January 28, 2005
Hockey Stick Climate Temperature Trend Theory Challenged

A pair of Canadian researchers, University of Guelph Canada economist Ross McKitrick and Toronto-based mineral exploration consultant Stephen McIntyre, have a paper coming out in Geophysical Research Letters that challenges the "Hockey Stick" temperature trends model which shows the 20th century as the hottest centure in the last 1000 years.

Until now, criticisms of the hockey stick have been dismissed as fringe reports from marginal global warming skeptics. Today, however, the critical work of two Canadian researchers, Ross McKitrick, an economics professor at Guelph University, and Toronto consultant Stephen McIntyre, will be published by Geophysical Research Letters, the prestigious journal that published one of the early versions of Michael Mann's 1,000-year tracking of Northern Hemisphere temperatures,

Publication in Geophysical Research sets McIntyre and McKitrick's analysis and conclusions in direct opposition to the Mann research. Their criticism can no longer be dismissed as if it were untested research posted on obscure Web sites by crank outsiders. Their work is now a full challenge to the dominant theme of the entire climate and global warming movement.

The paper will be published in February. So as of this writing it is not on the Geophysical Research Letters web site. However, a pre-publication version of the paper "“Hockey Sticks, Principal Components and Spurious Significance”" is available (PDF format).

For a graphical comparison of the original hockey stick chart and the McIntyre and McKitrick analysis see this page from McKitrick's web site. That page has a lot of other useful links. McIntyre and McKitrick also have another web site with a lot more useful links.

Dutch science journalist Marcel Crok has a two part series in the Canadian Financial Post on the McIntyre and McKitrick research paper.

Up to January, 2005, none of McIntyre and McKitrick's findings had been published by major scientific journals. Thus, in the opinion of established climate researchers, there was no reason to take them seriously. Climate researchers were quite comfortable in their consensus and repeatedly referred to this "consensus" as a basis for policy. The official expression of the consensus comes from the IPCC. This group, under the flag of the United Nations, comes out with a bulky report every five years on the state of affairs in climate research. Hundreds of climate researchers from every corner of the world contribute to it. In the third report in 2001, Mann himself was a lead author of the chapter on climate reconstructions.

McKitrick and McIntyre had a hard time getting access to the data and source used in the analysis by Mann and colleagues that led to their claim that the 20th century was the hottest in the last 1000 years. No other group had seriously tried to replicate the Mann analysis.

McIntyre sent an e-mail to Michael Mann in spring 2003, asking him for the location of the data used in his study. "Mann replied that he had forgotten the location," he said. "However, he said that he would ask his colleague Scott Rutherford to locate the data. Rutherford then said that the information did not exist in any one location, but that he would assemble it for me. I thought this was bizarre. This study had been featured in the main IPCC policy document. I assumed that they would have some type of due-diligence package for the IPCC on hand, as you would have in a major business transaction. If there was no such package, perhaps there had never been any due diligence on the data, as I understood the term. In the end, this turned out to be the case. The IPCC had never bothered to verify Mann, Bradley and Hughes' study."

Despite billions of dollars spent on climate research, academic and institutional researchers had never bothered to replicate Mann's work either. In 2003, McIntyre tackled the job and, from an unusual hobby, the task has since grown to become almost a full-time occupation. On an Internet forum for climate skeptics, he met Ross McKitrick, professor of economics at the University of Guelph, just outside of Toronto. Since meeting in person in September of 2003, the two have been working on the project together. McIntyre does most of the research and McKitrick asks questions and assists in the writing of papers.

When people tell us that we urgently need to spend hundreds of billions or trillions to fix some problem we ought to demand a higher standard of proof than the effort that went into the original Hockey Stick paper.

Read the full article. Keep in mind as you read it that published science should be transparent, verifiable, and reproducible. Science that can not be checked and reproduced has no place as a basis for public policy that could cost the world's collective economies hundreds of billions or even trillions of dollars..

A lone Canadian Gaspe peninsula cedar tree's rings were heavily weighted in Mann's model for North American temperature in the 15th century.

