There’s been a somewhat unfortunate spat involving Michael Mann, Robert Wilson and Tamsin Edwards, amongst others. I don’t really want to discuss the details of the spat (Sou has a post about it that includes some interesting comments) but there is an aspect that confuses me.
The whole thing started with a post by Andrew Montford on his Bishop Hill blog about a talk, in St Andrews, by Robert Wilson. Robert Wilson discussed, in his talk, aspects of the analysis done by Mann and colleagues for their 1998 paper that introduced the hockey stick. I’m aware that there are some issues with this work but, overall, it has been heavily scrutinised and the conclusions are, mainly, that these issues don’t influence the results particularly significantly. Furthermore, it appears to have been replicated in many other studies using many different proxies (although, I believe, that tree rings do dominate).
Andrew Montford seems to interpret Robert Wilson’s talk as being quite a dire criticism of Michael Mann’s hockey stick analysis, saying
“Ultimately a flawed study” was the conclusion, with a gory list of problems set out: inappropriate data, infilling of gaps, use of poorly replicated chronologies, flawed PC analysis, data and code withheld until prised from the grasp of the principals.
The post finishes with
Away from the Mann stuff, this was, as I have suggested a very fair representation of the science of millennial temperature reconstructions, with the overwhelming impression being of a field that is still trying to work out if is possible to constrain the answers to the point where they are useful.
So, here’s my confusion. Andrew Montford has written a book called The Hockey Stick Illusion. He runs a blog on which people regularly comment about how the Hockey Stick has been debunked. He appears to interpret Robert Wilson’s talk as being largely consistent with this. Both Robert Wilson and Tamsin Edwards comment on this particular post and yet neither seem to quite clarify this issue as far as I can tell. Could it be that there is actually a possibility that hockey stick reconstructions as not as robust as I had assumed? Could it actually be that we are less certain about our past climate history than I has assumed?
In Robert Wilson’s comment on the Bishop Hill blog, he lists a series of papers, one of which is a paper on which he is an author. The paper is called On the long-term context for late 20th century warming and, like Mann, Bradley & Hughes (1998), is a northern hemisphere tree-ring reconstruction. This paper actually compares various different analyses and produce the figure below. As far as I can see, this seems to show that the various reconstructions compare quite well (including that by Mann 1999) with what is presented in this paper.
The paper does conclude with the following comments
On the basis of the above comparisons and analyses, we conclude that the RCS reconstruction is superior to the more traditional STD method with regards to the ability to retain low-frequency (centennial to multi- centennial) trends.
Okay, so the newer method is better but doesn’t fundamentally change our understanding of our past climate history.
An apparent decrease in recent temperature sensitivity for many northern sites [Jacoby and D’Arrigo, 1995; Briffa et al., 1998] is evident in our reconstructions, with divergence from instrumental temperatures after 1986 (Figure 5). There are several hypotheses for this divergence [Jacoby and D’Arrigo, 1995; Briffa et al., 1998; Vaganov et al., 1999; Barber et al., 2000; Wilson and Luckman, 2003; D’Arrigo et al., 2004; Wilmking et al., 2005], none of which appear consistent for all NH sites.
So, this is presumably the well known divergence problem. The proxy temperatures diverge from the instrumental record in the latter half of the 20th century. This either means that there is a fundamental problem with using tree rings as a proxy (unlikely given that they seem to be consistent with models and other proxies prior to the mid-20th century) or that something has happened in the latter half of the 20th century to influence tree rings. This is actually partly addressed in another paper by, essentially, the same authors called On the ‘Divergence Problem’ in Northern Forests: A review of the tree-ring evidence and possible causes. The abstract of this paper ends with Although limited evidence suggests that the divergence may be anthropogenic in nature and restricted to the recent decades of the 20th century, more research is needed to confirm these observations. So, it appears that it might be anthropogenic, but we need to do more to confirm, or not, this possibility.
Maybe the most interesting conclusion in the paper relates to the Medieval Warm Period (MWP). Their results (see figure above) is that the MWP is cooler than today. However, they quite rightly point out that if there are issues with tree-rings as proxies at today’s conditions, then this could influence how tree rings have behaved in earlier periods when it was potentially similar to today. That seems like a perfectly sensible comment. Even if the MWP does turn out to have been as warm as today, that doesn’t really imply anything with respect to anthropogenic global warming today, as pointed out in this article that refers to another of Robert Wilson’s papers.
Essentially, I can’t find anything that makes me think that there is a real concern that proxy reconstructions of our past temperature history are fundamentally flawed. There may be better ways to produce the reconstructions, but that’s progress and doesn’t imply earlier work is fundamentally flawed. We do need to understand the “divergence problem” but there are hints that it might be anthropogenic and, if not, it likely only influences our understanding of earlier warm periods, like the MWP. Furthermore, the MWP is likely not global and its existence doesn’t change that our current warming is anthropogenic.
