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Climate Hustle

Unprecedented Warming in Lake Tanganyika and its impact on humanity

Posted on 20 May 2010 by John Cook

Lake Tanganyika, in East Africa, is the second largest lake in the world (by volume). The lake supports a prodigious sardine fishery which provides a major source of animal protein for the region as well as employment for around 1 million people. Direct observations over past 90 years find that Lake Tanganyika has warmed significantly. At the same time, there's been a drop in primary productivity in the lake impacting sardine populations. To further explore this matter, geologists took lake cores to determine the lake's surface temperature back to 500 AD (Tierney 2010). They found that warming in the last century is unprecedented over the last 1500 years.

Lake Tanganyika lake surface temperature
Figure 1: Lake Surface Temperature from Lake Tanganyika palaeorecord for the past 1,500 years, measured in core KH1 (red line) and MC1 (dark red line). Orange shading is 95% error bars.

What effect does temperature have on the lake's sardine population? To answer this question, a proxy for primary productivity was also reconstructed from the lake cores. Primary productivity was determined from the percentage of biogenic silica in the sediment. They found that over the last 1500 years, when temperature rose, primary productivity fell. In the last 150 years, productivity plummeted from relatively high levels during the early 1800s to some of the lowest sustained values during the past 1,500 years.

How does temperature affect primary productivity? When the surface of the lake warms, the waters become more stratified. This makes it harder for cold currents to rise from the bottom. These currents carry nutrients from the depths toward the surface as food for algae. Sardine then feed off the algae. A less productive lake means fewer fish and therefore less food and income for those living in the region.

The stratification is confirmed by deep-water instrumental measurements which find less warming at deeper layers, revealing an increased temperature gradient. Nevertheless, another possible cause in changing rainfall is explored. Higher rates of precipitation may increase primary productivity. Charcoal levels in the lake cores were used as a proxy for humidity (eg - low humidity leads to drought which corresponds with more bushfires). However, they found a weak correlation between charcoal levels and productivity. The stronger relationship between temperature and productivity led the authors to conclude that it's temperature, not rainfall, that is largely controlling primary productivity.

There's also a strong match between Northern Hemisphere temperature reconstructions and the Lake Surface Temperature reconstruction. Temperatures on Lake Tanganyika have largely followed global trends over the past 1500 years as well as the past half-century. From this, the authors infer that surface temperatures in this region vary in concert with the global average and that the recent anomalous warming is a response to anthropogenic greenhouse-gas forcing. As lake temperature and primary productivity are closely related, this is evidence of another impact of man-made global warming on humanity - in this case, the communities and regional economy around Lake Tanganyika.

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Comments 101 to 150 out of 160:

  1. doug_bostrom at 05:11 AM, there seems to be a lot of misunderstanding or confusion about what the findings of the report were.

    This is taken from the abstract,
    "We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming"
    http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo865.html

    LOL. Has anyone happened to notice that this study is basically about fishing for sardines?

    The method they used to arrive at their conclusion was to measure an indicator (BSi)of the lakes productivity (at one sole location) and correlate that with already reconstructed global temperatures.

    If the objective was merely to make the connection between the lakes surface temperature and global temperatures, would not it have been better just to check the temperature records from relevant locations around the lake? It would have saved a lot of the contortions that it appears to be causing.
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  2. doug at 92 - I think you answer your own question! If Willis & the commenters at WUWT are right and the the data is poor then any conclusion is invalid.

    e and Phila, 94 and 95. I think there are rather more skeptical climate scientists than you realise. - Spencer, Michaels, Christy

    And AGW getting stronger? More like DOA. Maybe you meant climate science - yes it will get stronger.

    I think the AGW argument is basically is lost. But that does not mean that all climate science is duff. It does mean it should be completely separated from energy policy. The reason climate science gets such attention is that is has a large bill attached.

    And yes it may be irksome to have to reiterate basic science - but that's education for you (some people are still arguing about evolution).

    So let's keep discussing and reading - it's a fascinating subject!
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  3. doug_bostrom at 07:07 AM, which particular congruency are you referring to?
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  4. Si...

    "doug. I dont think Willis makes the mistake you mention. He is having a critical look at Jessica's paper - thats what scientists do."

    Scientists do it competently. Willis is no scientist, and his personal track record is one of incompetency, so I for one won't bother to read his piece at WUWT (or elsewhere).

    " I think there are rather more skeptical climate scientists than you realise. - Spencer, Michaels, Christy"

    I could've sworn there were at least a dozen (/snark).

    Si clearly doesn't understand that three (or a dozen) vs. thousands isn't exactly a large percentage ...
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  5. doug_bostrom at 07:07 AM, actually a lot did go wrong with the samples, both at the top and the bottom.
    That is why only a portion of each was used, the equivalent of more than one core apparently discarded.
    As well, extrapolation was needed to date the bottom portion of the used portion as there was some reversal of age indicated at depth.
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  6. Si >"And AGW getting stronger? More like DOA."

    Considering the theory was built up slowly and methodically over the better part of a century, I fail to see how it is "DOA".

    To exand on dhogaza's comment on what constitutes a significant percentage of climate scientists, please see John's post on scientific consensus.
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  7. ...would not it have been better just to check the temperature records from relevant locations around the lake?

    You mean from the instrument shacks installed in the year 1000? No, that's not possible. You'd need a proxy for that. Maybe a core from the lake bottom?

    To summarize once again my objection to your objection, "I doubt it" is not a useful contribution.

    Si, you leave unaddressed the issue that Willis is obsessed with accuracy when accuracy is not the point. Same mistake as with the failed thermometer inspection project run by WUWT, debunked for the same basic reason Willis' critique of Tierney is pointless.
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  8. johnd
    > The method they used to arrive at their conclusion was to measure an indicator (BSi)of the lakes productivity (at one sole location) and correlate that with already reconstructed global temperatures.

