Cherry picking the Pine Trees for "Climate Science"
Climategate, the 2009 exposure of misconduct at the University of East Anglia, was a terrible blow to the reputation of climatology, and indeed to that of British and American science. Although that story hasn’t been in the news in recent months, new evidence of similar scientific wrongdoing continues to emerge, with a new scandal hitting the climate blogosphere just a few days ago.
And central to the newest story is one of the Climategate scientists: Keith Briffa, an expert in reconstructing historical temperature records from tree rings. More particularly, the recent scandal involves a tree-ring record Briffa prepared for a remote area of northern Russia called Yamal.
For many years, scientists have used tree-ring data to try to measure temperatures from the distant past, but the idea is problematic in and of itself. Why? Because tree-ring data reflect many variables besides temperature. Russian tree growth, like that of trees around the world, also reflects changes in humidity, precipitation, soil nutrients, competition for resources from other trees and plants, animal behavior, erosion, cloudiness, and on and on. But let’s pretend, if only for the sake of argument, that we can reliably determine the mean temperature 1,000 years ago or more using tree cores from a remote part of Russia. The central issue that emerges is: How do you choose the trees?
It was the way Briffa picked the trees to include in his analysis that piqued the interest of Steve McIntyre, a maverick amateur climatologist from Canada. The Climategate e-mails make it clear that McIntyre earned the public scorn of the most powerful U.N. climatologists, including James Hansen, Michael Mann, and Phil Jones, while simultaneously earning their fear and respect in private.
McIntyre noticed a few problems with the way Briffa chose the sampling of Russian trees, and he wrote to Briffa requesting the data Briffa used in a published tree-ring paper. Briffa declined. And so began a four-year saga involving multiple peer-reviewed journals, behind-the-scenes maneuvering by Briffa and his closest confidants, and a Freedom of Information Act request on the part of McIntyre that appears to be on the verge of being granted. Even without the final set of data, however, McIntyre has shown beyond the shadow of doubt that Briffa may have committed one of the worst sins, if not the worst, in climatology — that of cherry-picking data — when he assembled his data sample, which his clique of like-minded and very powerful peers have also used in paper after paper.
It was already known that the Yamal series contained a preposterously small amount of data. This by itself raised many questions: Why did Briffa include only half the number of cores covering the balmy interval known as the Medieval Warm Period that another scientist, one with whom he was acquainted, had reported for Yamal? And why were there so few cores in Briffa’s 20th century? By 1988, there were only twelve cores used in a year, an amazingly small number from the period that should have provided the easiest data. By 1990, the count was only ten, and it dropped to just five in 1995. Without an explanation of how the strange sampling of the available data had been performed, the suspicion of cherry-picking became overwhelming, particularly since the sharp 20th-century uptick in the series was almost entirely due to a single tree.
The intrigue deepened when one of the Climategate e-mails revealed that, as far back as 2006, Briffa had prepared a much more broadly based, and therefore more reliable, tree-ring record of the Yamal area. But strangely, he had decided to set this aside in favor of the much narrower record he eventually used.
The question of Yamal had rightly come up when Briffa was questioned by Climategate investigators. He told them that he had never considered including a wider sample than the one he went with in the end, and hadn’t had enough time to include a wider one. However, the specific issue of the suppressed record appears to have largely been passed over by the panel, and Briffa’s explanation, like so many others given to the Climategate inquiries, appears to have been accepted without question.
But the ruse has now been shot to pieces, by the recent decision from the U.K.’s information commissioner that Briffa can no longer withhold the list of sites he used in his suppressed regional record for the Yamal area. The disclosure of these sites has allowed McIntyre to calculate what the broad series would have looked like if Briffa had chosen to publish it. He has shown that it has no hint of the hockey-stick shape that Briffa’s cherry-picked data indicated. Briffa’s decision to publish an alarming but unreliable version of the Yamal series — instead of a more reliable and thoroughly unremarkable one — has been the talk of the climate blogosphere, with many prominent commentators openly speaking of dishonesty.
Two and a half years after the initial revelation of the Climategate e-mails, new controversies, on the part of the scientists and the investigators involved, continue to emerge. Many of the players involved are desperate to sweep the scandal under the rug. However, their machinations have only succeeded in bringing renewed attention to their questionable science and ugly behind-the-scenes shenanigans, reigniting hope that more complete and more independent investigations — on both sides of the Atlantic — will yet be performed.