On "Tricks" In Math And Science

Central to the debate over the significance of emails hacked from CRU's Servers back in late November is one from Phil Jones discussing the divergence problem--the divergence from instrumental temperature readings seen in Keith Briffa's tree ring chronologies after 1960. He writes:

Dear Ray, Mike and Malcolm,Once Tim’s got a diagram here we’ll send that either later today or first thing tomorrow. I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) amd [sic] from 1961 for Keith’s to hide the decline.

Of course the denialists jumped on this email, at first assuming that Jones was discussing a decline in temperatures, and then modifying their charges when it became clear that this was not the case. In any case, Jones defense was to argue that the term "trick" was "used here colloquially, as in a clever thing to do...". Well, can this defense be justified or, to put it another way, is the term "trick" used as a colloquialism in the statistical/mathematical/scientific literature?

Well, yeah. Here's what you get when you run inurl:pdf "computational trick" through google:

And here's is what you get when you run "inurl:pdf "mathematical trick"" through the same source.In fact, if you look at the first link, you will note that was "invented in the context" of theoretical physics, so if there is a conspiracy, it goes much deeper than anyone has currently suggested.

PS. Just reading Desmog, I notice that someone else thought of running these searches before me.

ClimateHackerGate! CRU First Hacked In October????

An interesting development:

E-mails alleged to undermine climate change science were held back for weeks after being stolen so that their release would cause maximum damage to the Copenhagen climate conference, according to a source close to the investigation of the theft.

[...]

The first hack was in October or earlier, the source said. The e-mails were not leaked until mid-November.

Interesting because, back on the 25th, I theorized that the hackers might have first shown a selection of illegally obtained emails to the BBC's Paul Hudson back in October and then--perhaps because he didn't write on them--hit the CRU server again for more of the good stuff. This new development would be consistent with that theory, which would be uncomfortable for Mr. Hudson, as it would mean he sat on illegally obtained emails without reporting them for a whole month.

Also--since the private CRU emails discuss Briffa's tree-ring proxies and Tijander and etc.--did the hackers delay their release in the hopes of harvesting more embarrassing material on this particular topic? That might put them in rather close proximity to Steve M's gang at CA, since he was the guy stirring the pot on these issues. In any case, it is clear that the emails were held back for weeks after being stolen so that their release would cause maximum damage to the Copenhagen climate conference. That's the takeaway message.

Briffa, Mark II: McIntyre Used Biased Sample

I think Steve has backed away from most of his accusations re the Yamal tree-ring chronology here, or had them convincingly refuted. Nevertheless, Briffa and several co-authors have decided to make a more thorough response to his various blog posts on the matter. From their abstract:

McIntyre's use of the data from a single, more spatially restricted site, to represent recent tree growth over the wider region, and his exclusion of the data from the other available sites, likely represents a biased reconstruction of tree growth. McIntyre's sensitivity analysis has little implication, either for the interpretation of the Yamal chronology or for other proxy studies that make use of it.

From their conclusion:

So what can we conclude on the basis of this and McIntyre's sensitivity tests? Does either version of the Yamal chronology as presented in Briffa (2000) and Briffa et al. (2008) present a misleading indication of the likely history of tree-growth changes near the tree line in the Yamal region over the last two millennia, or can McIntyre's 'sensitivity analysis' be taken as evidence that tree growth has not increased in this region in the second half of the 20th century as is clearly implied by the 'extreme' version of the Yamal chronology he produced? On the basis of the evidence we report here, the answer is very likely 'NO' on both counts."

McIntyre states "If the non-robustness observed here prove out .. this will have an important impact on many multiproxy studies ...". We have shown here that the "KHAD only" example constructed by McIntyre itself represents a biased chronology, contradicted by the evidence of other chronologies constructed using additional and more representative site data. The evidence does not support a conclusion that our previous work was in any way seriously flawed. The last 8 years of our chronology ARE based on data from a decreasing number of sites and trees and this smaller available sample does emphasise the faster growing trees, so this section of the chronology should be used cautiously. The reworked chronology, based on all of the currently available data is similar to our previously published versions of the Yamal chronology demonstrating that our earlier work presents a defensible and reasonable indication of tree growth changes during the 20th century, and in the context of long-term changes reconstructed over the last two millennia in the vicinity of the larch treeline in southern Yamal.

