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Global warming's discredited "hockey stick" chart


As I noted in a recent blog entry, I’ve recently encountered instances at conferences and other professional gatherings of people delivering presentations on the topic of global warming and climate change wherein they use the famous “hockey stick” chart to illustrate the idea that we’re living in the warmest period in the Northern Hemisphere in the past 1,000 years, and that temperatures are rising rapidly. The presentations I tend to attend focus on how greater recycling and composting can help us lower our contribution to global warming, but the presentations make use of the same research that’s put forward in other “environmental” venues.
Trouble is, this chart (and much of the data behind it) has been discredited. Yes, you read correctly.
The “hockey stick” chart is so named because of its long, stable shaft and fast rising blade. It’s often cited in global climate reports — particularly the United Nations Intergovernmental Panel on Climate Change (IPCC) — and illustrates the work of Michael Mann, Raymond Bradley and Malcolm Hughes, whose findings were fundamental to the assumptions behind the Kyoto Accord.
My most recent encounter with this chart was Maria Kelleher’s presentation last week at the Association of Municipal Recycling Coordinators (AMRC) conference. She presented on the benefits of waste diversion and energy efficiency in regard to lowering CO2 and methane emissions, to combat man-made climate change. The PowerPoint slides were borrowed from Ralph Torrie, a consultant on global warming who is popular with the folks at Environment Canada and who speaks regularly at their events. Maria acknowledged that the slides were Ralph Torrie’s (whose name was also in large type on the slides themselves), so I’ll ascribe the error that I’m about to describe to him. (Maria and I are friends and she knows I hold her in high esteem, so I’m sure she’ll forgive me for going on about this.)
Anyway, I got really ticked off when I saw the “hockey stick” chart in the slide presentation. Why? Because the chart, and the research behind it, has been discredited. And in peer-reviewed journals, no less. (More on that below.) The main point isn’t that global warming is or is not occurring, so much as that people need to understand there is no “consensus” among scientists on this matter, including climatologists. Opinions range much more than we are often led to believe.
I drew Maria Kelleher’s attention to this fact, for her benefit but really more for the benefit of the audience. It really bothers me, as a person who follows the climate change debate fairly closely, to see the hockey stick chart’s continued use as a propaganda tool. Does bad science really serve anyone’s interests? Including those of even the most alarmist subscribers to the global warming theory? I think not. Don’t get me wrong — although I am a “skeptic” about the theory that man-made global warming is under way, I don’t claim to know “for a fact” or “beyond all doubt” that it is not. I’ve simply encountered many documents written by credible people that indicate there are problems — some of them very serious — with the theory, and I find these don’t get reported very often. In environmental circles and the mainstream media, the concept that anthropogenic climate change is real and happening in a big way has become an article of faith, and anyone trying to prick that balloon, or any part of it, is accused of heresy, and is shunned. (I’m not kidding! I’ve been made to feel like a holocaust denier at some environmental gatherings.)
In the discussion afterward (in the conference room and also in the hallway) I took issue with several of the Ralph Torrie slides, including the one that claims that hurricanes have increased in number and/or intensity, doubling in the past ten years from the ten years prior. This is typical selective nonsense: if you look back over the past century, there are natural fluctuations in hurricane activity and things are no worse now than 40 or 50 years ago.
Anyway, I don’t want to rehash the whole climate change debate here. What I want to do is simply establish for the record that there are very serious problems with the hockey stick chart, which has been called “rubbish” by one peer-reviewer in the journal Science. (See article below.)
My challenge here is to offer readers something fairly short and accessible to summarize the situation. The trouble with this topic is that one can trot out articles to refute this or that point which are either too short, shallow or glib to be convincing, or way too long and technical for anyone to actually read. (“Inside baseball” as I like to call it.) I went through my files and have cut and pasted an article below that does a pretty good job summarizing the problems with the hockey stick chart, and the controversy triggered by the scientists and statisticians who revealed those problems. The article is by no means the last word on the subject, but it’s a good entry point for the lay person.
Please read the article below, and if you want to dig deeper, here are a couple of websites you might want to check out. Some are “skeptic” websites, but offer links to other material that is in the “pro global warming theory” camp. Again, my goal here is not to convince you that global warming isn’t occurring, but just to make you aware that there is quality information out there that questions the “common wisdom” on this, and suggests that, going forward, no one should trot out that hockey stick chart without at least acknowledging that it has been challenged and the science behind it is under serious review.
Websites you might find useful include:
The Science & Environmental Policy Project http://www.sepp.org/
Note that because this organization has received a very small amount of money from oil companies, global warming theory enthusiasts like to say that it has no credibility and that its founder, Fred Singer, Ph.D. (who was behind the global weather satellite system, ahem!) is just a shill for “Big Oil.” Nonsense! I’ve read a lot of entries at this site, enjoyed them and found them very informative.
