Was There a Second "Mike's Nature Trick" to "Hide the Decline?" Part 2 - Manufacturing Dissent
Just recently I saw a video by John Robson from what he calls a "Climate Discussion Nexus." I've seen several of his videos before, and for the most part they simply put a nice-looking polish on old, debunked contrarian talking points so that you can see them with a higher production value than what you might see in a Tony Heller video. I've largely ignored most of these; John Robson is a historian, and it's pretty clear that he doesn't understand the evidence he's trying to refute. But in this particular video Robson's credentials as a historian could have served him well, if he had chosen to use his expertise to uncover the facts involved.
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| The "Hockey Stick" as it Appeared in IPCC TAR |
In this video, John Robson attempts to describe the dissention between Michael Mann and his colleagues as they were preparing chapter 2 of the IPCC TAR. This chapter included the "hockey stick" graph with data from MBH99, Briffa 2000, Jones 1998, and the instrumental record. According to Robson, Keith Briffa had published a paper with contradictory evidence to the "hockey stick," but the IPCC squashed Briffa's data against his protests and essentially forced a unified narrative in favor of a hockey stick. In Robson's words, "a body needed to be buried for political reasons."
The climate science community was confronted with two studies at the same time, both using similar methods to study the same thing, and coming up with very different answers. Normally that kind of result means the science is not settled, the data may not be reliable, and the uncertainties need to be explained.
In this case, apparently, it meant instead that a body needed to be buried for political reasons. The story of the disappearance of the Briffa data is one of the darkest episodes in modern science.This Robson video was produced in 2019, some 20 years after the hockey stick was published, and it relies heavily on claims by Steve McIntyre originating from about 10 years ago (McIntyre is interviewed in the video). I responded to the "hide the decline" email in an earlier post. Here, I'd like to discuss the manufactured controversy between Briffa on the one hand and Mann & the IPCC on the other. The td;dr here is that there was some disagreement arising mostly from misunderstandings, but Briffa actually got what he wanted in the graph published in chapter 2. There was no buried body (metaphorical or otherwise) and there was no disappearing data.
Climate Audit and the Manufacturing of Dissent
The emails show that the late 20th century decline in the Briffa reconstruction was perceived by IPCC as “diluting the message”, that “everyone in the room at IPCC” thought that the Briffa decline was a “problem” and a “potential distraction/detraction”, that this was then the “most important issue” in chapter 2 of the IPCC report and that there was “pressure” on Briffa and other authors to show a “nice tidy story” of “unprecedented warming in a thousand years or more.”
Climategate correspondence on Sep 22-23, 1999 provides some contemporary information about the meeting. Mann noted that “everyone in the room at IPCC was in agreement that the [decline in the Briffa reconstruction] was a problem”:
What was deleted here was significant. The full context of the email from Mann says this:Keith’s series… differs in large part in exactly the opposite direction that Phil’s does from ours. This is the problem we all picked up on (everyone in the room at IPCC was in agreement that this was a problem and a potential distraction/detraction from the reasonably concensus viewpoint we’d like to show w/ the Jones et al and Mann et al series.
We demonstrate (through comparining an exatropical averaging of our nothern hemisphere patterns with Phil's more extratropical series) that the major discrepancies between Phil's and our series can be explained in terms of spatial sampling/latitudinal emphasis (seasonality seems to be secondary here, but probably explains much of the residual differences). But that explanation certainly can't rectify why Keith's series, which has similar seasonality *and* latitudinal emphasis to Phil's series, differs in large part in exactly the opposite direction that Phil's does from ours.
Perhaps Keith can help us out a bit by explaining the processing that went into the series and the potential factors that might lead to it being "warmer" than the Jones et al and Mann et al series?
But McIntyre asserts that Mann, Jones, and Briffa were concerned with the post-1960 decline, and he says that in these emails they each "experimented with different approaches to the 'problem' of the decline." He says Jones suggested using two versions of the graph (which is true), but then he then asserts that "the correspondence implies (though this is at present not proven)" that Mann wanted to "totally delete the Briffa reconstruction from the proxy diagram." But no one said or implied that. McIntyre seems to be taking Folland's claim that Mann thought the truth was closer to Mann's than Briffa's as implying that Mann wanted to delete Briffa's reconstruction - speculative at best.
