One of the very first contributions to realclimate was an FAQ from Jeff Severighaus on Dec 3, 2004. A year earlier, Severinghaus attempted (unsuccessfully) to get an explanation of the “divergence” problem from Mann and the rest of the Team. Severinghaus had become interested in the question following a presentation by Tom Karl of NOAA in which he had used a figure from Briffa and Osborn 2002, in which he wondered about the “flat” response of the tree ring proxies in the last half of the 20th century.
In nearly all defences of the deletion of the decline in spaghetti graphs that yield a rhetorical effect of coherence between the Briffa and other reconstructions in the last half of the 20th century, it’s been argued that the divergence problem was fully disclosed in a couple of 1998 Briffa articles and that this disclosure in the original technical literature constituted sufficient disclosure – a point that I contested long before Climategate.
The Severinghaus exchange is highly pertinent to this issue. Severinghaus was a climate scientist who was not a specialist in the area who asked specifically about a diagram in which the decline had been hidden (though Severinghaus was unaware that the decline had been hidden.)
Severinghaus was concerned merely by the flattening of proxy response. One can only imagine how the exchange would have read had Severinghaus been aware that the Briffa reconstruction actually declined sharply. Read and see whether Mann, Jones and/or Briffa drew Severinghaus’ attention to the early articles in which the divergence problem was disclose.
On the afternoon of Feb 1, 2003 California time (emails -2545, 19, 4355 Feb 2, 2003 00:15 GMT), Severinghaus wrote to Tom Karl of NOAA about his presentation at the MIT Global Change Forum the previous day. Severinghaus asked about the “flat” response of tree rings to late 20th century warmth, referring to an article by Briffa and Osborn in Science (2002). The diagram in question would be the following:
Figure 1. Briffa and Osborn (Science 2002) Figure 1.
Severinghaus observed that this lack of response is an “embarrassment” and that it “casts doubt on the integrity of the proxy”:
Subject: tree rings and late 20th century warming
Date: Sun, 2 Feb 2003 16:15:04 -0800
From: Jeff Severinghaus
to: Thomas.R.KarlDear Dr. Karl,
I enjoyed your presentation yesterday at the MIT Global Change forum. You may recall that I asked about the failure of tree rings to record the 20th century warming. Now that I look at my records, I realize that I remembered this wrongly: it is the LATE 20th century warming that the tree rings fail to record, and indeed, they do record the early 20th century warming.If you look at the figure in the attached article in Science by Briffa and Osborn, you will note that tree-ring temperature reconstructions are flat from 1950 onward. I asked Mike Mann about this discrepancy at a meeting recently, and he said he didn’t have an explanation. It sounded like it is an embarrassment to the tree ring community that their indicator does not seem to be responding to the pronounced warming of the past 50 years. Ed Cook of the Lamont Tree-Ring Lab tells me that there is some speculation that stratospheric ozone depletion may have affected the trees, in which case the pre-1950 record is OK. But alternatively, he says it is possible that the trees have exceeded the linear part of their temperature-sensitive range, and they no longer are stimulated by temperature. In this case there is trouble for the paleo record. Kieth Briffa first documented this late 20th century loss of response.
Personally, I think that the tree ring records should be able to reproduce the instrumental record, as a first test of the validity of this proxy. To me it casts doubt on the integrity of this proxy that it fails this test.
Sincerely,
Jeff
Severinghaus obviously didn’t know that the Briffa and Osborn diagram had deleted the post-1960 decline from the Briffa reconstruction. Had they shown the actual data, the diagram would have looked more like the one shown below.
Figure 2. Briffa and Osborn 2002 Figure 1, showing deleted portion of Briffa reconstruction in dark blue.
Had Briffa and Osborn shown the decline, instead of Severinghaus wondering about the “flat” response, he would presumably have been asking about the sharp divergence between the Briffa reconstruction (based on a very large population of sites identified ex ante as temperature limited) and the Mann reconstruction (based on bristlecones).
At 12:49 GMT (7:49 am Eastern, emails 19,2545,4355) Karl forwarded Severinghaus’ message to an email list that ultimately involved (during the single day) Chris Miller of NOAA, Verardo of NSF, Mann, Bradley, Hughes, Briffa, Jones, Wally Broecker, Ed Cook and R.F. Weiss of UCSD. Karl asked:
Colleagues,
Correct me if I am wrong, but I always thought the failure was a lack of tree cores subsequent to the 1980s. Please correct me if I am wrong, and if Jeff is correct, then indeed we have a significant implication.
Tom
At 14:15 GMT (emails 19, 2545, 4355), Mann denied admitting that the divergence problem was an “embarrassment”, referring back to an EGS meeting of 2002. Mann stated that they had discussed the issue “time and again in our own work” [SM – offhand, I can’t recall a clear discussion of the issue in Mann’s work to that date: dig here].
Dear Tom,
Have no fear, Jeff has still got his facts wrong, even after going back and checking once…First off, I never made any such comment to Jeff–he clearly misunderstood comments that I made at EGS a year ago in response to a question he asked. Of course, it is well know that there are a number of competing explanations [this is what I said–to quote this as offering “no explanation” is a bit unfair Jeff, don’t you think? As I recall, I even invited Tim Osborn in the audience to add his own comments–but he had little to say] for the fact that *high latitude*, primarily *summer responsive*, tree-ring *density* data have exhibited a noteable decline in the past few decades in the amplitude of their response to temperature variability. We have discussed this issue time and again in our own work, and Keith Briffa, Malcolm Hughes, and many others have published on this, w/ competing possible explanations (stratospheric ozone changes, incidentally, is the least plausible to me of multiple competing, more plausible explanations that have been published). See e.g.: Vaganov, E.A., M.K. Hughes, A.V. Kirdyanov, F.H. Schweingruber, and P.P. Silkin, Influence of Snowfall and Melt Timing on Tree Growth in Subarctic Eurasia, Nature, 400 (July 8), 149-151, 1999.
Mann re-iterated that the MBH reconstruction tracked temperature well to 1980 and blamed Severinghaus for “only looking” at Briffa and Osborn 2002 which “doesn’t properly align the 20th century means of the various reconstructions and instrumental record”.
It should *also* be noted that we used essentially none of these data in the multiproxy Mann/Bradley/Hughes (MBH) reconstruction, and that the MBH reconstruction tracks the instrumental record quite well through the very end of our calibration interval (1980–it stops then because there are far fewer paleo records available after 1980). This was shown in our 1998 Nature article quite clearly, and of course remains true today. Jeff made the mistake of only looking at the Briffa & Osborn paper, which doesn’t properly align the 20th century means of the various reconstructions and instrumental record.
As so often in Team discussions, Mann’s answer was unresponsive to the issue: Severinghaus was wondering about the failure of late 20th century tree rings to track increased temperature – this has nothing to do with alignment of the mean, but with the slope of the various curves. Mann continued with a reference to the “recent high-latitude decline issue” – note that Severinghaus had not actually mentioned the decline – saying (incorrectly) that these had been “discussed in IPCC” (they hadn’t – quite the opposite).
An appropriate alignment of all the records is provided in IPCC, and in the attached Science perspective from last year. This shows how well the Mann et al reconstruction (and several model-based estimates) track the entire instrumental record. There are some good reasons that some of the other purely tree-ring based reconstructions differ in their details, in addition to the greater influence of the recent high-latitude density decline issue, and these are discussed in IPCC and the Science piece.
Mann then asserted that MBH98 had provided “provided detailed calibration and verification statistics that establish the skill in our reconstruction” together with uncertainties calculated using “rigorous analysis of the calibration and cross-validation residuals”.
Of course, we have in, our own work provided detailed calibration and verification statistics that establish the skill in our reconsruction in capturing the details of both the modern instrumental record, and independent, withheld earlier instrumental data (19th century and, more sparsely, 18th century), and we publish uncertainties that are based on rigorous analysis of the calibration and cross-validation residuals. I know that Jeff has seen me talk on this many times, and probably has read our work (I would hope), so I’m frankly a bit disappointed at the comments. I would have liked to think that he would have approached us first, before broadcasting a message full of factual errors.
Please let me, or any of the others know, if we can provide any further information that would help to clarify (rather than obscure!) the facts,
cheers,
mike
At the time, it was not known that Mann had failed to “provide” the verification r2 and CE statistics that were then standard practice in the tree ring reconstruction community and that the MBH reconstruction failed these tests in its early stages. In addition, the methodology for Mann’s calculation of uncertainties was undecipherable prior to Climategate. (There is some Climategate information that I haven’t parsed yet and may provide clues.)
At 16:36 GMT, Jones endorsed Mann’s unresponsive reply, adding more inaccurate information:
Tom,
Mike’s answer is a fair response. Jeff has mixed some facts up and this is maybe because we’ve never explained them clearly enough. There are two facts:1. There are few tree-core series that extend beyond the early 1980s. This is because many of the sites we’re using were cored before the early 1980s. So most tree-ring records just don’t exist post 1980.
2. The majority of the recent warming is post-1980, so no proxy would pick this up. This warming has been large and it would be good to go back and see if the trees have picked it up. It would give more faith in tree-ring reconstructions, but any reconstruction method is being pushed to the limit by the rate of temperature rise over the late 20th century. Applies to other proxies but you have to note the following:
It is important to remember that locally few regions exhibit statistically significant warming. Highly significant at the hemispheric level, but not great at the local level due to high level’s of variability. The spatial scales are important and this is difficult to get across.
Cheers
Phil
The supposed lack of updated tree ring sites was a common meme in 2003 and was one that I encountered when I first entered the field. Mann argued in the early days of realclimate that the proxies were in difficult locations and it would be virtually impossible to replicate the heroic work of the 1970s. In 2005, I wrote an op ed urging climate scientists to update the proxies to prove that they were out-of-sample responsive and satirized Mann’s claim that the proxies would require undue effort to update.
At 17:55 GMT, in the wake of Mann’s counterattack, Severinghaus backed off, even apologizing for asking such a sensible question. However, he (quite correctly) didn’t understand what alignment of means had to do with the issue at hand and (quite correctly) pointed out that the Esper results went up to 1993 (thus the data didn’t stop in 1980 as Jones and Mann had proposed):
Gentlemen:
Please accept my apologies if I have gotten the story wrong. I am not a specialist in the tree-ring field, and was simply reporting what I saw in the Briffa and Osborne paper, several other papers, and what several tree-ring people have told me in conversations. I agree, we need to keep the level of misinformation out there down to a minimum! regret adding to it.I am still confused, however, about Mike’s explanation for the Briffa and Osborne paper’s curve appearing flat after 1950 AD. Can you try explaining this again, Mike, please? I don’t understand how aligning could change the slope of a curve. The curves appear to continue to 1990 AD or so, and the Esper et al. curve continues to 1993. So the explanation that the records only go up to 1980 doesn’t seem to hold in this case. The dashed black line is the instrumental record for warm-season >20 N latitudes and it does indeed diverge from the tree-ring records in the 1980s. Can you help me out here?
