneers in using radiocarbon and isotope dating to track historical climate change, and the influence of climate change on polar ice and ocean sediments. It was Broecker who coined the term “ocean conveyor belt.”

According to Lozier, work by Broecker and colleagues suggested that the ocean’s overturning was responsible for the rapid climate fluctuations experienced during Earth’s last glacial period. “Though the importance of the ocean’s overturning to Earth’s climate had previously been understood, Broecker’s work essentially cemented the role of the conveyor belt as an agent of climate change,” states her review. “Thus, just as Stommel’s work gave spatial structure to the overturning, Broecker’s provided a temporal context.” So what has changed oceanography's mindset enough to proclaim the conveyor belt—arguably the most important discovery in the history of oceanography—an idea whose time has past?

Since its proposal, oceanographers have understood that the conveyor model is an oversimplification of the way ocean overturning actually takes place. But it was believed to be a useful simplification, capable of providing an overall model of the ocean's transportation of heat energy, if not the exact details. But now it seems that some major features of the conveyor belt have been called into question. Here is a list of recent discoveries that have shaken the foundation of the conveyor belt theory.

  • Most of the subpolar-to-subtropical exchange in the North Atlantic occurs along interior pathways.
  • The deep deep western boundary current (DWBC) breaks up into eddies at 11°S.
  • There is little meridional coherence in the overturning transport from one gyre to the next .
  • Wind forcing, rather than buoyancy forcing, can play a dominant role in changing the transport of the overturning.
  • The southward transport of deep waters at 8°S, off the Brazilian coast, was shown to be carried entirely by migrating coherent eddies.
  • Floats launched within the DWBC at 53°N do not follow a continuous boundary current, but instead take multiple paths to the subtropics, including interior pathways far removed from the DWBC.
  • Two recent studies have found unexpected pathways in the upper ocean.
  • A recent study shows that MOC transport in the subtropical North Atlantic is susceptible to variability in the "leakage" of warm and salty water into the South Atlantic.
  • Studies showing little to no coherence across gyre boundaries have prompted interest in monitoring the overturning circulation in the South Atlantic and the subpolar North Atlantic.
  • The connectivity of the overturning and, more importantly, of the meridional heat transport from one basin to the next can no longer be assumed on interannual time scales.

When all of these observations are combined, they indicate that the conventional conceptual model of ocean overturning needs revamping. As Dr. Lozier put it: “In sum, the impact of eddies on our concept of a continuous lower limb for the ocean’s overturning has evolved from an understanding that eddies can detrain and entrain fluid along the DWBC to the recognition that the DWBC can, at certain locales and perhaps certain times, be a series of migrating eddies, to the realization that eddy-driven flow provides an alternate pathway for deep waters to spread globally.”

In other words, it doesn't work as simply as we thought. Lozier is in a good position to make such a judgment, since it is partly due to her work that scientists are revisiting the conveyor belt model. As noted on this blog in “Conveyor Belt Model Broken,” work by Lozier and Amy Bower of Wood’s Hole, using RAFOS float data, showed that there was something fundamentally wrong with how the ocean's overturning flow was being modeled.


By analyzing the divagating float paths, it was discovered that ocean currents did not behave as expected. Reported back in May of 2009, their discovery had the potential to affect both short term and long term climate change. This is because ocean currents not only redistribute surface warmth, the oceans themselves are a vast reservoir for heat and carbon dioxide. I concluded that this finding invalidated the IPCC's GCM climate model predictions, because the models were based on incorrect behavior of the ocean overturning currents.

At the time, Dr. Lozier took exception to my supposition, stating in an email, “the climate models care first and foremost about the return of the surface waters and our research has no bearing in the slightest on those waters.” I disagreed, saying that the discovery of significant eddies changed the assumptions on how the deep sea currents flow, which must change the boundary conditions between different masses of water. This cannot help but alter the long term reaction of the ocean to the energy flowing through it.