"More strangely," said McIntyre, "the series appears twice in Mann's data set, as an individual proxy, and in the North American network. But it is only extrapolated in the first case, where its influence is very strong." McIntyre and McKitrick went back to the source of the Gaspe series and then to the archived data at the World Data Center for Paleoclimatology."We found that although the Gaspe series begins in 1404, up until 1421, it is based on only one tree. Dendrochronologists (tree ring researchers) generally do not use data based on one or two trees. The original authors only used this series from 1600 onwards in their own temperature reconstructions. This series should never have been used in the 15th century, let alone counted twice and extrapolated."

Go and read the full articles I'm linking to. Note how McIntyre and McKitrick were able to find a Fortran program and crucial datasets on an FTP server used by Mann's group that led McIntyre and McKitrick to an understanding of how Mann and his colleagues made serious mistakes in how they did a mathematical analysis called principal component analysis (PCA) on their datasets. There is a larger lesson here: More data and source code on which scientific research papers are based ought to be available in the public domain to allow replication of mathematical analyses used in scientific research papers.

Note also that in climate research McIntyre and McKitrick are essentially self-taught amateurs. But they had the mathematical chops to use basic analytical techniques to datasets and apparently that is all that is needed do analyses on climate history data.

Finally, regarding the idea of a scientific consensus on global warming the words MIT meteorologist Richard Lindzen bear repeating:

"Do you believe in global warming? That is a religious question. So is the second part: Are you a skeptic or a believer?" said Massachusetts Institute of Technology professor Richard Lindzen, in a speech to about 100 people at the National Press Club in Washington, D.C.

"Essentially if whatever you are told is alleged to be supported by 'all scientists,' you don't have to understand [the issue] anymore. You simply go back to treating it as a matter of religious belief," Lindzen said. His speech was titled, "Climate Alarmism: The Misuse of 'Science'" and was sponsored by the free market George C. Marshall Institute. Lindzen is a professor at MIT's Department of Earth, Atmospheric, and Planetary Sciences.


According to Lindzen, climate "alarmists" have been trying to push the idea that there is scientific consensus on dire climate change.

"With respect to science, the assumption behind the [alarmist] consensus is science is the source of authority and that authority increases with the number of scientists [who agree.] But science is not primarily a source of authority. It is a particularly effective approach of inquiry and analysis. Skepticism is essential to science -- consensus is foreign," Lindzen said.

Alarmist predictions of more hurricanes, the catastrophic rise in sea levels, the melting of the global poles and even the plunge into another ice age are not scientifically supported, Lindzen said.

"It leads to a situation where advocates want us to be afraid, when there is no basis for alarm. In response to the fear, they want us to do what they want," Lindzen said.

If global warming eventually becomes a problem we will be able to handle it. We can switch to nuclear power. In time photovoltaic cells will become much cheaper and we may switch away from fossil fuels in 30 years because market forces cause the switch even without government regulations that force the switch. The most prudent action to take at this point would be to accelerate the rate of energy research to develop cheaper alternatives to fossil fuels and cheaper ways to capture and sequester CO2. The impositions of huge costs on economies to reduce CO2 emissions today is an excessive response to a potential problem that, if it comes, could be much more cheaply handled in the future.

Update: Check out the Prometheus blog on science policy and the post A Third Way on Climate?. For insights into the problems caused by scientists playing policy advocates while simultaneously trying to serve the role of providing authoritative answers about scientific knowledge to the public see these posts Chris Landsea Leaves IPCC, Follow Up On Landsea/IPCC, Landsea on Hurricanes, More Politics and IPCC, and A Good Example why Politics/IPCC Matters. There is a lot of sensible thinking in those posts. Hope you agree.

Share |      Randall Parker, 2005 January 28 03:22 PM  Climate Trends

wcw said at January 28, 2005 4:35 PM:

Science should be transparent, verifiable, and reproducible. Data and source ought to be available in the public domain to allow replication. Whether we limit CO2 today or mitigate it in the future is worthy policy question for which good science is needed. Alas, hanging your lecturer's hat on McIntyre and McKitrick is a yawning error that neatly undercuts your argument's ethos.

For a considered refutation of their paper by real climate scientists, you may see http://www.realclimate.org/index.php?p=8 It's a bit tedious, but it adequately demonstrates that McIntyre and McKitrick's critique of Mann et al is spurious.

The pull quote: "In short, the supposed ‘correction’ of [Mann et al] by [McIntyre and McKitrick] is seen to represent little more than a statistically meaningless, botched application of the [Mann et al] procedure that relies upon censoring key indicators from the [Mann et al] proxy data set."

