The Giant Global Warming Hockey Stick of Statistics…

Welcome one and all to the giant global warming hockey stick. The graph below was created by Michael Mann an eminent climatologist from Pennsylvania State University in 1999. The graph was later used in a series of presentations including the UNs’ IPCC meeting in 2001. The ‘hockey stick’ rose to prominence after 2001 and was used by various environmentalist and lobbyists as indefatigable evidence of anthropogenic global warming. The first hockey stick graph showed a reconstruction from several studies of Northern hemisphere temperatures from 1000AD to 2004. These temperatures were obtained through a variety of methods including dendrochronology, which uses the width and other characteristics of tree rings to infer temperature. Mann and the other scientists also used proxy data from ice cores, coral samples, bore-hole samples and other various data records to reconstruct temperatures before 1850. After 1850 Mann was able to rely upon instrumental data to reconstruct global temperatures.

The results

Using various statistical and mathematical methods Mann and his team were able to compile a graph which alluded to a sharp temperature rise being visible during the 1900’s – 2004. This rise is what gave the graph its’ ‘hockey stick’ title. The apparent rise is clearly above the average temperature recorded by Mann and his team for the previous 1000 years. The graph also shows fluctuating temps throughout the 1000 year period but with a noticeable rise towards the end of the 20th century. Using their findings and the anomalous temperature rise in the late 20th century, Mann and his team argued that this was a clear evidence of human assisted climate change. The graph quickly rose to prominence among environmentalists after its publication due to its’ visual reference alluding to anthropogenic global warming. Subsequently Mann and the ‘hockey stick’ also received a large amount of criticism from politicians, lobbyists, sceptics and concerned scientists. A lot of this critique revolves around S. McIntyre an ex-mining executive who argued that Mann’s mathematical methodology and composition of results was essentially flawed. In a published paper in 2005 McIntyre argued that hockey stick shape was the result of an invalid principal component method. By using the same steps as Mann, McIntyre argued that he was able to obtain a hockey stick shape as the first principal component in 99 percent of cases even if trendless red noise was used as input.

The Controversy

There is still a great deal of speculation concerning the hockey stick and its’ accuracy. Many of these arguments revolve around the accuracy of using tree rings and dendrochronology to assess temperature, the use of Mann’s statistical methodology and arguments about whether or not this apparent rise may still be attributed to natural cycles rather than to man. The use of Mann’s graph at the UNs IPCC meeting and its obvious conclusion supporting AGW provided environmentalists with a powerful hockey stick shaped tool to organise support for the green movement. However, there was also a considerable backlash fomented mainly by McIntyre’s objections and disputations. Two senate congressional hearings were organised in 2006 to assess the validity of Mann’s findings. The first report assembled by the National Research Councils Board of Atmospheric Sciences consisted of a team of 12 scientists that were asked to investigate into the findings and methodology of Mann’s research. The report was published in 2006 and a number of statements were issued supporting Mann’s arguments. The board stated several conclusions agreeing with Mann’s assessment with the rise in temperature during the late 20th century. The board also agreed that temps during the late 20th century were considerably higher than average from the prior four centuries. The report also suggested that reconstructed temperature showed a generally consistent picture of the temp trends of the last 1000 years, which included anomalies consistent with the medieval warm period and the little ice age in 1700. These phenomena were also backed by further evidence both statistical and historical. However, the report did concede that the average temps between 900AD-1500 were harder to substantiate and therefore more likely to include errors. All in all the 2006 NRCB report found little evidence to support McIntyre’s accusations and instead appeared to validate Mann’s research and its’ conclusions.

The second report known as the Wegman report was also commissioned in 2006 by the National Academy of Sciences’ Committee on Applied and Theoretical Statistics. The main job of the report was to validate the criticisms published by S. McIntyre. The Wegman report issued several statements concerning Mann’s methodology. The report also attempted to highlight perceived connections and potential conflicts of interest between Mann and his fellow researchers. The Wegman report also highlighted and upheld McIntyre’s criticisms of the ‘hockey stick’ mentioning that the dendrochronology used throughout the statistical evidence provided erroneous temperatures therefore invalidating sections of the graph. The Wegman report itself was also subject to a lot of controversy due to its perceived political connotation. Mann later stated that the Wegman report “uncritically parrots claims by two Canadians (an economist and a mineral-exploration consultant) that have already been refuted by several papers in the peer-reviewed literature inexplicably neglected by Barton’s ‘panel’.

Return of the Stick

The conflict between the hockey stickers and their protagonists is still ongoing. In the recent weeks Mann and a team of paleoclimatologists reconstructed the ‘hockey stick’ even further back almost 2000 years. In an attempt to deal with its’ detractors, Mann and his team took evidence, almost 1,200 pieces of proxy data, from both the northern and southern hemispheres. Using this data Mann constructed 3 graphs; one for the northern hemisphere, one for the southern hemisphere and one providing a global graph. In an article for National Geographic Mann states “To satisfy the critics, we now have enough other sources that we can achieve meaningful reconstructions back a thousand years without tree ring data, and we get more or less the same answer”–that global warming is not mainly due to natural variability.”

Mann's latest attempt

It yet remains to be seen whether or not Mann’s technique and methodologies will be accepted from both sides of the fence. If the revised version of the ‘hockey stick’ was to be accepted by the scientific community then this would further solidify the AGW theory. Mann’s work will surely be debated by both sides for a long time before any clear consensus is reached. Acceptance or denial is often a bitter pill to swallow and many from both sides are deeply entrenched within their own opinions. Gaining an objective perspective on these issues can be hard, especially as the internet is awash with large amounts of conflicting information. Time and rational analysis of the facts will prevail, hopefully leaving all the dogma and subjectivity at the doorway to reason.

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Don’t you think iit might be a good idea, in the interest of objectivity, to post the graph the IPCC used which clearly shows the Medieval Warm Period before Mann et. al. used totally unorthodox methods to disguise it by generating the Hockey Stick?
blog.co.ukmedievalperiod
March 10th, 2009

Judy Cross