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« Weather outlook: poor, expect gales - Josh 170 | Main | Gleick "cleared" »

Another Hockey Stick broken

There are some important findings at Climate Audit today. Once again I have tried to set out a layman's version of the discussion there.

One of the perennial problems with temperature reconstructions has been a lack of data covering the southern hemisphere - the Hockey Stick itself was a northern hemisphere reconstruction, although the IPCC billed it as global in extent. However, a recent paper by Gergis et al sought to partially remedy this by presenting an Australasian temperature reconstruction for the last millennium, based on 27 proxy records, primarily from tree rings and corals. The headline was, perhaps not unexpectedly, that late twentieth century warming was unprecedented:

The average reconstructed temperature anomaly in Australasia during A.D. 1238–1267, the warmest 30-year pre-instrumental period, is 0.09°C (±0.19°C) below 1961–1990 levels.

However, when the paper was examined in more detail, alarm bells began to be sounded. Concern centred around the proxy data sets used in the study.

Gergis et al reported that they had used 27 proxy series, but that they had selected these from a larger body of data. This was a critical step in the process and one that could well have led to a bias in the results. Many of the studies in the field of temperature reconstructions rely on "sorting" or filtering the data in some way, either choosing only proxy series that correlate well with their local temperature or alternatively weighting them according to how well they correlate. On the face of it, this is a reasonable approach, as the argument might well be made that if there is no correlation then the series is clearly not a proxy for temperature. However, the problem with this approach is that it amounts to a circular argument; it could be that the correlation between temperature records and proxy data is coincidental. This flaw has been demonstrated by studies in which the proxy series are replaced with dummy data series that wiggle up and down at random. In these studies, it has been shown that most of the time the resultant "reconstruction" is a hockey stick.

However, the good news was that Gergis et al were apparently aware of these issues and they declared that they had found a way around them. According to the paper:

For predictor selection, both proxy climate and instrumental data were linearly detrended over the 1921–1990 period to avoid inflating the correlation coefficient due to the presence of the global warming signal present in the observed temperature record.

In other words, when doing the correlation calculations to determine which proxies they would use, they first removed the twentieth century trend (actually, the 1921-1990 trend) from both the proxies and the temperature records, so that instead of filtering for series with a twentieth century uptick, they were picking records that appeared to match in their year-to-year wiggles.

So far so good, but this would have been a calculation that had to be done with immense care and a replication of it could therefore have been illuminating. However, in order to do this, it would be necessary to obtain all the Gergis data including the series that had been filtered out and not used, and unfortunately Gergis was not playing ball:

The compilation of this database represents years of our research effort based on the development of our professional networks. We risk damaging our work relationships by releasing other people’s records against their wishes. Clearly this is something that we are not prepared to do.

We have, however, provided an extensive contact list of all data contributors in the supplementary section of our recent study ‘Southern Hemisphere high-resolution palaeoclimate records of the last 2000 years’ published in The Holocene (Table S3):

This list allows any researcher who wants to access non publically available records to follow the appropriate protocol of contacting the original authors to obtain the necessary permission to use the record, take the time needed to process the data into a format suitable for data analysis etc, just as we have done. This is commonly referred to as ‘research’.

The refusal to release data was troubling, as it prevented anyone ever being able to replicate Gergis's work. And when Gergis's blog was unearthed and it was revealed that she was a committed environmentalist, the alarm bells became louder still.

Despite the flat refusal to allow replication of the paper, it was still possible to verify certain aspects of the filtering process. In particular, the data for the 27 proxies that had been used was available and so it would be possible at least to replicate the calculation that showed that these had significant correlations to their local temperature once the 1921-1990 trend had been removed. This task was taken up by statistician "Jean Sibelius" but rather remarkably he found himself unequal to the task:

Steve, Roman, or somebody, what am I doing wrong here? I tried to check the screening correlations of Gergis et al, and I’m getting such low values for a few proxies that there is no way that those can pass any test. I understood from the text that they used correlation on period 1921-1990 after detrending (both the instrumental and proxies), and that the instrumental was the actual target series (and not the against individual grid series).