McIntyre then quotes Briffa pushing back on Folland's email. He quoted Briffa saying,
I know there is pressure to present a nice tidy story as regards ‘apparent unprecedented warming in a thousand years or more in the proxy data’ but in reality the situation is not quite so simple… [There are] some unexpected changes in response that do not match the recent warming. I do not think it wise that this issue be ignored in the chapter.
But again, note the part that McIntyre deleted from the quote. Here it is in full.
There is still a potential problem with non-linear responses in the very recent period of some biological proxies ( or perhaps a fertilisation through high CO2 or nitrate input) . I know there is pressure to present a nice tidy story as regards 'apparent unprecedented warming in a thousand years or more in the proxy data' but in reality the situation is not quite so simple. We don't have a lot of proxies that come right up to date and those that do (at least a significant number of tree proxies ) some unexpected changes in response that do not match the recent warming. I do not think it wise that this issue be ignored in the chapter.
Here Briffa does seem to be concerned with the 20th century ("the very recent period") and points out that these biological proxies may be affected by CO2 fertilization or nitrate pollution (we'll come back to this in a moment). He is concerned about the certainty we can have about "apparent unprecedented warming" since we don't have a lot of proxies that come up to the present, and those that do are not reliable - for some tree ring proxies, "some unexpected changes in response that do not match the recent warming." So here we see (and this will be more clear below) that Briffa is not arguing for including tree ring proxies for the latter half of the 20th century; he's agreeing with Mann and others that the "decline" is unexpected and does not match recent warming. Briffa argues that uncertainties remain, and he's "not sure that this unusual warming is so clear in the summer responsive data. I believe that the recent warmth was probably matched about 1000 years ago." In the next section, we'll look more into what Briffa means by this, but for now, I want us to see how McIntyre is inserting a conflict about the "decline" into this discussion when no such conflict exists.
McIntyre does admit that Mann expressed willingness to include Briffa's reconstruction in chapter 2, and there are admissions both on the parts of Mann and Briffa that they may have misunderstood each other (at one point, it seems they may have been discussing different versions of Briffa's reconstruction). The differences between the two are real but collegial, and neither thought anyone was looking to strongarm one version of the graph at the expense of the others. I've copied the full text of these emails below (see the end of this post) in chronological order so that you can see this for yourself. There was some misunderstanding and disagreement among them, but these were also apparently resolved. The over-riding concern among all three is finding ways to reconcile what these reconstructions are saying, not choosing which ones fit a predetermined narrative. In fact, Briffa later added some clarifying points that I think are relevant (and not quoted by McIntyre).
My concern was motivated by the possibility of expressing an impression of more concensus than might actually exist . I suppose the earlier talk implying that we should not 'muddy the waters' by including contradictory evidence worried me . IPCC is supposed to represent concensus but also areas of uncertainty in the evidence. Of course where there are good reasons for the differences in series ( such as different seasonal responses or geographic bias) it is equally important not to overstress the discrepancies or suggest contradiction where it does not exist.
In other words, Briffa is trying to walk the line between over-emphasizing agreement between these proxies and over-emphasizing the discrepancies, since not all the discrepancies between the proxy reconstructions indicate contradictions because they do not all measure the same things. In fact, Mann had apparently assumed that Briffa's reconstruction was too similar to Jones' in seasonal and latitudinal emphases. Mann had said that what could explain the differences between MBH99 and Jones would not work for the discrepancies between Briffa and Jones, which have "similar seasonality *and* latitudinal emphasis, but differ in large part in exactly the opposite direction that Phil's does from ours." But Briffa wasn't so sure:
I am not sure this is true if the relevant series of ours is used. We need to reexamine the curves and perhaps look at the different regional and seasonal data in the instrumental record and over common regions in the different reconstructed series. We would be happy to work with you on this.
Briffa says differences between his "relevant series" and Jones and MBH99 may well be explained by seasonality and latitudinal emphases. What is absolutely clear is that while Briffa wanted all three reconstructions in the IPCC proxy graph, he did NOT want the Briffa reconstruction shown above in the "zero-order" draft. Briffa had been working to improve his reconstruction:
The latest tree-ring density curve ( i.e. our data that have been processed to retain low frequency information) shows more similarity to the other two series- as do a number of other lower resolution data ( Bradley et al, Peck et al ., and new Crowley series - see our recent Science piece).