Sincerely,
Jeff
At 19:16 GMT, Mann sent another lengthy and unresponsive reply. Mann re-iterated that the MBH reconstruction had the same amplitude as the increase in temperature over the calibration period and ignored the flattening out in the proxies that was worrying Severinghaus. Mann didn’t mention that Briffa and Osborn had deleted post-1960 values of their reconstruction nor did he suggest that Severinghaus consult Briffa’s 1998 article in which he had reported a noticeable decline in both tree ring density and widths in the last half of the 20th century.
Jeff, Choice of aligning has no influence on the slope of the curve, it simply changes the mean baseline for comparison. The Mann et al reconstruction has the same amplitude increase as the full Northern Hemisphere annual mean instrumental record over the calibration interval (1900-1980). On this simple point, there is no debate. And this seems to be the origin of your misunderstanding of the issues involved.
Briffa & Osborn use a slightly different convention from that used elsewhere (e.g. IPCC and in the attached Science piece which I’ve re-sent for the benefit of your expanded recipient list), and by their convention the instrumental record is observed to lie ever-so-slightly above the MBH reconstruction over the entire interval available for comparison (mid 19th century-> 1980). This difference is actually quite small, so I’m not sure why we’re even discussing it in the first place. It, however, does not in any case impact a comparison of the trends in the two series, which match remarkably well over that same interval. This is despite the fact that the MBH reconstruction represents the entire Northern Hemisphere (which gets half of its contribution from the tropics i.e., latitudes 30N) while the instrumental series shown by Briffa & Osborn is only the extratropics north of 20N. This is old stuff, and I would guess that the others cc’d in on this message (Ray, Malcolm, Keith, Phil) are not interested in re-hashing these old discussions.
The state of the the science here has moved well beyond these semantic and/or conventional arguments, focusing instead on detailed intercomparisons of methods and data (employing rigorous diagnostics of reconstructive fidelity (collaborative between Bradley/Briffa/Hughes/Jones/Mann/Osborn/Rutherford). There is little disagreement between us on the broad trends when seasonal and spatial sampling issues, and differing conventions for e.g. defining reference periods, have been taken appropriately into account. I hope you find that the above information clarifying Jeff. Due to other demands on my time, I have to sign out now on this series of exchanges.
best regards, Mike Mann
Mann’s statement that his reconstruction got “half of its contribution from the tropics” was untrue. The reconstruction was heavily weighted towards strip bark bristlecones. It only had a few tropical proxies. Briffa and Cook satirized Mann’s claims of tropical skill [-cite].
At 20:03 GMT (4355), Mann conceded that Esper reconstruction was also flat after 1950, “defying” the instrumental record. Although the Esper reconstruction was built on ring width data, Mann said that flatlining “generally doesn’t appear to be a problem with tree ring width data, at least those available through 1980”.
Jeff,
One final point I didn’t respond to, upon re-reading your previous email: My comments about the baseline period issue only refers to comparisons of the instrumental record against the MBH reconstruction (as shown in the Briffa & Osborn piece).Unlike the MBH reconstruction, which tracks the instrumental record well through the end of the calibration interval (1980), the Esper et al reconstruction indeed doesn’t show any warming after 1950 or so, which defies evidence from the instrumental record. This is similar to what has been noted, as discussed in the previous emails, with high-latitude summer-temperature sensitive maximum latewood tree-ring density chronologies (e.g. Briffa and coworkers) and it may relate to the same factors that have been discussed in that context. This generally doesn’t appear to be a problem with tree ring width data, at least those available through 1980.
Once again, the wisest approach is to make use of all annually-resolved proxy information available…
That’s my final word on this, promise…
mike
In fat, although there had been negligible recent discussion in the “peer reviewed literature” of divergence of ring widths, it had been mentioned in Briffa’s original 1998 articles. Mann’s assertion here was untrue.
Climate Audit 
111 Comments
Steve, did you ever formally write up the results of your Almagre/Starbucks expedition? From your blog posts, we learned about the strip-bark issue, but what were your conclusions about the data from “good” cores?
That is, does the decline show up in these cores to the same degree as in Briffa’s reconstruction?
Slightly off the main topic. Just wondering where this email from drdendro (edward cook) to keith Briffa, sent 1997 fits in. Is this the earliest discussion of the decline?
http://di2.nu/foia/foia2011/mail/0690.txt
date: Tue, 21 Jan 97 06:53:51 EST
from: drdendro@XXX (edward cook)
subject: Que pasa?
to: k.briffa@XXX
Hi Keith,
I was just wondering how you are making out with that Kalman filter mess
I sent you. I am only going to be around for about 2 more weeks before I
go downunder. So, if you have anything you want to pass by me, it ought
to be before then. In my conversations with Brendan, it has occurred to
me that something analogous to what you find in your data (a systematic
departure between tree rings and temperature over the past few decades)
also is apparent in some of the Huon pine data. Specifically, the BCH
site of Brendan’s, which is the second highest site compared to Lake
Johnston, shows the same effect as you see, at least in the ring widths
anyway. We don’t yet have density data for that site. The high-pass
variations in ring width lock in beautifully with temperature, better in
fact than does Lake Johnston. However, the low-pass side goes down over
the past 30 years years as temperatures have increased. Brendan and I
have speculated about this a lot. My pet theory is that temperatures
have risen sufficiently to cause net photosynthesis to go into deficit
occasionally (i.e. respiration exceeds primary photosynthesis). Of
course, this theory is pretty bad as is because it doesn’t explain why
the slightly higher (say 50m) Lake Johnston site maintains its temperature
response at all frequencies. I suppose it is arguable that what we are
seeing is a very sharply defined threshold response and the LJH site is
just cold enough to escape this effect. There also appears to be an
inversion layer over western Tasmania that kicks in at around 900m. I
don’t know. Maybe it is totally coincidental.
Cheers,
Ed
Steve – it’s a very early reference. Nothing was published until 1998. I haven’t parsed 1996 emails for the earliest reference, but it would be worth doing.
Steve, not a lot for 1996. This from 1997:-
$1554
subject: The devil …
Hi Keith,
The devil made me do it. I have nominated you for a LDEO Climate Center visiting Climate Scholar. If it comes about, you can of course tell them (me) to get stuffed! I really think that there would be keen interest here on your work.
Cheers,
Ed
P.S.
Here is my message to Broecker’s secretary:
Hi Moanna,
Sorry for not responding on that. Bob Dickson would be fine. My nomination for a CC visitor in the future is Keith Briffa from the Climatic Research Unit, University of East Anglia. He is doing some very interesting work with multi-millennial tree-ring records covering much of the Holocene and is working on understanding the
cause(s) of a very large-scale change in the response of trees to climate (e.g. over most of Siberia) that has resulted in an anomalous divergence between temperature and tree rings since ca. 1950.
Cheers,
Ed
PP.SS.
Any more luck with the Kalman files?
Wow. Mann blows smoke at everyone, even scientific colleagues, not just “deniers” and uncritical, unthinking journalists. What is astonishing is to think of the ego someone needs to perpetuate these untruths so arrogantly. And to think that Mann got away with it for so long.
Unfortunately, his admirers — at Real Climate, Joe Romm’s attack dog website, and in the media — still don’t appreciate the height of Mann’s obfuscations, although I’m pretty sure Joe Romm actually knows that Mann has been untruthful. Romm has good reason to understand that kind of behaviour.
Not only cannot he tell the truth to us, he can’t even tell the truth to other, presumably sympathetic, climate scientists. He is a real piece of work, I tell you. A well prepared and sharp cross-examining attorney could go to school on this guy.
“Stratospheric ozone depletion may have affected the trees” – hilarious! Talking about grasping at straws!
Hahaha – And don’t forget that the trees in question are in the NH, while the big bad ozone hole is in the SH.
There IS a much smaller one in the NH, true. But grasping at straws? yeah. Perhaps the trees got sunburned or melanomas.
Thanks Steve. I was trying to establish that chain myself and having trouble.
should have read, the Northern Hemisphere`s climate….
You have to applaud Severinghuas for even realising there was an issue – even knowing what to look for, and with suitable annotation, it’s a pain to see what’s going on and what the problem is on the graph.
Phil’s “2.” quote gave me a real WTF fit. Talk about nonsense. Current warming is so fast that reconstructions are pushed to their limits…what?!?!? And this supposed unprecedented warming wasn’t significant locally/regionally from 1980-end of 2004, at least not enough to be captured by proxies…but, of course, operate under the assumption that all warming in the past was significant at the local/regional level and therefore captured by the proxies.
See Craig Loehle 2009, http://www.springerlink.com/content/45u6287u37x5566n/
He does a fair attempt at moving toward a solution. I don’t think he has nailed it, but his analysis will be helpful further down the road.
There is also Esper, Frank 2009 at http://www.springerlink.com/content/873486u687j56246/
This addresses the Divergence problem (DP), too. Again, it gets nowhere, this being just a summary of what others have done.
D’arrigo et al 2007 at http://webcenter.ldeo.columbia.edu/res/fac/trl/downloads/Publications/divergence2007.pdf
This seems to be the one most refer to. It lists the possible causes for the divergence, but in fact leaves out the most likely. The one that utterly stupefies me – and this kind of thing really makes you want to take scientists out and introduce them to the real world – is the suggestion of “global dimming.” Speaking of them, this is truly one of my all-time WTF moments.
So, what is this obvious possible explanation for the DP?
See this paper: Stahle et al 2005 http://www.scribd.com/doc/51676257/Buried-Cypress-Forest-in-South-Carolina
This paper talks totally about using tree rings as proxies for PRECIPITATION. Not temperature at all.
Now, we all know from math that if we have two truly independent variables, the result comes from any combination of the two values, and neither value can predict the result by itself. This, then, argues that both camps are wrong, in using tree rings as proxies. Some years rain might be up and temps down, and it might be opposite, or both might be up, or both down. but looking at the tree rings themselves, it is not, then, possible to tell which variable – which forcing – produces the given tree ring width.
Therefore, the missing element is almost certainly precipitation.
D’Arrigo in her long list of possible “causes” mentions “temperature-induced drought stress.” But it doesn’t have to be drought for precipitation to affect tree ring widths negatively. IMHO, the “temperature-induced” part of that is the mandatory/obligatory nod to global warming. Droughts can exist without higher temperatures. (In fact, the Leaf Area Index on the edges of the Sahara is UP in many areas, indicating that – counter-intuitively – warmer climate has actually increased plant growth around the Sahara, not reduced it.)
