Climate Feedback

The decay of the hockey stick

(Posted by Olive on behalf of Hans)

In October 2004 we were lucky to publish in Science our critique of the ‘hockey-stick’ reconstruction of the temperature of the last 1000 years. Now, two and half years later, it may be worth reviewing what has happened since then.

The publication in 2004 was a remarkable event, because the hockey-stick had been elevated to an icon by the 3rd Assessment Report of the IPCC. This perception was supported by a lack of healthy discussion about the method behind the hockey-stick. In the years before, due to effective gate keeping of influential scientists, papers raising critical points had a hard time or even failed to pass the review process. For a certain time, the problem was framed as an issue of mainstream scientists, supporting the concept of anthropogenic climate change, versus a group of skeptics, who doubted the reality of the blade of the hockey stick. By framing it this way, the real problems, namely the ‘wobbliness’ of the shaft of the hockey-stick, and the suppressing of valid scientific questions by gate keeping, were left out.

Hopefully, sociology of science will later study this unfortunate period of climate science, but we may conclude now that science itself has indeed corrected claims of premature knowledge. We see now a healthy and broad discussion of the issue. We had the opportunity to respond to no less than four comments on our 2004 Science paper, but unfortunately only two comments were published. Similarly, Michael Mann and his coworkers had to respond to at least 2 comments to their Journal of Climate article in 2005.

At the EGU General Assembly a few weeks ago there were no less than three papers from groups in Copenhagen and Bern assessing critically the merits of methods used to reconstruct historical climate variable from proxies; Bürger’s papers in 2005; Moberg’s paper in Nature in 2005; various papers on borehole temperature; The National Academy of Science Report from 2006 – al of which have helped to clarify that the hockey-stick methodologies lead indeed to questionable historical reconstructions. The 4th Assessment Report of the IPCC now presents a whole range of historical reconstructions instead of favoring prematurely just one hypothesis as reliable.

When looking back we are satisfied with what has been achieved – namely an open, open-minded exciting discussion about the merits and problems related to different methods; an atmosphere where mere claims about the informational content of proxy-data meet a more critical response; an evolving practice of testing the skill of reconstruction methods in the laboratory of millennial forced global climate model simulations, where the formation of proxy-data is simulated in – so far too simplified – models.

Hans von Storch and Eduardo Zorita

Comments

  1. Report this comment

    Lubos Motl said:

    Dear Dr von Storch and Dr Zorita,

    the results are nice but would you agree that it is not a faithful description of history if you paint yourself as the main heroes who found serious problems with the hockey stick papers?

    I am convinced that you have realized – and even said – that McKitrick & McIntyre identified a problem that was arguably most transparent.

    I would appreciate if you credited them with their important contributions in an updated version of this text.

    Thank you very much,

    Lubos

  2. Report this comment

    cbone said:

    How can you discuss the ‘decay’ of the hockey stick without mentioning the two people who launched the inquiry into the hockey stick? Namely Steve McIntyre and Ross McKitrick.

  3. Report this comment

    Bernie said:

    Having tracked the various debates and discussions at Real Climate and Climate Audit and looked at the 4th Assessment Report I am nowhere near as optimistic as you appear to be that “normal science” will break out any time soon. As a researcher in a non-climate area I am stunned at (a) the lack of replication, (b) the tortured and frequently questionable use of certain statistical methods, © the overall underspecification of statistical models given the signifcance of the predictions being made and (d) the unwillingness of researchers to essentially treat anyone outside their immediate field with common courtesy. I hope you are right and I am wrong – but wishing does not make it so.

  4. Report this comment

    Joe said:

    I noticed no mention of McIntyre and McKitrick in this post. Unfortunate.

  5. Report this comment

    Mark Hamilton said:

    While I agree that the hockey stick has decayed, I am somewhat stunned by Von Storch and Zorita’s new found pollyanish view of paleoclimate science culture.

    As they well know, the hockey stick debate advanced in spite of intolerance and obstructionism by their peers. It advanced because of two investigators outside of the walls of climate science (McIntyre and McKitrick 2003 & 2005) relentlessly investigated, and published pointed critiques that outraged the science’s gatekeepers. And then it continued to advance because a few vetted “non-skeptic” climate researchers (starting with Von Storch and Zorita) were willing to risk the firestorm to challenge the methods behind the stick’s orthodoxy.

    And finally it advanced because of unwelcome politics – a Congressional investigation and request that made scientists confront the issues.