And later, he said, "I prefer a Figure that shows a multitude of reconstructions (e.g similar to that in my Science piece)." Briffa wanted his updated reconstruction plotted with the others in a manner similar to what had already been published in his Science piece. So this Science piece,[1] I believe, is where we must now turn.
Briffa's Science Piece
To this point, we've seen very clearly that McIntyre has completely misread the conflict in the emails. He has inserted (sometimes explicitly with brackets) the post-1960 "decline" into the conversation, where there is actually no hint of disagreement among them on this point. The disagreement is instead over to what extent Briffa's reconstruction disagrees with Jones' and MBH99 and to what extent these discrepancies can be explained by what seasonal differences, latitudinal emphases, or something else. Briffa says he believes his improved reconstruction in his Science piece is better and in closer agreement with Jones' and MBH99. Briffa's reconstruction in the Science paper is below.
Briffa here includes several reconstructions, including his own from 1550-1960 (with no post-1960 data) along with others, most notably reconstructions from Jones and MBH98/99. You can see very clearly here that there is much greater large scale agreement between them with a warm MWP, a cool LIA and significant recent warming surpassing anything during the MWP. It actually looks pretty similar to the graph published in TAR chapter 2 (see above) except it goes back 2000 years and has no confidence envelopes. Without the CIs, we don't know how certain we can be that recent warming exceeds the MWP from this graph alone, but the text from Briffa and Osborn go into this. They make several points here that appear to be relevant to what Briffa would later write to Mann and the others in the above correspondence. For instance, he notes that while these reconstructions do largely agree with each other and it may well be that these reconstructions corroborate each other, he also notes that "very few of the series are truly independent: There is a degree of common input to virtually every one, because there are still only a small number of long, well-dated, high-resolution proxy records." So it's possible that some of the corroboration is due to the interdependencies in the reconstructions. He also notes that some of the enhanced growth of trees in parts of the NH may be affected by elevated CO2 or nitrogenous pollution in the 19th and 20th centuries. So there are real and significant uncertainties that must be admitted in these reconstructions, and this appears to be motivating what Briffa said in September - even some of the wording is similar to what he had said here. However, Briffa does say,
The temperature histories that extend through the medieval period do indicate general warmth (see the figure), although with different maxima (in the 9th, 10th and 11th centuries). Clearly none of these reach the levels of warmth seen today [although the confidence ranges (not shown here) approach them]. On the basis of their analysis Mann et al. conclude that the 20th century is anomalously warm. Even with the very limited data available and the problems associated with interpreting many of them as unambiguous measure of hemispheric temperature change, this conclusion must surely be accepted.
The Final Briffa Reconstruction
Keith has asked me to send you a timeseries for the IPCC multi-proxy reconstruction figure, to replace the one you currently have. The data are attached to this e-mail. They go from 1402 to 1995, although we usually stop the series in 1960 because of the recent non-temperature signal that is superimposed on the tree-ring data that we use. I haven't put a 40-yr smoothing through them - I thought it best if you were to do this to ensure the same filter was used for all curves.The raw data are the same as used in Briffa et al. (1998), the Nature paper that I think you have the reference for already. They are analysed in a different way, to retain the low-frequency variations. In this sense, it is one-step removed from Briffa et al. (1998). It is not two-steps removed from Briffa et al. (1998), since the new series is simply a *replacement* for the one that you have been using, rather than being one-step further.
Conclusion
- Briffa agreed with using his updated reconstruction through 1960 without the post-1960 decline.
- It's impossible to hide data that has been publicly available in the peer-reviewed literature. There's no hidden data, and no metaphorical buried bodies.
- Briffa generally agreed with Mann's conclusion of "anomalous warmth" but wanted to make sure they were clear and accurate about continuing uncertainties.
- The resulting graph in the IPCC TAR was the consensus position of Briffa, Jones, Mann and Folland. since the discrepancies brought up by Mann and Folland had been largely resolved with Briffa's updated time series in his Science piece.