Essentially, I would be interested to have a better sense of how confident we can be about temperature reconstructions. Are they essentially robust and a reasonable representation of our past climate history, or are there issues that maybe imply that we should be less confident about how well they represent our past climate? Admittedly the reason I’m wondering about this is because of people in this field who seem happy to comment on “skeptic” blogs without – apparently – trying to make the case that, overall, these reconstructions are robust. Having said that, I’m much more interested in knowing more about the validity of the reconstructions than about the motives of those who choose to engage with “skeptics”. If that could be born in mind when commenting, that would be appreciated.
Nor can I, which suggests that there isn’t any. Somewhat uncertain, yes. Fundamentally flawed – no.
I really should have thought of this myself, but – as suggested by Oliver Bothe – a good place to find out more is the IPCC’s new WG1 report. In particular Chapter 5 section 5.3.5 and Figures 5.7 and 5.8. Largely seems to confirm my thoughts but does illustrate some level of uncertainty about some of the details.
You can look in any decent paleoclimate textbook, eg Cronin, Ruddiman or Bender and the result is the same. There is no justification for the claim that millennial climate reconstructions are flawed and uninformative in the way claimed by “sceptics” eg Montford quoted above. It is false framing.
“Both Robert Wilson and Tamsin Edwards comment on this particular post and yet neither seem to quite clarify this issue as far as I can tell. Could it be that there is actually a possibility that hockey stick reconstructions as not as robust as I had assumed? Could it actually be that we are less certain about our past climate history than I has assumed?”
The AR5 WG1 report being quite fresh, what does it say?
But I want to talk motives, especially because, exciting as they may be for some, the details of the Holocene recons lack much policy significance, the Pliocene being where it’s at. You continue:
“Admittedly the reason I’m wondering about this is because of people in this field who seem happy to comment on “skeptic” blogs without – apparently – trying to make the case that, overall, these reconstructions are robust.”
Hmm, is there anyone aside from Wilson who fits this description completely? In any case, I would say that for certain scientists the Bishop Hill blog and similar serve their purposes, one of which is attacking certain colleagues because of professional jealousy. FYI Wilson has been going after Mike on the internet for years. The volcano paper and EGU Oeschger award, both in 2011, probably rubbed salt in whatever wound he thinks he has.
Well, some level of uncertainty, yes, but given the nature of multi-proxy recons there’s always going to be some of that.
The following post looks at a paper that shows results with and without tree ring proxies:
The AR5 WG1 has essentially answered my main question. There are some uncertainties but, overall, the reconstructions provide a good representation of our past (last millenium) climate history.
I was unaware of Robert Wilson prior to this particular situation. I was trying to avoid delving into what might be motivating people but I did find it a little odd that he seemed to have vetted the Bishop Hill post. It’s conclusions don’t seem consistent with my understanding of the robustness of climate reconstructions.
Exactly. I don’t think we can expect to be able to use proxies to precisely determine our past climate history. There will always be uncertainties. However, it does seem that proxies can give us a great deal of information about our past climate. We shouldn’t underestimate uncertainties but we also shouldn’t use the existence of uncertainties to claim that something has no value.
In the DWJ06 figure above – or the latest 2K spaghetti plot in AR5 – there are actually quite large differences in reconstructed temperature amplitude (i.e. difference from coldest to warmest parts of these records). The aim of my lecture was to communicate why some reconstructions have less or more amplitude than others. These differences ARE important for understanding past climate forcing (i.e. why do the models and proxy composites NOT agree for the timing of peak warming in the medieval) and attribution and constraining model estimates for the future. We cannot say whether one NH record is better/worse than the others, but we can discuss their strengths and limitations.
I’ll make a quick observation before I have to run off to a meeting. I’ve just had a very interesting Twitter exchange with Oliver Bothe and Kevin Anchukaitis. I learned a lot from the discussion but it may also have highlighted why someone like myself gets confused by the dialogue associated with these climate reconstructions. When I look at the literature I see a general picture that indicates that these reconstructions suggest the existence of a MWP (the timing of which may change between NH and SH), a general cooling trend to the LIA and then the modern warming. It all looks consistent. The experts, however, are aware of all the issues associated with the details. Different choices of proxies, different statistical methods, fine details in the actual reconstructions themselves. Hence maybe the experts are willing to accept the criticisms of “skeptics” because they’re aware of all these issues.
However, what I conclude from my discussion with Oliver and Kevin is that none of these details are likely to change the general picture that someone like myself takes from these reconstructions. If the “skeptic” criticisms are indeed aimed at these details, then maybe their criticisms are valid. However, it seems to me at least, that a lot of the criticisms from “skeptics” are aimed at undermining the general picture being provided by these reconstructions. So, in a sense, maybe the experts are too willing to accept these criticisms (or maybe they’re actually unaware of them) and the debate might benefit from a clearer picture of what it is reasonable to criticise (the details) and what we should probably accept as being quite robust (the general picture).
I hope I’ve properly represented the discussion I had with Oliver and Kevin. It was certainly a very interesting and worthwhile discussion (from my perspective at least).
