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Resolved: The Hockey Stick is likely correct

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Voting Style: Open Point System: 7 Point
Started: 1/3/2014 Category: Science
Updated: 2 years ago Status: Post Voting Period
Viewed: 1,402 times Debate No: 43367
Debate Rounds (4)
Comments (4)
Votes (3)




You know, guys, I didn't know they extended the argument length characters. I have been gone for a while.

In this debate we will be arguing whether or not the famous hockey stick graph is likely (greater than 50%) correct.


Hockey Stick: The Hockey Stick graph is the infamous graph, first formulated by Mann et al. 1998, 1999, and recently updated in Mann et al. 2008. This graph purports the idea that the period of 950 - 1250, called the Medieval Warm Period (MWP) was much cooler--or virtually nonexistant--in the climactic record. Further, the study also shows no Little Ice Age (LIA) in the data, either. Instead it shows a continually linear decreasing trend up until the mid 1800s, where the temperature increases.

The Hockey Stick:

Correct: in this debate, since correct is a word with common knowledge definition, my opponent has the burden of proof (as pro) to explain why the Hockey Stick is likely (greater than 50%) correct.


I'll accept that challenge and thank Con for the opportunity.

THESIS: The Mean Surface Temperature of the Earth has risen by 0.74±0.18 °C over the period 1906–20012. Two-thirds of that increase (.6C/1F) has occurred since 1980. [1] 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.

I'll leave the body of my argument for Round2 after Con has had his chance, but we need to do some housekeeping regarding our shared assumptions.


I take exception to the proffered definition of the Hockey Stick Graph for 3 reasons:

1) BIASED- When it comes to defining shared terminology, the offered definition should be as impartial as possible, preferably citing an objective source. Use of the word "infamous" as the first adjective in Con's definition demonstrates significant bias.

Here's a definition of the word infamous from Merriam-Webster's


adjective \G2;in-fə-məs\
1: having a reputation of the worst kind : notoriously evil [2]

If Con wishes to conclude that the graph is evil during the course of his arguments that's his prerogative. Obviously, we're not going to agree that the graph is evil as part of our common set of assumptions.

2) INCOMPLETE- To simply attribute the graph to Mann et. all (MBH99) is to disregard the preponderance of data for which MBH99 is only an initial compilation. Dozens of subsequent studies have confirmed the "hockey stick" geometry to greater or lesser degrees. "Most later temperature reconstructions fall within the error bars of the original hockey stick. Some show far more variability leading up to the 20th century than the hockey stick, but none suggest that it has been warmer at any time in the past 1000 years than in the last part of the 20th century." [3] *

3) BURIED THE LEAD- Obviously, the defining element in any Hockey Stick graph is the post-1900 blade- the recent, sharp upturn. The point of the hockey stick is that temperatures have rapidly escalated over the 20th Century and have now achieved the high-water mark for the past millennium. Most hockey stick graphs document significant increases in variability correlating to older data, so the hockey stick has demonstrably less focus on subjects like the Medieval Warming Period (MWP) or the Little Ice Age (LIA) then on periods after recorded thermometer temperatures. To define the graph as primarily a description of the MWP or the LIA is misleading and ignores the central thesis of the hockey stick.

We might also note that Con's definition is undermined by the Hockey Stick graph he provides. Con's definition states that the MWP is virtually non-existent and that there's no LIA, but both events are discernible in the Wikipedia graph and conveniently labeled.

File:1000 Year Temperature Comparison.png

Therefore, allow me to offer a definition of Hockey Stick Graphs from Wikipedia, which should be more objective and complete than Con's personal definition of Hockey Stick Graphs.

"Hockey stick graphs present the global or hemispherical mean temperature record of the past 500 to 2000 years as shown by quantitative climate reconstructions based on climate proxy records. These reconstructions have consistently shown a warming in the 20th century with the instrumental temperature record by 2000 exceeding earlier temperatures. The term hockey stick was coined by the climatologist Jerry Mahlman, to describe the pattern shown by the Mann, Bradley & Hughes 1999 (MBH99) reconstruction, envisaging a graph that is relatively flat to 1900 as forming an ice hockey stick's "shaft", followed by a sharp increase corresponding to the "blade". The reconstructions have featured in Intergovernmental Panel on Climate Change (IPCC) reports as evidence of global warming. Arguments over the reconstructions have been taken up by fossil fuel industry funded lobbying groups attempting to cast doubt on climate science." [4]

*By way of example, here are a couple of additional graphs that qualify as Hockey Stick Graphs and which reinforce MBH99 data.

Here's a graph from the a 2009 New Scientist article comparing 8 later which corroborate 2001 IPCC Hockey Stick (based on MBH99).

<a href=; width="614" height="960" />

78 researchers from 24 countries spent seven years compiling data for the PAGES 2K project. They assembled 511 climate archives from around the world, from sediments, ice cores, tree rings, corals, stalagmites, pollen or historical documents and measurements to create the most comprehensive paleoclimate study yet.

Published this year in Nature Geosciences, this most recent and comprehensive analysis strongly corroborates the MBH99 Hockey Stick. Green dots are the 30-year average of the new PAGES 2K reconstruction. The red curve shows the global mean temperature. Blue is MBH99 with range of uncertainty. [6]

Debate Round No. 1


I forgot to say first round acceptance—that is my fault. 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].

Tree-ring Reconstruction

Graph from Esper et al. 2002.


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.



RE: I forgot to say first round acceptance—that is my fault. 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:

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.


Debate Round No. 2


16kadams forfeited this round.


That's too bad. There's plenty to refute in Con's argument, particularly the relative value of McIntyre & McKitrick and the consipiratorial steam rising off that sideshow. Alas, I expect that rebuttals would be a waste of time in view of Con's forfeit. Continue my arguments from R2.
Debate Round No. 3


I forgot about this debate so vote pro


Thanks to Con for the sportsmanlike gesture. Forward arguments and please vote PRO.
Debate Round No. 4
4 comments have been posted on this debate. Showing 1 through 4 records.
Posted by 16kadams 2 years ago
I wish I remembered because many of those studies cited dont support your position.
Posted by 16kadams 2 years ago
Oh sh!t I forgot about this
Posted by Oromagi 2 years ago
I'm just seeing this. I didn't really make my argument this round, just disagreed with the definitions, but my disagreement was long and I guess my argument is already pretty obvious. Hope I didn't "step on your toes." Good Topic! Look forward to your arguments.
Posted by 16kadams 2 years ago
I should have said first round acceptance.
3 votes have been placed for this debate. Showing 1 through 3 records.
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Reasons for voting decision: Pro didn't forfeit.