There have been increasing questions on the data that went into generating the “blade” of the hockey stick, which I discussed in an earlier post after it was revealed that the paper that Keith Briffa wrote that led to the generation of the blade, relied on a very small range of trees, including only one that showed the dramatic uptick of the hockey stick. Briffa recently commented
we noted that the final years of the Yamal ring-width chronology (Briffa, 2000; Briffa et al., 2008) should be used cautiously on the basis that the values for the most recent part of this chronology are based on relatively few individual measurement series and this smaller available sample emphasises the faster growing trees.Given the subsequent history of the use of that data (vide the movie An Inconvenient Truth inter alia) it can hardly be said that those words of caution were heeded, or even recognized.
Questions on the validity of using that particular data continue, and correlations are now being made with actual local temperature measurements in the same regions as the tree data came from. What emerges from that correlation is
“Warmist” tree ring proxy temperature evidence is falsified directly by local thermometer records.The data analysis is somewhat intense but well worth working through to understand exactly why that statement is justified.
And there has just been a new paper on this subject published by Devi et al. which argues for the consideration of ecotone movement in the analysis of the tree ring data, and shows that there was a change in the way in which the trees grow, a change which correlates with temperature, that can be traced back to early in the 20th century. (Thanks bender). But it blows another leg out from under the support of the shape of the hockey stick at the more immediate end of the line.
Meanwhile, if one travels back to the other end of the line, and the estimation of what the temperatures were like in the Medieval Warming Period, one has to remember that, prior to publication of the Hockey Stick, curve the IPCC did recognize the existence of those warmer temperatures.
Medieval Warming Period (IPCC 1996) and the curve generated from borehole temperature proxies by Huang and Pollack in 1997.
The difference between the IPCC curve, and that proposed by Mann was highlighted in a review of the borehole data, and can be seen in this curve:
Comparison of Mann’s plot (blue) with that of the earlier IPCC prediction (red), and the plot from Moberg (black). (Source )
Now it turns out that there were some significant questions about the data upon which Dr Mann generated those predictions of Medieval temperature. There exist a large number of scientific papers (which I have referred to in earlier posts) that show that the period did exist. (The very first paper that I looked at when I got curious about this subject showed its existence in the Sargasso Sea, for example). However the curve was itself underpinned among others by data from tree ring cores taken from bristlecone pine trees in the Western United States.
Bristlecone pine tree allowing historic temperature data acquisition.
The validity of using those tree rings has been questioned by experts in forestry and other contemporary evaluations have shown the Medieval warming period that Mann’s graphs did not.
However the curve was also based on other proxy data (i.e. other physical phenomena changes that can be correlated with temperature change). It is interesting to note that Dr Mann is now changing the basis on which his curve was produced though all the while arguing that the basic shape remains unchanged.
Mann’s latest plot of historic global temperatures.
Now given that this does not show any decline in temperature between 1940 and 1970, something clearly shown in the record, the accuracy of this plot, as with earlier ones, is up for grabs, but seems to indicate that the consistent valid criticism leveled at the paper by Steve McIntyre has yet to be completely addressed.
The controversy has moved on to the use of lakebed sediments from Lake Korttajarvi in Finland, which were cored by Mia Tiljander as part of a doctoral dissertation (hence the name Tiljander sediments). Analysis of the use of the data by others has recently led Kaufman to admit he made a mistake in the use of the data while reasserting that the correction merely strengthens his original argument.
That a correction that re-inverts the data strengthens a correlation seems to be odd to me, but then this whole basic argument over the data and its interpretation has been redolent with somewhat dishonest and manipulative practices on behalf of those generating the information that is used by the IPCC and our Secretary of Energy.
When one realizes that much of this manipulation comes from folk that work in the government and are supposed to be disinterested in the results it becomes more irritating. But then one must recognize that their funding and jobs do, to a significant extent, depend on Global Warming being real and man-made.
I would recommend reading the review of all this at the Skeptical Climate Science Primer since this story is told there with many more graphs and details than I can put in the posts that I produce.