I would like to read your answer to the following question:
“Admittedly the reason I’m wondering about this is because of people in this field who seem happy to comment on “skeptic” blogs without – apparently – trying to make the case that, overall, these reconstructions are robust.”
Do you think that overall, the reconstructions are robust? If so, have you made that clear in your engagement with “skeptics?”
Rob, thanks for the comment. I gather this is similar to what Tamsin was suggesting in the other paper that you highlighted. Indeed, it would seem very useful to use these reconstructions to better constrain model estimates for the future.
The issue that I was trying to get across in the post (maybe not all that well) is a confusion about the significance of the uncertainties. As an outside observer what I see are reconstructions that seem broadly similar. A medieval warm period (although the magnitude and timing – NH vs SH – may be uncertain), a cooling towards the LIA, and the modern warming. So, overall, the general picture seems robust. I then see “skeptics” being critical of reconstructions to the point where it appears that they are trying to suggest that there is so much uncertainty in these reconstructions that they really don’t tell us much (as per the end of Andrew Montford’s post). Rarely, however, do I see this being challenged (or, at least, not very successfully).
So, I guess my question to you is whether or not my general impression is correct (i.e., the general picture presented by reconstructions is largely robust) and, if so, shouldn’t a little more effort be put into clarifying what it’s reasonable to be uncertain about (the details) and what we should really be willing to accept (the overall picture).
wotts, if proxies do not capture the amplitude of centennial scale variability in the past, they may not be a reliable guide to similar present-day variability which may be super-imposed on whatever additional influences that are postulated to occur.
So CO2 forcing doesn’t exist?
Shub, I would agree if there was evidence to suggest that that were indeed a problem. From what I’m reading, it’s not. They appear to be confident that they’re capturing the temperature history on scales of about 30 years (based on reading WG1 Section 5.3.5).
Having said the above, however, this seems like an ideal opportunity for someone who is actually an expert in this to comment as to whether or not your comment is a valid criticism/issue with these reconstructions or not (or, how much of a problem it is expected to be).
I think that’s a fair assessment of the conversation, limits of 140 characters and all. As I said on Twitter, the general shape (long term cooling to the LIA, some sort of MCA ~similar or cooler vs 20th century, modern warming) emerges consistently from these type of studies. But as Rob indicates above, many of the important details are still uncertain to varying degrees, and for many of us the details matter quite a bit — I think I listed these as: amplitude of the multidecadal to centennial changes, choice and assumptions and consequences of methodology, seasonality, spatial skill, time uncertainty in lower resolution proxies, consequence and procedures for proxy ‘screening’ and selection, spectral fidelity and biases, stationarity and linearity, uncertainty estimation, sample size and representativeness particular before 1400 CE, spatial representativeness overall with respect to the tropics and oceans and southern hemisphere, divergence and detrending in dendrochronology, and a general understanding of proxy formation and biases (including forward modeling and process understanding, which Tamsin also alluded to on Twitter). Which of these ‘details’ are important depends on the question you want to ask. If you’re just interested in the general historical shape of the Common Era global mean temperature, many of these might not matter too much; however, and as Rob says above, if you’re interested in the response of the climate system to changes in radiative forcing, the spatial fingerprint of internal climate variability, the range of natural climate variability, the spectrum of variability in large-scale temperature, questions of seasonality, making probabilistic statements about trends or individual years, etc. some/many of these will become important to your ability to answer those questions within a certain degree of confidence. This doesn’t mean (to me at least) that we throw up our hands and give up; rather, we try and assess how right or wrong we might be and we work to improve our understanding of all those ‘details’.
Therein lies the difficulty in responding to many of the statements made online (Twitter or blogs) either in support or against the millennium large-scale temperature reconstructions. It is equally as difficult to respond to statements like ‘The [millennial reconstruction/s] are right!’ as it is to respond to ‘The [millennial reconstruction/s] are wrong!’ — to riff off of George Box, all of the reconstructions are likely to suffer from some of detrimental effects I describe above — the question is, does it matter? The answer to that question depends on the purpose to which you’re putting them, and ‘yes’ or ‘no’ is only the first step.
That Tamsin Edwards does not comment on the hockey stick seems natural to me. She is no expert in paleo climatology.
That would be similar to making comments on policy. 😉
What is meant by robust?
Yes – all the reconstructions express the same basic shape: a warmer medieval period, a cooling transition into the LIA, and then warming over the last century or so.
Is that any different from what we “knew” say 20 years ago? No – not really.
So – what are the issues. My opinion:
1. We need better estimates for the Medieval period – at least from a tree-ring point of view, there is very little data for the Medieval although the non-tree-ring composites are in general agreement with the timing.
2. Why was the Medieval warm – was this warming spatially consistent? What was the dominant forcing? Not the sun as peak solar activity is > 100 years after the peak in reconstructed temperature around 1000 AD.