- McIntyre inserted the post-1960 "decline" into this disagreement - there's no evidence they disagreed about this at all. Briffa wanted make sure that they were clear about the uncertainties in the IPCC report, but he had already gone on record in his agreement with MBH about anomalous warmth beginning in the 20th century.
There are two potential issues that remain:
- Was it correct for these scientists to not use the post-1960 tree ring data? I'm planning another post on the divergence problem, but the short answer for me is "yes." A good discussion of this is here. The short answer is that the divergence problem affects only high latitude trees in boreal forests. If you compare trees that do experience divergence with those that don't, they agree with each other prior to 1960, suggesting divergence is a recent phenomenon, and possibly due a sampling bias from younger trees.
- Why are these scientists so concerned about giving "fodder" to skeptics and "diluting the message" or feeling "pressure" to produce a "tidy story?" Some imply from these kinds of statements that Folland and Mann were interested in promoting a unified narrative and squashing dissent, but in reality, I think we've seen from McIntyre a big reason why this kind of language appears. As we can see, there is a subset of contrarians that have a history of contorting what is said on the basis of an assumption that climate scientists are biased. When these kinds of distortions become frequent (as they have) we understandably sometimes look to carefully craft what we say to avoid as much misrepresentation as possible. It could be that this systematic misreading (like what we've seen from McIntyre) is partly creating this concern among scientists.
These email discussions were personal and collegial, and the authors didn't feel the need to explain what they were saying to the general public, who ended up having access to this conversation years later. McIntyre (at best) read into this discussion what he wanted to find, and he very likely was careless in his reading of the discussion. Just a little bit of homework would have uncovered the problems with his reading. But it would seem McIntyre read these emails already believing there was a "trick" here (actually he believes there were several), and so he "found" what he was looking for. And 10 years later, videos are still being made about this, and McIntyre is still contributing to this distortion of the facts to be consumed by the public.
References:
[1] Briffa, K. R. (1999). CLIMATE WARMING:Seeing the Wood from the Trees. Science, 284(5416), 926–927. doi:10.1126/science.284.5416.92610.1126/science.284.5416.926
[2] Keith R Briffa, Annual climate variability in the Holocene: interpreting the message of ancient trees, Quaternary Science Reviews, Volume 19, Issues 1–5, 2000, pp. 87-105,
[3] Briffa, K. R., Schweingruber, F. H., Jones, P. D., Osborn, T. J., Harris, I. C., Shiyatov, S. G., … Grudd, H. (1998). Trees tell of past climates: but are they speaking less clearly today? Philosophical Transactions of the Royal Society B: Biological Sciences, 353(1365), 65–73. doi:10.1098/rstb.1998.0191
[4] Briffa, K., Schweingruber, F., Jones, P., Osborn, T., 1998a. Reduced sensitivity of recent tree growth to temperature at high northern latitudes. Nature 391, 678–682.
[5] Briffa, KR, Osborn, TJ, Schweingruber, FH, Harris, IC, Jones, PD, Shiyatov, SG and Vaganov, EA (2001) Low-frequency temperature variations from a northern tree-ring density network. Journal of Geophysical Research, 106. pp. 2929-2941. ISSN 2156-2202CRU Email Correspondence:
At 01:07 PM 9/22/99 +0100, Folland, Chris wrote:
Dear All
A proxy diagram of temperature change is a clear favourite for the Policy Makers summary. But the current diagram with the tree ring only data somewhat contradicts the multiproxy curve and dilutes the message rather significantly. We want the truth. Mike thinks it lies nearer his result (which seems in accord with what we know about worldwide mountain glaciers and, less clearly, suspect about solar variations). The tree ring results may still suffer from lack of multicentury time scale variance. This is probably the most important issue to resolve in Chapter 2 at present.