    You are missing a key detail, they also used the TEX86 temperature proxy to reconstruct lake temperatures for the past 1500 years. This is a separate method from the measurement of BSi; it is a temperature proxy, not a proxy of productivity like BSi. This yields three independent measurements: lake temperature record, global temperature record, and lake productivity. they found that all three of these measures correlate with one another, hence their conclusions.

    > If the objective was merely to make the connection between the lakes surface temperature and global temperatures, would not it have been better just to check the temperature records from relevant locations around the lake?

    The temperature record doesn't go back 1500 years.
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  9. doug you need good data. One tree does not a hockey stick make ;-)

    Saying over and over that it is just 'the big picture see the trees dont mind the quality feel the width' is entirely missing the point.

    You are going to have to wait for Anthony's surface station report but it is coming!
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  10. Si, SS and johnd,

    How many Vostok ice cores were made? And I am not talking about individual core samples. How about EPICA? At how many locations did they drill cores for those projects?

    Regarding the red herring of hydrothermal actvity. Authors addressed that see #79. Also, have you thought for a minute that those vents have probably been present for millenia, and that they are on the lake bottom and the authors are talkiing about warming of LST. That is akin to Monckton claiming that El Ninos are caused by undersea volcanoes, or thinking that that undersea volcanoes explain the increase in 0-2000 m glbal OHC.

    If the lake was being warmed from below, the lower depths would have locally been warming at a rate much higher than has been observed and the LSTs would not be consistent with the surrounding SATs, which they are. These data have clearly not been contaminated by hydrothermal activity.

    Really guys, you are grasping at straws and it is all too painfully apparant. SS says s/he has spent a few days looking at this on the internet. Wow, really? Scientists have devoted careers and students 5-6 years of their PhDs studying this issue and thereby reading hundreds, if not thousands, of papers. Not to mention that this paper was reviewed and critiqued by their peers, who are experts in the field.

    The contrarians do not like the findings because they are yet more evidence that AGW is an issue and add to an already coherent and cohesive picture. So the best they can do is to try and make some rather lame attempts undermine the scientists' credibility.


    Johnd @100, "LOL. Has anyone happened to notice that this study is basically about fishing for sardines?"

    Please gorow up and show some respect. If you have not noticed the obvious, we have not had thermometers around for anywhere close to 1500 years, nevermind isolated equatorial regions in Africa.

    Tierney is probably reading some of the contrarian comments on this read and shaking her head in disbelief, and who can blame her.

    And for those willing to accept Eschenbach's "critique" of the Tierney et al. paper at face value, I would caution you against doing so. Willis has a reputation for, how shall I say this, for playing loose with the facts as has been shown several times by Dr. Lambert and others. That and the fact that he is not an expert in this field. EOS.
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  11. From Tierney et al's web page:

    "What about Geothermal heating? Isn’t Tanganyika in a rift zone? Could that be responsible for the warming?


    Lake Tanganyika is indeed part of the East African rift system. But there is no evidence for increased deepwater volcanic activity in the lake in the 20th century. In 1971, a survey team found that the rate of geothermal heat flux in Tanganyika was 0.04 watts per meters squared, close to the global average (Degens et al., 1971, Naturwissenschaften). That’s 10-fold less than the estimated heat absorption of the lake since 1913 thought due to global warming (0.4 watts per meters squared; Verburg and Hecky, 2009, Limnology & Oceanography). What is more, were there increased volcanism we would detect a change in the water chemistry of the lake (which has not been observed), plus we would see a thermal “inversion” - warmer waters in the depths of the lake. In fact, as you can see below from an inset graph from our Nature Geoscience paper, the deep portion of the lake (hypolimnion) is cooler than the surface and middle-portion of the lake (110 meters depth) and the deep waters are warming more slowly than the surface waters. This is consistent with a heating source from above - not below - the lake."
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  12. Si >"doug you need good data. One tree does not a hockey stick make ;-)"

    You are misunderstanding Willis's argument. It's not that the reconstruction is "bad" per se, but that it hasn't been calibrated to surface temperatures. This suggests that the record may be off from absolute correct temperatures by a certain factor. That factor would remain constant however, so the overall shape of the trend (which is what we are interested in) would not be affected. This is the point that doug is making.

    >"You are going to have to wait for Anthony's surface station report but it is coming!"

    Thanks, we know. He's been promising it for a long time now. Ask yourself this: why does Watts spend so much time documenting "bad" weather stations, but never bothers to plot the temperature records of "bad" stations vs. "good" stations? It's a rather trivial thing to do. In any case, we don't have to wait for his report, others have done the work for him. You can read about the results here, and John's posts here and here. As it is off topic from this post, please post any followups to the weather station discussion to one of those two posts.
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  13. e @115,

    Don't forget Menne et al. (2010).
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  14. doug_bostrom at 08:24 AM, and e at 08:45 AM,
    the key point being missed is that the variations of layers of BSi deposited on the lake bottom was interpreted as variations of the lake productivity, in the scope of the study, further translated into sardine production.
    Using one core sample, which doesn't seem to allow for the reports on how variable the sardine productivity is over the 700km long lake, nor how the lake surface temperature varies, the study was able to find some correlation of the inferred variations in productivity with ALREADY reconstructed GLOBAL temperatures over the same time frame.
    The supposed proof of the relationship is that sardines catches have fallen in recent decades whilst lake surface temperatures had risen as recorded by instruments over the last 90 years.
    The problem I see is that for the connection to be validated the rate of BSi deposition over the last 90 years has to correlated with the lake surface temperatures that have been recorded, and that is where this study is weak.