No, it doesn’t have to be drought. It might just be lower rainfall or less snow. And that might be from air current changes, and that might have to do with cycles like the PDO.
It seems these people aren’t using their imaginations and are missing some likely candidates.
Loehle suggests that the problem is that when a threshold is reached the tree rings cannot respond linearly anymore. There IS a limit to how wide tree rings can get, after all. He seems to imply that that limit has been reached and passed. But he says that this phenomena is happening in any number of various tree species. If that is the case, then he would have to explain how all of them are reacting in the same way at the same temperature, which seems completely impossible. The temperature range since 1960 has only been about 0.4C. But it also does not explain the seriously NEGATIVE trend. It is one thing to reach a limit and flatten out when a ceiling has been met. It is altogether another thing to indicate a DROP of 0.4C as the Briffa data show.
Basically, then, they don’t really have a clue why the DP is occurring.
As in many fields, it is the anomalies that show the direction in which lies the next breakthrough in the overall understanding. They have not asked the right question(s) yet. I think they need more data to work with, and someone needs to have a “?” moment, followed by a “!” moment.
For the moment, I don’t see tree rings as valid proxies – for temperature OR precipitation. Perhaps that will be the end result. I think it the likeliest outcome – but if it comes, WOW! are there going to be some red faces!
I see further down that Steve M says it is mostly the tree ring density – not width – that is being addressed n the papers. I was sloppily referring to tree ring widths, not having checked. My bad.
Yeah, I learned from that too. One person has done their homework. Because of the contempt with which he’s routinely treated it’s easy to forget that.
by ‘tree ring density’ I take it we are not dealing with density in any normal sense, you know, like weight per unit volume.
This is climate science after all, so my guess is that ‘tree ring density’ is in fact ‘tree ring X-Ray absorbance’.
Click to access TRBvol30_11-22.pdf
Now the absorbance of X-Rays, in wood, MUST correlate with temperature. One should NEVER suspect that in wood the high levels of metal chelator, Tannic Acid, could hold metals with a strong X-Ray absorbance spectrum.
Click to access b1206.pdf
Zinc is really, really, good at absorbing X-Rays.
It is no way possible that metals mobilized from soil, due to a switch from alkali to acidic soil, would end up in particular tree rings.
http://www.ncbi.nlm.nih.gov/pubmed/19111374
Now way could alkalinization of soils in the Northern Hemisphere, due to the ‘Clean Air Act’, could affect the uptake of Cu and Zn by trees and cause a drop in apparent tree ring X-Ray ‘density’.
There is no possible mechanism for a change in pH causing changes in the levels of Zn/Cu in wood and manifest themselves as changes in ‘tree ring density’.
Any suggestions that this impossible mechanism could exist are figments of the deranged imaginations of big-oil funded conspirators.
Fascinating, thanks.
I have just found a rather good paper which looks at Mercury levels in the tree rings:-
Mercury concentration in tree rings of black spruce (Picea mariana Mill. B.S.P.) in boreal Quebec, Canada
Li Zhang, Jun-Long Qian and Dolors Planas
Water, Air, & Soil Pollution
Volume 81, Numbers 1-2, 163-173, DOI: 10.1007/BF00477263
http://www.springerlink.com/content/t0715r4721875383/
The siting of the trees appears to be important, as does the age, in the amount of Hg.
In one tree series there is a huge Hg spike from about 1945 to about 1985. This was caused by the increase in coal burning, releasing Hg into the biosphere, and then the introduction of scrubbers.
Now mercury has a lovely X-Ray absorbance spectrum. Is it possible that mercury levels alter the X-Ray derived ‘density’ of tree rings?
Fascinating! Does anyone know enough about tree-ring density measurement methodology to comment on this?
I would maybe correct myself on my “almost all dendro studies are for density” statement. Looking at the BEST data listing, 27 sites listed are dendro studies, with 23 being of tree-width>temperature, 3 being dendro-density>temperature, with one dendro not specifying width or density. Sizes of site samplings is not spelled out. Either BEST is atypical or most studies are width vs density.
I realize this is getting off topic (because we’re discussing the divergence itself rather than Severinghaus), but the effect of precipitation on tree ring [] was actually tested in a NASA experiment. Scientists “exclude[d] rainfall from a 100-meter-by-100-meter (1 hectare) plot of rainforest” by covering the ground with plastic sheet gutters. the result surprised the scientists:
“The fact that drought interfered with the tree growth isn’t surprising. What is surprising, says Nepstad, is where in the tree this slow-down occurs. “We thought that early drought stress would show up first in leaves—that leaf area would decrease significantly and that litterfall would increase as leaves died and dropped off the trees,” said Nepstad. “Instead, we found only small decreases in leaf area, and litterfall actually decreased. It turns out that wood production is the most sensitive to drought stress. Trees just stop growing in diameter, which has important consequences for timber production.””
http://earthobservatory.nasa.gov/Features/AmazonDrought/stealing_rain4.php
Steve Garcia, thanks for citing my work. I argue that growth rate (ring width) can flatten out OR decline at higher temperatures, depending on what happens with precipitation. So a growth decline can make biological sense, but you can’t just carry on as if linear is ok once you detect divergence. Furthermore, divergence is always lurking as a possible confounding factor for any temperatures warmer than the calibration period.
It is NOT the case that all species are showing divergence, just some species and some sites are, so I don’t have to explain that.
One of the assumptions of the dendro guys is that they are picking sites where only temperature is limiting (so they can ignore it as a factor). If you think of high elevation western USA sites with lots of snow, maybe so (though these can be quite dry in summer). But in Alaska, Canada, and Siberia, the sites are not all moist and precipitation IS important and destroys the ability to characterize past climates because it is an unknown for past dates. In the primary dendro literature, precip is often a variable and they just ignore it.
Craig –
Thank you for every fact you just pointed out. All of them seemed to be the reality, from what I think I know, and it is good to have so much confirmed. These people make a lot of assumptions and ignore just about anything that will get in the way of “the cause.” Precip – how can it NOT be a factor? Ignoring it is the height of embicility.
And once divergence is recognized, no one in his right mind would continue as if it didn’t exist. One either needs to track it down fully and recalibrate accordingly (in a non-linear way, if possible), or the rest of the conversions are useless.
Re: “negligible recent discussion”
according to Web of Science, Briffa et al (Nature, 1998) was cited 72 times by the end of 2002. While some of these would not have been particularly substantive, that is a lot of papers talking about the issue. I don’t think you can dismiss that as negligible, and in fact, I doubt very much you’ve examined those 72 papers at all.
Just because they cite Briffa does not mean they discuss the decline at all–please demonstrate that they do.
Ah, I see how this works. Steve makes an unsubstantiated claim, but that must be believed because the person who points out it is unsubstantiated has not gone through each of the 72 papers that likely discuss this issue to pull out each of the relevant sections or paragraphs. Isn’t this the wrong way around? Why aren’t you asking Steve to go through them to show that in fact no-one discussed this? I made no specific claim of my own.
Dude,
If you want to disagree with Steve and falsify his claim show us the paper that did discuss the matter.
It is you who is asserting that
a) Steve didn’t read the papers
b) The lack of discussion is implausible.
Otherwise, at this point, you are making unsubstantiated claims that Steve is likely to be wrong. 😉
Are you disputing Steve’s assertion that it is the two papers of Briffa that are used by defenders of the the various spaghetti graphs to demonstrate that the divergence problem was discussed in the literature? They don’t mention the other 72 papers as having discussed it so why should Steve or anyone else be required to wade through them? Most importantly the IPCC, including its summary for policymakers, hid the decline, through the highly untransparent offices of Mann and friends. The defence they offered is not remotely credible. This looks like a red herring.
Everyone ought to read Briffa’s papers. They are very straightforward. He says he has no idea why the divergence occurred.
Steve – they’ve been discussed and criticized at length here. Briffa’s argument that the divergence problem can be ignored is so cargo-cult that it made me incredulous that a professional scientist could hold such a view. It was one of the things that inspired me to get involved in the field.
CoPete, shouldn’t all those papers be withdrawn?
The fact that the paper might have been cited 72 times is irrelevant. Who cited it would be more informative. Briffa et al. could be cited repeatedly by – probably was – Jones, Mann, Trenberth and other “team” members, as well as by Briffa himself, and none of them would have even acknowledged the existence of a “divergence” publicly. They had already hidden it.
One very well known trick to building your “citation index” is by citing your own work repeatedly. A simple quick WWW fishing expedition yields Shindell et al. (2001) which is co-authored by Mann among others – it cites two other papers co-authored by Mann – as well as the Briffa et al 1998 paper. Schindell cites himself at least four times. Other well known names in the citations include Jones, Hansen, Hughes, Bradley Crowley, and Schmidt. There is no mention of divergence or decline. Of course there are still 71 other papers that might have addressed the divergence problem in Briffa et al.
Could be a simply answer some papers get an almost automatic citing , without them in fact having any part in the research. As group-think is a problem in science as much as any other area and sometimes papers get cited becasue ‘everyone else is citing them ‘ And they there is gaming the system such as getting your name on a authors list for a paper when you give virtual no or none import as a ‘favor’ . I seen a few where basically it is clear they never really read the article they cited as it does not support what they said it does or they simply not seen its actual rubbish . While in some areas , there are even papers still being cited which are know to be worthless but form part of the ‘standard list ‘ of papers to included.
Re: CoPete (Nov 28 12:46),
I had said:
You said:
Two things.
First, in Mann’s commentary, he distinguished between a decline in MXD (density) and a decline in ring widths and so did I. Briffa published a number of articles in which the decline in density was discussed. In older CA posts, I did a thorough canvassing of this corpus with exact quotes and pictures. The decline in ring widths which was also illustrated in the original article was seldom mentioned after the original article.
Most of the subsequent references to briffa et al (1998 -Nature – 291) – there’s a second Briffa 1998 nature article which is also cited – are for the density series, not ring widths.
I am very familiar with the subsequent literature and have canvassed it thoroughly.
I stand by my comment that there were negligible recent references in the literature as at the time of the Severinghaus correspondence to the decline in ring widths pointed out in Briffa et al 1998.
I’d be happy to correct the statement if untrue, but I think that you’ll find that it is true.
Be that it as it may, do you agree that Mann and associates failed to alert Severinghaus that the problem was not simply one of the proxies “flattening” out, but, in the case of the Briffa reconstruction, actually diverging?
Steve
Interestingly enough in the Climategate II emails there is a request to Keith Biffra to review a paper on the divergence problem in tree ring proxies.
http://di2.nu/foia/foia2011/mail/0635.txt
This was from QSR
Looks like it made it through the mill.
http://www.ldeo.columbia.edu/~liepert/pdf/DArrigo_GPC2007.pdf
Of course this was three years after the incident that you relate here.
