Resolved: The Hockey Stick is likely correct

I ask my opponent simply doesn’t post rebuttals last round, but he can summarize his arguments. Instead of a rebuttal I will simply write my case. The “issue” of the MWP Between 1995 and 2001, there was a complete revision on how the IPCC looked upon paleoclimate reconstructions. You could say there was a consensus—haha joke, funny. The MWP disappeared—it was considered a myth, a regional event, and modern warming was unprecedented. This change in views was influenced by one main graph: the hockey stick. To understand the change in views, one has to look no further than the 1990 IPCC report. In 1990, the IPSS displayed the MWP as warmer than the current warm period, as well as a prominent little ice age (LIA). However in 2001, we see a steady decrease in temperatures—almost linear—and then exponential increase in temperatures near 1900. This was based on MBH 1998, 1999. Since then, debate has ensued whether or not these proxy studies are reliable. Criticism begins After the IPCC 2001 report, there was very little criticism of the MBH 1998 and 1999 reconstructions. Since 1999, it looked like smooth sailing for the hockey stick with official IPCC approval. But this began to change in 2003, when retired mineralogist Stephan McIntyre and Economist and statistical expert Ross McKitrick published criticism of the Mann reconstructions. The results of their study showed that the hockey stick curve happened as a result from poor data handling, obsolete data, and incorrect calculation of principal components [1]. Let me explain some terms. Principal components are, essentially, a weighted average of the original group series. These weights are chosen to maximize explained variance. MBH98 used these components to simplify both temperature and proxy data. Essentially, they shrink 1082 grid cells into 16 principal components. MBH98 described 112 proxies, 71 of which are individual and 31 are principal components computed from different networks of individual proxies, all of which contain more than three hundred original series. Mann never released how he calculated these, but 5 of the 6 of his groups were published in Nature through the Supplementary Information page. McKitrick and McIntyre both attempted to recalculate and reproduce Mann’s data. See, principal components only work when data was missing. Using the data directly from Nature and the IPCC, they found that a lot of data was missing. They attempted to contact Mann how he dealt with this issue—there was no response. After working long hours attempting to verify the tree ring data, they calculated the component value. They didn’t match Mann’s results. At all. After investigation of the errors, McIntyre and McKitrick (M&M) found that Mann’s data suffered from large collated errors. McKitrick, after McIntyre sent him the data, found areas where one pair of series where two different columns had the same data for almost thirty years. After the research, M&M found when odd data series—which had no place in the data set—were removed, the Hockey Stick chart disappeared. After the calculations, the MWP reappears and the 20th century isn’t so scary [2]. To further explain the issues M&M found: “Almost all the NOAMER series selected for overweighting were of a single type and from a single researcher, Donald Graybill. The series were high-altitude bristlecone pine tree-ring chronologies… The sites were selected for “cambial dieback,” that is, the bark had died around most of the circumference of the tree. Graybill and Idso reported anomalously high twentieth-century growth for trees with cambial dieback, as compared with “full bark” trees at the same site. ” (see [2], pg 41) MBH98 recalculated looks like this: As we can see, it was actually slightly warmer around 1400 than it was in 2000. Although the study doesn't measure anything previous to 1400, we see, at least, part of the MWP, and see that it is likely warmer than the 20th century. Indeed, what occurred was that Mann’s statistical techniques accidentally (as I presume no scientific malpractice was intended) weighted the trees with hockey stick shapes. This weighting was, in part, one of the large reasons why a hockey stick shape occurred. Spurious weighting amplified the warming result. In sum, the differences between M&M and MBH98 are as follows: The cedar ring width series as well as principal component one—yes, these two things are the reason for the different results. For these data series, although Mann shrugs these changes as “conventional”, Mann changes his statistical techniques. The changes cause those datasets to be dominated by specific bristlecone pines which, as stated above, are anomalous. These pines are not considered good measurements of temperature. For a second dataset, the Cedar trees, Mann creates an extrapolation, unique to those 350 data series, and misrepresents the start date of the data series [3]. Yes, red noise an irregular statistical techniques always resulted in the hockey stick shape. Alternative reconstructions Some reconstructions—who attempt to act as independent verification, but are part of the hockey team, have published reconstructions which purport to claim “the 20th century is the most anomalous interval in the entire analysis period, with highly significant occurrences of positive anomalies and positive extremes in the proxy records. ”[4] However, this view is challenged by the majority of the reconstructions published. Recent research using lake sediments in Europe have found that the MWP was likely 0.9 degrees C warmer than today. The study even comments on other literature, saying “several other reconstructions from the Northern Hemisphere also show [recent] warm inferred temperatures that were not as warm as the [MWP]”[5]. Other work, based in Russia however obtains data from elsewhere, relies on a vast array of proxies as well as historical evidence from writings. In many cases, the authors find that the MWP was warmer than the latter part of the 20th century. Furthermore, they find that the MWP and LIA was a global event—not a regional one as Mann and team espouse [6]. Work from the same year, by Esper et al. shows that the warming in the 20th century was not unprecedented at all—if anything, the MWP was slightly warmer than the modern warm period [7]. Graph from Esper et al. 2002. Conclusion: I have presented evidence that: (1) Early evidence opposes the Hockey Stick graph (2) The Hockey Stick studies are flawed due to tree ring methodology (3) New evidence, too, generally disconfirms the Hockey Stick graph 1. McIntyre, Stephen, and Ross McKitrick. “Corrections to The Mann Et. Al. (1998) Proxy Data Base and Northern Hemispheric Average Temperature Series. ” Energy & Enviroment 14.6 (2003): 751-70. 2. Ibid. Also see Shattered Consensus (McKintricks chapter is available online I think). 3. McIntyre, Stephen and Ross McKitrick “The M&M Critique of the MBH98 Northern Hemisphere Climate Index: Update and Implications. ” Energy and Environment 16.1 (2005) pp. 69-100. 4. Osborn, T. J. , and K. R. Briffa. , 2006. “The spatial extent of 20th-century warmth in the context of the past 1200 years. ” Science, (2006) 841-844. 5. Larocque-Tobler, I. , M. M Stewart, R. Quinlan, M. Traschel, C. Kamenik and M. Grosjean “A last millennium temperature reconstruction using chironomids preserved in sediments of anoxic Seebergsee (Switzerland): consensus at local, regional and Central European scales. ”Quaternary Science Reviews, (2012) 41: 49-56. 6. Krenke, A. N. and M. M. Chernavskaya “Climate changes in the preinstrumental period of the last millennium and their manifestations over the Russian Plain. ” Isvestiya, Atmospheric and Oceanic Physics (2002) 38: S59-S79. 7. Esper, J. , E. R. Cook, and F. H. Schweingruber “Low frequency signals in long tree-ring chronologies for reconstructing past temperature variability. ” Science, (2002) 295, 2250-2253.