    Firstly, the relevant top of one core was unable to be used, and the bottom of the other one was not used for some unspecified reason, so there is only assumed continuity.

    Secondly other studies, one which I provided the link for in an earlier post, collected samples in a more controlled manner taking surface samples along a designated transect in two different locations and found variations of BSi in the order of 0.01-1.07% and 0.1-2.9% at an assumed sedimentation rate of 1mm/year.
    The Teirney study determined a sedimentation rate of 0.5mm/year which was used to model age for the top 100mm, and their analyse yielded a BSi content varying from 10-60%.
    The BSi difference may be due to different lab procedures, but as can be seen the Tierny % varies by a factor of 6 whereas in the other study by factors of up to 100 or even closer to 300 across the two, hence their noting of the high variability and the need to recognise this if paleoclimate studies are to be conducted in the lake..

    Thirdly, overfishing appears as not to have been considered a possibility, whereas elsewhere in the world declining fish numbers are blamed on that.

    My comment about checking the local temperature was having a shot at those who had gone off on a tangent drawing all manner of conclusions about AGW when the study was primarily about sardine production.
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  15. Here's a nice example of cognitive disconnect:

    My comment about checking the local temperature was having a shot at those who had gone off on a tangent drawing all manner of conclusions about AGW when the study was primarily about sardine production.

    Title of article under discussion as it appears in Nature:

    Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500

    I'm sorry johnd but I find you unreasonable in the technical sense of the term.
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  16. Johnd,
    Perhaps if you read some of the references that Chris gives you you will be less confused. In post 50, he refers to the Nyanza Project. This paper was written as part of that project. One of the lead scientists is a FISHERIES expert. I expect that Dr. Teirney discussed overfishing with them at some time during the month she was in Africa, and considered that information when she wrote this paper. Several other scientists are lake productivity specialists. These people spend their lives doing this work. Your insinuation that they are stupid and uninformed, because you have not bothered to read the background information is unconvincing. This paper is part of a large series of papers which document the lake. Your claim that they neglected some important facts because they wrote a different paper you have not read reflects only on you.
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  17. doug_bostrom at 10:19 AM, apparently it is not only me that you consider to suffer from cognitive disconnect.

    In case you haven't read to the end of the article abstract as yet, or the lead at the top of this thread.

    Here is the last sentence from the abstract which I think I already had referred you to earlier.

    "We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery."

    Note that the word productivity is mentioned repeatedly.

    It measured evidence of historic productivity.
    It attempted to correlate recent temperatures with recent productivity.
    Finally it reached conclusions about future fishery productivity, of which sardines are the primary catch.

    In addition, carefully read the post which leads this thread and look at the only two questions John posed.
    I imagine they were asked as part of initiating the direction of the topic for discussion.
    "What effect does temperature have on the lake's sardine population?"
    "How does temperature affect primary productivity?"
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  18. michael sweet at 10:47 AM, it would be appreciated if you would stop assigning your own meanings to my posts which you tend to twist into a supposed insult against someone else.
    It is not what reflects on me that should concern you.

    If I'm not mistaken, one of the studies I referred to earlier on a couple of occasions was part of the Nyanza Project, there are numerous such papers available.

    Variability was a matter that seemed to pop up quite frequently which is what the focus of my posts have been on, and whether or not is has been accommodated or allowed for.
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  19. #101

    "e and Phila, 94 and 95. I think there are rather more skeptical climate scientists than you realise. - Spencer, Michaels, Christy"

    Yes, there are some skeptical climate scientists out there, and they've been making their views known for years, as they should. I fail to see what this has to do with people who lack any relevant expertise casually accusing working scientists of not understanding their own fields.

    How does such behavior make science "more robust"? More to the point, how could science ever progress if it were obliged to cater to that odd combination of arrogance and ignorance?

    Look, I'd love to revolutionize evolutionary biology, or any other field...but realistically, what are the chances I'm going to do that without educating myself to at least the level of a grad student, not just in the subject itself but also in the nuts and bolts of scientific practice and discourse?

    The skeptical scientists you've named have so far failed to convince very many of their colleagues that they're right and everyone else is wrong. But they do have credentials and they've more or less followed the rules of the game. As such, their contributions are valuable even if they're incorrect. But too many amateur "skeptical" arguments -- including some of the ones on this thread -- fall under the category of "not even wrong."

    We agree that it's healthy to have people get more interested in and involved with science. But we seem to disagree about the amount of time, effort, and humility it takes to get good at it. As I see it, no one deserves an 'A' just for showing up.
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  20. You're of course entitled to your opinion that the paper under discussion here is "primarily about sardine production" when sardines are not mentioned in the title.

    I'm uncomfortably prepared to concede that the paper would possibly have been better focused if it had confined itself to paleotemperature reconstruction but technically speaking I don't have the background to say that. For my part-- concerned as I am with climate change-- the significance of the paper lies in what its title says. Probably needless to say, but the reason I found my way here was because of climate problems, not a shortage of sardines.

    At the end of the day, your argument still consists of "I doubt it." But there's no such thing as a last word in a venue such as this so I'm going to ignore what you have to say next about this unless you veer off in some other direction.
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  21. Phila #118,

    The science on these threads can, and will, progress, irrespective of whether skeptics arguments turn out to be correct or not.

    As a (skeptical) scientist, I am here because the topics under discussion are being used in a semi-technical geopolitical debate that involves subjects very dear to my heart (life, death, money, taxes, etc).

    That's inevitably going to bring more scrutiny, from people at all levels of scientific education and competence. Yes, it's uncomfortable.