More recently, variations in continuous data measurements from cable-moored instrument arrays identified large and unexpected yearly fluctuations in conveyor flow. As additional discoveries have unfolded, it was also found that there are large reservoirs of CO2 stashed away in the deep ocean, again previously unexpected. As the evidence has piled up, Dr. Lozier has been forced to admit that there are implications for climate change and the way the Earth system is modeled. In her own words:

Added impetus for revamping comes from a recent study revealing a considerable reservoir of anthropogenic CO2 in the deep North Atlantic, surmised to result from the production of high-latitude water masses and their subsequent equatorward spread. Clearly, an improved understanding of the pathways of the upper and lower limbs of the ocean’s overturning will aid assessments of the ocean’s role in the uptake, transport, and storage of heat and CO2, crucial components of Earth’s climate system.

This reinforces the claim that previous climate models—which are highly dependent on the coupling between ocean and atmosphere and, hence, the ocean circulation models they contain—cannot be considered accurate reconstructions of Earth's climate system. I repeat my earlier assertion: if the conveyor belt model is wrong then none of the IPCC's model results can be taken seriously. This point is underscored by recent work that found small changes in high latitude insolation, driven by Earth's orbital cycles, can trigger significant changes in lower latitude ocean and atmospheric circulation. The circulation of Earth's oceans is now known to be much more complex and nuanced than even a decade ago, which has significant implications for climate modeling.

This spate of recent discoveries serves to underline a fundamental tenet of science—that no theory, no matter how elegant or widely believed, is sacrosanct. As the great philosopher of science, Karl Popper, stated, science progresses by moving from one false theory to another, still false theory that is nonetheless closer to the truth. There is nothing wrong with dismissing the conveyor belt model for another, more correct model. In fact, a scientist incapable of realizing that a cherished, comfortable old theory is false and must be discarded is not capable of doing good science at all. Keeping that in mind, here is Lozier's summary of the case against the conveyor belt:

Though appealing in its simplicity, the ocean conveyor-belt paradigm has lost luster over the years, precisely because it has overdistilled the complexity of the ocean’s overturning. This complexity has slowly been revealed as the ocean has increasingly been observed at finer scales in space and time and in places previously only sparsely sampled. As discussed, the ocean’s eddy field, unaccounted for just decades ago and now uncovered by measures at appropriate scales, figures prominently in the dismantling of the conveyor-belt paradigm. Another player in this dismantling is the ocean’s wind field. The traditional assignation of surface ocean gyres to wind-forcing and overturning to buoyancy forcing has ignored the vital impact of winds on overturning pathways and mechanics. As the study of the modern ocean’s role in climate continues apace, the conveyor-belt model no longer serves the community well— not because it is a gross oversimplification but because it ignores crucial structure and mechanics of the ocean’s intricate global overturning.

So, after very logically and methodically making the case for dismissing the conveyor belt model, Dr. Lozier claims we should not discard it because it is a gross oversimplification, but because it “no longer serves the community well.” I would call any theory that ignores the intricate mechanics and crucial structures of the thing is is attempting to describe as worse than a gross oversimplification—I would call it wrong. It seems that Dr. Lozier just cannot bring herself to say the words, “this theory is false.”

Regardless, oceanography is in the process of moving on to new, hopefully less false theories. Some period of grief and denial is probably to be expected from those who literally grew up with the conveyor belt theory. Now, if climate science would only face up to the falseness of the gross oversimplification they have promoted over the past few decades—anthropogenic global warming.

The failure of anthropogenic global warming is not only tied to the recent discoveries in oceanography, but to scores of other scientific advances in biology, geology, atmospheric physics and Earth sciences. The fiction that human generated CO2 is responsible for climate change, and that our continued emission of that greenhouse gas will damage this planet's ecosystem is as gross an oversimplification as has ever been postulated.

While simplicity is generally considered a good thing, and it is no sin for a scientist to invent a theory which proves to be false, it is a great sin to refuse to recognize a theory's falseness. Only by dismissing old false theories can science move on to new, more correct ones. Climate science has damaged its credibility, and the reputation of all science, by clinging to this outdated, failed theory. It is time for the climate science community to prove that they are real scientists by openly pronouncing anthropogenic global warming a false theory.