I didn’t see that. Anyone able to help me?
Mann, Briffa and the others should have
a) been delighted that another scientist like Severighaus from outside their group was asking, rather than subtly denigrating him
b) at once showed him the severity of the problem of the decline since 1960 (or earlier?) in Briffa’s work and knocked it around by email.
That would have been a version of open science. OK, not on the Cameron Neylon, open notebook level, with the whole world able to see the results of experiments in real time. But it would have been a cool thing to do and in the end would have advanced the science, one way or the other.
The idea that the deceptive graphs in IPCC TAR 2001 were fine for politicians and the general public because of clear mention of the divergence problem in obscure papers by Briffa in 1998 is laughable in the light of the main man of dendroclimatology not even being open about the problem to a close colleague in a closed email discussion two years later.
This suggests to me that the core Team had internalized belief, that the world was warming unusually in recent years, and that they were on the case, to such an extent that any evidence against this had to be hidden from the unwashed, their colleagues, and even from their own perception and memory.
I read Mann’s use of the word “discuss” in this way:
“discuss” = distract, deny, obfuscate, blow smoke – thimblerig
“discuss time and again” = relegate to “Censored” folder in both computer records and personal memory
Richard –
I have to agree with where you are going on this.
But can we glean anything from their reaction? Why would they not welcome Severinghaus’ input? If there is this anomoalous phenomenon (real or artifactual) wouldn’t one think the top climate scientists in the world would be hot to trot to get it figured out?
Instead, what do they do? Mann answers off-topic. Is that an attempt at “Move on! Move on! Nothing here to see!” ? He bloviates at length for no reason. Jones, the Mann sycophant, nods in meek compliance. After the bloviating, Severinhaus, all chastized or intimidated, says he must have misunderstood what he was looking at.
Only later on – when the others cc’ed have left the conversation, does Mann even respond to the initial inquiry, when the audience is gone. Yet he still does not address the DP being hidden – especially, as Steve M points out – that it doesn’t just flatten, but declines. And notice that the (indicated) decline is a full -0.4C – basically the entire rise since the post-war cooling period. To me, a 0.4C divergence (in only 3 decades) shows not only a non-linearity between tree rings and temps, but tells me there is no reliable relationship at all.
It would be hard to imagine that many out there aren’t wondering this, too: Are tree rings even a decent proxy for temps? And that is exactly what Severinghaus is addressing.
Before Mann bullied him into submission.
I would say that forty years of divergence between tree ring width and thermometer readings found in data that you or your colleagues collected is overwhelming evidence that tree ring width is not a reliable proxy for temperature.
Maybe that’s so, Theo. But it could also be that the proxies are accurate, and that the problems lie with the temperature record. There have been so many “sdjustments”, ignoring of UHI effects, and careful selection of stations that support the AGW story, that we should at least ask whether the temperature record could be the problem. Also, remember that most trees being sampled are truly rural, and so could reflect flat to declining rural temperatures.
Ha, this is one of my favorite CA threads….. Anyone attending one of Mann’s AGU talks this week should be aware of his … ER…. record.
@Richard –
“and in the end would have advanced the science, one way or the other.”
It is way late in this game to comment again, but this is a very good point you made here:
Their actions did NOT advance the science, so one has to ask what they prioritized.
The obvious answer, based on the emails and other similar actions, is that they were putting their careers and reputations above the science, if not grant moneys.
reminds me of the characters Vince Vaughn often plays, able to spout bs at any moment on any topic…
Should
“drew Severinghaus’ attention to the early articles in which the divergence problem was disclose.”
be
drew Severinghaus’ attention to the early articles in which the divergence problem was disclosed. << missing 'd'.
Steve, yet again, you have come up with a gem and have added fascinating context. It would be great to get Jeff Severinghaus’ take on this – probably privately. Severinghaus appears to be very current on the proxy temperature record and has developed measures of multi-millenial temperature records of Greenland based on trace gases in ice cores. The Kobashi et al 2009 paper has some nice comparisons to recent Mann reconstructions. See link at http://icebubbles.ucsd.edu/Publications/pubs.html
Steve:
Severinghaus has responded in a complimentary fashion to an inquiry from James Padgett.
Not very private at all as it turns out. To repeat what’s posted below in an easier to read form:
That is a pretty straight answer, thanks Professor Severinghaus.
The most important message besides tricking the collegues is in my view
“this is what I said–to quote this as offering “no explanation” is a bit unfair Jeff, don’t you think?”
AND written to several of the most influential climate scientists.
No wonder, the first thing Jeff does, is to apologize and to promise to keep his mouth shut towards the outside.
In that way, this may have been one of the defining emails of climate science, but the perhaps most important so far, in my view, may have been this:
#2088 (Tickell = Sir Crispin Tickell)
date: Fri, 17 Mar 2000 17:11:20 +0000
from: Trevor Davies
subject: Research Director for TC
to: m.hulme@uea
Mike, Be aware that Tickell dislikes Tom Wigley; this isn’t hearsay – I know this for a fact. After Tom published that “delaying -emissions cutbacks – scenario” analysis in Nature, Tickell told me that Tom was irresponsible, & had damaged the likelihood of the cc issue being addressed seriously. There is also the baggage about Tickell pinching some of CRU’s ideas & Tom telling him so rather unsubtly. So – he needs to be the “sort of top research scientist we know is interested”.
Trevor
Severinghaus says:
” But alternatively, he says it is possible that the trees have exceeded the linear part of their temperature-sensitive range, and they no longer are stimulated by temperature. In this case there is trouble for the paleo record. Kieth Briffa first documented this late 20th century loss of response.”
Hah, maybe he actulally knew MORE about tree rings than the team “experts.” I always wondered if those guys grappled with the quadratic growth/temperature relationship. Looks like they were aware of it and just didn’t want to discuss it?
One of my colleages, an ecological modeller, insisted his entire career that systems (box mass transfer models) could be modeled with linear coefficients–because, I believe, this made the math tractable. Never mind reality, he insisted the real world MUST match the nice math.
Similarly, if they allowed the nose of the nonlinear camel under the tent, pretty soon they have a whole camel in their laps. (what an image, eh?)
some of the older chemists and physicists I know are wedded to box models connected by first order rates.
Some fit traces to three exponent’s and report the changes in both rates and amplitude’s of the ‘fast, medium and slow’ changes; even though the rates only cover an order of magnitude.
What I never understood previously was that the calibration period, which returns such a poor r2, is done on pooled data, and not on individual trees.
So it is not a single trees response that is being reported, but pooled data.
That’s basically the rationale for using linear control systems theory on nonlinear systems. Don’t look now, but a lot of business is done that way.
As long as you stay within the range where the linear approx works…and you better know where those bound are.
re:
The true irony here is that if this explanation were correct, it would also mean that the trees may have exceeded the linear part of their temperature-sensitive range gawd knows how many times or for what duration in the past also, and therefore failed to show us past temperature increases similar to or worse than that of the past half century.
In other words, this possible ‘explanation’ provided is completely illogical and serves to totally debunk the use of trees as temperature proxies altogether. The only way it can possibly explain the divergence while supporting the use of the proxy is if one uses circular logic and assumes that there was no similar temperature increase during the MWP or any local/regional warming out of cold snaps, etc., which “exceeded the linear part of their temperature sensitive range.” This rational would also imply that by definition the treemometers will provide one with a significantly flattened record that fails to actually follow significant temperature changes.
And unless I’m missing something, the ozone rational is just more flailing around also, since I don’t believe we have any calibrated proxies able to accurately show what the historical ozone cover was over the areas where the tree rings were collected during all of the years each of the applicable tree rings were formed.
It also strikes me yet again just how much these people – I can’t bring myself to call them scientists anymore – waste far more time complaining, rationalizing, scheming, claiming that ‘rotten’ science is so bad it doesn’t deserve a response (without ever saying how it’s supposedly ‘rotten’ of course) and so on, than it would take to just answer the questions, debunk the ‘bad’ science, or respond to FOI’s, etc. That sort of behavior of course begs the question of whether they are at all capable of responding with actual meaningful answers, refutations, or data as applicable.
They are safe because it is known (Mann told them) that the MWP was not warm…so there is no problem with the linear assumption. Pretzel logic.
Rational Db8:
Yeah, it’s true. In fact the shape of the quadratic is an upside-down U, so that after a certain temperature is reached (generally around 25 C for many plants, IIRC)growth rates decline very quickly with increasing temperatures.
Rational Db8 –
Your points are well worth taking into account, regardless of whether all of them pan out.
Absolutely. And tehre is no way the Team was not cognizant of this implication. A: It would explain that the MWP shows up as such a small increase in almost all reconstructions. It would NOT explain what tesmp were actually reached in the MWP. This latter would explain why Greenland is not now farmable, while in the MWP it was. Ditto the vineyards in northern England.
Yet, in doing so, as you say, it would invalidate using trees as thermometers with memories. I DO believe that trees can be used that way, but with great caution. But with NO expectation for precision, such as the 0.1C gradations now presented with confidence.
NOW, we can understand the flatness of the reconstructions. However, we cannot get ahead of ourselves. Is the flatness also happening at the low end of the spectrum? While it sounds possible, I wonder what Craig says.
But does the ring density flatten out, or does it begin declining?
And is it linear within that declining, after the curve begins its downward slope? Might it be useful at all? If the curves can be found to follow specific curves (for specific species), would it be possible to read the curves? Yes, I know, we’d have one value for two possible states, and we would have to be able to distinguish which one is being represented. But if we knew it had approached the zero-slope at a point in time, we might be able to reconstruct (showing our work transparently, of course) even though the max had been reached. I am not saying this is doable, but as something to explore, it seems worthwhile.
“If the curves can be found to follow specific curves (for specific species), would it be possible to read the curves?”
I was thinking about this and came up with a perhaps.
In the same local, trees at a higher elevation are exposed to lower Tmin and Tmax, than those lower down the mountain (lapse rate).
If the divergence is due to atmospheric temperatures passing the growth optimum temperature, then trees in a valley will, during hot periods, have an inverted “VV” growth pattern, whereas those higher up, which are never exposed to too high a temperature, will have a broad inverted “V”, over the same period.
Indeed, if we had two pools of tree rings/densities, from tree grown at two different altitudes, we could test the correlation of growth w.r.t. temperature.
If we know the average difference in seasonal/annual Tmax/Tmin at the lower (warm) and upper (cool) elevations, we can establish how good trees are as thermometers.