    My adviser used to tell us (his research group) that if we "couldn't explain what we did, and why it was important, to a truck driver in a honky-tonk bar in Texas, and why they should be paying for it", then we should ask ourselves some serious questions.

    Frankly, what I read on this particular thread, is a bunch of people being quite rude and disparaging towards (a few) other people who are clearly scientifically competent and seem to be raising valid points.
    That approach is not going to get very far with the truck drivers.

    Without being (too) rude, I sometimes wonder if climate science thought it could 'run with the big boys' yet still go on 'providing weather forecasts'.

    Another thing my supervisor told us is "that we're a kinetics lab". The kinetics in that lab taught me a lot about waiting to see if measurements bore out predictions and, when they didn't, it was a learning opportunity.


    Unfortunately climate science doesn't work on the same time scale as most other sciences, and the hubris seems to be commensurately greater.
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  22. thefrogstar @120

    "climate science thought it could 'run with the big boys' yet still go on 'providing weather forecasts'."

    There is so much wrong that statement-- I'm not sure whether your erroneous comparsion with weather forecasts was intentional or not. Anyhow, I'll leave it there.

    As for your claim about some of the points being raised by contrians here being "valid". I strongly disagree, and that is exactly why I and others are getting frustrated. Do you not see how arrogant and rude it is by some here to presume to know more than the people (e.g., Dr. Tierney and her colleagues) who have worked so hard on this, those who have researched the topic at hand (i.e., literature review), wrote the proposal, invested the time and effort to collect the data, processed it, analysed it, checked the numbers, written it up, gone through several iterations, and then finally gone through peer review (a very humbling and exhausting experience in most cases), only to have some people posting on an internet blog (who are not even qualified or experienced in the field and who have not taken the time and effort to understand the problem in the first place)cavalierly dismiss it as sardine research. And worse yet, doing so not using rational and informed scientific critique and methods, but essentially taking cheap shots. I sense no inclination whatsoever from certain contrarians to learn form this paper, or other climate papers, or to concede when they have been shown to be wrong. Does that not tell you something or concern you?

    Moreover, most of the criticisms raised here have been addressed by the authors, and people who have published on the subject prior to this study (this study does not stand in isolation, it is part of a much bigger picture of scientific understanding), yet the contrarians it seems could not be bothered to first do the leg work to determine whether or not their "concerns" had been addressed before making condescending remarks. This has happened repeatedly in recent years in the field of climate science and related disciplines, and to be candid, it is getting incredibly tiresome.

    I'll agree with you that the IPCC has done a relatively poor job at communicating the science. That said, they are, believe it or not, reliant on the volunteer work of hundreds of scientists and have very few full time staff. They do not have a well-oiled, experienced and politically savvy PR team. Anyhow, let us hope that they are provided the means required to communicate the science and the gravity of this situation in AR5.

    And frogstar, the hubris I am seeing (on an increasing scale) is coming from the contrarians and "skeptics". I am pretty highly qualified in my field, but I don't not presume to know more, or feel inclined to be contrary or question the science of an oncologist, for example. Additionally, I acccept that they are highly trained, experienced and professional, and that it would be incredibly arrogant and disrespectful (paranoid even?) of me to feel obligated to openly question their work simply because they were the bearer of bad news or news that their findings did not sit well with me. And, in the event I did elect to attack or question their research after Googling for a few days, I would not be offended (or surprised) if they set me straight, were rather snarky or accused me of hubris even if I do happen to have post graduate degree/s in another unrelated field.
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  23. Presumably frogster is referring to such serious and enlightening remarks from so-called skeptics as:

    One tree does not a hockey stick make ;-)

    or

    LOL. Has anyone happened to notice that this study is basically about fishing for sardines?

    Regarding speaking to truckers, frogster, I think it would not be too difficult to show how Willis' critique of Tierney's paper is not aimed at the side of the correct barn. "Your oil pressure gauge is wrong, you know that it reads 50psi when it really is measuring 60psi. If the reading on the gauge drops to 40psi you know you've got a loss of oil pressure, even if you know the reading is 'wrong'." Not complicated.
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  24. #120 Frogstar

    "As a (skeptical) scientist, I am here because the topics under discussion are being used in a semi-technical geopolitical debate that involves subjects very dear to my heart (life, death, money, taxes, etc)."

    The policy implications are well worth discussing and there's plenty of room for honest disagreement. It's a serious subject, and ideally, we'd all be having an serious conversation about it.

    Unfortunately, that discussion is largely being postponed so that we can argue over whether CO2 is actually a greenhouse gas, whether Jessica Tierney actually knows how to conduct research, or what have you.

    "The kinetics in that lab taught me a lot about waiting to see if measurements bore out predictions and, when they didn't, it was a learning opportunity."

    That's a reasonable approach in many situations. This situation is a bit trickier, obviously, because the prognosis gets worse as we wait and there are no do-overs, as far as we know. The better analogy here would be to medicine: With some conditions, you can wait for measurements to bear out predictions. With others, doing so would be...well, let's just say "unwise."
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  25. 63
    johnd at 08:34 AM on 22 May, 2010
    "Whether taking simple surface sediment cores or cores from deep below in the search for natural resources, there is a strict regime on what is required to satisfy firstly those who will decide whether to proceed further or not, and an even tighter requirement for it to become part of a bankable feasibility study, and then even tighter beyond that."

    johnd-
    As a research geologist with some small amount of experience in mineral exploration, I think your criticisms are off base. In the world of publicly-funded science, "those who will decide whether to proceed further or not" and for work to "become part of a bankable feasibility study" are the peer reviewers of the journal where the work is published. The fact that Dr Tierney's paper appears in Nature Geoscience - a very prestigious journal with a low acceptance rate - means that your quality-control concerns would have been met more than adequately in the review process. Your continued questioning in this regard is as inappropriate as would mine be of your professional work. The difference of course is that your proprietary output is protected from comment by the ignorant whereas the work of those who publish in the peer-reviewed literature is available to all to pick over.
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  26. Albatros quotes:
    "...But there is no evidence for increased deepwater volcanic activity in the lake in the 20th century. In 1971, a survey team found that the rate of geothermal heat flux in Tanganyika was 0.04 watts per meters squared, close to the global average (Degens et al., 1971, Naturwissenschaften). ..."