3. On a related note, why do the models and large scale reconstructions not agree prior to 1300? Is there some aspect of internal variability that the models are not capturing well? Is that why the models don’t capture the current slow down well?
4. The paleo-community needs to come to grips with the differing “flavours” of NH reconstructions – see the latest AR5 spaghetti plot. The differences are related to methods, proxy processing methods, seasonal differences, proxy replication etc, but there is certainly scope for improvement as new records are developed and are added to the pot.
Like the “divergence issue” in dendrochronology, the so-called “slow down” just highlights that we don’t have all the answers. Interesting times I say!
time to disappear back into obscurity.
Thanks, Kevin. I think I have learned something that I hadn’t appreciated. I’ve been looking at these reconstructions as just simply a history of temperatures for the last millenium which indicate that we are likely warmer today, than we have been for last 1000 years (maybe longer). If we aren’t actually warmer today, then we will soon be. I believe that this is a fair conclusion to draw.
What I hadn’t appreciated is that there is a desire (quite rightly so) to use these as a way of determining how the climate system responds to forcing, internal variability etc. I can see how this would indeed be valuable, but also how complicated and difficult this is likely to be. I guess I still have the concern that some are using these uncertainties to undermine the whole picture but I can also see how difficult it is to address this.
Thanks, Rob. That does answer my question and does indeed seem to be the same as what we know 20 years ago. Maybe some people just need reminding of this every now and again 🙂
I do appreciate, though, that something I have misunderstood is the subtleties associated with this work. The details are important and there are clearly very interesting question that can still be answered. That’s what makes science interesting. It’s just unfortunate that there still seem to be some (including some in the media) who regularly roll out the claims that the “hockey stick” has been debunked. Maybe this is intended to apply to the details rather than the general picture, but the intent is almost certainly to suggest that these reconstructions are not correct. Quite how this is addressed, I must admit that I don’t really know.
Maybe that’s a fair comment. I thought though that Tamsin had an interest in using the reconstructions to constrain some of the climate responses though. I may, of course, be wrong 🙂
You might be interested in this:
Frank et al. 2010, A noodle, hockey stick, and spaghetti plate: a perspective on high-resolution paleoclimatology, WIREs Clim Change, 10.1002/wcc.53.
(Google Scholar will lead you to a free PDF. Note the et al. includes Rob Wilson).
While now naturally a bit dated, it is a nice discussion of the progression of large-scale temperature assessments over the last few decades, including discussion of some of the same issues raised in comments above.
Just had a look. You are right. I only knew her work on the cryosphere, but her first paper after her PhD was about the use of paleo information to constrain climate sensitivity. That at least makes her a much bigger expert as I am.
Was the model-T ford, the first car to achieve mainstream success, a bad car? No air-conditioning, no anti-lock brakes, no air-bag, and only available in black – but revolutionary.
Was the ZX80 Spectrum, one of the first home computers, the perfect computer? Hardly with 1kb of RAM, but it inspired a generation of computer coders.
Likewise it would be remarkable if there were not some issues with Mann et al (1998), the first attempt at something new can usually be improved on.
There are two significant narratives here, one confined to a relatively small group of researchers and another encompassing a much larger and mostly passive audience, the latter of which has bigger implications beyond satisfying our natural curiosity.
Something to bear in mind is that Andrew Montford’s objective is not to be part of the first narrative, that of the conversation among peers, but instead to be an author of another story, as story being being told to the public and one not bounded by scientific inquiry.
People playing a peer role in the first narrative who don’t stop to think about the other, separate story being told are at risk of blundering from one narrative thread to another. Montford’s narrative is not a pleasant place to be and as well is a place where damage can be caused by the most innocent of remarks, if those remarks are repurposed. And we know that innocent remarks will be recast into a more sinister light. We have lots of history around conversations being plucked from one narrative and thrust into another.
Here is the result of Montford’s story weaving, as it’s emerging even now thanks to Montford’s mining of academic conversation for purposes of enhancing the impression he’s promoting:
That’s a quote from some poor, hapless person who’s mind has been twisted, popping up at a mariner’s blog and trying to make a case that Arctic sea ice is in a normal condition. The “dendro is crap” fallacy is surging now; there’s a signal rippling from Montford’s story.
See how Montford has stripped all the worth from dendrochronology in the minds of his audience? Montford effectively (in more than one sense of the word) conveys nothing about teasing more details from dendro records; the payload delivered to his audience is a message that dendrochronology is worthless.
It’s hard to say how to inoculate the minds of the general public from malicious work such as Montford’s. Obviously academics must be able to have free and easy discussion, including cursing at one another and describing work in colorful language, but that entirely natural repartee is at the same meat for people such as Montford in their pursuit of extra-scientific objectives.
Yes, I think is what I’m discovering through the various comments and exchanges. There are, not unsurprisingly, aspects of the reconstructions that are still uncertain and could be improved. Seems like a normal part of a complex science. This, however, appears to be being used by Montford and others to suggest that there are serious issues with the general picture being presented by these reconstructions.