Sibelius's difficulties were confirmed by others, including Steve McIntyre, but perhaps most significantly, by CSIRO's Nick Stokes, who is no sort of a sceptic. Stokes agreed with Sibelius that, when detrended, the correlations for the 27 proxies used in the Gergis reconstruction were insignificant, completely contradicting Gergis's paper. However, extraordinarily, Stokes also ran the calculations without detrending and found correlations that were significant.

I’ve run Steve’s code with and without detrending, and with and without the Quenouille correction. Without detrending (but with zero mean) or AR1 correction all (exc maybe Madang) proxies do seem significant

This seems to suggest that Gergis's declaration that the correlations were based on detrended data was false and that she and her co-authors had indeed fallen foul of the circular argument noted above. The finding of unprecedented warmth reported in the Gergis paper appears as though it is a function of the methodology used rather than of the underlying data.

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  • Response
    Never done this before, so it may go pear shaped. But I would really like some ideas on how to cut this down to something that can be sent out to the press.
  • Response
    (I have updated the item with comments below after the Post-Libertarianism blog responded). I suppose it is inevitable that people who are unconvinced by a supposedly strong "consensus" in favour of CAGW are going to be branded as conspiracy theorists, putting them into the same category as 9/11 Truthers, Holocaust revisionists, ...

Reader Comments (121)

"We need to be prepared to defend our science in the face of intense public scrutiny, concisely, with conviction and in plain English"

Totally what she did with her email to McI

Jun 8, 2012 at 3:43 PM | Unregistered Commentershub

The requested article is not currently available?

Jun 8, 2012 at 3:48 PM | Unregistered Commenterhum

I am certainly learning something about dendrochronology and the modus operandi of the "-ologists". What I think I have learned recently is the following. Perhaps others might care to comment:

-Individual trees are interviewed to determine temperatures in the unrecorded past according to the thickness of their past growth-rings.

-Trees are selected if their RECENT increasing [or decreasing] growth matches increases or decreases of measured RECENT, local, temperatures. No rationale is offered for causation. It is a purely statistical approach.

-Other, apparently identical, local trees will show no pattern at all, or actually show DECREASES when the selected trees show INCREASES. These trees are ignored and other trees are interviewed until enough "correct" answers are obtained, even if a whole forest might disagree with a handful of trees.

-Other factors affecting tree growth such as water, fertilisation, predation, or disease, are ignored because they are largely unknown.

-For the selected trees, there is no guarantee that the pattern-match they displayed recently will also have been the pattern in the unrecorded past. They were after all, selected on a purely statistical basis of correlation, without reference to any other physical, chemical, or biological reasons for doing so.

Jun 8, 2012 at 3:55 PM | Unregistered Commentermichael hart

I know I said I was done on this but I keep seeing these gems that show how "politicized" her own agenda is.... Is she more activist or scientist? This is a different version of her thoughts after that "Science Meets Parliament 2010" and here she fervently embraces the Chris Mooney/Michael Mann "guerrilla war" and "asymmetric warfare" narratives.

In fact she thinks the talk she heard by Mooney was "fantastic" so we don't need to worry that we are misunderstanding the fervor of her commitment to upholding the CAGW narrative in a guerrilla war against "well orchestrated" critics (by the way, Bish, who is the orchestra conductor, you or SM or AW or....?? I keep wondering who our conductor is, oh and why don't I have some lavish funding from fossil fuel industries??).


Conference Report // Communicating climate change: advice from Science meets Parliament 2010
Joëlle Gergis and Ailie Gallant

Conference Report // Communicating climate change: advice from Science meets Parliament 2010
Joëlle Gergis and Ailie Gallant
School of Earth Sciences, University of Melbourne

Bulletin of the Australian Meteorological and Oceanographic Society Vol. 23 page 26

"....On day 2 we were treated to a fantastic guest speaker, American science writer Chris Mooney,[emphasis added] at the National Press Club. He gave an incisive overview of the nature of the ‘guerrilla war’ being waged on climate science in the untamed jungles of the online world. He said it was naïve for scientist to feel that the ‘truth will prevail’ in the global warming debate as the mountain of peer-reviewed evidence grows. Instead he suggested that as a community we need to equip ourselves with the professional communication skills needed to combat the very targeted tactics of our opponents. In a recent interview Professor Michael Mann (co-creator of the ‘hockey stick’ temperature reconstruction) referred to the ‘asymmetric warfare’ between trained global warming contrarians and climate scientists as ‘literally like a battle between a Marine and a Cub Scout’. In the 11 March 2010 issue of Nature, the editor warned that ‘scientists must acknowledge that they are in a street fight, and that their relationship with the media really matters’...."