    If volcanic activity is perfectly constant, but the lake level decreases, the temperature just might be affected after a while. Now the difficulty arises... is this due to the volcanic activity, global warming or maybe just a local climate change?
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  27. Oh well, this illustrates why science pseudoskeptics organise their own climate "conference" and real scientists don't go. It's simply impossible to discuss straightforward issues of science with individuals that use ignorance as a debating point, adopt a null hypothesis that everything they think of that might be a problem is a problem, and consider that the point of reading a scientific paper is to attempt to trash it (by misrepresentation if necessary).

    Relating to some of the stuff that’s been thrown at the paper on this thread, it isn't difficult for a non-expert to quite easily establish the following:

    ONE: the paper isn't about sardines. "Primary productivity" refers to productivity at the bottom of the food chain and in marine/lake environments usually relates to the photosynthetic fixing of CO2 which is the primary source of biological productivity at all levels of the food chain. In other words assessment of primary productivity in oceans and lakes usually relates to algae. It doesn't mean sardines!

    TWO: Despite assertions that the proxy temperature record isn't calibrated against the lakes surface temperature, in fact the proxy data that overlaps (top of the core) contemporary direct measurements were cross correlated with direct lake surface temperatures (at Kayla and Mpulunga; see Figure 2 of Tierney et al, 2010). In addition the temperature proxy was calibrated with a large amount of additional data that relates lake surface temperatures to the TEX proxy temperatures (see Supplement of Tierney et al, 2010).

    Even if the top of the TEX data wasn't extensively calibrated (it was) or the core proxy temperatures matched with direct lake surface temperatures (it was) the interpretation that current lake temperatures are the warmest in 1500 years is independent of any uncertainties in calibrations, or offsets relative to current temperatures.

    THREE: Hydrothermal vents. Skepticstudent linked to a paper about hydrothermal vents in lake Tanganyika but failed to do the obvious assessment of whether these were near the coring site. Hydrothermal vents are found in the Uvira fault region at or near the N end of the lake (in the waters near Pemba and Cape Banza). Inspection of a map indicates that these are 300 km or more from the coring site.

    FOUR: Hydrothermal vents. Significant warming from hydrothermal vents would yield a distinctive pattern of warming in the water column. Sampling of the water column and multiple sites throughout the lake indicates that there is no significant contribution from bottom warming and that the thermal pattern of water column is as expected from surface warming.



    FIVE: non-representativeness of a single core. Similar arguments apply to Antarctic cores. Single cores give data that are representative of particular spatial regime as long as an appropriate proxy is used. Thus a single core can give good insight into CO2 levels worldwide since CO2 levels are well averaged globally on the timescales of core resolution. Temperature proxies also give good representation of a wider spatial extent since it is well known that temporally-averaged temperature variations are correlated across significant distances (up to 1200 km). In this particular case (Tierney et al, 2010) analysis of lake surface temperatures and temperature profies through the water column indicate that single sites within Lake Tanganyika are likely to be more widely representative (see Figure just above).

    SIX: The warming not due to man-made global warming. Since the site chosen for coring was in an isolated area with little human population, little deforestation or agriculture (which could impact on nutrient loading by runoff), there is little evidence that local direct human impacts affect the analyses. The observation is that the Lake Tanganyika surface has warmed very considerably especially in the last 50 years, and is likely warmer than it has been for 1500 years. The warming of the last 50 years has been directly measured and is in line with the wider understanding of enhanced greenhouse-induced warming both locally and more widely. The attribution of the warming to anthropogenic global warming is a pretty reasonable one in the context of what we know.

    SEVEN: General point. This paper seems like a pretty good analysis of paleoproxies for lake surface temperatures, primary productivity (and charcoal deposition as a proxy for local forest fires). However (and with greatest respect to Dr. Tierney and her coauthors) its interpretations and conclusions are a small input to our broad understanding of the Earth response to human enhancement of the grrenhouse effect. It really isn't worth a frenzy of attempted trashing!
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  28. Chris @152,

    "It's simply impossible to discuss straightforward issues of science with individuals that use ignorance as a debating point, adopt a null hypothesis that everything they think of that might be a problem is a problem, and consider that the point of reading a scientific paper is to attempt to trash it (by misrepresentation if necessary)."

    I would second that, especially the last portion of the sentence. You really did hit the nail on the head there.

    As for the rest of your post. Thanks. Thanks too for bringing the thread back on track again-- you make some excellent points.

    Si @154, two words "cumulative impacts". And please don't spam this thread by desperately throwing out there every contrarian speaking point which has long been debunked.
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  29. chris. you say,
    "The observation is that the Lake Tanganyika surface has warmed very considerably especially in the last 50 years, and is likely warmer than it has been for 1500 years. The warming of the last 50 years has been directly measured and is in line with the wider understanding of enhanced greenhouse-induced warming both locally and more widely."

    I asked a fair question in an earlier post relative to what you are stating here in point six. That is, why does it seem appropriate to make a case for global warming about a geographically localized condition?