I must admit that although I have learned a lot through the various exchanges around this topic, I’m now slightly more confused about how one deals with the existence of these two narratives. Scientists obviously want to be open about uncertainties in their work. This then seems to provide ammunition for those who want to make more of these uncertainties than is probably reasonable. Deciding where to draw the line is, however, maybe harder than I had thought a day or two ago.
I agree about the two narratives.
This it the kind of narrative promoted by the “skeptics”:
Anthony Watts: IPCC throws Mann’s Hockey Stick under the bus?
“Bishop Hill points out what was said in IPCC’s AR4 in 2007:
Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years.
So, they’ve gone from saying warmest in the last 1300 years to the last 800 years. Where does that figure in on Mann’s hockey stick graph from AR3 in 2001?
So basically what they are saying is that at the year 1200 (2000AD minus 800 years), temperatures were warmer (or at least equal to) temperatures today.
This is curious, because it looks like we are back to what the IPCC said in the first report in 1990. Notice the bump, peaking at 1200AD: [Image with Huber Lamb’s graph from FAR]”
This is miles away from the issues that Robert and Kevin (among others) mention above.
Indeed, I’m always surprised that this keeps coming up. Well, I guess I’m not really surprised by anything anymore, but what you say seems fairly obvious to me.
“Disinformation” as the process not only of providing wrong information but nullifying useful information already present. 🙂
Note that the origin of this particular flavour of the “skeptic narrative” is the blog “Bishop Hill” by Andrew Montford.
And here is a little cartoon by Josh, hosted by Montford.
Near the start of his article, Watts writes:
As it happens, the quote with additional “bloat” reads:
You will notice the additional information about the period to 1400 years. Given that the point of Watt’s post is the difference between the 1300 years in AR4 and the 800 years in AR5, the mention that the temperatures averaged over the last thirty years are “likely the warmest 30-year period of the last 1400 years” is hardly bloat, and very relevant. Indeed, in the AR4 technical summary, we learn that:
So relative to AR4, AR5 extends the “very likely” (90% confidence) period back 300 years from 500 to 800 years ago, and the “likely” period (66% confidence) back 100 years from 1300 to 1400 years ago. At the same time, it reduces the comparison interval from 50 to 30 years, a reduction which strengthens the result given that shorter periods are likely to show more variability. Watts’ portrays this as a weakening of the result.
It should be noted that Watts’ comment that his quote is “a fair summary” indicates that he has compared his quote to the report. He cannot hide behind the inaccurate quotation of others.
I am sure Shub will be forth coming with a post on misquotation by Anthony Watts any time now …
In the “millennial large-scale temperature reconstructions are wrong’ department, have any of the paleo research groups attempted to reconcile their work against that of the paleo sea level research?
Sea level is rising in a globally-coherent manner including the low latitudes – allowing for the confounding effects of gravitational loading and the movement of water mass due the the current phase of the ocean circulation. But from the Holocene Climatic Optimum to the onset of the Industrial Revolution sea level was falling in the low latitudes. The tropics are littered with “3 metre beaches” – beaches that reveal sea level was 3 metres higher than present earlier in the Holocene.
This suggests a static ocean volume, with sea level in the low latitudes (away from the rebounding effects of the ice sheets) falling due to the subsidence of the ocean basins and the consequent siphoning of seawater to fill these regions. Sea level, and therefore global ice volume, throughout the Holocene is incompatible with paleo temperature reconstructions which have global warmth approaching anything near that of today.
I’ll just add, only two of 71 comments point out this obvious error by Watts at WUWT. Of those, one is from the author of the blog from which Watts obtained his original, and misinterpreted quote. For his efforts at correcting the record, he receives no thanks, but cops some abuse from WUWT regulars.
And they call themselves “skeptics”.
Rob Wilson, for the record, does Andrew Montford fairly represent the contents of your lecture?
Shub’s argument would be less ridiculous if the only climate history we knew was the late Holocene. That’s why denialists love to focus on it so much.
Also, Wotts, in the course of the above exchange you appear to have let Wilson off the hook for playing politics with Montford. What Wilson and Edwards have done is intentional damage to the needed progress on climate policy, and that should not be ignored or forgotten. By all means be collegial, but don’t forget that a line has been crossed.
Steve, I may well have let Rob off the hook a little. Maybe I shouldn’t but if someone I discuss in a post is actually willing to comment then I do try to avoid the discussion becoming too confrontational. I would hate the site to become a place where I can criticise someone in a post and they felt that they couldn’t comment because they would then be attacked. So, maybe Rob wasn’t challenged by me as much as maybe he should have been, but we got something out of it (I think).
This is very difficult. I agree with Steve, and I agree with Wotts’ decision to avoid the overtly confrontational. Personally it makes me despair every time scientists play with/into he hands of the contrarian spinners. Whether this is naivety or calculation, I wish to f*** they would not do it.