The nice thing about trees is that they do not move. Trees at the top or bottom of a mountain have always been there. Paired tree population, at the top and bottom of a mountain, should have been subjected to the same amplitutinal changes in deltaT; but crucially, have been exposed to a different ‘average’ temperature.
Of course, if the altitude diff is enuf, however, you’d likely have issues with different lengths of time in shadow vs. daylight, wind conditions (not just temps), possibly both rainfall and humidity levels, and so on… comparing altitude effects this way might be adding more variables rather than reducing them… But I would think it would make an interesting line of study if it hasn’t already been well done.
When it turns around and heads South, that’s not a “loss of response”. Or alternatively, he’s admitting that there are other factors that are at least as powerful as temperature.
We’ve had discussions of the non-linear response of trees with increased temperature here at CA in the past. No one here seemed to be surprised that this could be happening, maybe because many of us have seen it happen in other fields, ie, radio receiver saturation. If they would have came out and just said, we have a divergence problem, looks like this may foul up our paleo reconstructions because the same thing may have happened in the past, nearly everyone here would have understood. Its hiding the decline that has got them into hot water.
I freaking HATE it when supposedly smart scientists put ONE straight line on a graph and think that is the end-all and be-all. Nature doesn’t work in straight lines very often. I always thought straight line regressions were merely a first peek.
YES, they can be used – from time A to time B – as long as one does not expect that to hold for all future cases. Or past cases. It can be a guide, no more.
Mann’s mendacity and bluster are absolutely unbelievable, particlarly when contrasted with the unpersuasive nature of his writing style and rhetoric. The big mystery in all this continues to be why so many of these professionals allowed themselves to be bullied in such a crude and transparently dishonest way. This would be a fascinating study at the boundary between psychology and sociology.
Tom C –
From what I understand, Mann is a superstar at garnering funding. I get the impression that he has a say in who gets it and who doesn’t. So, if that is true, he gets to hold that over their heads. The way Briffa caved on the “hide the decline,” it appears that they have all had a dose of Mann holding the funding over their heads.
It is much like most of us do when our bosses lean on us – we go as far as we can, and then we back down when it comes to push and shove. It isn’t that Mann is their boss, but money talks.
If I am wrong, I’d like if someone corrects me on it, but I am certain I’d read several times about Mann’s ability to get huge amounts of money, and it seems like it is much more than climate science has ever gotten before. So, now they are in the big leagues, and they don’t know how long they will be on the gravy train – but Mann is the funnel, so they have to supplicate on the altar of Mann.
It would be a huge task for ATI to collect affidavits from all the individuals such as
Jeff Severighaus who Mike Mann deliberately gulled, cullied, and diddled either in person
but especially by e-mail.
One documented lie-by-email by Mike Mann proffered in the Prince County FOIA case would
roughly balance against one gratuitous letter from a group of Team members supporting the
red herring argument of “academic freedom” to hide Mike’s 30,000 emails from view.
An affidavit attesting to the situation from someone like Jeff Severighaus, who sent Mann
an e-mail, and who received a misleading, incomplete or non-responsive reply from Mann could,
perhaps. lay claim to the origial sent together with Mann’s reply and the various discussions
among the “Team” bandying about Severighaus’s name as his person property too, rather
than being under Mike Mann’s exclusive control.
These Mann-held e-mails are government documents. Folks like Jeff Severighaus
have the right </i to review them under Federal and most state laws.
Mike Mann is trying to make sure the University of Virginia e-mails never see the light of day.
His “personal & private” claims could be shredded like cheap tissue paper should other “private”
folks stake their claims to parts of those e-mails too.
1. To Mike Mann: Several competing explanations are not “an explanation”, just as several competing alibis are not an alibi.
2. Does this quote by Phil Jones strike anyone as odd? “It is important to remember that locally few regions exhibit statistically significant warming. Highly significant at the hemispheric level, but not great at the local level due to high level’s of variability.”
How do you get a hemispheric temperature trend when you have mostly noise at a local level?
from the sea?
Steve controls neither the IPCC nor the editorial staff of major publications nor a major national broadcaster, and takes no public funding. Nor does he demand that governments spend trillions on “fighting climate change”.
So why would you care what is in his emails, other than to try to establish a spurious equivalence between an independent blogger on the one hand, and a network of state-funded UN-sponsored politico-scientists and journo-activists on the other?
WUWT has an email from Severinghouse up where he states “But I did indeed feel at the time that Mike Mann had not
given me a straight answer. So if there is a response written, it won’t be
one defending Mike:.
This comment is in the spirit of inquiry. It is not judgemental or accusatory.
Preamble: I was ejected from an excellent job because I protested to the MD that the Chairman had just make a statement at an AGM that was untrue, and should have been known untrue. It was on the important topic of our share price performance, which such people follow very closely indeed.
………………
My present question is “Why did Jeff Severinghaus not make this interchange more public among scientists in a world seeking explanations of climate uncertainty?” Perhaps he did; and if he did, it would be interesting to sample some responses. I am referring to the time of the interchanges, 2004-5, not to the present statement on WUWT of “But I did indeed feel at the time that Mike Mann had not given me a straight answer. So if there is a response written, it won’t be one defending Mike.”
The reason for this question is to encourage other scientists who are wavering, to inform themselves better on whether they should sit tight with blinkers on, to shut up for the good of their future careers or to start the ball rolling by calling out the many instances of scientific abuse that Steve is able to run off at about one a fortnight.
Somewhere on a crashed disc I have an email to Phil Jones ca 2005 in which I suggested rather bluntly that he owed the world an explanation for his (possible) cherry picking of stations used for Russia, China & Australia in a Nature 1990 paper on UHI. I went on to print letters to newspapers and blogs when the retraction did not materialise. It’s even on the older part of CA somewhere.
…………..
Prof Severinghaus, it would be valuable to many of us if you would expand upon your thoughts and reactions at the time of 2004-5, not through any pressure from here, but as a voluntary act of your choice.
Geoff –
It appears this might be the comment you are referring to:
Thank you Steve Garcia – found it earlier today. It’s easy to get into information overload in this business, there’s so much going on.
Cheers Geoff.
Steve,
I much appreciate your thinking as shown here, (though better on your previous post which was quite wonderful – can’t always be perfect!). I’m a chap who came across your site by a lucky accident in 05′ and have paid some kind of attention, ever since. I loved the old days when obscure statistics and mathematics were discussed late into the night and next day. I couldn’t follow it! There is no pressure on you to be the perfect ‘McIntyre’. Don’t worry. But I thank you for the intellectual pleasure you give and I hope it continues for a long time.
Now Jeff Severinghaus says:
“In general Steve has gotten most of this right. There really is a problem with the trees not being sensitive to temperature after about 1950. My current best guess is that the higher CO2 since then has caused greater warming at night (which is corroborated by minimum temperature trends, since minimum temperatures usually occur at night). Trees respire more at higher temperature, so they lose carbon when nights are warmer than average. So their ring width has not increased as much as it would
have if the warming had been uniformly distributed over the diurnal cycle. I think this is all published now so it should be possible to set the whole record straight. But I did indeed feel at the time that Mike Mann had not given me a straight answer. So if there is a response written, it won’t be one defending Mike.”
This “best guess” should also be valid for any past period with higher CO2, and makes all long tree ring proxy based graphs become less reliable.
I wish Jeff had given a cite for where “this is all published now”.
Anyone?
This might be a start at chasing it down. From Wilson and Luckman, “Tree-ring reconstruction of maximum and minimum temperatures and the diurnal temperature range in British Columbia, Canada”, Dendrochronologia 20/3 pp. 1-12 (2002), “Alward et al. (1999) hypothesized that elevated night-time Tmin would cause an increase in nocturnal respiration rates in grassland vegetation without a compensatory increase in daytime photo-synthesis. A similar process in trees would lead to a reduction in carbon allocation to rings in each year as night-time Tmin increases.”
The reference is to Alward, Detling and Milchunas, “Grassland vegetation changes and nocturnal global warming”, Science 283, pp.229-231 (1999). Available here, (free) registration required.
This should be fairly easy to verify. Diurnal temperature range is much larger at inland locations than near costs or large lakes. If this theory is correct, then trees should grow better at inland sites than coastal sites with similar average temperature and precipitation. I must say that my impression is that the opposite is true.
Academically speaking, how do you correlate daylight intensity with day and night near to the Arctic or Antarctic circles, where day/night is less clear than at the tropics?
FWIW, I can find no pattern of diurnal temperature range variation over the years in Australia. Although I’ve looked at Tmax and Tmin from only a few hundred sites, some diverge over time, some converge, some stay parallel and rise, some fall .. in short, just about every pattern imaginable, but little systematic pattern. Others who have looked at different sets of stations might have found a pattern, so I’m not being dogmatic.
Just a note on a small typo leading off your last paragraph. I think it should read “In fact”, and not “In fat”.
Theo –
Not only do arkies use C14 (they are not the only ones who do, of course), but the C14 rate of decay was found long ago to not be quite linear, so there has been much work put into identifying the causes that might affect it and nailing down the variations for different periods in the past. Though close to being linear, it is NOT – and people allow for the differences.
To be precise, though, it is not the arkies who “use C14.” It is the testing labs who do. The arkies take what numbers come out – and fairly often reject dates that don’t fit their preconceived dates. These are rejected out of hand as “contaminated samples.” The arkies are much worse than climate scientists regarding “settled science.” That is why it took them decades to accept that the Clovis First principle was wrong.
Your main thrust (as I agreed with at WUWT) is correct, though. Too few empirical studies have been undertaken. I, for one, believe that in time even the water vapor “problem” will be solved – but only with empirical studies and probably only over several decades.
Severinghaus’ fears expressed to Jones and Mann are valid concerns.
BTW, the Team did not conjure up tree rings as proxies. Dendrochronologists did.
Wondering about the missing cite for Briffa and Cook mocking Mann’s tropical skill, bet it’s a hoot, hope you update for that soon!
“In fat, although there had been negligible recent discussion in the “peer reviewed literature” of divergence of ring widths, it had been mentioned in Briffa’s original 1998 articles. Mann’s assertion here was untrue.”
D’Arrigo et al 2008 give a good overview of the literature on the divergence issue. There are a number of papers prior to 2003 besides Briffas’.
Click to access D_ArrigoetalGlobPlanCh2008.pdf
D’Arrigo cites these papers specifically on the divergence issue.
Jacoby and D’Arrigo, 1995; Briffa et al., 1998a,b; Vaganov et al., 1999; Barber et al., 2000; Briffa, 2000; Jacoby et al., 2000; Wilson and Luckman, 2003
I don’t think that list is exhaustive if you include papers where climate reconstructions aren’t the focus of the paper.
“Mann continued with a reference to the “recent high-latitude decline issue” – note that Severinghaus had not actually mentioned the decline – saying (incorrectly) that these had been “discussed in IPCC” (they hadn’t – quite the opposite).”