    By the way, the question is not directed necessarily to you. It is actually rhetorical in that it refers to what I thought was rule number one around here, not to use local conditions to make a case about global warming. In fact, just the opposite was true when it was pointed out that there were surface waters in the Artic that were actually cooler, this data being discounted as actually proof of global warming for other convoluted reasons.

    I would add that where I made the comment earlier, it was done in tandem with another remark, and as I have found many times in the past, those that take up points with me typically choose what appears to be the easier issue almost as if to tactically distract readers from what might be embarrassing or controversion.
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  30. sorry, not Artic, Antartic
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  31. RSVP,

    I think your point was addressed in the course of discussion, though perhaps not directly. Nobody here is claiming that this single data point proves or disproves global warming. It is just another data point consistent with the so-called "hockey team" global reconstructions. It is the summation of this data point and many many others that makes the case for global warming, not any one data point on its own. The point is not that local conditions should be ignored, but that they must weighed in summation with other local conditions across the globe.
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  32. Si:
    Again why the ad hom attacks? (and yes I do lack the simple comprehension why some regular posters on this site sneer and belittle others - it is why I read this blog so seldom)
    Our host has deleted both of our most recent comments, no doubt because they violated the comments policy -- sorry John, I'll be more careful.

    Your reaction to perceived attacks is further evidence that you're not acquainted with how science is actually done. In the community of scientific peers, debate can be pretty rough-and-tumble, and that's a good thing. This piece (h/t Hank Roberts) by a former member of that community lays it out succinctly:
    Science doesn’t work despite scientists being asses. Science works, to at least some extent, because scientists are asses. Bickering and backstabbing are essential elements of the process.
    The point of my original comment is that if you want to challenge the AGW consensus, you need to follow the same long, arduous process as the scientists who contributed to it. There are easier ways to make a living, believe me. I don't think it's beyond your abilities, but until you've covered all the ground the experts have, your sense of your own competence is illusory. That's not an attack, that's just sincere advice.
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  33. mike at 17:51 PM, perhaps everyone needs to clear all preconceptions and agendas from their minds and get back to the basics by reading past the headlines for a change and locating what are the central issues addressed by both the study and this thread.

    If you haven't read the lead post of this thread in it's entirety there were two, and only two questions posed which should have provided a clue to those alert enough as to what the central issue was.
    The questions are
    1. "What effect does temperature have on the lake's sardine population?"
    2. "How does temperature affect primary productivity?"

    Sardines are mentioned four times, primary productivity eight times.

    Additionally the abstract for the article published in Nature concludes with the following statement,

    "We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery."

    In addition the study did the following,
    It measured evidence of historic productivity.
    It attempted to correlate recent temperatures with recent productivity.
    Finally it reached conclusions about future fishery productivity, of which sardines are the primary catch.

    What this thread makes painfully obvious is how easy it is for some people to be led simply by placing a notion in their mind so that everything after that then becomes related to that notion and used to further support what they now believe, even if it has to be distorted to do so.

    Before I go on perhaps you should go back to the lead post posted by John Cook, plus read the article in question through to the conclusions, or failing that, the abstract just to clarify what were the questions that the study set out to answer and what were the conclusions reached.

    Having said all that, with your background you probably appreciate how big an area the lake covers, about 700km by 50km, and just how variable everything could be over such a vast area.
    There is quite a bit of literature available from previous studies, and as one might expect, some of them note how highly variable many of the relevant factors and indicators are.
    Lake surface temperatures in different locations can vary by 4 degrees at a given time, climatic conditions vary so that different winds and currents mean local conditions vary across and around the lake, and so too do the fish catches across the different regions of the lake.

    Given the study was based on collecting samples of BSi which is considered an indicator of primary productivity, and there is information that primary productivity from the lake is not only declining but highly variable across the regions, whilst data indicating such may be available for current and recent times, core sampling has to be undertaken to obtain historical data.
    This brings us back to the point I have been making all along, I have serious doubts that a single core sample can represent all the variables that form part of subject being studied, namely primary productivity, in particular sardines, as so clearly stated in the lead post of this thread.

    With you background I imagine that you are aware of how often it has happened, often famously or more often, infamously, where on the basis of a single sample, major new discoveries have been announced only to fizzle out when it was found that the single sample was anything but representative.
    Perhaps you have heard of Bre-X where after the initial euphoria of a major discovery failed to be sustained, those involved then worked hard to ensure the evidence being collected matched the expectations created by the initial discovery, the similarity not lost when some of the work on tree proxy reconstructions was closely scrutinised.
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  34. Something that should have been raised, but wasn't, is the matter of the splicing of the data obtained from the core samples together.
    Recently the matter of splicing temperature data in graphs was the subject of intense scrutiny and debate with certain graphs rejected because of some perceived flaw.

    So what is different here? The only difference perhaps is that there is no other benchmarks that can validate or otherwise the appropriateness of splicing this particular set of data.
    Where are all those posters critical of the temperature graphs?
    Any comments that remain consistent with similar previous critical analysis?
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  35. As a point of reference, perhaps it would be useful to have the abstract available here directly:


    Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500

    Jessica E. Tierney1, Marc T. Mayes1,2, Natacha Meyer1, Christopher Johnson3,4, Peter W. Swarzenski5, Andrew S. Cohen3 & James M. Russell1

    Instrumental observations suggest that Lake Tanganyika, the largest rift lake in East Africa, has become warmer, increasingly stratified and less productive over the past 90 years (refs 1,2). These trends have been attributed to anthropogenic climate change. However, it remains unclear whether the decrease in productivity is linked to the temperature rise3, 4, and whether the twentieth-century trends are anomalous within the context of longer-term variability. Here, we use the TEX86 temperature proxy, the weight per cent of biogenic silica and charcoal abundance from Lake Tanganyika sediment cores to reconstruct lake-surface temperature, productivity and regional wildfire frequency, respectively, for the past 1,500 years. We detect a negative correlation between lake-surface temperature and primary productivity, and our estimates of fire frequency, and hence humidity, preclude decreased nutrient input through runoff as a cause for observed periods of low productivity. We suggest that, throughout the past 1,500 years, rising lake-surface temperatures increased the stratification of the lake water column, preventing nutrient recharge from below and limiting primary productivity. Our records indicate that changes in the temperature of Lake Tanganyika in the past few decades exceed previous natural variability. We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery.


