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. Please note that I didn't make an argument in Round1. Rather I made an appeal for a more complete, less biased definition of the term "hockey stick" and offered Wikipedia as an objective source. So far, this request has been ignored. I will make my argument in Round2, same as Con. I will refrain from rebuttals in Round4 on the condition Con does likewise. THESIS: The mean surface temperature of the Earth has risen by 0.74±0.18 °C over the period 1906–2012. Two-thirds of that increase (.6C/1F) has occurred since 1980. This peak represents both the highest global temperature of the past 1000 years and the most rapid escalation. As a kind of shorthand, some scientists refer to the graphed geometry of this peak as a "hockey stick" to evoke a rapid rise after a sustained period of less dramatic change. To the limited degree by which the image of a hockey stick can approximate well-established recent changes in climate, the Hockey Stick is likely correct. Science is not in the business of asserting truths about our world. Rather, the process of science is to offer theories, create experiments to test those theories, analyze and publish results, offer alternative theories that might falsify results. Theories are then adjusted in response to critique, new experiments are created to test, and so on. The scientific method is a conversation, a continuously refocused and improved loop. To the extent that experimental results are repeatable and reliable, those theories are accorded increasing degrees of certainty. One example of a theory that has acquired a very high degree of confidence in the scientific community is the assertion that the last few decades have been the warmest of the millennium in terms of global mean surface temperature. Sometimes referred to as the "Hockey Stick Graph" as a way of describing the short, sharp rise in temperature, data supporting this theory goes back at least to Jacoby & D'Arrigo 1989 [1] but received an increased degree of public attention after the release of the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report in 2001, [2] which included a preliminary version of a Hockey Stick Graph reproducing the work of Mann, et al 1999 (MBH99). [3]What was MBH99? MBH99 was a study of 12 paleoclimatic indicators that illustrated a global pattern of annual surface temperature rise, demonstrating that temperatures over the previous decade were the highest of the millennium. What is the IPCC? The IPCC is a scientific body set up by the World Meteorological Organization and the UN in 1988 to provide comprehensive scientific assessments of current scientific information worldwide about the risk of climate change. Representing the consensus of 2500 unpaid leaders in the scientific community and 100 participating national governments, the IPCC is the single largest collective international scientific effort in history. The IPCC was awarded the 2007 Nobel Peace Prize "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change. " This is not to make an argument from authority or to pretend that IPCC findings are unimpeachable. However, if one wishes a careful and comprehensive summary of the scientific consensus, the IPCC is unmatched in the study of climate change, or indeed, by any other field of scientific study. Here is the IPCC Hockey Stick in 2001: Following the public attention given to the IPCC publication of the MBH99, there has more than a decade of reaction and response, including those studies provided by Con in his arguments. Many, many studies have expanded upon and, to a remarkable degree, supported the MBH99 Hockey Stick. When the IPCC released its Fourth Assessment Report in 2007, that body offered the following summary:"Paleoclimatic information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1,300 years. The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 m of sea level rise. Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years. " [4]We should note here that the AR4 assigns a probability to likely as greater than 66%. "the following terms have been used to indicate the assessed likelihood, using expert judgement, of an outcome or a result: Virtually certain > 99% probability of occurrence, Extremely likely > 95%, Very likely > 90%, Likely > 66%, More likely than not > 50%, Unlikely < 33%, Very unlikely < 10%, Extremely unlikely < 5% " [4]That is, the single most significant survey of scientific opinion up to 2007 asserted a 2:1 probability that the Hockey Stick was correct. To support these findings, the IPCC listed the following studies: Jones et al. (1998), calibrated by Jones, Osborn & Briffa 2001 "The Evolution of Climate Over the Last Millennium" Briffa (2000), calibrated by Briffa, Osborn & Schweingruber 2004 "Large-scale temperature inferences from tree rings: a review" Crowley & Lowery 2000 "How Warm Was the Medieval Warm Period? " Briffa et al. 2001 "Low-frequency temperature variations from a northern tree ring density network" Esper, Cook & Schweingruber 2002 "Low-Frequency Signals in Long Tree-Ring Chronologies for Reconstructing Past Temperature Variability" Mann & Jones 2003 "Global surface temperatures over the past two millennia" Pollack & Smerdon 2004 "Borehole climate reconstructions: Spatial structure and hemispheric averages" Oerlemans 2005 "Extracting a climate signal from 169 glacier records" Rutherford et al. 2005 "Proxy-based Northern Hemisphere surface temperature reconstructions: Sensitivity to method, predictor network, target season, and target domain" Moberg et al. 2005 "Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data" D'Arrigo, Wilson & Jacoby 2006 "On the long-term context for late twentieth century warming" Osborn & Briffa 2006 "The spatial extent of 20th-century warmth in the context of the past 1200 years" Hegerl et al. 2006 "Climate sensitivity constrained by temperature reconstructions over the past seven centuries" And here those studies are graphed against MBH99: So we can see that most reconstructions since MBH have found the Medieval Warm Period to be even cooler than MBH99. None of these studies found that the MWP rivaled the last two decades for mean temperature increases. Since IPCC AR4 in 2007, there have been many more studies using increasingly large sampling sizes from increasingly disparate paleoclimatic indicators and geographies and going even further back in time. The more often the experiment is repeated, the more evident and less deniable the hockey stick becomes: Smith et al. 2006 "Reconstructing hemispheric-scale climates from multiple stalagmite records". Juckes et al. 2007 "Millennial temperature reconstruction intercomparison and evaluation". Lee, Zwiers & Tsao 2008 "Evaluation of proxy-based millennial reconstruction methods". Huang, Pollack & Shen 2008 "A late Quaternary climate reconstruction based on borehole heat flux data, borehole temperature data, and the instrumental record" Mann et al. 2008 "Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia" Kaufman et al. 2009 "Recent warming reverses long-term arctic cooling". Tingley & Huybers 2010a "A Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time". Ljungqvist 2010 "A New Reconstruction of Temperature Variability in the Extra-Tropical Northern Hemisphere During the Last Two Millennia". Christiansen & Ljungqvist 2011 "Reconstruction of the Extratropical NH Mean Temperature over the Last Millennium with a Method that Preserves Low-Frequency Variability". Ljungqvist et al. 2012 "Northern Hemisphere temperature patterns in the last 12 centuries". Christiansen & Ljungqvist 2012 "The extra-tropical Northern Hemisphere temperature in the last two millennia: Reconstructions of low-frequency variability". Marcott et al. 2013 "A Reconstruction of Regional and Global Temperature for the Past 11,300 Years" Ahmed et al. 2013 (PAGES 2k Consortium) "Continental-scale temperature variability during the past two millennia" As I stated in Round1 that last study, the PAGES 2K Consortium is the single most comprehensive study to date including 511 paleoclimatic indicators from around the world (see the map in Round1 and the graph substantiating MBH99). Here is Marcott's 2013 Hockey Stick compared to MBH99: CONCLUSION: Our confidence in any scientific proposition increases as experiments are reliably repeated with the same results. Since MBH99 and the IPCC Third Assessment, the theory that current global warming is unprecedented for at least a millennium has been supported by repeated, rigorous experimentation. To the degree that the IPCC represents the cautious consensus of Climate Change expertise and those experts have assigned a 66% probability to the data illustrated by the Hockey Stick Graph, the Hockey Stick is likely (greater than Con's defined 50%) correct. I'll offer rebuttals to Con's argument in Round 3. [1] . http://link.springer.com...[2] . http://www.grida.no...[3] . http://www.meteo.psu.edu...[4] . http://www.ipcc.ch...