I think you’ve misread there. Mann’s email goes:
“There are some good reasons that some of the other purely tree-ring based reconstructions differ in their details, in addition to the greater influence of the recent high-latitude density decline issue, and these are discussed in IPCC and the Science piece.”
‘These’ is plural, referring thus to the ‘reasons’ tree-ring based reconstructions ‘differ in their details’, as well as the divergence issue. I checked TAR, and these issues are briefly discussed with references.
“Several important caveats must be borne in mind when using tree-ring data for palaeoclimate reconstructions. Not least is the intrinsic sampling bias. Tree-ring information is available only in terrestrial regions, so is not available over substantial regions of the globe, and the climate signals contained in tree-ring density or width data reflect a complex biological response to climate forcing. Non-climatic growth trends must be removed from the tree-ring chronology, making it difficult to resolve time-scales longer than the lengths of the constituent chronologies (Briffa, 2000). Furthermore, the biological response to climate forcing may change over time. There is evidence, for example, that high latitude tree-ring density variations have changed in their response to temperature in recent decades, associated with possible nonclimatic factors (Briffa et al., 1998a). By contrast, Vaganov et al.
(1999) have presented evidence that such changes may actually be climatic and result from the effects of increasing winter precipitation on the starting date of the growing season (see Section 2.7.2.2). Carbon dioxide fertilization may also have an influence, particularly on high-elevation drought-sensitive tree species, although attempts have been made to correct for this effect where appropriate (Mann et al., 1999). Thus climate reconstructions based entirely on tree-ring data are susceptible to several sources of contamination or non-stationarity of response. For these reasons, investigators have increasingly found tree-ring data most useful when supplemented by other types of proxy information in “multi-proxy” estimates of past temperature change…”
Chapter 2, TAR.
I am very familiar with the TAR section that you quoted and carefully considered it in my original postings about Hide-the-Decline in the IPCC diagram, which was prior to Climategate. First, nothing in this paragraph justifies hide-the-decline. Nor does the TAR paragraph clearly disclose that the tree ring information is going the wrong way and that this poses a very substantial potential problem in the usability of the proxy reconstructions. The language shows that the authors are aware of the problem but they have gone to some pains not to disclose the problem to readers, while leaving themselves some plausible deniability.
Yes, there were discussions of the divergence problem in technical literature. Indeed, my first realization that IPCC TAR had used hide-the-decline came from trying to reconcile the graphic in Briffa et al 1998 to the misleading and deceptive IPCC diagram.
I think a key point here is that “discussions in the literature” of divergence do not mean 1) that the reasons are nailed down, just hypotheses made and 2) the problem has not been fixed wrt past climates to be reconstructed. If there are lots of candidate reasons for divergence, there is no way to know in the past that these were not in play and goofing up your signal.
More precisely, a reference to hand-waving in the literature is still hand-waving.
So, in summary, alongside a highly deceptive graph used throughout the document and in worldwide publicity a single paragraph in TAR refered to hand-waving in the literature, without making clear the problem to readers but providing the authors plausible deniability in the unlikely event someone difficult like McIntyre should come along.
And they say the age of the great scientist is over.
Nowadays Jim Bouldin is saying that dendro as a field has even more fundamental problems than this “divegergence” issue because the key analytical and empirical methods for doing long term temperature reconstructions from tree ring proxies are simply not nailed down:
It’s great that Craig Loehle is here to comment. I was re-reading Loehle 2007/08 not long before I posted, coincidentally.
As far as I understand it, the divergence issue affects certain groups of NH trees but not others. The divergent MXD tree-rings show good correlation to local temps prior to divergence. They also show good correlation further back against other tree-ring proxies (and other proxy types?) that do not exhibit the late 20th century divergence (eg, Cook el at 2004).
“If there are lots of candidate reasons for divergence, there is no way to know in the past that these were not in play and goofing up your signal.”
I’m no expert on the matter, but I do know that you can make predictions about behaviour without having to know the cause of that behaviour, Eg, science does not know exactly what causes gravity, but we can send a probe to Jupiter based on what we know about how gravity works. Or early astronomers could still make fairly good predictions about the movement of the planets even when they thought the sun revolved around the Earth. There are probably better analogies, but you get the idea.
Are saying that the scientists looking at this issue have not done much testing to discern if the MXD proxies are useful prior to the 20th century? That is the impression your comments give, and that runs counter to what I’ve been reading.
Severinghaus notices the divergence issue as flat-lining and Mann replies, describing it more properly as a decrease. In the email exchange, Mann is not trying to hide the decline. Rather, he introduces it (as you say, Steve).
As a relative latecomer to the party, what I’m seeing on one hand is critics of Michael Mann and hockey sticks suggesting that because the cause of the late 20th century divergence in certain tree-ring proxies is unknown, that therefore the proxies are “useless,” and that Mann et al gloss over this (in graphs and email comments etc).
On the other hand, Mann et al believe they have a sufficient handle on the divergence issue, despite not knowing the cause/s, to have the confidence that they do (complete with caveats) about millennial reconstructions.
In other fora I’ve recently been told that the divergence issue has ‘never been looked at,’ as if the graphical ‘trick’ reflects the scientific approach to the matter entirely. I suspect I’ll get a more reasonable response here.
Craig and Steve, have you done tests (like Cook et al 2004) to see if the MXD proxies can be useful or not before the 20th century? I ask because the issue re the emails seems to boil down to a disagreement on the pre 20th century utility of these proxies. What makes you confident that your view is superior?
Barry;
The extant Yamal chronologies created with RCS methods have fatal flaws. Briffa’s (flawed) version had both a steep increase (which was preferred because it seemed to match recent surface temp increase), and an counter-message ‘decline’, which caused graph viewers to doubt the importance of the incline.
In a conspicuous display of ‘confirmation bias’, Mann et al have variously hidden the decline to emphasize the incline. (not unlike depicting only the chest portion of a bloated-yet-buxom woman).
The Finn’s have spent a lot of time thinking about tree rings and what they can tell us.
See;
lustiag.pp.fi/yamal_models.pdf
and other papers at lustiag.pp.fi
It is an academic site, with plenty of english stuff.
RR
Barry –
If temperature was the only factor in tree rings (width or density), the whole issue would be a lot simpler. But with precipitation, crowding from other trees, etc., being involved it is another story altogether. Schweingruber even has a controlled field study of CO2 and Nitrogen in the atmosphere that shows real, tangible effects from what is directly in the air (basically: more CO2 gives more ring growth). So, with all of these factors, the claim of a tree-ring>temperature linear relationship is on tenuous ground to begin with. So, when the two diverge, it is almost certain that one or more of the other factors was affecting the growth. And if those other factors are affecting things since 1940 (or 1960, take your pick), then not only do the researchers using the tree-rings as proxies for temperature need to delineate what is going on since then, but they have to then project that backward, too – and show all the reasons for all of that and then show the new, corrected, results of the past, as the proxy picture shows it.
What it boils down to then, in the long view, is that they need to vet every aspect of it empirically, in controlled field experiments. Until they do, the tree-ring>temperature proxy correlation is in doubt. The relationship(s) that underlie the basic proxy claim simply may not exist. The relationship that seemed to exist may have just been a coincidental correlation for a few decades – one that has stopped being coincidental now for 70+ years.
The thing is, from the emails, it is clear that these folks KNOW that the linkage is on thinner and thinner ground all the time, the longer the divergence continues. But even if it turns around, the non-correlation period has to be explained, and with more than mere speculations. In the end – without tree-rings, which make up the great bulk of all the proxies, paleoclimatology is a cooked goose – there would be no substance to the proxies.
THAT is what they are really trying to avoid.
Hi Steve,
“And if those other factors are affecting things since 1940 (or 1960, take your pick), then not only do the researchers using the tree-rings as proxies for temperature need to delineate what is going on since then, but they have to then project that backward, too – and show all the reasons for all of that…”
I think this would be ideal, but if it is difficult or impossible to do so, does that mean that the other tests for pre-divergence fidelity are invalid? I am not persuaded so far that this is the case. There are many examples in science where ignorance of cause does not prevent the winnowing of useful information. I’m seeing objections here, rather than analysis of the work that has been done. (I’ll look for the Schweingruber paper, thanks – do you have a ref?)
From the emails above, I read that Mann used very few MXD in one of his studies. I don’t see much discrepancy between them knowing about the divergence issue and being confident in millennial reconstructions. I’m aware that other reconstructions that don’t use MXD proxies, or that don’t even use tree-ring proxies, or use come combination – most come to conclusions that are not markedly different to Mann’s (Huang, Juckes, Moberg, D’Arrigo, Kaufman (based on Arctic temps, mind you) etc). In this respect, I don’t understand why Mann’s confidence about millennial reconstructions is such a big issue. The divergence problem is just one of many problems with proxy data, and I see no evidence of these issues being waved away in the literature. Rather, such problems lead to highly qualified conclusions, even in the controversial hockey stick papers.
Thanks for the abstract, Steve. Although it is not really enough to go on with, it raises some questions. Perhaps we could consider my replies as devil’s advocacy rather than a product of confirmation bias (if we need to characterise them at all)?
Doesn’t the relative stability of atmospheric CO2 prior to the 20th century suggest that this factor is not affecting tree-ring development prior to the 20th century?
The factors contributing to tree growth are, of course, numerous. Teasing out all impacts on tree-ring growth, trying to balance them against each other to winnow temperature data, seems difficult enough, but I suggested it might be impossible because not all the factors could be traced back in time, differently to CO2. Would it be possible, for example, to reconstruct soil content with hydrology washing the evidence away? If not, then other less direct methods which have been essayed should not be dismissed out of hand.
(BTW, I came across a similar study to Schweingruber while looking for a full version of that paper http://journals.uzpi.cz/publicFiles/00413.pdf – just for your interest, if you’re not aware of it)
“To have all this based on tree-ring proxies that have KNOWN FLAWS, flaws that they (the Hockey Team) recognize and yet do no work toward solving (Schweingruber is not one of them), this is not useful science. It is not science at all.”
What?!
Schweingruber has co-authored at least 4 papers with Briffa and Jones and least 2 specifically on the divergence issue. Cook, who investigated the divergence issue by intercomparing NH divergent and SH non-divergent tree-rings, has written at least one study with Jones on tree-rings…. look, I’m just going through the author list of the overview paper I cited upthread. Unless I’m very much mistaken about who ‘The Team’ is meant to be, your assertion here is flat out wrong. I haven’t come across any papers co-written by Mann specifically on the divergence issue, but he has co-authored papers with people who have (and not just Briffa).