    As a layman, if I concur w/johnd on any point it's probably down to conclusions beyond the temperature signal indicated as the primary result of the paper but frankly my opinion on that is not worth much.

    On a tangential note, the discussion here is exemplary of how much friction is introduced when an article cannot be read in its entirety because of proprietary concerns, in this case the need for Nature to balance its books so it may continue to publish.
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  36. johnd at 06:24 AM on 24 May, 2010

    johnd, you're grasping at straws here. And why the efforts to shift the essential observations of this paper to secondary aspects?

    I noticed this paper before it was described on this site. It didn't really seem that big a deal to me. The data indicate that the very marked surface warming of Lake Tanganyika has likely produced temperatures higher than found for the last 1500 years, and that proxy estimates of primary productivity and temperature show an inverse relationship over this period (there's also an interesting mild warming temporally displaced from the Medieval Climate Anomaly that are observed in N. hemisphere temperature reonstructions).

    Those are the essential points aren't they? Otherwise the rest is interpretation. The high surface water temperatures are not really very surprising. These are well documented - e.g. see a very detailed analysis of Lake Tanganyika warming published last year [*]:

    [*] Verburg, P. and Hecky R. E. (2009) The physics of the warming of Lake Tanganyika by climate change Limnol. Oceanogr., 54, 2418–2430.
    abstract here

    Likewise Verburg and Hecky analyze primary productivity and show that this has decreased during the 20th century, and also conclude that warming may be contributing to the reduction in per-effort fish yields in the lake. Large lakes worldwide are warming in response to atmospheric radiative imbalance caused by enhanced greenhouse effect. [**] Similar data on 20th century warming and reduced primary productivity has been measured for Lake Malawi [***], etc. etc.:

    [**] Schneider, P., et al (2009), Satellite observations indicate rapid warming trend for lakes in California and Nevada Geophys. Res. Lett., 36, L22402
    abstract here

    Vollmer, M. K. et al (2005) Deep-water warming trend in Lake Malawi, East Africa Limnol. Oceanogr. 50: 727–732
    abstract here

    So the essential new data presented by Tierney et al (2010) is (i) to extend the direct measure of lake surface temperature through the last century back around another 1500 years by using paleoproxy temperature data, (ii) to document an inverse relationship between primary productivity and temperature during this period, and (ii) to highlight what looks like a mild warming period that seems temporally displaced from the N. hemisphere Medieval Climate Anomaly documented in other paleoanalyses. That's what the paper's about. It says so in the title and the abstract and the text and the Figures and their legends. The interpretation that the apparently unprecedented warming is due to global warming is pretty straightforward in the light of data from seas, lakes, land and atmosphere from 1000's of sources. It seems a straightforward interpretation that the warming "has potentially important implications for the Lake Tanganyika fishery".
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  37. johnd at 06:46 AM on 24 May, 2010

    That's really desperate johnd. If you've got a quibble with the data from the cores then define it - vague aspersions relating to some unspecified "certain graphs" and "perceived flaws" is scientifically meaningless. In any case the core proxy temperature data weren't spliced as is obvious from the Figure in the top article (and Figure 2 of the paper). The data from each core is displayed as a seperate line.

    In this case confidence in the equivalence of the cores results from the facts that:

    (i) the cores were from the same location.

    (ii) the analyzed proxies are identical.

    (iii) analysis of the core stratigraphy allowed a temporal alignment of the end of the long KH1 core with the start of the short MC1 core.

    (iv) the reconstructed temperatures during the regions of core overlap (top of KH1 with bottom MC1) are very similar.

    (v) the reconstructed productivity proxy (biogenic silica) during the regions of core overlap (top of KH1 with bottom MC1) are very similar.

    (vi) the reconstructed charcoal content during the regions of core overlap (top of KH1 with bottom MC1) are also similar.
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  38. chris at 08:28 AM, all I can suggest is that you contact the authors direct and complain that what you describe as secondary aspects, namely using the study to find any connection between declining primary productivity and rising temperatures, and the implications it has for the fisheries, has in your opinion taken the focus off what you consider the primary aspect, which appears to be of providing further proof of AGW.
    Perhaps they will issue a revision that better suits your interpretation of their work.
    Lets us all know what response you get.

    It appears as if here in this thread we see a classic example of the confusing of cause and effect, and the difficulty many have of relating their theoretical readings to the real world.
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  39. What an odd remark, coming from the person who is on record as saying has anyone happened to notice that this study is basically about fishing for sardines when the title of the paper is Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500. Why would Chris be the one to complain that someone else can't grasp what the central conclusion of the paper is despite it being in black and white?

    Chris has pointed out that the paper's central finding is entirely in keeping with much other research conducted elsewhere by other parties. Once again we're faced with what some folks claim are conclusions based on flawed data coincidentally resembling other independent findings.

    This resort to unknown, unstated defects as a counterargument is an yet another eerily familiar aspect to the paper at hand; we are expected to believe that all research in polyphony confirming what is expected as a result of predictions from physics is flawed yet produces congruent findings. How likely is that?