Chris
From: Keith Briffa <k.briffa@uea.ac.uk>
To: "Folland, Chris" <ckfolland@meto.gov.uk>, 'Phil Jones' <p.jones@uea.ac.uk>, "Michael E. Mann" <mann@multiproxy.evsc.virginia.edu>Subject: RE: IPCC revisions
Date: Wed Sep 22 16:19:06 1999
Cc: tkarl@ncdc.noaa.gov
Hi everyone
Let me say that I don't mind what you put in the policy makers summary if there is a general concensus. However some general discussion would be valuable . First , like Phil , I think that the supposed separation of the tree-ring reconstruction from the others on the grounds that it is not a true "multi-proxy" series is hard to justify. What is true is that these particular tree-ring data best represent SUMMER temperatures mostly at the northern boreal forest regions. By virtue of this , they also definately share significant variance with Northern Hemisphere land and land and marine ANNUAL temperatures - but at decadal and multidecadal timescales - simply by virtue of the fact that these series correlated with the former at these timescales. The multi proxy series (Mann et al . Jones et al) supposedly represent annual and summer seasons respectively, and both contain large proportions of tree-ring input. The latest tree-ring density curve ( i.e. our data that have been processed to retain low frequency information) shows more similarity to the other two series- as do a number of other lower resolution data ( Bradley et al, Peck et al ., and new Crowley series - see our recent Science piece) whether this represents 'TRUTH' however is a difficult problem. I know Mike thinks his series is the 'best' and he might be right - but he may also be too dismissive of other data and possibly over confident in his (or should I say his use of other's). After all, the early ( pre-instrumental) data are much less reliable as indicators of global temperature than is apparent in modern calibrations that include them and when we don't know the precise role of particular proxies in the earlier portions of reconstruction it remains problematic to assign genuine confidence limits at multidecadal and longer timescales. I still contend that multiple regression against the recent very trendy global mean series is potentially dangerous. You could calibrate the proxies to any number of seasons , regardless of their true optimum response . Not for a moment am I saying that the tree-ring , or any other proxy data, are better than Mike's series - indeed I am saying that the various reconstructions are not independent but that they likely contribute more information about reality together than they do alone. I do believe , that it should not be taken as read that Mike's series (or Jone's et al. for that matter) is THE CORRECT ONE. I prefer a Figure that shows a multitude of reconstructions (e.g similar to that in my Science piece). Incidently, arguing that any particular series is probably better on the basis of what we now about glaciers or solar output is flaky indeed. Glacier mass balance is driven by the difference mainly in winter accumulation and summer ablation , filtered in a complex non-linear way to give variously lagged tongue advance/retreat .Simple inference on the precidence of modern day snout positions does not translate easily into absolute (or relative) temperature levels now or in the past. Similarly, I don't see that we are able to substantiate the veracity of different temperature reconstructions through reference to Solar forcing theories without making assumptions on the effectiveness of (seasonally specific ) long-term insolation changes in different parts of the globe and the contribution of solar forcing to the observed 20th century warming .
There is still a potential problem with non-linear responses in the very recent period of some biological proxies ( or perhaps a fertilisation through high CO2 or nitrate input) . I know there is pressure to present a nice tidy story as regards 'apparent unprecedented warming in a thousand years or more in the proxy data' but in reality the situation is not quite so simple. We don't have a lot of proxies that come right up to date and those that do (at least a significant number of tree proxies ) some unexpected changes in response that do not match the recent warming. I do not think it wise that this issue be ignored in the chapter.
For the record, I do believe that the proxy data do show unusually warm conditions in recent decades. I am not sure that this unusual warming is so clear in the summer responsive data. I believe that the recent warmth was probably matched about 1000 years ago. I do not believe that global mean annual temperatures have simply cooled progressively over thousands of years as Mike appears to and I contend that that there is strong evidence for major changes in climate over the Holocene (not Milankovich) that require explanation and that could represent part of the current or future background variability of our climate. I think the Venice meeting will be a good place to air these isssues.
Finally I appologise for this rather self-indulgent ramble, but I thought I may as well voice these points to you . I too would be happy to go through the recent draft of the chapter when it becomes available.
cheers to all
Keith
From: Phil Jones <p.jones@uea.ac.uk>
Mike,
If we go as is suggested then there would be two diagrams - one simpler one with just Mann et al and Jones et al and in another section Briffa et al. This might make it somewhat awkward for the reader trying to put them into context.
The most important bit of the proxy section is the general discussion of 'Was there an MWE and a LIA' drawing all the strands together. Keith and I would be happy to look through any revisions of the section if there is time. One other thing, did you bring up the possibility of having a proxy-only chapter ( albeit short) for the next assessment ?
How is life in Charlottesville ? Do you ever bump into Michaels or is always off giving skeptical talks ?