Be safe, enjoy the interglacial and stay skeptical.

Simple does not equal stupid.

You state "I would call any theory that ignores the intricate mechanics and crucial structures of the thing is is attempting to describe as worse than a gross oversimplification—I would call it wrong."

So you would also dismiss the Norwegian Model in meteorology? Despite the fact that this simple model adequately (practically) explains why it rains sometimes and why winds shift direction in/near those rain areas?

Theories are just an academic exercise unless they can be put to use. No-one needs to understand "the intricate mechanics and crucial structures of the thing" to know that flight is not just for birds.

So einfach wie möglich und so kompliziert wie nötig

I did not say that simple equates to stupid, that is you applying your own misunderstanding to the article above. If you had spent any time on this site you would have found the prior article on what makes a good scientific theory, including such topics as complexity and falsifiability. For a discussion of appropriate simplicity see my comment “Simple is good, wrong isn't.”

Anthropogenic?

Doug, could I ask one question with reference to a quote by Dr Lozier produced in your post.

I refer to the "A recent study revealing a considerable reservour of Anthropogenic CO2 in the deep North Atlantic".

I know I am a litle late at this post but how was the CO2 proved to be Anthropogenic?

Anthropogenic CO2

Basically by measuring how much 14C is present in the CO2. Because 14C is produced by cosmic rays in the atmosphere, CO2 isolated for a long time in deep waters loses its 14C content through radioactive decay. The same is true of carbon sequestered in coal, oil and gas deposits. When people burn fossil fuels, the CO2 released will also be 14C-depleted.

I don't recall which study Dr. Lozier was refering to but the evidence for massive amounts of anthropogenic CO2 being stored in the North Atlantic is less than conclusive. In “Uncorking the Southern Ocean's Vintage CO2,” Anderson and Carr discuss the presence of 14C-depleted CO2 in the deep ocean and its interaction with the atmosphere under different climatic conditions:

CO2 records from ice cores and 14C records from marine archives reveal that the 14C content of atmospheric CO214Catm) declined as CO2 rose during the last deglaciation. This relationship supports hypotheses that attribute the rise in CO2 to the release of 14C-depleted CO2 from a reservoir long isolated from the atmosphere.

The deep ocean (below ∼2000 m) is thought to provide such a reservoir. Respiratory CO2 can build up in the deep sea during glacial periods, when masses of relatively cold, dense water are trapped deep in the ocean and there is reduced exchange with surface waters.

Note that methane released from ocean floor clathrate deposits can also be poor in 14C, depending on when they were formed. Also, only part of human generated CO2 comes from fossil fuels. A large portion comes from agriculture and land use (de-forestation), further complicating the picture. The claim is, identifying the mixture of carbon isotopes that should be released by human activity allows the CO2 to be “fingerprinted.” Given the complicating factors, I would not simply assume any “anthropogenic” CO2 really came from human activity.

Global warming: only the sun can heat the oceans

A recent article in Energy and Environment 'A Null Hypothesis for CO2' 21(4) 171-200 (2010) argues that it is impossible for the observed changes in CO2 concentration to cause any climate change. The penetration depth of the long wave IR from CO2 into the oceans is less than 100 microns, the width of a human hair. The entire 100 ppm anthropogenic increase in CO2 over the last 200 years has produced an upper limit to the increase in downward atmospheric LWIR flux from CO2 of 1.7 W.m-2. This evaporates a 65 micron thick film of water per day at the ocean surface. This is too small to have any effect. Similarly the total enegy flux at the ocean surface varies from at least +1000 W.m-2 to -200 W.m-2. Solar flux to night time cooling. A change of 1.7 W.m-2 has no effect.
It is not just the ocean circulation part of the GCM models that is wrong, it is the fundamental assumption that changes in atmospheric CO2 concentration have had any effect at all. This is just 'hard wired' into the climate models using empirical 'radiative forcing constants'. Sun and wind need no help from CO2 in stting the Earth's climate.

