As many readers will know, much of the basis for the anthropogenic climate change scare came from a set of results published by Mann et al., which purported to show a massive uptick in temperatures in the twentieth century. This "hockey-stick graph" also flattened an earlier temperature period—which was well documented in historical records—known as the Mediaeval Warm Period.
The Hockey Stick Graph
This chart is Figure 1(b) from the Intergovernmental Panel on Climate Change Third Assessment Report, (c) 2001 The Intergovernmental Panel on Climate Change. Sourced from Wikipedia and, ultimately, from the IPCC Report [PDF].
The significance of the graph should not be underestimated: the graph showed unprecedented temperature levels and was used as the foundation for the IPCC Reports and, ultimately, the anthropogenic climate change (ACC) thesis.
What is less well known is that the reports by Mann et al. (as well as many others investigating similar trends) were actually based on previous reports by Keith Briffa (whom your humble Devil has mentioned before) of the Climate Research Unit (CRU) at the University of East Anglia—and it was he who had constructed the hockey stick graph.
Now, obviously we do not have really accurate temperature measurements for further back than about thirty years—and we have no even vaguely accurate direct temperature measurements for any time before the US land network stations were set up in 1896 (previous blogs at The Kitchen have discussed the accuracy of those temperature measurements).
As such, climate researchers use proxies such as ice cores or, in Briffa's case, cores from the trunks of long-lived trees such as the bristle-cone pine. The research is basically as scientific as counting the tree rings and measuring their widths and assuming that there is a correlation between these widths and the temperature prevailing at the time.
Over the last few years, some problems with this method had become evident, not least the fact that the ring widths have not reflected the temperatures that we have been able to measure in the last few years—an inconvenient truth that has been called "the divergence problem".
Steve McIntyre—who, both solo and with Ross McKitrick, has been a thorn in the side of AGW alarmists for some time now—has been doing some excellent research over the last few years into this area (indeed, because of the entirely unscientific reluctance of climate scientists in general, and Keith Briffa in particular, to make their raw data available—this latest breakthrough has been some three years in the making) the so-called hockey-stick controversy was caused by McIntyre's discovery of the unreliability of the so-called Polar Urals data.
At this point, I am going to start referring to Bishop Hill's excellent and comprehensive summary of what he is calling the Yamal Implosion.
With Polar Urals now unusable, paleclimatologists had a pressing need for a hockey stick shaped replacement and a solution appeared in the nick of time in the shape of a series from the nearby location of Yamal.
The Yamal data had been collected by a pair of Russian scientists, Hantemirov and Shiyatov, and was published in 2002. In their version of the data, Yamal had little by way of a twentieth century trend. Strangely though, Briffa's version, which had made it into print before even the Russians', was somewhat different. While it was very similar to the Russians' version for most of the length of the record, Briffa's verison had a sharp uptick at the end of the twentieth century -- another hockey stick, made almost to order to meet the requirements of the paleoclimate community. Certainly, after its first appearance in Briffa's 2000 paper in Quaternary Science Reviews, this version of Yamal was seized upon by climatologists, appearing again and again in temperature reconstructions; it became virtually ubiquitous in the field: apart from Briffa 2000, it also contributed to the reconstructions in Mann and Jones 2003, Jones and Mann 2004, Moberg et al 2005, D'Arrigo et al 2006, Osborn and Briffa 2006 and Hegerl et al 2007, among others.
So, the new data became the absolute corner-stone of a almost all climate research because, as is often the way, the climatologists were not actually gathering their own data—they were simply remodelling using the same one or two data sets. The flaw in this is obvious: if you are feeding nonsense data into a model, then the results will obviously be nonsense too.
Steve McIntyre wanted to examine the original datasets but was turned down flat by Briffa, and other avenues failed to yield results. It was only when the Royal Society—one of the few, it seems, scientific publications actually willing to enforce their data policy—published some of Briffa's research that a way in was found. After more frustrations (Briffa—deliberately?—had removed, or not archived, any metadata (including the origins) for the tree ring measurements) and more hefty research, McIntyre seemed to be making progress.
When McIntyre started to look at the numbers it was clear that there were going to be the usual problems with a lack of metadata, but there was more than just this. In typical climate science fashion, just scratching at the surface of the Briffa archive raised as many questions as it answered. Why did Briffa only have half the number of cores covering the Medieval Warm Period that the Russian had reported? And why were there so few cores in Briffa's twentieth century? By 1988 there were only 12 cores used, an amazingly small number in what should have been the part of the record when it was easiest to obtain data. By 1990 the count was only ten, dropping still further to just five in 1995. Without an explanation of how the selection of this sample of the available data had been performed, the suspicion of `cherrypicking' would linger over the study, although it is true to say that Hantemirov also had very few cores in the equivalent period, so it is possible that this selection had been due to the Russian and not Briffa.