    More disappointingly, the authors also seemed to have forgotten that the hockey stick was jsut the immediate symptom, that both they and M&M had raised more fundamental issues regarding paleo-climate science core culture – the lack of full disclosure, the acceptance of journal unenforced policy, the lack of informed and robust peer reviews, etc.

    What then has really changed? Von Storch, et. al. have recently gotten fairer hearings, and they are back within the walls of acceptable opinion. None the less, the cultural practices that led to this crisis have NOT changed, and that Von Storch and Zorita found it necessary to studiously ignore mentioning the two researchers that are most responsible for the stick’s decay suggest they know the walls remain, and the gatekeepers are vigilent.

    Von Storch and Zorita should not confuse their own serenity with peers as a change in culture – nor should they give up fighting for their (former?) ideals.

  6. Report this comment

    Jo Calder said:

    I think there are some things left unsaid in this brief comment. The first real critique of the Hockey Stick came from outside climate science itself and not from the present authors; climate science doesn’t seem to have got much better in its data and code archiving practices (and there remain some spectacular lacunae); many climate scientists continue to confuse their vocation with advocacy. So, still plenty of distance to travel before the Hockey Stick is finally decomposed.

  7. Report this comment

    Jason Smerdon said:

    Hi Hans and Eduardo – Thanks for a great post and I am looking forward to reading what will undoubtedly be great blogging in the future. One thought that occurred to me while reading this entry is how critical evaluation of millennial reconstructions in general, and criticisms of the hockey stick specifically, are often attributed to specific events or dates that represented a watershed moment. While it is true that things have accelerated over the last several years, I think it is important to point out that the skepticism wasn’t started with one paper or at one moment. As is often the case in science, many voices have weighed in on this issue and it has been a work in progress for some time (although not always represented as such). Nevertheless, it lately seems en vogue to cast the hockey stick supporters as the reconstruction triumphalists who managed to squelch skepticism for so many years until a specific event turned the tide. There is likely some truth to the idea that it was harder to publish results that were critical of the hockey stick view, but there has been a growing and healthy debate about millennial climate reconstructions at least since MBH was published. Just a couple quick examples: the boreholes were an early dissenter and entered the scene around the same time as MBH; Wally Broecker published a letter in Science criticizing the MBH curve very shortly after it’s publication; divergence and curve standardization issues associated with the tree rings were widely being discussed by the late 90’s and Esper et al. (2002) was an important later contribution in that regard, the prospect of a localized or global LIA and MWP was (and is) a hot topic before MBH, and so on. I mention this not out of concern for being inclusive, but because I do think it is an important point about the sociology of this particular field of science. I just don’t buy the view, ala the Wegman report, that the field has been cheering happily along for one particular research team’s result. To the contrary, many people have expressed skeptical views of the hockey stick result since its publication and time has simply added more and more voices to the mix, albeit more sophisticated and insightful ones. That is healthy science!

  8. Report this comment

    Hans Erren said:

    http://www.climateaudit.org/?p=1518

    They then proceed to discuss various articles on the Hockey Stick mentioning Bürger, Moberg, borehole papers, the NAS report, but failing to mention McIntyre and McKitrick. Pretty annoying.

  9. Report this comment

    Milan Salek said:

    I appreciate the bold scientists who maintains the debate about scientific methods of climate change research; however, I miss a mention of the first challengers, McIntyre and McKitrick, who were the first scientists who questioned the statistical methods leading to hockety stick shape of paleoclimate reconstructions.

  10. Report this comment

    Deltoid said:

    Nature climate blog off to rocky start

    Nature has started Climate Feedback, a blog on climate change. One of the first posts is by Roger Pielke Jr, who claims Even the venerable New York Times is prone to completely botching a discussion of the science of climate…

  11. Report this comment

    B. Ströher said:

    At least it would be fair to mention the role of Steven McIntyre who has done most of the work and who is not a member of the community, but was keen enough to fight for true science.

  12. Report this comment

    William Connolley said:

    The omission of M&M is indeed curious; as indeed is the omission of the various crits of your own paper.

    I rather doubt some of your assertions – is the “gatekeepering” stuff reliable? – but “The 4th Assessment Report of the IPCC now presents a whole range of historical reconstructions instead of favoring prematurely just one hypothesis as reliable.” is also odd. In 2001, there was only one… now there are many. Rather than some conspiracy, isn’t it more plausible that the IPCC just used what was available, in 2001 and 2007?