From: "Michael E. Mann" <mann@multiproxy.evsc.virginia.edu>
From: Keith Briffa <k.briffa@uea.ac.uk>
To: "Michael E. Mann" <mann@multiproxy.evsc.virginia.edu>, "Folland, Chris" <ckfolland@meto.gov.uk>, 'Phil Jones' <p.jones@uea.ac.uk>
Subject: RE: IPCC revisions
Date: Thu Sep 23 18:29:05 1999
Cc: tkarl@ncdc.noaa.gov, mann@virginia.edu
Dear Mike ( and all)
Some remarks in response to your recent message
I believe strongly that the strength in our discussion
>will be the fact that certain key features of past climate estimates are
>robust among a number of quasi-independent and truly independent estimates,
>each
>of which is not without its own limitations and potential biases
Mike , I agree very much with the above sentiment. My concern was motivated by the possibility of expressing an impression of more concensus than might actually exist . I suppose the earlier talk implying that we should not 'muddy the waters' by including contradictory evidence worried me . IPCC is supposed to represent concensus but also areas of uncertainty in the evidence. Of course where there are good reasons for the differences in series ( such as different seasonal responses or geographic bias) it is equally important not to overstress the discrepancies or suggest contradiction where it does not exist.
And I
>certainly don't want to abuse my lead authorship by advocating my own work.
>
I sincerely hope this was not implied in anything I wrote - It was not intended
>I am perfectly amenable to keeping Keith's series in the plot, and can ask
>Ian Macadam (Chris?) to add it to the plot he has been preparing (nobody
>liked my own color/plotting conventions so I've given up doing this myself).
>The key thing is making sure the series are vertically aligned in a reasonable
>way. I had been using the entire 20th century, but in the case of Keith's,
>we need to align the first half of the 20th century w/ the corresponding mean
>values of the other series, due to the late 20th century decline.
>
Again I agree. Also , I am not sure which version of the curve you are now refering to. The original draft did show our higher frequency curve i.e. the version with background changes effectively filtered out (intended to emphasise the extreme interannual density excursions and their coincidence with volcanic eruptions) . The relevant one here is a smoothed version in which low-frequency changes are preserved. I can supply this and it will be in press by the time of the next reworking of the text.
Your above point on correct scaling is relevant also to Phil's curve which was not originally calibrated ( in a formal regression sense) with the summer temperature data - it was just given the same mean and standard deviation over a specific period. Hence the issue of equivelent scaling of all series is vital if we are to discuss specific period temperature anomalies in different series or compare temperature trends in absolute degrees.
>So if Chris and Tom (?) are ok with this, I would be happy to add Keith's
>series. That having been said, it does raise a conundrum: We demonstrate
>(through comparining an exatropical averaging of our nothern hemisphere
>patterns with Phil's more extratropical series) that the major
>discrepancies between Phil's and our series can be explained in terms of
>spatial sampling/latitudinal emphasis (seasonality seems to be secondary
>here, but probably explains much of the residual differences). But that
>explanation certainly can't rectify why Keith's series, which has similar
>seasonality
>*and* latitudinal emphasis to Phil's series, differs in large part in
>exactly the opposite direction that Phil's does from ours. This is the
>problem we
>all picked up on (everyone in the room at IPCC was in agreement that this
>was a problem and a potential distraction/detraction from the reasonably
>concensus viewpoint we'd like to show w/ the Jones et al and Mann et al
>series.
>
I am not sure this is true if the relevant series of ours is used. We need to reexamine the curves and perhaps look at the different regional and seasonal data in the instrumental record and over common regions in the different reconstructed series. We would be happy to work with you on this. Also remember that our (density )series does not claim hemispheric or annual coverage.
>So, if we show Keith's series in this plot, we have to comment that >"something else" is responsible for the discrepancies in this case. Perhaps
>Keith can
>help us out a bit by explaining the processing that went into the series
>and the potential factors that might lead to it being "warmer" than the Jones
>et al and Mann et al series?? We would need to put in a few words in this
>regard. Otherwise, the skeptics have an field day casting
>doubt on our ability to understand the factors that influence these estimates
>and, thus, can undermine faith in the paleoestimates.