University of Guelph http://www.uoguelph.ca/~rmckitri/research/trc.html
This site leads directly to material gathered by Steven McIntyre and Ross McKitrick, known as “M&M” in climate change circles. Their work, alluded to in the article below, was crucial in exposing problems with the hockey stick data sets. I find their observations about the games played by some of the peer-reviewed journals to try and exclude their findings very funny, and more than a little frightening. If you read enough of their material, including the book Taken By Storm (Key Porter Books) you’ll never sit through another Environment Canada cliamte change presentation with a straight face again, no matter where you stand on these issues.
Steve McIntyre’s blog: http://www.climateaudit.org/ The message threads and blog posts here are very interesting, and McKitrick has posted some full papers on the “hockey stick” chart and related (or unrelated) topics in paleoclimatology.
Climate Science: http://climatesci.atmos.colostate.edu/
A blog site that offers detailed technical information and opinion about the leading-edge issues of climate change.
Now, here’s the short article. And please note that I couldn’t easily reproduce in my blog a couple of charts that go with this article, so I deleted reference to them from this text. I’m not hiding anything, so if you want the whole article, go here: http://www.tcsdaily.com/article.aspx?id=102704F


Is the Hockey Stick Broken?
By Dr. Willie Soon
Co-Authored by David R. Legates *

It’s dubbed the hockey stick. It is a rather simple looking graph — with a long, stable shaft and a fast rising blade — that purports to represent averaged Northern Hemisphere temperatures over the last thousand years. More than that, in global climate reports — particularly the United Nations Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR) in 2001 — its used as proof that mankind’s industrial revolution has over the last hundred years started dangerously pushing up global temperatures, thus justifying restrictions on emissions of human produced greenhouse gasses.
But there’s a problem. The hockey stick may well be broken.
A research paper recently published in the journal Science by Professor Hans von Storch and colleagues has found significant problems with the hockey stick. Von Storch, the leader of the research team at the Institute of Coastal Research at Geesthacht, Germany, calls the hockey stick junk or rubbish.
How important is that in the debate about what, if anything, the world should do about climate change? Perhaps quite a bit.
A little background is needed here.
The IPCC hockey stick was originally produced by Michael Mann, Raymond Bradley and Malcolm Hughes, first in 1998 for the period 1400-1980 and then, with no major progress in the science or database, was quickly expanded to the full 1000-1980 interval in 1999. We will call the studies MBH98, MBH99 hereafter.
Now, since no thermometer readings were available for almost 850 of the 1,000 years, MBH98 and MBH99 first selected what were the then-available temperature proxies. Those proxies were based on tree-growth, coral and ice core records from about 105 sites across the globe. To verify the accuracy of the temperature data derived from those proxies, the methodology of MBH98 and MBH99 tested recent proxy data to see if it fit the available geographical patterns of temperature observed by available thermometer measurements for the last 80-150 years or so. Those proxies that did not fit the pattern were essentially ignored. For those that did, it was assumed that the same geographical pattern of change seen in the very short thermometer record would hold true for the full 1,000 years into the past.
It was with those two critical, but unsubstantiated steps, that MBH99 then came up with the well-known IPCC hockey stick temperature averaged for the Northern Hemisphere.
Since 1999, several climate researchers have challenged those underlying assumptions for deriving the hockey stick, but with little effect on limiting the hockey sticks use as an illustration purportedly helping prove human induced global warming.
The heavy criticism by Von Storch and colleagues in Science may change that. It exposes a clear methodological problem in the MBH99 hockey stick rendition of the 1000-year Northern-hemisphere temperature history. That rendition improperly smoothed out large temperature variations over the 1000-1900 interval that made up the supposedly stable shaft of the hockey stick.
How did Von Storch and colleagues show this?
As the researchers explained it in Science, they used computer climate model outputs to generate the test temperature data series at a number of locations on Earth. By using such computer model climate outputs, rather than actual temperature proxy records, the researchers could take advantage of a completely known set of information about temperature variability in every location on Earth (true, of course, only in a computer model) to perform various sensitivity tests. These tests could then show how different combinations of locations for available test temperature data series throughout the 1000-year climate history could systematically influence or bias the statistical reconstruction of the Northern Hemisphere-wide temperature record. Biased results from different statistical methods of combining the computer-produced temperature data for the selected geographical locations could then be compared with the benchmark model results that captured the full range of variability, accurately averaged over the whole Northern Hemisphere.
Von Storch and colleagues added confidence to their adopted methodology by showing that their primary conclusion and results held true using the sophisticated computer climate models from both the Max Planck Institute for Meteorology (results labeled ECHO-G or ECHO-G II in Figures 2 and 3) and the U.K. Meteorological Offices Hadley Centre. (Those results are not shown here but were shown in Von Storch and colleagues paper).