    This is becoming quite boring.
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  40. johnd at 08:51 AM on 24 May, 2010

    No that's just incorrect johnd; you're being far too defensive. This paper has got nothing to do with "providing further proof of AGW", and it's pretty obvious from my posts that I think no such thing. Perhaps if you relaxed the notion that every single paper has to be either a "proof" or a "disproof" of global warming, you wouldn't need to spend such efforts in attempting to trash the ones you don't like!

    This paper neither proves nor disproves global warming. What it says is that the warming of Lake Tanganyika in the last 50 years has taken the temperatures to values likely higher than during the last 1500 years. The recent very marked warming really isn't surprising given that oceans and lakes (and land surface and the atmosphere) have risen globally, especially during the last 50 years (see my post just above). Although the paper isn't specifically about global warming it's entirely appropriate to interpret the work in the light of a massive wealth of prior knowledge. After all science isn't a Hermann Hesse-like "Glass Bead Game" where measurements are made but these don't have any meaning. It's entirely appropriate to interpret the data in the light of a vast amount of prior knowledge.

    But as far as "proving global warming", you're way off the mark. Of course one can say that the data is largely consistent with what we know of contemporary and paleotemperatures both locally and globally, and the causal relationships involved with these...
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  41. Johnd @ 133. On the issue of splicing data-it's not as big a deal as you might think, it occurs all the time. As long as the splicing makes sense, & as long as the spliced data fits the same Y-axis (or uses an appropriately labeled 2nd Y-axis) then its not really a big issue. Why the splicing in the McLean paper is so controversial is (a) it didn't make real sense (why use a mix of weather balloon & satellite data, when he could have used just a continuous weather balloon record) & (b) the data used completely different Y-axis scales, but he failed to adjust either of the data sets to make the scales match. This led to a situation where the temperature graph has a significantly smaller incline than if it had been properly scaled. He also failed to acknowledge either the splice or the difference in scales to his readers. McLean then made correlations based on this incorrectly spliced graph. Now, if you can show that the splicing of data by Tierney, that you're referring to, has been done in a way that has resulted in the same kind of erroneous final product seen in McLean's paper, then please be so kind as to point it out-otherwise, as others have noted here, you're really grasping at straws.
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  42. How about we just leave it to the authors of the study whom both Chris and Doug may consider contacting, or John Cook, who posted the lead post, to clarify what were the primary questions being asked that the study hoped to answer rather than second guessing evryone.
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  43. Johnd, I especially like the "How about we just leave it" part, no further action required. :-)
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  44. So further to my above post, johnd. If the data was obtained from the same site-& if the values of measurement used the same scale (either in meters or degrees C-or both) then there is absolutely nothing wrong with splicing the data. By contrast, McLean spliced weather balloon data (which was based off a 1961-1990 average) with satellite data (which was based off a 1979-2000 average), without acknowledging he'd done so, & without adjusting the scale of either data set. Because the satellite data contained a smaller anomaly (because average temperatures are warmer) it makes it look like temperatures level off around the 1970's to 1980's. This helped make the correlation between temperature & the Ocean Oscillation Index look much stronger than it really was. So you see it was how he handled the data-post splicing-which earned him brickbats, not the act of splicing itself.
    For a more enlightening analysis, check Here
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  45. Marcus at 09:28 AM, of course it occurs all the time. My post wasn't examining the splicing of the core data itself, but examining if the same scrutiny was being applied to it as had been applied to other such instances as the temperature data you referred to with the Briffa tree ring proxy temperature reconstruction springing to mind.
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  46. Albatross (#121), Doug Bostrom (#122), Phila (#123)

    [This topic has been plagued by remarks diverging entirely away from discussion of the Tierney paper. Thefrogstar's comment while very long did not actually refer to the paper under discussion even once. After editing out the irrelevancies, all that is left is this.]
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  47. @jtierney
    "Given this long paleoclimate contexte, the recent warming really does Appear To Be Atypical for the lake."
    Looking at the combined graphs of your works - papers in 2008, and 2010, even without the use of statistical calculation to smooth the data (eg average filter, or Fourier analysis), shows excellent activity cycle of the sun - circa 6000 years (Xapsos and Burke, 2009).

    What has to rely so that "recent warming really does appear to be atypical"?
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  48. I think that "threatening" Africa's alleged harmful effects of climate change - for the people (here fisheries), finished as those for malaria: "Climate change and malaria, the global recession" - Gething et al., 20.05.2010, Nature. (I hope separate comment JC on this)
    "First, widespread claims that rising mean temperatures have already led to increases in worldwide malaria morbidity and mortality are largely at odds with observed decreasing global trends in both its endemicity and geographic extent. Second, the proposed future effects of rising temperatures on endemicity are at least one order of magnitude smaller than changes observed since about 1900 and up to two orders of magnitude smaller than those that can be achieved by the effective scale-up of key control measures. Predictions of an intensification of malaria in a warmer world, based on extrapolated empirical relationships or biological mechanisms, must be set against a context of a century of warming that has seen marked global declines in the disease and a substantial weakening of the global correlation between malaria endemicity and climate."

    I hope that this ERROR WHO, WWF, UNEP and, the parts, IPCC (here, the fact in IV report presents the question, but ...) once again makes people think about the REAL effects - "impact on humanity" - of global warming ...
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  49. I hope that people appreciate the amount of time it takes people like Chris to find and reference all the papers he brings to our attention. This allows us to read the original data and see the science develop.

    Thanks for your carefully researched posts Chris
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  50. Chris also takes the time to digest his findings and produce synopses with some useful remarks on relevance. Worth emulating, if you're claiming to have better insight than experts.
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