McIntyre and McKitrick appear to be to climate science what folks like Doug Feith are to proliferation intelligence: useful idiots. If you believe in science, you'll read the many and varied critiques of their paper, revise your post, and resubmit.

Randall Parker said at January 28, 2005 5:22 PM:


McIntyre and McKitrick just managed to get published in a journal that Mann himself thought worth getting published in. They had reviewers for their paper. Are those reviewers, faced with all the known criticism of McIntyre and McKitrick, also wrong? Does the journal not select appropriate reviewers? Is its mechanism for review defective?

I went and read your link. As near as I can tell the writer of that page "mike" is Michael Mann himself. Of course he is going to defend his work. How am I supposed to know whether he is correct in the various assertions that he makes about his own analyses? He's making assertions that are unchecked by peer reviewers. Now we have McIntyre and McKitrick coming out with a peer-reviewed paper making assertions to the contrary. I don't have all these datasets or the source code used to analyze them. You are basically telling me to trust Mann.

As for Mann's pointing out that his critics are a private industry consultant and an economist: This is irrelevant. I've met brilliant people in private industry and some economists are first class mathematicians.

wcw said at January 28, 2005 8:53 PM:

My wife does peer review. It's better than nothing, but it's not perfect. I didn't think your post was about peer review -- I thought it was about McIntyre and McKitrick's work.

Econometrics produces some fine math. Then again, it also produced John Lott, that human public service announcement on the dangers of model misspecification. I didn't think your post was about the validity of econometrics.

Mann (I assume you're right that he's the poster) makes some cogent points with reasonable evidence. I found his work more persuasive that McIntyre and McKitrick's, without needing to attack them. I think that, like Feith, they're utterly sincere -- and like Feith, dangerously wrong.

There is independent, peer-reviewed, non-Mann analysis that confirms that parts of McIntyre and McKitrick's 2003 paper was, "an artifact of (a) the use by these latter authors of an incorrect version of the Mann et al. (1998) proxy indicator dataset, and (b) their misunderstanding of the methodology used .." It's linked from the blog post I cited -- one or two clicks take you to the full text.

How are you supposed to know whether the mainstream of climate science or McIntyre and McKitrick are right? The same way you concluded the paper was worth a post -- read it, read the literature, do your own due diligence. Isn't that what you did before your post?

Randall Parker said at January 28, 2005 10:18 PM:


Econometricians and John Lott: If my post is not about the validity of econometrics then why the gratuitous swipe at John Lott in your response?

The vast bulk of the public lacks the training or the time to examine each research paper relevant to public policy. Heck, even experts can not do that because there is so much coming out.

I attach a lot of importance to the fact that the paper made it thru peer review, especially under the circumstances. Are you telling me this journal can't get people more experienced than me at analysis climate history or at the use of statistical methods to review such a paper? After all that has been written about the hockey stick debate wasn't this paper receiving a huge amount of pre-publication scrutiny? If this paper was around in draft form wouldn't these errors that you think are obvious have been pointed out then? Wouldn't an important paper have especially talented people recruited to review it?

Garson Poole said at January 28, 2005 11:55 PM:

One aspect of this affair is particularly interesting and somewhat disturbing. According to the National Post article the researcher McIntyre has attempted to examine the data and programs that were used in other climate science research reports and has been unable to obtain them. Here is the relevant excerpt:

McIntyre: "Mann's archiving may be unsatisfactory, but other researchers, including Crowley, Lowery, Briffa, Esper, etc, are even worse. After 25 e-mails requesting data, Crowley advised me that he had misplaced his original data and only had a filtered version of his data. Briffa reported the use of 387 tree ring sites, but has not disclosed the sites. Other researchers haven't archived their data or methods or replied to requests."

I hope that anyone interested in climate science would consider this situation unsatisfactory. Perhaps the data and programs that are used in a scientific paper should be archived together with the paper in a repository that is open to all fellow researchers. As wcw says above "Science should be transparent, verifiable, and reproducible." It may not be necessary to put this material into the public domain as wcw suggests above. For example, the researcher may wish to keep a copyright in some cases, but the material should be made available.

