Another claim the media featured prominently was that temperature increases over the last century are unprecedented, at least when considered on a time-scale of the last 1,000 years. According to the IPCC, the 1990s were the warmest decade on record, and 1998 was the warmest year since temperature records began in 1861. The basis for this claim is the so-called hockey stick graph, which has become the iconic symbol of global warming alarmism.
The graph was constructed by Dr. Michael Mann of the University of Virginia and his colleagues using a combination of proxy data and modern temperature records. The hockey stick curve showed a gradual cooling beginning around 1400 AD (which is the hockey stick handle) then a sharp warming starting about 1900 (the hockey stick blade). Its release was revolutionary, overturning widespread evidence adduced over many years confirming significant natural variability long before the advent of SUVs. The IPCC was so impressed that the hockey stick was featured prominently in its Third Assessment Report in 2001.
As Dr. Roy Spencer, the principal research scientist at the University of Alabama, noted, “This was taken as proof that the major climatic event of the last 1,000 years was the influence of humans in the 20th century.” One of its authors, Dr. Michael Mann, confidently declared in 2003 that the hockey stick “is the indisputable consensus of the community of scientists actively involved in the research of climate variability and its causes.”
The hockey stick caused quite a stir, not just in the scientific community, but also in the world of politics. It galvanized alarmists in their push for Kyoto. It is supposedly ironclad proof that man-made greenhouse gas emissions are warming the planet to an unsustainable degree.
But here again, one of the essential pillars of alarmism appears to be crumbling. Two Canadian researchers have produced the most devastating evidence to date that the hockey stick is bad science. Before I describe their work, I want to make a prediction: the alarmists will cry foul, saying this critique is part of an industry-funded conspiracy. And true to form, they will avoid discussion of substance and engage in personal attacks. That’s because one of the researchers, Stephen McIntyre, is a mineral exploration consultant. Dr. Mann already has accused them of having a conflict of interest. This is nonsense. First, Stephen McIntyre and his colleague Ross McKitrick, an economist with Canada’s University of Guelph, received no outside funding for their work. Second, they published their peer-reviewed critique in Geophysical Research Letters. This is no organ of Big Oil, but an eminent scientific journal, the same journal, in fact, which published the version of Dr. Mann’s hockey stick that appeared in the IPCC’s Third Assessment Report. Apparently the journal’s editors didn’t see much evidence of bias. The remarks of one editor are worth quoting in full: “S. McIntyre and R. McKitrick have written a remarkable paper on a subject of great importance. What makes the paper significant is that they show that one of the most widely known results of climate analysis, the ‘hockey stick’ diagram of Mann. et. al., was based on a mistake in the application of a mathematical technique known as principal component analysis.” Further, he said, “I have looked carefully at the McIntyre and McKitrick analysis, and I am convinced that their work is correct.”
What did McKitrick and McIntyre find? In essence, they discovered that Dr. Mann misused an established statistical method called principal components analysis (PCA). As they explained, Mann created a program that “effectively mines a data set for hockey stick patterns.” In other words, no matter what kind of data one uses, even if it is random and totally meaningless, the Mann method always produces a hockey stick. After conducting some 10,000 data simulations, the result was nearly always the same. “In over 99 percent of cases,” McIntyre and McKitrick wrote, “it produced a hockey stick shaped PCI series.” Statistician Francis Zwiers of Environment Canada, a government agency, says he agrees that Dr. Mann’s statistical method “preferentially produces hockey sticks when there are none in the data.” Even to a non-statistician, this looks extremely troubling. But that statistical error is just the beginning. On a public website where Dr. Mann filed data, McIntyre and McKitrick discovered an intriguing folder titled “BACKTO_1400-CENSORED.” What McIntyre and McKitrick found in the folder was disturbing: Mann’s hockey stick blade was based on a certain type of tree—a bristlecone pine—that, in effect, helped to manufacture the hockey stick.