On the one hand I see people waving away, or defending/explaining the emailers a little bit too easily, giving over-confident narratives from ambiguous language. But from the critics, there is, often enough, a sheer separation from reality, most commonly assumptions about what work has NOT been done. It’s rather ambitious to claim that work has not been done if your metric is only what has been published in the literature – but even so, the literature almost always belies this common claim, as in this case.
“Read the CG1.0 emails re “hide the decline.” That isn’t just a skeptics’ inside joke – they really WERE trying to hide the divergence (the decline). Briffa did NOT want to present it; everyone else was wringing their hands over it; Mann came in and bullied them all into faking it. Briffa didn’t want to, but in the end Mann’s bullying pushed him into doing it, anyway. If those emails aren’t “evidence of these issues being waved away in the literature,” to you, you must be suffering from confirmation bias.”
I may not have read the relevant emails. It was Phil Jones, wasn’t it, who talked of ‘hiding the decline’ by adding in the instrumental record. I am in no way qualified to assess the validity of such splicing, but I can follow the email trail. If you don’t mind walking me through this just a little bit further, could you indicate the climategate 1 emails you are referring to, exactly? Particularly where Michael Mann bullies Keith Briffa into faking stuff, but getting all relevant for as much context would be greatly appreciated.
I don’t understand why you can’t accept that a perfectly good reason for the “decline” is that either this particular set of data or the methodology used (or both)are not suited for the purpose when no specific valid scientific reasons have been offered as a proper explanation. Somehow you seem to think that the reconstruction is perfectly fine for the time period before 1960.
For the record, in the case of this “divergence”, after dropping that post 1960 portion, the comparison between the reconstruction and the temperature record was done using decadal “smoothing” (basically weighted moving averages) of both series correlated on an annual basis for the 80 year period 1880 to 1960 so that the reported correlation was extremely exaggerated and not interpretable as a simple correlation might be. Furthermore, from the latest emails, it appears that although earlier temperature records were available, they were not used because they did not contain a “temperature signal” presumably meaning that the match with the reconstruction was not particularly good. A bit of cherry-picking …
I can appreciate trying to save all the work spent on acquiring the proxy information, but the continual justification for its use borders on the ridiculous.
Hi Roman,
“Somehow you seem to think that the reconstruction is perfectly fine for the time period before 1960.”
I do not, and I highlight this comment of yours to speak to a meta-issue here. I’ve made it quite clear more than once that I do not know either way on this point. I don’t know if it is hang-over from the long debate, but I wish people would not put words into my mouth or try to ascribe to me a position I do not hold.
My argument is to do with commenters here saying, with absolute conviction, that the pre-1960 reconstructions are necessarily invalid due to the divergence issue. I am not persuaded because: a) they have not spoken at all of the kind and quality of work that has been done to address this question – it is ignored, presumably dismissed out of hand; b) they (Steve G) avows that none of ‘The Team’ has examined the issue, when clearly they have, working alongside and publishing with the very Schweingruber Steve nominates as doing the necessary type of work (according to Steve G) on the matter. Basically, the work that has been done, and the fact that ‘Team’ members were involved with it, is either overlooked (deliberately?) or denied.
I have had similar (but more benighted) conversations at WUWT, where people likewise insist no work has been attempted to address the divergence issue WRT pre divergence fidelity. There is much work that I can clearly see in the literature that is being casually swept under the carpet. This all reinforces my impression that objectivity has been overwhelmed by the general stoush. People are omitting stuff on both sides.
“For the record, in the case of this “divergence”, after dropping that post 1960 portion, the comparison between the reconstruction and the temperature record was done using decadal “smoothing”…”
You may well have a valid criticism of a particular study (I cannot say), but I am looking at the matter from a few paces back, where non-tree ring reconstructions, or reconstructions with alternative tree-ring series give similar results. In light of this, are we discussing the robustness of temperature reconstructions, which seems to matter scientifically, or questionable manipulations by paleoclimatologists, which would seem to have a more political bent?
Or more simply, why is this discussion occurring at all? To improve scientific understanding or for some other reason?
Barry –
I’d refer you to Jawaworski’s 1997 paper at http://www.warwickhughes.com/icecore/
In it he points out the funny games and cherry picking that went into the calculations of 19th century CO2 levels. Just to make sure Jawaworski wasn’t himself playing fast and loose with the facts, I did go to read the Callendar paper he referenced and others relating to it. The CO2 19th century levels if ALL the data is included was not the 290 ppm as commonly reported, which was Callendar’s number. It was 335 ppm. Callendar REALLY cherry-picked his data, leaving out almost all higher values. Callendar was all but accused IN PEER-REVIEWED PAPERS of cherry-picking even at the time, but the “almost” accusers drew a very careful line just short of that, out of professional respect as much as anything. If you want, I can look that bit up again.
What that means, is that instead of a rise from 290 to 385 ppm, there is only a 335 to 385 rise since the 19th century. Prior to those studies, there wasn’t enough data to pee on, so any assertions of “relative stability of atmospheric CO2” have a very flimsy basis.
You are missing the point altogether. The point is that those papers that menttion the divergence are NOT papers that are looking to study it in a methodical way and determine its cause. Yes, there are speculations in the Briffa and other papers as to cause – but speculation isn’t nailing it down. To nail it down, they need to have – as I said – specific controlled field studies for each possible factor. Show me one paper where Briffa or Mann did that. Of course they didn’t. Briffa and Mann are paper pushers, desk jockey scientists. They are not field scientists. The closest they got to the divergence was typing the word on their PCs.
Exactly. And if you’ve got X number of factors (a,b,c,d,…) in an equation (the full equation for the tree-ring widths or densities), then try to assert that b (temperature) is the one that you can nail to a high precision as a cause, in just such and such a linear correlation, you’d better be ready to back up your assertion with the exact reason why the other factors did not affect the linearity. From my moderately full reading of the papers, no one has delineated how much a, b, c, d,… are weighted. With precipitation being the FIRST factor tied in with tree-ring proxies, and one that is still done, certainly they need to at least explain why precipitation isn’t even mentioned in the Briffa papers. As to other factors, you are absolutely correct that no one can know what happened in the soil in past centuries. The more you read on it, the more one wonders how they can use tree-rings as proxies for temperature at all. The divergence problem only underscores that questionable correlation: If TRW or MXD don’t align in the period when we have the best instrument data to compare it to, then was the earlier, less precise instrument period just a fluke?
I will address the “hide the decline” email question in another comment. This one is long enough as it is.
BTW, I see that to Roman you are asserting that I am claiming that the pre-1960 reconstructions are NECESSARILY invalid. That is not the case at all. You are putting words in MY mouth there. I have said that they need to show WHY the reconstructions are not invalid. My arguments are stated above in this present comment. One can’t claim that b. (temperature) is the sole proxy extraction from tree rings, not unless you’ve delineated what proportions the other factors represent. If they can lay all that out, then well and good. But they are the ones making the basic assertion of TRW>temps and MXD>temps, when they haven’t separated out the other factors. How that is good science (or logic), I don’t know. I am just asking them to explain it.
And if one of your Briffa or Mann collaborations shows where they’ve done empirical field tests, please point me at it.
Bernie,
I work in the arts. My maths is very poor, barely high school level. I’m a complete amateur at science, but I’ve read on it avidly since childhood. I’m 44. What I’m good at is research, reading comprehension, recognizing and understanding social systems and behaviours, and logic.
Can I ask some candid questions of you? It isn’t going to go anywhere. I hope other people reflect on them.
How much of the dendrochronological literature do you believe you are you familiar with? (I’m discovering dozens of papers just on latewood density response to various factors, and the divergence issue)
What would you say is the ratio of your education on the matter and on the general topic of reconstructions between a) popular media (news articles, blogs etc), and b) the peer-reviewed, scientific literature.
My answer to the first question would be: dendro – barely scratched the surface; millennial reconstructions – more in depth.
For the second: a) 75%, b) 25%. With a caveat that I follow through from popular media to the underlying scientific literature about 40% of the time, so b) could be higher.
barry:
I actually have read the basics plus the articles that are discussed on this site, Jeff Id’s and Real Climate. But I do have far more background in designing and validating various metrics. The issue here is both theoretical and statistical. The link between tree ring properties and climate properties are very complex with multiple variables and interactions among variables, which makes the identification of the temperature signal very difficult to statistically separate – especially when there are not clear measures of the key variables of interest including precipitation, temperature, soil conditions, soil conditions, diseases, shading, etc. The fact that some trees show a correlation with local temperature is not sufficient. You have to do your sampling on an a priori basis. You cannot pick and chose which cores to use and which ones to exclude. All the above make the reluctance of dendros to fully archive the data and methods for extracting the temperature signal and to fully investigate issues like the divergence highly problematic.
Bernie,
Why are you so sure that the dendros are ‘reluctant’ to archive data and methods and fully investigate issues?
You are, like many others here, including the blog owner, suggesting that these people are lazy and/or mendacious. I think the narrative on this comes not from any deep knowledge of the time, money, pressures, staffing, managerial directives etc that these people work with, but on the disaffection of critics willing to turn any snippet of an email and problems with data into an accusation.
IOW, I think you (and others) are making sweeping statements with very little knowledge of the facts on the ground. This has been amply demonstrated on particular matters where I’ve pointed out work done in the literature that critics assumed had not been done – above and at other venues. This happens regularly. The picture I’m seeing is a kind of self-reinforcing groupthink amongst a milieu that are drawn, for whatever reasons, to repudiate various of the scientific factors connected with the issue of anthropogenic global warming, and they do this with conviction despite knowing little of the work done in the field they are discussing.
One of the mental habits that I retained since childhood is to invert every statement into its negative and see if the reverse could be true. It is as automatic as breathing. As I got older I became better at weighing the likelihood of either. I think some of the emails I’ve read are potentially dubious. But I’m much more convinced that the skeptical narrative surrounding them comes from fitting their interpretation to a predetermined view of the issues and the emailers.
(caveat – I cannot say this for certain about Steve McIntyre, who is far more knowledgeable than me about these issues, although some posts I’ve read suggest to me he is not a neutral commentator – I’m speaking of interlocutors here who are demonstrably not knowledgeable about the issues they are discussing)
Barry –
I have come to the conclusion that you are a troll.
You 100% discount every exposé of Steve M and those who side with him, while playing the “Poor little me, I don’t really know anything about this subject” card over and over again, and 100% giving the benefit of the doubt to the Hockey Team.
You are skeptical of what you hear here, but accepting of everything the scientists say. You “explain away” every Team mendacity as something anyone would do. Your balance is non-existent. Playing the “little old me” card while claiming to be sitting in the fence has gotten tiring. Then evidence has been presented ad infinitum to you, and you still play the “independent thinker” role – either because you are a troll or because you are slow. After several gives and takes with you, I conclude that you HAVE made up your mind (in favor of the Team) and are just stroking all of us here.