The lack of twentieth century data was still more remarkable when the Yamal chronology was compared to the Polar Urals series, to which it was now apparently preferred. The ten or twelve cores used in Yamal was around half the number available at Polar Urals, which should presumably therefore have been considered the more reliable. Why then had climatologists almost all preferred to use Yamal?
Yet more research was required—not only to answer the above question, but also to match up the raw core data with the locations from which they were taken.
As so often in McIntyre's work, the clue that unlocked the mystery came from a rather unexpected source. At the same time as archiving the Yamal data, Briffa had recorded the numbers for another site discussed in his Royal Society paper: Taimyr. Taimyr had, like Yamal, also emerged in Briffa's Quaternary Science Reviews paper in 2000. However, in the Royal Society paper, Briffa had made major changes, merging Taimyr with another site, Bol'shoi Avam, located no less than 400 kilometres away. While the original Taimyr site had something of a divergence problem, with narrowing ring widths implying cooler temperatures, the new composite site of Avam–Taimyr had a rather warmer twentieth century and a cooler Medieval Warm Period. The effect of this curious blending of datasets was therefore, as so often with paleoclimate adjustments, to produce a warming trend. This however, was not what was interesting McIntyre. What was odd about Avam–Taimyr was that the series seemed to have more tree cores recorded than had been reported in the two papers on which it was based. So it looked as if something else had been merged in as well. But what?
With no metadata archived for Avam-Taimyr either, McIntyre had another puzzle to occupy him, but in fact the results were quick to emerge. The Avam data was collected in 2003, but Taimyr only had numbers going up to 1996. Similarly, the Taimyr trees were older, with dates going back to the ninth century. It was therefore possible to make a tentative split of the data by dividing the cores into those finishing after 2000 and those finishing before. This was a good first cut, but the approach assigned 107 cores to Avam, which was more than reported in the original paper. This seemed to confirm the impression that there was something else in the dataset.
Having identified some of the other core locations, and running yet more processes on the others, McIntyre found that the final set came from a rather unexpected—and, in Briffa's paper, unacknowledged—source.
Forty-two of the cores turned out to be from a location called Balschaya Kamenka, some 400 km from Taimyr. The data had been collected by the Swiss researcher, Fritz Schweingruber. The fact that the use of Schweingruber's data had not been reported by Briffa was odd in itself, but what intrigued McIntyre was why Briffa had used Balschaya Kamenka and not any of the other Schweingruber sites in the area. Several of these were much closer to Taimyr–Aykali River was one example, and another, Novaja Rieja, was almost next door.
And the significance of this...?
By this point then, McIntyre knew that Briffa's version of Yamal was very short of twentieth century data, having used just a selection of the available cores, although the grounds on which this selection had been made was not clear. It was also obvious that there was a great deal of alternative data available from the region, Briffa having been happy to supplement Taimyr with data from other locations such as Avam and Balschaya Kamenka. Why then had he not supplemented Yamal in a similar way, in order to bring the number of cores up to an acceptable level?
In other words, core data from a wide area were merged together in order to provide a reliable record for the past 1,000 years or so, but this was not done for the twentieth century data. Why?
The reasoning behind Briffa's subsample selection may have been a mystery, but with the other information McIntyre had gleaned, it was still possible to perform some tests on its validity. This could be done by performing a simple sensitivity test, replacing the twelve cores that Briffa had used for the modern sections of Yamal with some of the other available data. Sure enough, there was a suitable Schweingruber series called Khadyta River close by to Yamal, and with 34 cores, it represented a much more reliable basis for reconstructing temperatures.
The results are... interesting, to say the least. [Emphasis mine.]
McIntyre therefore prepared a revised dataset, replacing Briffa's selected 12 cores with the 34 from Khadyta River. The revised chronology was simply staggering. The sharp uptick in the series at the end of the twentieth century had vanished, leaving a twentieth century apparently without a significant trend. The blade of the Yamal hockey stick, used in so many of those temperature reconstructions that the IPCC said validated Michael Mann's work, was gone.
This significance of this cannot be underestimated—it absolutely strikes at the root of the entire AGW scare. The effective conclusion is that the hockey-stick graph—and the huge temperature uptick in the twentieth century that underpins the entirety of AGW alarmism—is false.
Let us be absolutely clear about what this means: if the AGW alarmists are indeed motivated by genuine concern that humanity is causing a catastrophic warming of the planet, then they will now retract their protestations.
If, however, the motivation is different from this—if the scientists are, for instance, motivated by money or by power or by political machinations—they will continue to prophesy doom and destruction.
If you read Bishop Hill's entertaining narrative—which I really recommend that you do—and comprehend the significance of the obfuscation, cherry-picking and outright dishonesty displayed by Briffa and others, then you will know which way I'm betting.
But make no mistake, if honesty still exists—assuming that it ever did—in the climate science community, then the concept of anthropogenic climate change is dead.