Deniers ascribing the term “skeptic” to themselves has got to be one of the biggest misrepresentations and misuse of any word in the English language.
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“Could it be that there is actually a possibility that hockey stick reconstructions as not as robust as I had assumed? Could it actually be that we are less certain about our past climate history than I has assumed? ”
You bet there is. Scientists, and science publications, are not error-free, and even major conceptual or math/stat errors can persist for a long time.
Just look at those reconstruction curves in the figure. Not only do they (1) differ, obviously, from each other, but (2) the sum thereof is does not represent even close to the full story of the total uncertainty of estimate. Certain scientists (a small but aggressive and untrustworthy group) have created such a huge problem: they have not given an accurate account of the full uncertainty of the system, and this cannot but get them in trouble. There are only two possible reasons for this: (1) they themselves don’t understand the full set of issues involved, or (2) they understand the issues but are not honest about disclosing them. Neither is acceptable, although the second is far worse, because it involves conscious deceit, not just incompetence. For the purposes of setting the science right, which we might reasonably consider to be our first and main objective, we can ignore which of the two is the case, and focus efforts on taking full account of this uncertainty, and then setting about finding legitimate ways to reduce it. That’s what scientists are supposed to be doing.
Dendroclimatology, upon which many reconstructions are based, is between a rock and a hard place right now, because it is forced to admit that its analytical procedures are insufficient to the task for which they have been applied. The field’s been presented with very damning evidence on this point, but have either ignored or rejected it, to a man (with the possible exception of Rob Wilson). Those evidences are (1) Loehle (2009) and (2) the series of 14 posts at my blog on why existing dendro analysis methods cannot accurately recover a long term trend if there is one.
It’s not nearly as much of a white vs black hats issue as some would have us believe. Anybody who has an understanding of the basics of the biology, and the relevant statistical and mathematical procedures, can see the problems. Quickly. Readily.
Please read this stuff:
And please drop the anonymity.
Jim, I will certainly read what you’ve presented. Why would you care whether I was anonymous or not? Any particular reason? I can’t see any real benefit at this stage and am not sure how my anonymity is harming anyone else.
That’s a fair point; I probably shouldn’t worry about that.
Jim, maybe you can clarify – to a non-expert – the implications of what you’re suggesting. My impression from the comments here (including from Rob Wilson) is that the broad picture is roughly correct. A Medieval Warm Anomaly, a gradual cooling, the recent warming. There are some issues with the divergence which may have implications for the MWA. There are also issues with respect to uncertainties. However, the broad picture is agreed and is unlikely to change. Is what you’re suggesting that this may not be true, and that our understanding of the climate of the last millenium could be completely wrong, or are you referring to details that would be relevant for an expert or that might have implications for some of the details, but not to the broad picture?
The implications are very serious indeed. No bones about it.
If I remove myself from the picture for a moment, so as to avoid accusations of attention seeking, Loehle’s paper alone is an *extremely* important piece of work. Why? Because (1) it’s based on a very well known and fundamentally important principle of biological response to temperature, and (2) it’s very clearly written and to the point, and demonstrated with simple but very clear mathematics. If anything, he under-sells the issue by referring only to the divergence phenomenon in the title, which is commonly associated with the latter 20th century, where in fact he is describing a more general problem that can occur at any time in a reconstruction. It’s as close to a full conceptual failure as you can get, it really is. I could write pages on this topic. So could Loehle, I guarantee that.
The degree to which existing, dendro-based reconstructions are in error at longer timescales (e.g. century and longer) is impossible to say, for multiple reasons. And that itself is a big problem–we don’t have a good handle on the uncertainty. For this reason, I don’t agree with Rob Wilson, or anyone else for that matter, who says that we have a good handle of the dynamics over the last 1000 years or whatever. A bunch of smoothed spaghetti strands, that are in no way coincident with each other, but which supposedly estimate temperatures mostly lower than the current, is not my idea of high quality science, to say the least. And that would still be my conclusion even if the methods that created each strand were uniform and well accepted, which they most definitely are not remotely close to. Indeed, one of the real nightmares and time sinks in reading tree ring based reconstructions, is the time spent trying to figure out just exactly what the authors did; I often never really get there. Some of it’s just unreadable frankly.
There’s another very important point here. I wandered into the climate change debate about four years ago, fully trusting that the science was basically sound–because as a scientist I too have a basic trust in the system, overall. And indeed, I still think most of it *is* sound. But now it’s specifically that part of it which is based most highly on well understood physics and chemistry. I don’t know Craig Loehle–never met him, probably never will. But I do remember reading ecology papers by him in grad school, some of which were quite good. I do know why his paper on the topic is being ignored though. And it’s not for reasons that are valid, I can tell you that.
The fundamental fact of the matter is this: estimating climatic parameters from biological growth processes is highly problematic, conceptually, for several reasons. Gloss it over at our own peril. But don’t expect others who know something about it to give you a free pass on it.