All that is really left now is for McIntyre, and Pielke Jr., to apologize.

Keith Briffa Strikes Back

The Yamal ring-width chronology of Briffa (2000)

My attention has been drawn to a comment by Steve McIntyre on the Climate Audit website relating to the pattern of radial tree growth displayed in the ring-width chronology "Yamal" that I first published in Briffa (2000). The substantive implication of McIntyre's comment (made explicitly in subsequent postings by others) is that the recent data that make up this chronology (i.e. the ring-width measurements from living trees) were purposely selected by me from among a larger available data set, specifically because they exhibited recent growth increases.

This is not the case. The Yamal tree-ring chronology (see also Briffa and Osborn 2002, Briffa et al. 2008) was based on the application of a tree-ring processing method applied to the same set of composite sub-fossil and living-tree ring-width measurements provided to me by Rashit Hantemirov and Stepan Shiyatov which forms the basis of a chronology they published (Hantemirov and Shiyatov 2002). In their work they traditionally applied a data processing method (corridor standardisation) that does not preserve evidence of long timescale growth changes. My application of the Regional Curve Standardisation method to these same data was intended to better represent the multi-decadal to centennial growth variations necessary to infer the longer-term variability in average summer temperatures in the Yamal region: to provide a direct comparison with the chronology produced by Hantemirov and Shiyatov.

These authors state that their data (derived mainly from measurements of relic wood dating back over more than 2,000 years) included 17 ring-width series derived from living trees that were between 200-400 years old. These recent data included measurements from at least 3 different locations in the Yamal region. In his piece, McIntyre replaces a number (12) of these original measurement series with more data (34 series) from a single location (not one of the above) within the Yamal region, at which the trees apparently do not show the same overall growth increase registered in our data.

The basis for McIntyre's selection of which of our (i.e. Hantemirov and Shiyatov's) data to exclude and which to use in replacement is not clear but his version of the chronology shows lower relative growth in recent decades than is displayed in my original chronology. He offers no justification for excluding the original data; and in one version of the chronology where he retains them, he appears to give them inappropriate low weights. I note that McIntyre qualifies the presentation of his version(s) of the chronology by reference to a number of valid points that require further investigation. Subsequent postings appear to pay no heed to these caveats. Whether the McIntyre version is any more robust a representation of regional tree growth in Yamal than my original, remains to be established.

My colleagues and I are working to develop methods that are capable of expressing robust evidence of climate changes using tree-ring data. We do not select tree-core samples based on comparison with climate data. Chronologies are constructed independently and are subsequently compared with climate data to measure the association and quantify the reliability of using the tree-ring data as a proxy for temperature variations.

We have not yet had a chance to explore the details of McIntyre's analysis or its implication for temperature reconstruction at Yamal but we have done considerably more analyses exploring chronology production and temperature calibration that have relevance to this issue but they are not yet published. I do not believe that McIntyre's preliminary post provides sufficient evidence to doubt the reality of unusually high summer temperatures in the last decades of the 20th century.

We will expand on this initial comment on the McIntyre posting when we have had a chance to review the details of his work.
K.R. Briffa 30 Sept 2009

Briffa, K. R. 2000. Annual climate variability in the Holocene: interpreting the message of ancient trees. Quaternary Science Reviews 19:87-105.
Briffa, K. R., and T. J. Osborn. 2002. Paleoclimate - Blowing hot and cold. Science 295:2227-2228.
Briffa, K. R., V. V. Shishov, T. M. Melvin, E. A. Vaganov, H. Grudd, R. M. Hantemirov, M. Eronen, and M. M. Naurzbaev. 2008. Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia. Philosophical Transactions of the Royal Society B-Biological Sciences 363:2271-2284.
Hantemirov, R. M., and S. G. Shiyatov. 2002. A continuous multimillennial ring-width chronology in Yamal, northwestern Siberia. Holocene 12:717-726.

Origonal here.

PS. All Steve's data froma single location? His accusation of cherry-picking is supported by cherry-picked data? The irony abounds.

PPS. All accusations of deliberate scientific misconduct on Mr. Briffa's part will be deleted from the comments. Keep that stuff for the birthers with slide-rulers and spreadsheets over at CA.

RealClimate Strikes back here.