The best approach here is for us to circulate a paper addressing all the above points. I'll do this as soon as possible.
I don't think that
>doubt is scientifically justified, and I'd hate to be the one to have
>to give it fodder!
>
>
>The recent Crowley and Lowery multiproxy estimate is an important
>additional piece of information which I have indeed incorporated into the
>revised draft. >Tom actually estimates the same mean warming since the 17th century in his >reconstruction, that we estimate in ours, so it is an added piece of
>information that Phil and I are probably in the ballpark (Tom has used
>a somewhat independent set of high and low-resolution proxy data and a very
>basic compositing methodology, similar to Bradley and Jones, so there is >some independent new information in this estimate.
>
fair enough - but I repeat that the magnitude of the observed warming in the 20th century is different in summer and annual data
>One other key result with respect to our own work is from a paper in the
>press in "Earth Interactions". An unofficial version is available here:
>
>http://www.ngdc.noaa.gov/paleo/ei/ei_cover.html
>
>THe key point we emphasize in this paper is that the low-frequency
>variability in our hemispheric temperature reconstruction is basically the
>same if we don't use any dendroclimatic indicators at all (though we
>certainly resolve less variance, can't get a skillful reconstruction as far
>back, and there are notable discrepancies at the decadal and interannual
>timescales). A believe I need to add a sentence to the current discussion
>on this point,
>since there is an unsubstantiated knee-jerk belief that our low-frequency
>variability is suppressed by the use of tree ring data.
>
>We have shown that this is not the case: (see here: >http://www.ngdc.noaa.gov/paleo/ei/ei_datarev.html
>and specifically, the plot and discussion here:
>http://www.ngdc.noaa.gov/paleo/ei/ei_nodendro.html
>Ironically, you'll note that there is more low-frequency variability when
>the tree ring data *are* used, then when only other proxy and
>historical/instrumental data are used!
>
This is certainly relevant and sounds really interesting. I need to look at this in detail. The effect of the including tree-ring data or not, is moderated by the importance of the particular series in the various reconstructions ( relative coefficient magnitudes). There is certainly some prospect of affecting (reducing) the apparent magnitude of the 20th century warming by loading on high-pass filtered chronologies , but equally a danger of exagerating it if the series used or emphasised in th calibration have been fertilized by CO2 or something else. As you know we ( Tim, Phil and I ) would love to collaborate with you on exploring this issue (and the role of instrumental predictors) in the various approaches. The key here is knowing much more about the role of specific predictors through time and their associated strengths and weaknesses.
>SO I think we're in the position to say/resolve somewhat more than, frankly,
>than Keith does, about the temperature history of the past millennium.
>And the issues I've spelled out all have to be dealt with in the chapter.
>
I certainly do not disagree with you - the scale of your input data undoubtedly must contain more information than our set . I have never implied anything to the contrary. I do not believe that our data are likely to tell us more than summer variability at northern latitudes . The discussion is only about how close our and your data likely represent what they are calibrated against , back in time. Let's not imagine a disagreement where there is none.
>One last point: We will (like it or not) have SUBSTANTIAL
>opportunity/requirement to revise much of this discussion after review, so
>we don't have to resolve everything now. Just the big picture and the
>important details...
>
>I'm sure we can can up with an arrangement that is amenable to all, and I'm
>looking forward to hearing back from Keith, Phil, and Chris in particular
>about the above, so we can quickly move towards finalizing a first draft.
>
>
Yes indeed. The reviewing will lead to much comment and likely disagreement by the masses. This is the way of these things. It is always a thankless task undertaking these drafting jobs and I think you are doing a good job. Tommorrow I'll send some very minor comments on typos and the like if you want them - or have you picked many of them up? Anyway , keep up the good work .
best wishes
Keith
From: "Michael E. Mann" <mann@multiproxy.evsc.virginia.edu>
To: Keith Briffa <k.briffa@uea.ac.uk>, "Folland, Chris" <ckfolland@meto.gov.uk>, 'Phil Jones' <p.jones@uea.ac.uk>
Subject: RE: IPCC revisions
Date: Thu, 23 Sep 1999 13:47:22 -0400
Cc: tkarl@ncdc.noaa.gov, mann@virginia.edu
Thanks alot Keith,
Your comments and suggestions sound good on all counts.