  13. Report this comment

    Hans Erren said:

    I’m guessing that the MBH one was used because it had nice error bars on it

    Yes and these error bars are yet to be replicated.

  14. Report this comment

    Steve McIntyre said:

    The Briffa version used in the IPCC spaghetti diagram was truncated in 1960 to remove an Inconvenient Divergence in which the series goes down after 1960. You have to look closely to see the truncation – see

    http://www.climateaudit.org/?p=194.

    Had they used the actual series from their citation (Briffa 2000), the visual effect would have been very different.

  15. Report this comment

    John A said:

    Whatever is Connelley referring to? The critical reason why the Hockey Stick featured so prominently was that Mann headed the group writing about paleoclimatic reconstructions. Conflict of interest, anyone?

    See Ross McKitrick’s paper on the genesis of the Hockey Stick: http://www.climatechangeissues.com/files/PDF/conf05mckitrick.pdf

  16. Report this comment

    Armand MacMurray said:

    William, I believe Hans is just commenting that the error bars have yet to be shown to be correct.

  17. Report this comment

    LogicallySpeaking said:

    Don’t worry, I’m sure when Storch and Zorita do a blog entry on the difference between radians and degrees, they’ll be happy to credit McIntyre and McKitrick for bringing this confusion to the forefront.

  18. Report this comment

    Hans von Storch said:

    For clarification- when we wrote in our comment about the IPCC and the hockey-stick, we referred to the policy maker summary and the synthesis report, in which only the hockey-stick were featured. The technical chapter itself was more balanced on reporting about published results at that time.

    It would, however, be interesting to learn, why at that time most published results were consistent with the hockey-stick, and later inconsistencies among different reconstructions became evident. We assume that the original consistency was related to successful gate-keeping.

    We would also like to add that the question of the error bars in MBH-diagrams is still open for debate. Important questions have not yet answered.

    On the role of Steve McIntyre we will comment on a few days.

    Hans von Storch and Eduardo Zorita

  19. Report this comment

    Will Richardson said:

    Dear Mssrs. von Storch and Zorita,

    Do you think it would be appropriate to convince Nature to add Climate Audit to the blogroll associated with this blog? Since you take Climate Audit seriously enough to occasionally participate in some of the discussions there, it does not appear that you would have any scientific objections.

    Of course, I would understand if Nature decided not to accede to your requests on non-scientific grounds, but it seems that you could at least make the suggestion.

  20. Report this comment

    John Hanson said:

    This blog post is simply an astonishing and rather self-serving distortion of the history of the “hockey stick” and of Von Storch’s and Zoritas own role. The main thesis that “valid scientific questions were suppressed” is grave, but it is both implausible and unsupported by any evidence.

    Von Storch and Zorita modestly call the publication of their own paper a “remarkable event”, but when they “review what has happened since”, they oddly fail to mention that the main thing that happened since is that major errors in their paper were uncovered in two comments published subsequently in Science, which invalidated their main result. A rather more realistic discussion of this was provided by the colleagues of Realclimate some time ago: http://www.realclimate.org/index.php/archives/2006/04/a-correction-with-repercussions/

    It is clear that Von Storch and Zorita had been aware of the errors for months but did not publish an appropriate correction. In my view, the decent response would have been to withdraw the paper instead of bragging about it. “Have you no shame Sir?”

  21. Report this comment

    Steve McIntyre said:

    We have a discussion of what we’ve been able to decode about MBH98-MBH99 confidence intervals at http://www.climateaudit.org/?p=647 . MBH98 confidence intervals are simply 2-sigma in the overfitted calibration period. Both Hans von Storch and us raised the non-replicability of MBH99 confidence intervals at the NAS Panel, in the hope that they would resolve the matter. They failed to do so. The source code provided to the House Energy and Commerce Committee did not include code for the calculation of confidence intervals. Nature has refused to require Mann to disclose anything further. So it all remains a mystery.

    Maybe this blog entry will help move this off the dime.

  22. Report this comment

    Volker Rodnick said:

    Von Storch and Zorita present us with a rather strange story in which they are the heroes: before publication of their paper in late 2004, scientific discussion on reconstructions of the past millennium was supposedly stifled, while afterwards a healthy discussion arose. Alas – where is the evidence for this self-serving story? None in the post itself, while in his comment later on Von Storch remarks that “at that time most published results were consistent with the hockey-stick”, interpreting this as an ominous sign of gate-keeping. If only the facts would support this.