-Roy Clark

Disclaimer

Every so often we get a post that treads the line between science and pseudo-science. My general response is to not publish such items. However, if there is some small merit to the article in question, I will publish it with a disclaimer, just to ensure that publication is not taken as an endorsement. I downloaded the paper referenced above and found its analysis naive and incomplete. It is another example of a supposedly scientific paper that is based on erroneous assumptions. Rather than dissect the paper in detail, one only need look at the null hypothesis stated at the end of the document text. The stated null hypotheses is as follows:

It is impossible to show that changes in CO2 concentration have caused any climate change to the Earth’s climate, at least since the current composition of the atmosphere was set by ocean photosynthesis about one billion years ago.

A null hypotheses generally asserts a default position that there is no relationship between two measured phenomena, linking that assertion to an alternative hypothesis. Here the second hypothesis is obviously false, invalidating the argument. Earth's atmospheric composition was not “set” by photosynthesis a billion years ago.

Photosynthesis caused the “oxygen catastrophe” around 2.4 billion years ago. Since then the composition of the atmosphere has varied significantly, as has Earth's climate. That there is a relationship between mean global temperature and greenhouse gas concentrations is well established. This does not imply that CO2 normally initiates climate change but that it participates as a feedback mechanism. There have been events where a sudden burst of GHG (probably methane) has cause a spike in temperature. The rapid warming during the PETM cannot be attributed to any orbital variation or major change in solar activity (isotope data would have showed such a change).

Simply stated, there is more at work here than the penetration of ocean water by LWIR radiation, as Dr. Clark, who evidently has a PhD in chemical physics, should know. Returning to “first principles” does not mean ignoring factors that are inconvenient or that you don't understand. The publication of such papers does not strengthen the skeptical cause and only serves to reinforce the view that climate change skeptics are addle-brained deniers of real science. I have to side with Fourier, Tyndall, Arrhenius and Al's mentor, Rudy Hanel, on this one: the “greenhouse effect” is real and measurable, it just isn't as potent as the IPCC claims.

Theory and refutation vs usefulness

While you are correct in your interpretation of Popperian scientific philosophy, you should remember that that 'truth' is not only impossible to achieve (since you can never prove the theory) nor is it necessarily the only goal. Kuhnian philosophy - that a theory is useful while it can give accurate predictions and should be discarded once it does not - is actually how we do most things. In real life, we constantly use simplifications that give satisfactory answers even though we know they are not perfect and this may be what Dr Losier is referring to. How many of use include relativity into calculations of motion? We know that ignoring it makes our results inaccurate, but they are still satisfactory and highly useful.

There is a difference between an inaccurate answer and a wrong answer and there is a grey area in determining between the two. This is why the AGW alarmists can justify continuing to use their models because they refer to them as 'inaccurate, but useful' well beyond the point that any real scientist would have discarded them.

I don't work in this field so I don't know if working with a simplified model is going to give you a wrong or an inaccurate but useful result in the case of ocean circulation. It seems to me that Dr Losier is referring to newer, better, models that now do a better job and thus the old 'conveyor belt' theory has now finally lost its usefulness even though it was formally falsified a number of years ago. Great, we've reached the stage where the Kuhnian approach has caught up with the Popperian - until we find a case where the new model also doesn't fit our observations. But at that stage what do we do if we still want to work in any applied way? We can't stop using the falsified model because we don't have anything to replace it with - we have to accept the inaccuracy and be prepared to change when the better model comes along.

Your final image on the definition of science is the critical one here - error is always present in science and the skill of the scientist is to evaluate that error to determine if it is acceptable within the particular needs of that piece of work. It is in forgetting this that bad science is performed. When you ignore it, then you are not a scientist anymore and have become an activist.

Thanks for your excellent articles on this site, I am commenting here merely to add some nuance to the article and pointing out that we are operating in a world that is not black and white and we should be careful not to castigate someone who tries to explain these areas of grey.