Clearly there is one overiding thing to make sure of here: that we have the right version of your series. I *think* that we do, and you might have been looking at an old version of the comparison Figure??
Please check out the data here ASAP:
ftp://eclogite.geo.umass.edu/pub/mann/IPCC/MILLENNIUM/
This directory has all the series, aligned as I described to have a 1961-90 base climatology (or in the case of your series, a pseudo 1961-90 base climatology achieved by actually matching the mean of your series and the instrumental record over the interval 1931-60 interval). These are the data that Ian Macadam is hopefully presently plotting up, and I don't think the discrepancies between the different series are as bad as we percieved earlier (other than the late 19th century where you are somewhat on the warm side relative to the rest). Please confirm ASAP that we have the right version of the series (note, these have all been 40 year lowpassed)...
One other thing, I think you misinterpreted my statement:
>
>SO I think we're in the position to say/resolve somewhat more than, frankly,
>than Keith does, about the temperature history of the past millennium.
>And the issues I've spelled out all have to be dealt with in the chapter.
>
I wasn't talking about the comparison of our two series! I was talking about our two different opinions on how confident we are about our ability, as a community, to assess the actual climate changes over this timeframe. And perhaps we're closer here than I assumed anyways. Sorry about the\ misunderstanding. With your interpretation, my comment must I have sounded really obnoxious!
From: Tim Osborn <t.osborn@uea.ac.uk>
To: mann@virginia.edu,imacadam@meto.gov.uk
Subject: Briffa et al. series for IPCC figure
Date: Tue, 05 Oct 1999 16:18:29 +0100
Cc: k.briffa@uea,p.jones@uea
Dear Mike and Ian
Keith has asked me to send you a timeseries for the IPCC multi-proxy
reconstruction figure, to replace the one you currently have. The data are
attached to this e-mail. They go from 1402 to 1995, although we usually
stop the series in 1960 because of the recent non-temperature signal that
is superimposed on the tree-ring data that we use. I haven't put a 40-yr
smoothing through them - I thought it best if you were to do this to ensure
the same filter was used for all curves.
The raw data are the same as used in Briffa et al. (1998), the Nature paper
that I think you have the reference for already. They are analysed in a
different way, to retain the low-frequency variations. In this sense, it
is one-step removed from Briffa et al. (1998). It is not two-steps removed
from Briffa et al. (1998), since the new series is simply a *replacement*
for the one that you have been using, rather than being one-step further.
A new manuscript is in preparation describing this alternative analysis
method, the calibration of the resulting series, and their comparison with
other reconstructions. We are consdering submitting this manuscript to J.
Geophys. Res. when it is ready, but for now it is best cited as:
Briffa KR, Osborn TJ, Schweingruber FH, Harris IC and Jones PD (1999)
Extracting low-frequency temperature variations from a northern tree-ring
density network. In preparation.
Keith will be sending you a copy of the manuscript when it is nearer to
completion.
I have also attached a PS file showing the original Briffa et al. (1998)
curve, with annotation of cold years associated with known volcanic
eruptions. Overlain on this, you will see a green curve. This is the new
series with a 40-yr filter through it. This is just so that you can see
what it should look like (***ignore the temperature scale on this
figure***, since the baseline is non-standard).
With regard to the baseline, the data I've sent are calibrated over the
period 1881-1960 against the instrumental Apr-Sep tempratures averaged over
all land grid boxes with observed data that are north of 20N. As such, the
mean of our reconstruction over 1881-1960 matches the mean of the observed
target series over the same period. Since the observed series consists of
degrees C anomalies wrt to 1961-90, we say that the reconstructed series
also represents degrees C anomalies wrt to 1961-90. One could, of course,
shift the mean of our reconstruction so that it matched the observed series
over a different period - say 1931-60 - but I don't see that this improves
things. Indeed, if the non-temperature signal that causes the decline in
tree-ring density begins before 1960, then a short 1931-60 period might
yield a more biased result than using a longer 1881-1960 period.
If you have any queries regarding this replacement data, then please e-mail
me and/or Keith.
Best regards
Tim
Calibrated against observed Apr-Sep temperature over 1881-1960
averaged over all land grid boxes north of 20N
<data series follows>
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