Jun 8, 2012 at 3:59 PM | Registered CommenterSkiphil

Re: michael hart

Other, apparently identical, local trees will show no pattern at all, or actually show DECREASES when the selected trees show INCREASES. These trees are ignored....

Trees that show decreases when temps increase are inverted and then used.

Jun 8, 2012 at 4:06 PM | Unregistered CommenterTerryS

Michael Hart

"Individual trees are interviewed ..."

Indeed. And when they don't cooperate they are tortured in a variety of ways.

Jun 8, 2012 at 4:16 PM | Registered CommentersHx

Another one bites the dust.

Jun 8, 2012 at 4:28 PM | Unregistered Commenterredc

...and another one's gone.

I could probably do this all day, removing content like this is silly.

Jun 8, 2012 at 4:45 PM | Unregistered Commenterredc

Re: TerryS
"Trees that show decreases when temps increase are inverted and then used."

So if they use trees from one extreme and also use the anti-correlated "upside down" trees from the other extreme [I see a Josh cartoon there], why can't they find a way to use the ones in between?

Jun 8, 2012 at 5:29 PM | Unregistered Commentermichael hart

give them time...

Jun 8, 2012 at 5:58 PM | Unregistered CommenterTerryS


Starting in the 1950s and increasingly influential in the '60s,'70s and later, you run into the influence of "post-modernist" philosophy (PMT) on science. Postmodernist thinkers emphasize the "synthetic" nature of knowledge and how it is "constructed." Reality is also treated as "synthetic." The argument going so far as to insist that there is no "empirical" reality and therefore no possibility of "empirical content" in a scientific hypothesis. Effectively that reduces you ideas about reality - things like "keep out of the way of that bus" to the same level of significance as the fellow who wears the aluminum foil hat to keep out "government rays." They are both "legitimate" "understandings" of reality in postmodernist thought. I consider it poppycock and have suggested empirically testing the reality of the bus. The postmodernist can stand in front of it and I will record the results. No postmodernist has ever taken up the challenge. They have however occasionally become quite angry and abusive when I argue their reluctance stems from an abiding confidence in external, empirical reality. The upshot of this change is that coupled with the competition for grant money, there seems to have been an increase in "fraud" in ALL science. Gergis is at least rational enough to go out and seek real data. If you check into recent scandals in physics, there are incidents of the data it self being fabricated rather merely adjusted. Looked at that way, climate science might be seen as a bastion of "near" integrity in its science.

Jun 8, 2012 at 7:25 PM | Unregistered CommenterDuster

Josh, would you do us a cartoon of this saga of all the vanishing pages under a "Ghostbusters" title or such? Richly merited I think.

Ten thousand thanks to all the intrepid big-oil-underpaid volunteer contributors here. Especially thanks to Bishop for putting the new saga on the table fair and square and open and comprehensible and checkable (unlike the Team of course).

Jun 8, 2012 at 8:45 PM | Unregistered CommenterLucy Skywalker

Skiphil, what a great find where they say "In a recent interview Professor Michael Mann (co-creator of the ‘hockey stick’ temperature reconstruction)"...

co creator is absolutely right since this is made up stuff. Usually in science something is discovered not created, but in climate science they are just making it up.

Jun 8, 2012 at 8:51 PM | Unregistered Commenterhum

The perennial problem with proxy paleotemperature reconstructions is that they're pseudoscience.

They're based on no physical theory, their purported significance lies in qualitative judgments of temperature sensitivity, and even when physically real proxies are used, such as dO-18, the physical meaning is methodologically discarded.

People get waxed about statistical methods, and have long erudite conversations about which and whether proper statistical forms have been followed. That's all a tempest in a scientific teacup. The central point of proxy paleotemperature reconstructions is that they have zero physical meaning.

The people who enter the field from dendroclimatology are probably naifs when it comes to physical methods and don't realize that their work is meaningless. But the physicists who do it, and in particular Michale Mann, must know that they're publishing propagandistic garbage.