    The millennium reconstruction that differs most from Mann et al. 1999 ist the one by Esper et al. 2002, see the overview of all curves at

    http://en.wikipedia.org/wiki/Image:1000_Year_Temperature_Comparison.png

    or the latest IPCC report at http://www.ipcc.ch (Chapter 6). Other reconstructions were published by Crowley and Lowery (2000) or by Briffa et al. (2001). It is clear that a healthy scientific debate was alive and kicking, as it should, well before Von Storch et al. published their faulty Science paper in 2004! Crediting their own erroneous paper with starting a healthy debate is, pardon me, simply “Quatsch”.

  23. Report this comment

    piglet said:

    It is disgusting that these authors are allowed such a bragging self-congratulation on Nature blogs when their Science paper they are bragging about contained serious errors and was subject to a correction in Science in April 2006. One would really wish for humbler scientists. From what I have been reading on this blog to date, the editorial policy seems dubious. Pielke’s “confusion” post contains confusions that any attentive reader would have spotted (and many did indeed spot them). These mistakes are difficult to justify as made in good faith, especially since Pielke insists in his confused opinion even after admitting that it is based on a clear-cut mistake on his part.

    What’s going on here? Is this intended as a playground for self-apointed climate mavericks?

  24. Report this comment

    Hans von Storch said:

    In our submission to the nature-weblog, we have presented how we have perceived the fate and responses of our paper to science about the methodical problems behind the hockey-stick technique. In this account we have not mentioned many other articles, which have been critical to the hockey-stick result.

    It has been noted that we have made no reference to Steve McIntyre’s work. This was on purpose, as we do not think that McIntyre has substantially contributed in the published peer-reviewed literature to the debate about the statistical merits of the MBH and related method. They have published one peer-reviewed article on a statistical aspect, and we have published a response – acknowledging that they would have a valid point in principle, but the critique would not matter in the case of the hockey-stick.

    In our understanding, McIntyre has raised two objections to the hockey-stick reconstruction; one was the statistical problem just mentioned, the other the selective selection of proxy data (the bristlecone question). It may very well be that this critique is valid; it has never been properly discussed, as far as we know – among other things because McIntyre has not published a regular review paper on this issue in a peer-reviewed journal. We have advised Steve McIntyre several times that he should write a paper just on this issue, without blending many other aspects into such a paper. He has not done so, it seems. The example of the GRL paper on the EOF problems has demonstrated that he has a chance to publish in peer-reviewed journals.

    Thus, we see in principle two scientific inputs of McIntyre into the general debate – one valid point, which is however probably not relevant in this context, and another which has not been properly documented.

    On the other hand, Steve McIntyre is to be applauded to have made the hockey-stick result an issue in the public debate; without his efforts, we guess, there would have been not Barton letters, thus no inquiry by the National Research Council and subsequently no hearing in a subcommittee of the House. This was a political achievement, not a scientific one. And the Barton letters were questionable.

    Another important aspect was his insistence on free availability of data, for independent tests of (not only) important findings published in the literature. It is indeed a scandal that such important data sets, and their processing prior to analysis, is not open to independent scrutiny. The reluctance of institutions and journals to support such requests is disappointing.

    We would also like to emphasize that we consider Steve McIntyre often unfairly treated by the scientific community. He has, as everybody else, the right to be heard and to participate in the debate as long he is contributing scientific arguments. His GRL paper has demonstrated that he is qualified to participate. We have supported Steve McIntyre in his quest to be heard; that does not mean that we agree with all his views and knowledge claims. Indeed, we mostly do not.

    Hans von Storch and Eduardo Zorita

  25. Report this comment

    Will J. Richardson said:

    Dear Mssrs. von Stroch and Zorita,

    I am somewhat astonished at your May 11 comment. You dismiss Steve McIntyre’s contributions to the Hockystick debate not on the basis that his critisisms lack substance, rigor, or validity, but because his work has not published in journals to which you ascribe authority.

    This is a neat, if disingenuous, evasion of the issue. The issue regarding McIntyre’s work is whether or not his conclusions are accurate, not whether some journal approves of his work. Both of you are aware of McIntyre’s substantial body of work as documented on Climate Audit. McIntyre provides both the data and computer code which underlies his work on his website. It should be a simple matter for scientists of your standing to determine the merit of McIntyre’s work independently (i.e. do your own peer review) without relying on “journals” to tell you what to think.