Randall Parker said at January 29, 2005 12:58 AM:


Yes, exactly. The researchers arguing for the hockey stick aren't just arguing for some a point in some esoteric scientific controversy in an obscure research area. They are arguing for the existence of an importance of a problem which some advocate we respond to by imposing costs on ourselves that run into the hundreds of billions or trillions of dollars. Yet their responses to requests for datasets to substantiate their claims do not exactly inspire confidence.

Holding back data: No, I find that unaccceptable. There is no point in public funding of climate research if the data collected is not going to be freely available. We need a huge degree of transparency in how the analyses are done and every single step of these analyses needs to be verifiable. The scientists should not have the expectation that it is acceptable to hold back or lose the location of tree ring sites. They can't not remember where the source code is for some analysis.

What may be acceptable standards of conduct for scientists most in fields of research are acceptable as soon as scientists want to go to the public and say that we have to impose huge costs on ourselves based upon their findings. Climate research is receiving so much funding because we need to know whether we need to impose huge costs on ourselves. That research should be conducted in a way that is far more open and auditable than what these articles describe.


You refer to the use by McIntyre and McKitrick of an incorrect version of a dataset. Yet McIntyre and McKitrick mention how they were referred to one dataset and then later criticized for using that one rather than a later correct one which they were not told about.

I do not think it is unreasonable for a topic which has such huge implications for public policy and for all of our living standards to expect scientists to make their raw data and all source code and models available so that their work can be checked at every step.

TangoMan said at January 29, 2005 2:05 AM:

Let me add some more concerns to how climate scientists conduct their work. Many work with proxy data and this introduces a whole other realm of potential error into their analysis. Also, from what I understand it is a common practice to design the experiment, settle on proxy data, gather the data, and run the analysis. They've never heard of double blind process or for that matter, splitting up the taks so that one interested party isn't fully in charge of all of the experimental parameters.

Then look at the issue of replicability and validity of climate modeling. Take a look at this site (Click on the graphic) and tell me which model best mirrors reality.

Then there is the sloppy logic, even in papers published in Nature such as "Extinction risk from climate change" by Thomas et al. The article is chock full of conditionals and the authors reference a range of climate scenarios in their models. Further the model that they use for this study is built upon a compositional fallacy. They state:

The approach has been validated by successfully predicting distributions of invading species when they arrive in new continents and by predicting distributional changes in response to glacial climate changes; (emphasis added)

I think that the model falls apart logically when it is extended beyond what is known. The model was validated so that we knew that parts of the whole X have characteristics A, B, C and then extended to the conclusion that therefore the whole X must have characteristics A, B, C.

I think that the root of the problem is that climate scientists are much like political scientists and sociologists, in that they strive for the rigor of the physical sciences but are limited by the nature of their field to be working with very complex systems. To combat this complexity they overstep quite frequently as I've detailed here and in fact McIntyre and McKitrick forced Mann et al to issue a corrigendum in Nature.

Regardless of how people perceive McIntyre and McKitrick, and relying on Real Climate to give an unbiased opinion on this challenge is beyond the pale, this is the process of science being done in full daylight. The debate between these two parties should be fought for all to witness. McIntyre and McKitrick have performed a valuable service in highlighting the sloppy data processes employed by Mann et al and other researchers, which to an outside observer, seem designed to thwart replication efforts. This is indeed a black-eye for IPCC for it makes them look more political than they are when they don't validate the studies that go into their statements.

In the end, the double dealing and sloppy research methodology take away from the science, which should stand on its own in the full light of day.

wcw said at January 29, 2005 9:55 AM:

RP -

Thing is, I absolutely agree with your main points. Datasets are not routinely made available, as they easily could be (copyright almost effortlessly prevents their use by others without permission). Sloppy coding is the rule, not the exception. Data errors are common enough that an error rate of a couple percent in large data sets is considered quite good. However, because of their work's own sloppiness, McIntyre and McKitrick should not have been the centerpiece example. An ideal case would have been a well-settled example of bad work which was caught and corrected, not an ongoing catfight.

I named an analytically bankrupt econometrician to underline the point that said profession is no guarantee of competence. John Lott specifically gets a gratuitous swipe because his work is so incredibly bad (see the NAS report), and yet he still gets op-eds and funding as if he had a clue.

I can't answer your questions about that particular journal. From what I have observed, peer review is like democracy -- it's the worst possible system, except for all the other ones. Just to harp on him once more, John Lott has at least one peer-reviewed article under his belt in AJ/Public Health, so we have at least one data point that horrendous work makes it through peer review.