Scientists, Truth and Reality

Your points are well taken. When I said that Dr. Lozier refuses to admit the conveyor belt model is false, it is in the Popperian sense, where all theories are false, but better theories are less false than others. I think that intellectual honesty demands that a scientist be able to openly dismiss old theories when they are found wanting. This is the way science is supposed to work: each newly accepted theory explains things more accurately than its predecessors, but is still destine to be replaced by even more correct theories. The process of making such a decision, to dismiss a theory and move on, has always vexed scientists. Scientists and philosophers continue to wrestle with the true form of the “scientific method” to this day (witness this exchange of messages).

Popper's approach was more theoretical or philosophical, an abstract vision of how science should work. Kuhn considered acceptance by the scientific community as the ultimate test of a scientific theory. This is closer to how science really works, which also establishes the need for “scientific revolutions.” When a relevant community of scientists has clung to a theory beyond its useful life, then a sharp break with the past and a period of intellectual chaos ensues. Of course, change doesn't always happen this way either. Sometimes science does advance one funeral at a time.

In all, I cannot agree with Feyerabend's rejection of method—science needs some way to separate truth from fiction—a way to judge the “goodness” of a theory. Usefulness is certainly a component of the worth of a theory, but not the only metric. In the end, a theory's utility may be trumped by inaccuracy, and that can only be established by empirical measurement. Seems we are stuck with experiment and observation as the arbiters of our scientific knowledge.

Proving truth is impossible, so falsification becomes the usual method of choice, whether provided by a single glaring example or by scores of lesser ones accumulated over time. As Feynman said: “It does not make any difference how smart you are, who made the guess, or what his name is – if it disagrees with experiment it is wrong.”

While debating the philosophy of science is fun, it is more an intellectual sport than a quest for fundamental truth. Science is ultimately judged by how well it describes the workings of the physical universe, and particularly how well it can predict future behavior. Because of their nature, some theories take significant amounts of time to be discredited. I have described this as the death of a thousand cuts, where flaws and inaccuracies are accumulated over time until the weight of the evidence cause a theory to be discarded.

This is what happened to the conveyor belt, and this will also be the fate of anthropogenic global warming. I sometimes have a vision of a scientist, thousands of years in the future, saying to a colleague, “too bad that global warming thing didn't pan out,” as resurgent glaciers advance on the cities of the Northern Hemisphere.

Anthropogenic Global Warming & other lies!....

This paragraph gave me a good chuckle:

"This is what happened to the conveyor belt, and this will also be the fate of anthropogenic global warming. I sometimes have a vision of a scientist, thousands of years in the future, saying to a colleague, “too bad that global warming thing didn't pan out,” as resurgent glaciers advance on the cities of the Northern Hemisphere."

The quote attributed to Abraham Lincoln:

"You can fool some of the people all of the time, and all of the people some of the time, but you can not fool all of the people all of the time."

Could easily be applied to the Anthropogenic Global Warming myth. It's possible that the myth grew out of good intentions. Such as the need to reduce reliance on depleting fossil fuels until renewable sources were available and reliable. There might have been a political aspect as well. The need to reduce dependence upon middle-east oil, subject to restricted supply during conflicts.

However it started, the Global Warming myth has conned a lot of gullible people and convinced them to change their behaviour. Like all theories though, the holes in the hypothesis eventually wear thin and people see through it. Likewise, the conveyor belt will be modified to more accurate description of the truth. Just as Global Warming 'scientists' will eventually realise that anthropogenic carbon has no appreciable effect upon the climate and that the reverse is true, that PCO2 is actually a feedback system dependent on the climate.

Mind you, I doubt we'll see those glaciers for some time, unless you were referring to Martian ones!

Quality stuff

I have got to say that the quality of the articles and the discourse on this site is among the best out there. No fan-boys or kooky rants, just informative postings. Please, keep the good stuff coming.

Site Content.

"I have got to say that the quality of the articles and the discourse on this site is among the best out there. No fan-boys or kooky rants, just informative postings. Please, keep the good stuff coming."

I second that.

Best regards, Ray Dart.