Remember, the hockey stick shows a relatively stable climate over 900 years, and then a dramatic spike in temperature about 1900, the inference being that man-made emissions are the cause of rising temperatures. So why is the bristlecone pine important? That bristlecone experienced a growth pulse in the Western United States in the late 19th and early 20th centuries. However, this growth pulse, as the specialist literature has confirmed, was not attributed to temperature. So using those pines, and only those pines, as a proxy for temperature during this period is questionable at best. Even Mann’s co-author has stated that the bristlecone growth pulse is a “mystery.” Because of these obvious problems, McIntyre and McKitrick appropriately excluded the bristlecone data from their calculations. What did they find? Not the Mann hockey stick, to be sure, but a confirmation of the Medieval Warm Period, which Mann’s work had erased. As the CENSORED folder revealed, Mann and his colleagues never reported results obtained from calculations that excluded the bristlecone data. This appears to be a case of selectively using data—that is, if you don’t like the result, remove the offending data until you get the answer you want. As McIntyre and McKitrick explained, “Imagine the irony of this discovery…Mann accused us of selectively deleting North American proxy series. Now it appeared that he had results that were exactly the same as ours, stuffed away in a folder labeled CENSORED.”
McIntyre and McKitrick believe there are additional errors in the Mann hockey stick. To confirm their suspicion, they need additional data from Dr. Mann, including the computer code he used to generate the graph. But Dr. Mann refuses to supply it. As he told the Wall Street Journal, “Giving them the algorithm would be giving into the intimidation tactics that these people are engaged in.”
Just a second: Who are “these people”? And what “intimidation tactics”? Mr. McIntyre and Mr. McKitrick are trying to find the truth. What is Dr. Mann trying to hide? For many scientists, McIntyre and McKitrick’s work is earth-shattering. For example, Professor Richard Muller of the University of California at Berkeley recently wrote in the MIT Technology Review that McIntyre and McKitrick’s findings “hit me like a bombshell, and I suspect it is having the same effect on many others. Suddenly the hockey stick, the poster-child of the global warming community, turns out to be an artifact of poor mathematics.” Dr. Rob van Dorland, of the Royal Netherlands Meteorological Institute, and an IPCC lead author, said, “The IPCC made a mistake by only including Mann’s reconstruction and not those of other researchers.” He concluded that unless the error is corrected, it will “seriously damage the work of the IPCC.”
Or consider Dr. Hans von Storch, an IPCC contributing author and internationally renowned expert in climate statistics at Germany’s Center for Coastal Research, who said McIntyre and McKitrick’s work is “entirely valid.” In an interview last October with the German Newspaper Der Spiegel, Dr. von Storch said the Mann hockey stick “contains assumptions that are not permissible. Methodologically it is wrong: rubbish.” He stressed that, “it remains important for science to point out the erroneous nature of the Mann curve. In recent years it has been elevated to the status truth by the UN appointed science body, the Intergovernmental Panel on Climate Change (IPCC). This handicapped all that research which strives to make a realistic distinction between human influences and climate and natural variability.”
If McIntyre and McKitrick’s work isn’t convincing enough, consider the recent paper published in the Feb. 10 issue of Nature. The paper, authored by a group of Swedish climate researchers, once again undercuts the scientific credibility of the Mann hockey stick. The press release for the study by the Swedish Research Council says, "A new study of climate in the Northern Hemisphere for the past 2000 years shows that natural climate change may be larger than generally thought.”
According to the paper’s authors, the Mann hockey stick does not provide an accurate picture of the last 1,000 years. “The new results,” they wrote, “show an appreciable temperature swing between the 12th and 20th centuries, with a notable cold period around AD 1600. A large part of the 20th century had approximately the same temperature as the 11th and 12th centuries.”
In other words, here’s evidence of the Medieval Warm Period and the Little Ice Age, demonstrating that climate, long before the burning of fossil fuels, varied considerably over the last 2,000 years. The researchers note that changes in the sun’s output and volcanic eruptions appear to have caused considerable natural variations in the climate system. “The fact that these two climate evolutions,” they contend, “which have been obtained completely independently of each other, are very similar supports the case that climate shows an appreciable natural variability—and that changes in the sun’s output and volcanic eruptions on the Earth may be the cause.”