Randall Parker said at January 29, 2005 10:38 AM:


I did not mean to imply and I do not think I implied that having the title of econometrician automatically and assuredly bestowed competence. But the same is true of a great many other fields. I've worked with Ph.D.s in a number of fields who were shockingly bad. I've worked with others who were astonishingly good even when thinking well outside their field of expertise.

Yes, I know bad work makes it through peer review. Lots of papers turn out to be totally wrong.

My reaction to the so-called climate consensus, the ongoing catfight, and the revealed practices of handling and releasing data and methods in climate research is pretty simple: Some of these people are telling us to up end our civilization because they just know what the past history of climate was and what the future holds. That demands an awfully higher standard of practice and proof than they have so far been willing to provide. I resist their demands we accept their condescendingly arrogant advice and their demands to just basically accept their claims on faith.

I realize that some of them may not see they are being condescending and arrogant. But that is what it amounts to. I am very reluctant to take advice when the advice is so expensive to put into practice and the methods used to reach findings are basically unverifiable. If astrophysicists spend decades believing something mistaken about quasars before finding out the truth I don't care. If paleobiologists disagree with each other about something that happened at the K-T boundary and some of their research methods are dodgy again I can be totally indifferent. But I want to be damned sure that the underlying data and methods in climate research have been validated by people outside some specialist field because too many times I've seen some consensus form in some specialty where no one outside the consensus can get grant money and finally decades later someone comes along disproves the consensus. The madness of the crowds can and does extend into the process of science.

Speaking as someone who is neither a professional mathematician or a professional physicist it seems obvious that math and physics departments have, on average, the sharpest tools in the shed. Some of these sorts of people, without the professional reputations invested in climate research and basically outside of the granting apparatuses and social networks of climatology and climate history, need to be able to easily access all the data and tools these climate scientists are using in order to be able to verify the most important work of the climate scientists.

Many more people than McIntyre and McKitrick would have attempted to verify this work if doing the verification had been easy to do. Now after a lot of detective work and overcoming a lot of resistance McIntyre and McKitrick have lots of datasets and code pieces up on their web site from Mann et. al. that would not have been available had McIntyre and McKitrick not been willing to spend years trying to get together what was needed to even attempt a verification of that work. For that alone McIntyre and McKitrick deserve some credit and Mann et. al. (and I suspect all of climate research as a field) deserve some criticism.

Bob Badour said at January 29, 2005 12:41 PM:


Copyright most emphatically does not protect information--only the expression of information. Science, especially, requires the free sharing of information. Since I see no evidence of patentability in any of the works discussed, which might require a short-term and very temporary withholding of information, I see no need for any kind of secrecy or protection at all.

More than political bias, I conclude from the difficulties finding the raw data again that the original researchers lack both competence and rigor. Good science requires good (even meticulous) record-keeping, which is why I very early in life lost all interest in doing any real science.

I might even go so far as to suggest that behind any really important advance in science, you will find a good clerk. Names like Brahe, Einstein and Darwin come to mind.

Randall Parker said at January 29, 2005 12:50 PM:


Regard's Chris Landsea's resignation from the IPCC in response to : Read Roger Pielke Jr.'s commentary on the whole affair. Trenberth should have stated that he is advancing a hypothesis. His position is yet unproven and is just speculation (albeit not unreasonable speculation) at this point. Does Trenberth think the public should take him at his word that he is telling the absolute truth?

I agree with your point about how climate science is like the social sciences in a lot of ways. Experiments are hard or impossible to do to prove most arguments. There are just tons of uncontrollable and even unmeasured variables and undiscovered cause-effect relationships. Yet some climate scientists are trying get the public to think that the predictive ability of their field is far greater than it is.

Frank Quist said at January 29, 2005 3:55 PM:

Small note, your link to the Crok article in the canadian financial post seems to be broken. It needs something inbetween the a tags.

Jim said at January 29, 2005 4:03 PM:

global warming is a useless topic to worry about.

nobody can model such complex system accurately.

there is very limited data, and researchers don't even really know all the variables that must be considered.

the main variable researchers focus on is CO2, which will continue to be pumped out almost irregardless of any 'scientific' conclusions because (as previously discussed here) replacing all carbon based energy sources is not feasible in the near future.

finally, why do canadians care?? they are probably one of the few nations to benefit from global warming.... they could start using the other 95% of their country that's not right at the u.s. border.