Dendroclimatological proxies are only one among an array of proxies used in millennial reconstructions. Surely if there were serious issues with them it would be very obvious as they would be in disagreement with everything else. At which point, the shortcomings would be acknowledged in the literature.
I believe there are serious issues with the Loehle study. Julien Emile-Geay sets them out here.
For these two reasons I am unwilling to regard the millennial climate reconstructions as uninformative.
BBD, do you think you’re telling me news when you say there are other proxies besides tree rings?
Your objections are just the ones typically repeated in these discussions, and are not correct. Specifically:
1. The post is about tree ring-based reconstructions, hence the points I made.
2. Tree rings form the basis for the vast majority of high temporal resolution reconstructions of surface air temperature, for the terrestrial biosphere no other proxy comes close in importance for the last millennium or two.
3. Each proxy has it’s own characteristics and is applicable to a certain type of environment. They are by and large not comparable with each other. If the different tree ring recons, which sample the same environment at the same temporal resolution, are not telling us the same story, then how much confidence are we supposed to have in comparisons of them with other proxies, which do not sample the same environment in the same location at the same resolution?
4. Use of the term “surely” before the fact is a great way to get yourself into trouble.
5. A simple click on the link I gave would have told you that I was not referring to Loehle’s temperature reconstruction, but rather to his paper on unimodal ring responses and the consequences thereof for temperature reconstructions from tree rings.
6. You might want to consider that some scientists might have a vested interest in promulgating particular interpretations of the data at the expense of more inclusive considerations. See the link that Kevin Anchukaitis gave on that issue, above, the paper by Frank et al.
If Loehle were not a regular speaker at Heartland conferences, I might be more inclined to pay attention to him, and to accord your (6) some weight. But he is, so I will do neither.
Something tells me this conversation is going to be unfruitful. Your insistence on the predominant role of dendro proxies in millennial reconstructions being top of the list. I think this is your hobby horse and I do not feel like standing here watching you ride it around.
“If Loehle were not a regular speaker at Heartland conferences, I might be more inclined to pay attention to him, and to accord your (6) some weight. But he is, so I will do neither.”
Brother, I really don’t care what you think or do and I sure as hell am not going to waste my time discussing it with you, because you don’t have any idea what you’re talking about and probably even less desire to learn.
I’m afraid I’m going to have to disagree completely. Some points:
* Starting with Mann et al 1998, the quantification of uncertainty has been a central element in (most) paleotemperature reconstructions – Loehle, I’ll note, being an exception in its lack. Claims that the uncertainty in those is vastly under-reported is not supported by the literature, and argument by assertion continues to be a logical fallacy. If you disagree with the stated methods for and estimates of uncertainty, perhaps you could point to the published peer-reviewed work indicating that? Note that I consider claims regarding “gate-keeping”, grants, or group-think holding back such work to be conspiracy nonsense.
* The divergence problem you have referred to has been discussed quite broadly for almost two decades. While it adds to the uncertainties in tree-ring proxy reconstruction, it does not invalidate them. And it is wholly irrelevant to non-tree-ring reconstructions that agree with the tree-ring reconstructions over the common periods (Mann et al 2008).
* Accusations that the vast majority of scientists are either incompetent (999 of 1000 times, if you disagree with all the experts, _you_ are wrong – the Galileo fallacy), or duplicitous (documentably wrong, as per the numerous independent investigations of the original Mann et al paper and the multiple works in agreement) – these are insulting, in poor taste, and are in fact counter-evidence. If your argument requires unsupported ad hominem claims of idiocy or deception, it’s a pretty weak argument.
Are tree ring reconstructions perfect? By no means. Do the known issues with a single proxy invalidate all work with them, let alone unrelated proxy measures? No, they do not,
Addendum to my previous post:
Current works on paleotemperature reconstructions are by no means the last word – not as long as new papers on the subject get published. If you feel the current literature is _wholly invalid_, however, you will need evidence supporting your point. You will need to show where previous authors went wrong, and support your own (and hopefully better) reconstruction based on the evidence (something McIntyre has failed to do over the last decade, oddly enough). In short, you need to put in effort on a similar scale, and make an argument sufficient supported to convince those familiar with and working in the field.
Argument by assertion, by ad hominem, and by claiming (possible) issues with one data source invalidate unrelated proxies? That fails to prove anything.
Pay attention KR, whoever you are, because I’m only going to write this once.
1. I don’t make these statements lightly and without good reason.
2. I don’t give a damn about regurgitated, generalized statements about what is and is not valid on the issue from some anonymous internet poster who likely has no background in the area.
3. You have **no** idea how much work and thought I’ve put into this issue, but you can get a decent idea by reading the series at my blog, should you actually have any interest in understanding the issues, which I pretty seriously doubt you do.
Read the stuff that I (and Anchukaitis) linked to if you really want to understand the issues I’m raising.
