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The Hockey Stick Trial: Science Dies in a DC Courtroom

By Rupert Darwall

Excerpt: “Science,” wrote the philosopher Karl Popper, “is one of the very few human activities – perhaps the only one – in which errors are systematically criticised and fairly often, in time, corrected.” The sub-title of Popper’s 1963 book Conjectures and Refutations, in which he argued that science progresses through inspired conjectures checked by attempts to refute them through criticism, is “The Growth of Scientific Knowledge.” Now, a six-person jury in Washington, DC has refuted Popper’s formulation of the uniqueness of science, finding in favor of climate scientist Michael Mann in the defamation suit he brought against Rand Simberg and Mark Steyn dating back to 2012.

Central to Mann’s case was his attempt to reconstruct global temperature over the previous millennium – the iconic “hockey stick” graph. The graph shows global temperatures purportedly falling for centuries and suddenly shooting upwards with the advent of the Industrial Revolution. Mann’s hockey stick representation was derived principally from selected tree ring data based on the assumption that tree rings constitute accurate proxies for temperature and are not contaminated by confounding factors such as rainfall, seasonal variability, and levels of carbon dioxide in the atmosphere. The results that Mann produced are also sensitive to decisions on and application of statistical techniques.

There can be little doubt of the hockey stick’s historic importance in the development and propagation of what became the dominant scientific paradigm of climate change. In 2001, the hockey stick was given star billing in the Intergovernmental Panel on Climate Change’s (IPCC) Third Assessment Report, where it appeared twice in the synthesis report, twice more in a diagram combining past and future temperature change, and again on the third page of the Working Group I Summary for Policy Makers. Gerald North, a leading atmospheric physicist at Texas A&M University and one of the most cited authors in the geosciences, had no doubt as to the significance of the hockey stick. “The planet has been cooling slowly until one hundred and twenty years ago, when, bam! It jumps up,” North told Science in 2000. “We’ve been breaking our backs on [greenhouse] detection, but I found the one-thousand-year records more convincing than any of our detection studies.” For Mann, the hockey stick was his ticket to climate super-stardom.

In keeping with Popper’s premise about science, however, Mann’s hockey stick aroused criticism from its first appearance. In response, Mann engaged in distinctly anti-Popperian efforts to suppress all criticism of the hockey stick and discussion of rival temperature reconstructions that might raise awkward questions about its scientific validity. A rival reconstruction by fellow paleo-climatologist Keith Briffa, for example, derived from tree ring data obtained from northern Canada and Siberia, showed a noticeable decline in temperatures over the latter part of the 20th century – opening up a divergence with the instrumental record. If tree rings suggested declining temperatures when temperatures were actually rising, then how could climate scientists put any confidence in tree rings as thermometers? Up could really mean down.

Briffa then wrote a paper for Science comparing the rival reconstructions. As we know from the Climategate emails leaked in 2009, Mann contacted the editor of Science. “Better that nothing appear, than something unacceptable to us,” he wrote, copying in one of his co-authors, Raymond Bradley. After Science published Briffa’s paper, Mann tried to patch things up. “Thanks for all the hard work,” he emailed colleagues. The sentiment didn’t go down well with Bradley. “Excuse me while I puke,” Bradley emailed Briffa.

Such shenanigans are small beer compared to the surgery undertaken on the graphs of proxy reconstructions showcased in the IPCC’s Third Assessment Report. To deal with Briffa’s question-inducing temperature decline, Mann, as lead chapter author, and a tight-knit team resorted to the simple expedient of truncating adverse data that could serve as a “potential distraction/detraction,” Mann explained to his colleagues, and thereby hiding the temperature decline shown by Briffa’s proxies when temperatures were rising. The gambit also involved using actual temperature data to smooth the proxy curves in what became known as “Mike’s Nature trick,” something Mann had done previously in a paper submitted to that journal.

There was a more fundamental problem with the construction of the hockey stick. Analysis conducted by Canadians Steve McIntyre, a former mining engineer with a strong grounding in mathematics, and environmental economist Ross McKitrick using an algorithm based on a fragment of Mann’s computer code, found that running statistically trendless “red noise” produced hockey stick shapes 99 percent of the time. In other words, you could get hockey sticks from random junk data if you had enough of it.

Mann included in his proxy data set a series of bristlecone and foxtail pines from the western United States that had been selected by researcher Donald Graybill to study the possible effects of carbon dioxide fertilization on tree growth. To get the hockey stick from the data, Mann needed both the algorithm and Graybill’s tree ring data. Did Mann know what he was doing? Inside his directory of North American proxy data, Mann had a folder which he had labelled BACKTO_1400-CENSORED containing the North American data except all sixteen of the Graybill series. When the numbers from the CENSORED folder were run, the blade of the hockey stick disappeared.