The MIT guy had it correct, this is a matter of faith, not science.

Bob Badour said at January 29, 2005 7:10 PM:


Canadians care because idiotic politicians up here seem hell bent on implementing Kyoto just to be different from the US. At least, that's why I care.

wcw said at January 31, 2005 7:48 AM:

Easy enough to say that you see no need for any kind of secrecy in science. I agree, in the same ideal world in which I see no need for any kind of property rights. We live, alas, in a very different place than that.

Copyright does not prevent use, but it restricts publication, which I find strikes the right balance to motivate greedy, self-interested individual scientists to share. The alternative seems to be more of the same: data collected and sold as a trade secret, whether by commercial vendors or individual scientists.

If the Copyright Office considers such datasets to be uncopyrightable compilations, then we need another method to strike that balance. Whether it should be shrink-wrap licenses or NDAs is a question for the lawyers. What interests me is that individual scientists start sharing data as much as possible.

jlw said at January 31, 2005 9:56 AM:


If you (and anyone else here) is interested in a fuller discussion of this topic, try http://davidappell.com/archives/00000579.htm

That's my blog-pimping duty for the day.

DigitalDjigit said at February 1, 2005 10:01 AM:

No evidence of climate change, eh? Look out the window. Records frost all over Russia and Europe. Heatwaves across the US the last few years, record snowfall several times in the last 10 years.

If there was a widespread will to switch from carbon, it could be done and would be feasible. Just wait till oil prices spike and you will see.

Canadians should care because the effects of global warming are unpredictable and even if they do make Canada warmer, it won't necessarily make the northern reaches inhabitable.

This whole cost argument is bogus since we have no idea about the costs involved if we continue acting the way we do or if we change. There's also the fact that dollar values for many things don't exist. What value would you place on an endangered species?

ziel said at February 2, 2005 12:44 PM:

The M&M critique (MM05) looks quite damning - and rightly or not, Mann et al's protestations that the validity of the hockey stick is beside the point in the Global Warming debate will soon look like Dan Rather's protestations that the validity of the Killian documents was irrelevant to the Bush TANG story.

Bob Badour said at February 4, 2005 12:11 PM:


I look out my window today and I see a very normal Canadian winter. I examine what (albeit very indirect) evidence I have seen about climate, and I conclude that the weather today is much warmer than 14 thousand years ago and somewhat cooler than other periods since then.

I see nothing remarkable about today's climate nor do I see any reason to believe humans have accelerated the natural warming that has been ongoing for the better part of the last 14 thousand years.

I can tell you with complete confidence that the climate 10,000 years from today will be different from today's -- with or without trillions of dollars of wasted money and effort.

wcw said at February 10, 2005 7:25 AM:

Two notes.

One, Canada is not the world. While North Americas was "unusually cool" it was the fourth-warmest year on record.

Two, that article cites the author of the article our host ought to have used instead of M&M's flawed work to challenge the "hockey stick" analysis. Moberg's paper is consistent not only with other reconstructions of historical temperatures, but even finds a local maximum around 1000-1100 consistent with the Viking settlement of Greenland -- not to mention a local minimum around 1600 that congrues with other work as well as tending to undermine faith that M&M's 1400-1500 minimum might be real.

Moberg, for what it's worth, both believes that the hockey stick is far too simplistic and that global warming is real.

The lesson I take from this? When attacking orthodoxy, be sure the horse you ride has some clue how to run the track.

wcw said at February 10, 2005 7:27 AM:

..er, that should have read M&M's "1400-1500 maximum".

Steve D said at February 28, 2005 1:02 PM:

WCW wrote "so we have at least one data point that horrendous work makes it through peer review."

Good point - it is particularly acute w/r/t the type of science required in the climate field. E.g., the large scale statistics required to undertake proxy temperature reconstructions. I doubt the initial peer-review process is going to change much - too labor intensive to make the reviews really effective. But what is very reasonable to do is to insist that there is at least the possibility of audit (that means all the data sets, software, working papers, etc. must be safely archived so that if an audit is merited, then an independent team can do so promptly).