“Accusations that the vast majority of scientists are either incompetent (999 of 1000 times, if you disagree with all the experts, _you_ are wrong – the Galileo fallacy), or duplicitous (documentably wrong, as per the numerous independent investigations of the original Mann et al paper and the multiple works in agreement) – these are insulting, in poor taste, and are in fact counter-evidence. If your argument requires unsupported ad hominem claims of idiocy or deception, it’s a pretty weak argument.”
Dude, you are 100% clueless.
I’m merely pointing out the unreasonable accusations in your post here. To quote:
“There are only two possible reasons for this: (1) they themselves don’t understand the full set of issues involved, or (2) they understand the issues but are not honest about disclosing them. Neither is acceptable, although the second is far worse, because it involves conscious deceit, not just incompetence. “
Dude, that’s what you claimed – mass idiocy or deception. Such claims, unsupported as they are by your posts, are ad hominem fallacies.
A quick look through your academic website and Google Scholar reveals only one relevant AGU poster presentation of yours on the topic – nothing that has entered the literature as a whole for critical review. You have pointed to no other support beyond your own blogs and Loehle’s problematic reconstruction (lacking in statistics, in error bars, and even proper area weighting of his few proxies) to support your assertions. While your poster’s calibration methods are quite interesting, they seem as yet unproven. Perhaps a reconstruction effort of your own, checked (as others have done) against independent proxies? Or an article submitted to a relevant journal?
Instead, you have attacked others in the field, and dismissed volumes of work by assertion. Not only is that unconvincing, I find it predisposes me to take any actual science you might present with a serious grain of salt, and a very careful examination, before accepting any of your arguments.
KR, like most in this debate who don’t actually understand things, you are pre-disposed to believe what you want to believe. The rest of it’s just excuses and rationalizations and I really don’t give a damn what you think. At all.
Coampare and contrast:
(1) X is wrong because he’s either Y or Z.
(2) X is wrong because of A, therefore he’s either Y or Z.
In the two cases, there’s an ad hom, but only in 1 could there be the fallacy you claim Jim commits.
Jim does not say 1.
Jim, never attribute to malice what can be attributed to misconception.
I also have a question. You seem to say that there’s a conceptual failure in dendrochronology. This sounds like a proof. Do you claim there’s such a proof?
If you could refute dendrochronology, more power to you. Is that what you’re aiming, or am I reading you too categorically?
Rob Wilson – “Is there some aspect of internal variability that the models are not capturing well? Is that why the models don’t capture the current slow down well?”
Just noticed this comment after reading the heated exchange going on above.
Yes Rob, the models as a whole tend to underestimate the variability of the tropical easterly trade winds and mid-latitude westerlies which drive the export of surface water out of the tropics, and the downward mixing of heat into deeper layers via the subtropical ocean gyres. There is quite a collection of published scientific peer-reviewed literature on this topic.
And for the benefit of readers, please note he is referring to surface air temperatures only. The accumulation of heat in the climate system, especially the ocean, has actually increased in the last 16 years when compared to the previous 16.
Rob Painting, thanks I’d missed that too.
Why would Craig Loehle speak at a Heartland Institute conference? Is there a reasonable explanation for this?
I have one other question. The recent Marcott reconstruction uses a variety of proxies – I think – is it considered to be as flawed (by the people here who think they’re flawed) as the ones using tree rings only? If not, then didn’t it find the same general pattern emerge and wouldn’t that seem to support the tree ring analyses?
And there’s the PAGES2K which I also thought was multi-proxy.
Rachel – Loehle is a contrarian. It’s a logical choice for him. Which is not to say that the study referred to by Jim Bouldin has no merit. I haven’t read it, and am unlikely to. Maybe someone else might care to illuminate its key points?
Loehle published a flawed millennial temperature reconstruction in Energy & Environment, then got into bed with organised denial, speaking at the Heartland conferences in 2009 and 2012 as well as allowing that organisation to list him as an “expert”. That goes beyond mere contrarianism. That is a political statement. And that’s enough for me.
People riding their hobby-horses is fine. People lining up with the industry-funded denial machine is not. The former can be done through publication in the reviewed literature – and Loehle didn’t even do that.
Mann08 vs Marcott 13 (sediment cores)
PAGES-2k vs MBH99
I want to say something else here about the relevance – or lack of it – surrounding the fuss over dendro proxies and millennial reconstructions. I don’t think it matters nearly as much as contrarian opportunists and professional disinformers would have us believe (and no, I certainly don’t think Jim Bouldin is one of these).
The exact nature of the MCA is interesting in its own right but has no bearing on future anthropogenically-forced climate change. None whatsoever. Unfortunately, the contrarian opportunists and professional disinformers – perhaps unwittingly aided by the owners of hobby-horses – have made a huge and distracting fuss about this with the sole and partially successful aim of creating an impression that the fundamentals of climate science are uncertain and even flawed.
I personally would not aid and abet such a politically and financially motivated endeavour and I get very angry with those who do because they have failed to see that their actions have wider consequences. They fail because their egos have clouded their wider judgement and they need to be reminded of the context in which they operate frequently and forcibly.
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