While the blade of the hockey stick showed a sharp, anomalous rise in global temperature coinciding with the onset of the Industrial Revolution, its shaft also performed a critical function in radically revising the previously accepted climatological record by showing a steady decline in temperatures from the end of the first millennium. What previous generations of climatologists called the Medieval Warm Period had disappeared.

The Medieval Warm Period presented a twofold problem to the new climate change orthodoxy. It implied a much greater amplitude of natural variability beyond the bounds posited by the new scientific consensus of human-driven climate change, and it challenged the catastrophist narrative of global warming. If the prosperity of the Middle Ages and Viking settlement of Greenland occurred during an extended period of unusual warmth, then modern societies, too, could survive and prosper in a period of rising temperature.

In written congressional testimony in 2011, the climate scientist John Christy recalled discussions on the preparation of the Third Assessment Report when he pressed for inclusion of the findings of a 1998 paper in which Greenland ice-borehole temperatures provide a 20,000-year reconstruction. “Their result indicated a clear 500-year period of temperatures, warmer than the present, centered about 900 AD,” Christy testified. Despite – or, perhaps, because – of the importance of the paper in contradicting the hockey stick, the Third Assessment Report ignored the paper altogether.

Mann went further in a 2008 paper that presented a 2,000-year temperature reconstruction. The reconstruction was derived from sediments from Lake Korttajarvi in Iceland analyzed in a paper by the Finnish geologist Mia Tiljander. But Mann’s reconstruction inverted the Tiljander proxies, so warming became cooling and cooling became warming. According to Matti Saarnisto, one of Tiljander’s co-authors, the Medieval Warm Period was shown in a mirror image. In an email he’d received from Bradley, who despite his previous experience was still one of Mann’s co-authors, a large group of researchers had been handling extensive material and “at some point it happened that this graph was turned upside down.” Was this done on purpose or by mistake? “It has been turned upside down twice in Science, and now I doubt if it can be a mistake any more,” Saarnisto said, adding that the authors belong to a group “skeptical about this Medieval Warm Period and have tried to hide it to some extent.”


Mann’s defamation suit revolved around two issues. The first relates to Simberg and Steyn linking the investigation of Mann at Penn State, where he was professor of meteorology, to the university’s investigation and cover-up involving football coach and convicted child rapist Jerry Sandusky. Penn State president Graham Spanier was later convicted of child endangerment for his role in the Sandusky cover-up. As Steyn told the court in his opening statement:

the same scoundrel who protected Sandusky also protected Michael Mann. So, we’re not comparing Mann with Sandusky; we’re comparing the investigation of Mann with the investigation of Sandusky – because both investigations were controlled by the same chap: a corrupt convicted criminal called Graham Spanier.

Of the two defendants, Simberg’s language was the less delicate and more direct. As Steyn told the jury, quoting directly from his original piece, “I’m not sure I would have extended that metaphor all the way into the locker room showers with quite the zeal Mr. Simberg does, but he has a point,” distancing himself from Simberg’s statement that Mann could be regarded as the Jerry Sandusky of climate science.

The second issue relates to Simberg and Steyn describing Mann’s hockey stick as fraudulent. Though this was less inflammatory than the linkage made between Mann and Sandusky via Penn State’s respective investigations into their conduct, the jury believed that it was the greater offense. It imposed just $1,000 in punitive damages on Simberg but $1 million – one thousand times more – on Steyn. (The jury awarded Mann a dollar each from Simberg and Steyn to compensate him for damage to his reputation.) The massive differential in punishments the jury meted out to the two defendants can only be explained by the jury’s political bias. Steyn has a high profile as one of the most accomplished of conservative commentators. Evidently, the DC jury decided to make an example of Steyn and discourage any public questioning of today’s consensus of human-caused climate change.

In his opening statement, Steyn argued that it is not for the courts to adjudicate science. “A scientific theorem that requires validation by a courtroom verdict is not science at all,” Steyn argued. In principle, a court should be able to assess whether evidence used to make a scientific claim has been knowingly distorted, omitted, concealed or, in some other way, manipulated to produce a desired result. After all, fraud is not limited to theft but includes the tort of fraudulent misrepresentation.

Mann’s lawsuit demonstrates that the courts – at least, a court in the nation’s capital with politically biased jurors – are not capable of objective evaluation. Such cases also involve federal rules on the admissibility of evidence proffered by expert witnesses and the Daubert standard for scientific evidence. In a 39-page report, climate scientist Judith Curry gave her opinion that it is “reasonable” to have referred to the hockey stick in 2012 as “fraudulent” in the sense that “aspects of it are deceptive and misleading.”


As Popper argued, free argument and debate are not only essential for the advance of scientific knowledge. They also constitute the fundamental requirement for the maintenance of a constitutional republic.

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Rupert Darwall is a senior fellow of the RealClear Foundation and author of  Green Tyranny.