Please. Go troll somewhere else.
barry:
What are you talking about. You have missed the point entirely. Doing multivariate analysis with underspecified models, small samples and metrics with large error terms is questionable at the best of times. The documentation of the recent divergence calls the entire dendro effort into question and requires dendros to essentially go back to square one if they want to use tree rings to reconstruct past climates. This is not a matter of confirmation bias, it is a matter of reality and the requirements of this type of statistical analysis.
Your habits of thought are really neither here nor there. Besides they are certainly not unique on this site.
Ed Cook uses the following logic to maintain the divergence problem is not an issue for past reconstructions, and that it is caused by anthropogenic factors (email #1661):
” In my QSR paper I noted that when the northern chronologies were compared to the southern chronologies (QSR Fig. 6) used in the Esper et al. paper, the northern ones showed a clear downturn or divergence in the latter part of the 20th century
and this did not show up in the southern chronologies. Yet back 1000 years in the past, no such clear separation between north and south was indicated. In fact, the late-20th century divergence is unique in the data back to AD 800. This, I argued, suggested an unspecified anthropogenic (i.e. pollution) cause for the 20th century divergence in the northern chronologies. Hence, the temperature estimates prior to about 1970 were probably reasonably accurate given the data and methods used. Until we understand the cause(s) of the 20th century divergence, I think that anthropogenic agents should be the working hypothesis for explaining it, not the other way around, because I have not seen evidence to
support the other side of the argument.”
This argument is a fallacy of presumption.
Cook’s argument is one for discarding all NH TR data since 1970, even for purposes of calibration to temperature. But of course it’s the post-1970 surge of Mann’s stripbark bristlecones, the Yamal Doozy Dozen, etc, that make them look like plausible treemometers, so that this would shut down the entire dendroclimatology industry if applied consistently.
And while this would rationalize deleting post-1970 MXD along with the others, it provides no excuse for truncating MXD at 1960 — or at 1940 as in EOS — unless the other NH series are truncated there as well.
In fact there is a post-1950 factor that could easily make the late 20c behave differently than earlier times, namely elevated CO2. But that is easily incorporated into the calibration equation, even if the Team has failed to do so. This would attenuate, but not necessarily eliminate, any correlation of TRW or MXD with temperature.
How would this affect the error bars quoted with the reconstruction? I don’t see any quantification in Cook’s argument
So possibly a fuzzy truth value could be associated with it. So each proxy could have a truth value and the combination of these could be weighted by each’s contribution the reconstruction such as in 3.5 +/-0.1 with a truth value of 0.7 or likely. As proxies come in and out of the reconstruction, the truth value would vary. Each point in the reconstruction would have a truth value and this would be a measure of the faith that can be placed in each estimate.
Kan –
Thanks. I hadn’t seen that email.
Right. Cook’s speculation isn’t science, just a scientist’s speculation. As such it carries validity, but only as a direction for further research, and not till the research is done can it be put out as an explanation. And if that research isn’t done, it is intellectual laziness, at best. I’ve seen several speculations, even within peer-reviewed papers. This begs the question of why they never followed any of these ideas up. And it suggests that they were afraid of finding out the “inconvenient” answer.
But Cook’s “explanation” is a vacuous argument, another “blame everything on CO2” catch-all. I’ve seen this kind of argument/explanation/speculation in archeology a lot, where any unexplainable artifact or structure is termed “ceremonial,” with the same phrasings and tales of ancient peoples huddled under the skies, seeking to propitiate their gods. It is also common in geology and evolution, where “time” is the answer to any unanswerable question: with vast amounts of time nature can do anything. But they aren’t science; they are only empty speculations.
barry:
Could you briefly state your relevant background? I am not trying to play a credentialling game, I just want to understand. As to your issues – logically I think that you are correct. It is possible that tree rings in some form were previously acceptable temperature proxies and now are less so. It is possible but not proven. Empirically, statistically and practically, however, divergence means that what was previously argued as being true has been in fact falsified. In my view, the fact that they now appear to be very flawed proxies means that any prior or indeed current happy correlation between tree rings and temperatures are best treated as an artefact of statistics and core sampling. This is what one might expect from a highly underspecified model of the causes of the width and or density of tree rings. At this point, those advocating the use of tree rings as temperature proxies must go back to square one and not only fully explain the recent divergence but also respecify in compelling detail the link between tree rings and temperature before anyone places any weight on such proxies.
Bernie, don’t know if it’s because I’m now being moderated or I stuffed up, but my answer to your question is above (I think)
“Actually, the divergence problem is THE problem with the data”
I’ve read conflicting commentary on this.
From you and other commenters I get the impression that proxies exhibiting the divergence problem have been used in most/every millennial reconstruction. Or are you suggesting that because certain tree-ring sets exhibit this problem, then each and everytree-ring proxy out there is therefore suspect? The implication would seem to be that we can have no confidence whatsoever in millennial reconstructions based on tree-rings (and perhaps the criticism could be extended to just about any proxy type – known and unknown unknowns).
On the flip side, I’ve read commentary saying that even reconstructions not using diverging proxies are similar enough to those that incorporate them. And also that non-tree ring proxies tend to roughly corroborate tree-ring reconstructions (eg, Huang, Loehle [with caveats]). The message being that the divergence issue appears to have been treated appropriately in reconstructions.
As for hiding the decline, I brought up chapter 2 of the TAR, and the instrumental temps are clearly labelled as such in the spaghetti graph. The reconstructions are truncated in the late 20th century, so I suppose the decline is ‘hidden’ there, but that then devolves to the question of pre-20th century fidelity, on which I’m not persuaded in any direction. The divergence issue is alluded to in that chapter, but not specifically regarding the graph. I’m not able to make a call on whether that is deceptive or not. Accusations of not detailing caveats to the full degree could be laid anywhere within WG1; where to draw the line is a matter of judgement, and in the end it’s a question of whether the assessors’ judgement is valid.
One thing I have not got so far from the emails is mendacity amongst the emailers. They all genuinely believe what they are saying, they believe in the quality of their work, and they genuinely believe that some criticisms of their work is just poor quality science. I also think there are strong implications in the emails that various players want their work emphasised over others, but then again, it’s not clear to me whether they genuinely think such work is invalid, or whether there are other factors at play. The ’cause’ mentioned in some emails has been much talked about, but having read those ones, I find the meaning equivocal. (If only others were as skeptical as they’d like to think they are)
I find I’m spending an awful lot of time in these debates trying to separate rhetoric from substance and politics from science. Would you say the meta-issue here is political or scientific?
First, not every tree-ring sampling has shown the DP. But the ones Briffa decided to include in his reconstruction did. Was he aware that some other ones didn’t? I am sure he did know that. Yet the data for MANY of the tree-ring studies that include the post-1940 period DO show it.
In case you don’t know it, the vast majority of dendro work used is in high-latitude regions. I have assumed this is because those give the best tree-ring data. Not all do, and not all regions do equally as well. Tropical ones don’t because the summer-winter variation is not wide enough. The denrochronologists look for sample local areas that give good contrast, then, from what I know, they get two cores from each tree. They evidently like to get more than a dozen sample trees from each local area.
Evidently, something in the high-latitude regions is going on that is different from what was going on in the 1880-1940 period (when the correlation of temps and TRW/MXD was “good”). Prior to 1880 the correlation was also not “good,” and that proxy has been left out of at least some reconstructions, too:
Addressing your question if the DP-inclusive proxy data has been used in all reconstructions, I don’t know for sure, but all reconstructions I can think of were done by Team members, except for the recent BEST reconstruction. BEST’s was done using a wider swath of data (but still data that was processed in an early stage by Team members at CRU, as far as I am aware). BEST’s output graphs that I recall seeing didn’t even include the post-1998 temperature decline. If BEST had proxy-only graphs, I can’t remember seeing them. You’ll have to look that up yourself.
Barry,
“One thing I have not got so far from the emails is mendacity amongst the emailers. They all genuinely believe what they are saying, they believe in the quality of their work, and they genuinely believe that some criticisms of their work is just poor quality science. ”
It appears that you have not read the relevant emails. Read Steve’s recent post about “perpetuating rubbish”. The authors of Mann et al 2003 knew that some of the material they included in their own paper was rubbish.
Also, read emails 3373, 4241, 4758, 2346, 2009, 0497, 1656, 3234.
These show that many of the climate scientists have private doubts about the validity of much of the work.
Paul,
I read half of the emails you noted (I would have read them all if you’d provided links). I’m not sure why disagreement amongst scientists is news. Did you assume that these people agreed with every tittle of each other’s work? I’m not convinced from the post you nominated that there is anything mendacious going on. The quality of the work choices made during those exchanges is a different matter, and there may be good cause for criticism (I don’t know).
More generally,
One of the reasons given that these emails should remain private is that it allows researchers to fully express themselves in ways that are inappropriate or potentially damaging in a public forum. Others argue that all emails within government funded institutions should be public property, but if the researchers operated under that assumption then they would be less open, for reasons that are not nefarious. Private beefs around the water cooler should not be annotated and put on a notice board, obviously. I think those arguing for the surrendering of private communications have not thought through what that means for the working environment. You’d get access, but then the workers would stop being candid. It’s a lose lose scenario.
What puzzles me is why the Team didn’t just omit the Briffa 01 MXD series altogether in later graphs as failing (for unknown reasons) to correlate with temperature as desired. Did Briffa and CRU have too much invested in the series in terms of grant money to drop it from later publicity stunts?
There would still be an element of cherry picking if only the “good” series were portrayed, but there wouldn’t be the overtly deceptive act of pretending the MXD series supports the contention in question when in fact it does not when viewed in its entirety.
5 Trackbacks
[…] the full post at Climate Audit Rate this: Share this:TwitterFacebookStumbleUponRedditDiggEmailLike this:LikeBe the first […]
[…] Read the full post at Climate Audit […]
[…] had a brief email exchange with Professor Severinghaus about Steve McIntyre’s recent post on his discussion with Mann and others about the divergence problem. I post it without comment, […]
[…] had a brief email exchange with Professor Severinghaus about Steve McIntyre’s recent post on his discussion with Mann and others about the divergence problem. I post it without comment, […]
[…] https://climateaudit.org/2011/11/28/severinghaus-and-hide-the-decline/ http://www.bishop-hill.net/blog/2011/12/2/tim-barnett-on-the-hockey-stick.html http://wattsupwiththat.com/2011/12/05/tim-barnett-on-the-hockey-stick-statistics-were-suspectthe-rest-of-the-team-knew-of-problems-with-manns-reconstruction/ […]