As expert reviewers commenting on Von Storch et al.’s paper for the Science magazine noted:
“Accepting Von Storch et al.’s results does not mean that we must also accept that their simulated temperature history is close to reality — merely that it is a reasonable representation of climate behavior for which any valid reconstruction method should perform adequately.”
In short, the temperature records from the computer model over the last 1,000 years need not be absolutely correct as long as the model outputs can be shown to simulate observed reality in recent years reasonably well. That was the case.
Von Storch et al. show that their ECHO-G computer simulation yields realistic temperature variability similar to the observed Northern Hemisphere temperature (labeled NCEP Reanalysis) in the test period 1948-1990. By contrast, the hockey stick curve, adopted by the IPCC TAR, already underestimates the observed range of temperature change from 1948-1980.
Going back through past centuries, Von Storch and colleagues identified a peculiar problem with the method used to develop the hockey stick. Using the same statistical averaging method on the computer simulated temperature sampled at the 105 sites from where the original hockey stick proxies were taken, and adding a realistic estimate of error and uncertainty of temperature at each geographical locations, Von Storch and colleagues came up with a remarkable finding. The finding agreed reasonably well with the original hockey stick results.
What does such agreement mean? Not confirmation of MBH99s results, but a refutation. As Von Storch and colleagues noted that the hockey stick methodology systematically and significantly underestimated the full range of temperature variability of the last 1,000 years. By ignoring the hockey sticks rules for statistical averaging and instead computing the simple arithmetic average of the temperatures from the same 105 sites, Von Storch and colleagues produced a temperature curve that agreed well with the full range of variability.
Bottom line: the large underestimation of temperature change is mainly an artifact of the hockey stick’s averaging rules.
The authors of the Science paper put it this way:
“…widely-used methods [e.g., IPCC TAR 2001] to reconstruct past global climate variations … probably underestimate the amplitude of the real variations by a factor of up to two, and possibly more.
Von Storch bluntly summed up his results with the following comment reported in Der Spiegel on October 4:
“We were able to show in a publication in Science that this [hockey stick] graph contains assumptions that are not permissible. Methodologically it is wrong: Rubbish [or Junk, from the German phrase Quatsch].”
Von Storch and colleagues aren’t the only ones who reached that conclusion.
In a recent popular article in MIT’s Technology Review, Professor Richard Muller, through the careful re-assessment and checking by the two independent Canadian researchers, Stephen McIntyre and Ross McKitrick, highlighted another very serious methodological problem in the IPCC rendition of the 1,000-year hockey stick temperature history — adopting the hockey stick methodology, the hockey stick shape of the temperature history curve can be automatically generated by using random data series (i.e., in contrast to data series from actual climate proxies or computer model outputs) from each locations.
Muller remarked that:
“A phony hockey stick is more dangerous than a broken one — if we know it is broken. It is our responsibility as scientists to look at the data in an unbiased way, and draw whatever conclusions follow. When we discover a mistake, we admit it, learn from it, and perhaps discover once again the value of caution.”
In short, the new paper in Science by Von Storch and colleagues confirms what several other climate researchers have long stipulated. The hockey stick curve — which is a mathematical construct, as opposed to actual temperature information recorded at individual locations — is problematic because it yields air temperature changes on timescales of a few decades to a century that are simply too muted to fit the phenomena of the Medieval Warm Period (ca. 800-1300) and Little Ice Age (ca. 1300-1900), which are well recorded in historical documents and recognized in indirect climate data from growths of tree-rings and corals or isotopic content in ice cores and stalagmites collected around the world.
This is traditional science, with results from one group tested by others. What makes this case important, though, was explained by Von Storch in Der Spiegel:
“The Mann graph [i.e., the hockey stick of IPCC TAR] indicates that it was never warmer during the last ten thousand years than it is today. … In recent years it [the hockey stick] has been elevated to the status of truth by the UN appointed science body, the Intergovernmental Panel on Climate Change (IPCC). This handicapped all that research which strives to make a realistic distinction between human influences and climate and natural variability.”
* Willie Soon is physicist at the Solar, Stellar, and Planetary Sciences Division of the Harvard-Smithsonian Center for Astrophysics and an astronomer at the Mount Wilson Observatory. His book (with Steven Yaskell) The Maunder Minimum and the Variable Sun-Earth Connection (http://www.wspc.com/books/physics/5199.html) was published by World Scientific Publishing Company earlier this year. David Legates is Associate Professor in Climatology in the Center for Climatic Research at the University of Delaware. The views presented here by Soon and Legates are solely of their own and do not represent the view of the institutions where they work.
Adapted from TCSDaily.com which is published by Tech Central Station, a division of DCI Group, L.L.C. Small edits have been made only in reference to three illustrative charts or figures which were not copied with this article.
– ed.


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