    Regards,

    WJR

  26. Report this comment

    Ron Cram said:

    Dear Drs. von Storch and Zorita,

    I was amazed to see your posting on “The Decay of the Hockey Stick” and your follow up posting on the contributions of McIntyre and McKitrick. In the first you claim your 2004 journal publication a “remarkable event” because the Hockey Stick was such an unassailable icon in the science community. However, the shine on the Hockey Stick had already been removed by the 2003 paper published by McI and McK in E&E.

    You also claim that McI and McK were correct when they showed that Mann’s statistical method produces hockey stick shapes from trendless red noise but then you write “they would have a valid point in principle, but the critique would not matter in the case of the hockey-stick.” This is an extraordinary claim. Are you unaware that McI has published a response showing why it does matter in the case of the hockey stick? Since you have not publicly replied, I was forced to presume you had conceded the point. If you have not conceded the point, please do publish a response.

    You also claim that McI and McK only looked at statistical problems with Hockey Stick paper and that you looked at methodical problems. Speaking only as an interested layman, I do not think your claim obtains. McI and McK criticized Mann’s selection of the bristlecone pine series, an issue you agree may be valid but have not researched yourselves. But you then go on to make the strange claim that no one else has researched the issue either. This is hardly accurate since the U.S. NRC published a report (at the request of Congress) agreeing that bristlecone pine series is not a temperature proxy and should not be used.

    You also proclaim yourselves satisfied with what has been achieved – an open debate. I find this most surprising of all, because I am completely unsatisfied. The temperature reconstructions in 4AR all continue to use the bristlecone pine series.

    Perhaps most unsatisfying to me is the lack of accountability in the science community. As you know, Dr. Mann withheld results of validation tests in a subdirectory called “BACKTO_1400-CENSORED” that were contrary to his conclusions. According to published reports (see ”http://www.uoguelph.ca/~rmckitri/research/Climate_L.pdf" rel="nofollow">http://www.uoguelph.ca/~rmckitri/research/Climate_L.pdf ), the folder showed Mann knew his method did not get a hockey stick shape without the bristlecone pine series. Despite this knowledge, Mann made claims that his method was robust and not dependent on any particular proxy. If the science community does not have any ways to insure honesty in science, what credibility does anyone’s work really have?

  27. Report this comment

    Craig Loehle said:

    When asking about whether recent decades have been warmer than some past period such as the Medieval Warm Period, it is helpful to know whether a given set of data are capable of detecting a given difference. This is known as power analysis in standard statistics. In a recent paper (Loehle, C. 2005. Estimating Climatic Timeseries from Multi-Site Data Afflicted with Dating Error. Mathematical Geology 37:127-140) I showed that the effect of dating error in proxy records is to reduce the amplitude of peaks in historical series. This is because the existence of dating error when multiple proxies are combined is equivalent to applying a smoothing filter to the data (such as a Gaussian filter). This removes peaks as if they were noise to be “filtered out”. Thus care must be taken to do a proper analysis when asking about extreme events.

    I also note that I have had a shot at the hockey stick at the basic level of whether tree rings are even valid as a proxy for long term temperature reconstruction (Loehle, C. 2004. Using Historical Climate Data to Evaluate Climate Trends: Issues of Statistical Inference. Energy & Environment 15:1-10).

  28. Report this comment

    Hans Erren said:

    I learned that Stephen McIntyre was invited for a guest blog here, but the invitation was soon retracted.

    You can’t keep a secret these days in blogosphere.

  29. Report this comment

    Michael Strong said:

    It is ironic that the primary rationale that von Storch and Zorita give for ignoring M&M is that M&M have not published sufficiently in the official organs of science; just as Nature has withdrawn its offer to allow McIntyre to respond here. Commentary such as Robert Higgs, “Peer Review, Publication in Top Journals, Scientific Consensus, and So Forth,” explaining that editors tend to pick referees that will validate their notions seems increasingly relevant.

    For those of us who used to admire science, and who are concerned about the possible adverse effects of human activity on the environment, the behavior of the climatological community gatekeepers of credibility is disappointing. Given a traditional scientific commitment to skepticism, combined with the magnitude and gravity of the issue at stake, I would expect no less than 100% support for the work being done at Climate Audit.

    “We are trying to prove ourselves wrong as quickly as possible, because only in that way can we find progress.” Richard Feynman

  30. Report this comment

    Beverly Boos said:

    Hi All,

    I am not a scientist, just an ordinary person who is giving presentations on global warming to groups of people of all ages, as I was trained to do by the Hon. Al Gore and The Climate Project.

    I have followed this conversation because I have been asked about this by my audiences from time to time.