Jun 8, 2012 at 9:34 PM | Unregistered CommenterPat Frank

This paper provides a good explanation of the "selecting on the dependent variable" problem inherent in selecting trees that appear well correlated with temperature as a basis for doing temperature studies.

If you only select trees that appear correlated with temperature, you are ignoring the large body of trees that are telling you that trees are not a good proxy for temperature.

For example, say we selected companies that were highly profitable to study why they were profitable. We found that factor X was common to all successful companies. This might lead us to conclude that factor X causes companies to be profitable.

However, by not studying unprofitable companies, we overlooked the fact that factor X was common to unprofitable companies as well, and thus had little or no influence of profitability.

The same situation with trees. The assumption is that temperature (factor X) determines tree growth (profitability). By only studying trees that correlate with temperature, climate science has ignored the large body of trees telling us that temperature (factor X) is also common to trees that show no growth (low profitability) and thus had little or no influence on tree growth (profitability).

Jun 9, 2012 at 7:59 PM | Unregistered Commenterferd berple

"This list allows any researcher who wants to access non publically available records to follow the appropriate protocol of contacting the original authors to obtain the necessary permission to use the record, take the time needed to process the data into a format suitable for data analysis etc, just as we have done. This is commonly referred to as ‘research’."

I should have tried this disclaimer on my masters thesis - I can bet that I would have not recieved my degree if I had refused to show my data.

Jun 9, 2012 at 9:27 PM | Unregistered CommenterPhysics Grad

"Upside-down proxies are not by definition a problem - why shouldn't trees dislike hotter weather? Selecting both ways up within a similar temp range is a problem.

Jun 7, 2012 at 1:12 PM | steveta"

Nah nah nah, Dude. "Hotter"? 0.2C or 0.4C (the range shown on the output graph) isn't "hotter"; it is a tiny bit warmer and basically the same temperature. Trees are not going to start showing inverse correlation over 0.2C or 0.4C. The temps from day to day vary 10-20 times that. And don't throw the old "Weather isn't climate" b.s. at this. Minuscule increases are not "hotter" - they are minuscule increases.

Jun 10, 2012 at 7:30 AM | Unregistered CommenterSteve Garcia

As long as the conclusion supports the Scam Regnant, you can get any kind of Climate Science horse pucky published. In the natural course of things, after enough embarrassments at the hands of the blogosphere, where real experts have no gatekeeping blocking their analyses, the journals will start to apply at least a minimum of quality control. But it's taking years and years to force them to that point.

Jun 10, 2012 at 8:28 AM | Unregistered CommenterBrian H

Seems to me that Gergis lied but didn't think she was going to be caught. Not too swift.

But what is wrong with using negatively correlated proxies? Seems to me calling them "upside down" is a mere debating trick and unworthy.

Jun 10, 2012 at 6:16 PM | Unregistered CommenterEd

".. so that instead of filtering for series with a twentieth century uptick, they were picking records that appeared to match in their year-to-year wiggles.

So far so good,.."

Better, but still not good.

The selected series now follow the year to year wiggles and look like temperature proxies. Most may then also replicate the uptick in the calibration period, but some may have a downtrend.

There are 2 issues that remain:

First issue, outside the calibration period, some proxies may stop to correlate with temperature. This will inevitably flatten temperature maxima and minima outside the calibration period.

Second issue, the series with the wrong trend within the calibration period may receive negative weighting, making the reconstruction meaningless. If they would be excluded instead, we would be halfway back to the even poorer case with no detrending in the first step.

Jun 11, 2012 at 6:04 AM | Unregistered CommenterMarkus

Perhaps I'm missing something big here, but when I read a phrase like "The headline was, perhaps not unexpectedly, that late twentieth century warming was unprecedented:" I always look at the data plot.

In this case, looking at Figure 4, I see a very sharp spike upwards at approximately year 1320. The rate of change was very high, appearing quite possibly higher than the last decade or two. There's substantial uncertainty as well, I know, but it raises questions of what's so unprecedented, especially when the uncertainty of the data are so variable in the combined series.

Also, given all the discussions about proxies, I have to wonder if thermometer data were tossed in as well, acknowledged in the paper or not.

Frankly, though, Gergis' data does not make much of a hockey stick, unless one looks solely at the black lines (i.e., completely discount the uncertainties of the data).

Jun 11, 2012 at 5:13 PM | Unregistered CommenterEugene

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