Randall has already linked to the Prometheus A Third Way on Climate? Over at SeekerBlog I've been struggling with these particular issues, well summarized by Hans von Storch et al:

This then is the classical set-up of a modern science with high policy relevance – high stakes (implementation of Kyoto and beyond) and high uncertainty (in the assessment of ongoing change and in perspective of what may come)....

Judgments of solid scientific findings are often not made with respect to their immanent quality but on the basis of their alleged or real potential as a weapon by "skeptics" in a struggle for dominance in public and policy discourse.

Re: the Mann 1998 work vs. M&M. It's early days yet on the review of the M&M work - what I've seen so far is compelling - in that "Third Way" post, I've assembled a reasonable set of "clean sources" who have analyzed the issue. I think you'll find them very interesting - and would LOVE to hear criticism back thru the comments.

E.g., in this just-published Feb. 1, 2005 Kyoto Protocol Based on Flawed Statistics in Natuurwetenschap & Techniek, we get some reaction from the referees of the to-be-published M&M Geophysical Letters paper (emphasis added):

The same referee also writes:“McIntyre and McKitrick found a non-standard normalization procedure in the Mann et al.analysis.Their paper describes this procedure;it was an apparently innocent one of normalization, but it had a major effect on their results. The Mann et al. normalization tends to significantly increase the variance of data sets that have the hockey-stick shape. In the Mann et al.data set, this turned out to be bristlecone pines in the western United States. Thus the hockey stick plot, rather than representing a true global average of climate for the past thousand years, at best represented the behavior of climate in the western US during that period.This is an astonishing result. I have looked carefully at the McIntyre and McKitrick analysis, and I am convinced that their work is correct.”

The referee ends with:“I urge you not to shy away from this paper because of its potential controversy. The whole field of global warming is currently suffering from the fact that it has become politicized. Science really depends for its success on an open dialogue,with critics on both sides being heard. McIntyre and McKitrick present a cogent analysis of the global warming data.They do not conclude that global warming is not a problem;they don't even conclude that the medieval warm period really was there. All they do is correct the analysis of prior workers,in a way that must ultimately help us in our understanding of past climate,and predictions of future climate.That makes this a very important paper. I strongly urge you to publish it.

Alex J said at April 6, 2005 1:26 PM:

"False Claims by McIntyre and McKitrick":

And What If the Hockey Stick WERE Wrong?:

JP Koch said at December 12, 2005 12:09 PM:

The very large error rates in Mann's graphs, his ignoring proxie data from other works, as well as his total reliance on tree ring data, calls his graph into question. Trees grow on land; earth is 80 percent water. Ignoring samples from the ocean clearly limits the accuracy of his data. Another problem I saw in Mann's graph was the lack of data concerning the years 1991-1993. Mt Pinatumbo errupted and spewed huge amounts of sulfuric dioxide into the upper atmosphere. The amount of global cooling was pronounced, and was easily picked up by satelite TOV sensors. The cooling in the Northern Hemisphere was obvious (nealry 1.5 deg C cooler than the 1000 year mean. No proxies needed). Yet, nowhere is this depicted as a sharp downward spike.

Steve Sadlov said at February 13, 2006 2:19 PM:

In addition to the use of the questionable Gaspe proxy (and possible cooking of the books by using it twice in slightly different forms) there is at one other highly questionable proxy used by the Hockey Team.

Namely, Bristlecone Pines. The running theory in using tree ring proxies is that trees in a four season climate grow faster when it's warm. Hence, warming = greater growth. This theory has merit, but only given the following proviso: All other growth control factors such as moisture, fertilisation and light remain relatively constant. Allow any of these to vary significantly and the use of tree rings as a proxy becomes suspect. Now back to those bristlecones. They live in places known for vast swings in temperature on a daily, day to day and longer time frame basis. Also, in the areas where they grow, in the transition zone between arid mid latitude and arid sub tropical climates, there is immense variability in precipitation and temperature year to year, in terms of the annual mean. Bristlecones are adapted to resist great temperture swings and to survive long droughts. They grow when moisture is available during a narrow seaonal window and in years where the moisture does not arrive during the window, they are semi dormant. Think "cactus" instead of "conifer" and you are on the road to understanding. So, why, I ask, would anyone in their right mind use a bristlecone as a *temperature* proxy - unless they specifically wanted to substitute an effect of moisture for an effect of temperature?

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