    My question is…on a practical level today, where does this leave us on the issue outside of the framework of the dispute? Is it possible to make a common statement, from the place of all being on the same team, even with the divide?

    I want to ask the help of the scientific community to inspire us and help us get closer to the information we need to guide us forward.

    Thanks so much for your hard work, all parties.

    Bev

  31. Report this comment

    paul said:

    Beverly: Please do not use “Hon” when reffering to Al Gore. Also if you want simple answers then you need to ask Al.

  32. Report this comment

    julian braggins said:

    Hi Bev,

    The short answer is – you will never get a concensus in any specialty blog.

    Following the Climate Change argument daily from a pro AGW position 7 years ago I have come to the conclusion that the specialisation of Science itself precludes agreement on a subject so all encompassing as Climate, it covers so many disciplines that there is no independant body that covers them all, even if there was, there is violent disagreement between branches, i.e. Cosmology – gravity v electrical universe theory.

    IMHO the Solar influences, (not all quantified yet ), have the most convincing long term record of being the driver of all climate change, which has always been changing.

    I am no longer a ‘believer’ in human caused global warming, there is simply no evidece for more than a small fraction of one degree C per century – and without that and the fertilisation effect of the increased CO2 that we are enjoying, the human race would starve.

    I doubt this would go down very well with your audiences, ah well !

  33. Report this comment

    Steve McIntyre said:

    In their summary of the change in consensus over the hockey stick, von Storch and Zorita (VZ) at first did not mention our work, then, in light of criticism, they dismissed our contributions as minimal and largely irrelevant.

    We note with some pride that the NAS took a very different and more favorable view of our work, even crediting us with a revival of research on fundamental methodological issues, saying :

    “A second area of criticism focuses on statistical validation and robustness. McIntyre and McKitrick (2003, 2005a,b) question the choice and application of statistical methods, notably principal component analysis; the metric used in the validation step of the reconstruction exercise; and the selection of proxies, especially the bristlecone pine data used in some of the original temperature reconstruction studies. These and other criticisms, explored briefly in the remainder of this chapter, raised concerns that led to new research and ongoing efforts to improve how surface temperature reconstructions are performed. (p.110)”

    While we are pleased that some of our observations, in particular, about verification statistics and non-robustness, have attracted academic interest (e.g. from Bürger), it was not our intent to develop methodological innovations or tell paleoclimatologists how to do their job.

    Our initial objective was simpler: despite the prominence of the MBH98 reconstruction, no one seemed sure how it was done, and nobody had verified the results. Did the reconstruction possess the claimed “statistical skill”? Did it have the claimed “robustness” to the presence/absence of all dendroclimatic indicators? Had the proxies been “rigorously” selected according to objective criteria?

    Notwithstanding claims in the MBH papers (e.g. verification r2 skill as shown in MBH98 Figure 3), we showed the answer was, in every case, No. Early segments of the MBH reconstruction fail verification significance tests, a finding later confirmed by Wahl and Ammann and accepted by the NAS Panel. Far from being “robust” to the presence or absence of all dendroclimatic indicators, we showed that results vanished just by removing the controversial bristlecones, a result also confirmed by Wahl and Ammann and noted by the NAS Panel. We showed that the PC method yielded biased trends, an effect confirmed by the NAS and Wegman panels. We showed that pivotal PC1 was not a valid temperature proxy due to non-climatic contamination in the dominant-weighted proxies (bristlecones, foxtails). Here again the NAS panel concurred, saying that strip-bark bristlecones should not be used in climate reconstructions.

    The VZ Comment did not refute our research, as we explained in our published Reply and here .

    VZ criticize us for supposedly only publishing one peer-reviewed study; however, the IPCC AR4 cites five peer-reviewed studies by us, one of which contains the requested discussion of bristlecones.

    While we believe that VZ’s views are unjustified, we believe that they hold them in good faith. Almost uniquely among climate scientists, they have been cordial to us both publicly and privately and we would have no hesitation in requesting either of them as a reviewer. However, we deserve more credit than they give us and we do not agree that their GRL Comment overturned our results.

    Steve McIntyre and Ross McKitrick

  34. Report this comment

    Gerd Bürger said:

    I agree here with McIntyre & McKitrick.

    1. How can their AHS argument be applied to a non-HS shaped reconstruction such as that of VZ?

    2. Under what outcome would VZ have concluded that the AHS does matter?

    (And is the VZ result possibly based on detrended calibration?)

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