McIntyre belongs to the school of skeptics known as "lukewarmers"—those who believe the planet is warming and humans are playing a role (see our Field Guide to Climate Change Skeptics), but don't think this is as much of a problem as it has been made out to be.
"I'm not particularly comfortable with either side of the US debate," McIntyre told me. "There are obviously competent and intelligent people that view it as a serious problem. That doesn't mean that they're right, but it's not a hoax." Nor does he oppose government regulations on principle, as do some of the free-market think tanks that regularly invite him to DC for speaking engagements. "I'm a Canadian," says McIntyre. "I think governments can do things."
McIntyre's entrée into the climate debate came with a paper he coauthored with economist Ross McKitrick that critiqued an earlier version of Mann's (PDF) hockey-stick graph. The paper was published in the November 2003 issue of Energy and Environment. It's a publication known for providing a platform to skeptics—which is why, among the trove of hacked emails, there's one from Mann urging colleagues to "dismiss this as [a] stunt, appearing in a so-called 'journal' which is already known to have defied standard practices of peer-review." Mann predicted that "the usual suspects are going to try to peddle this crap."
Sure enough, McIntyre and McKitrick were soon invited to Washington for a briefing (PDF) arranged by the George C. Marshall Institute and the Competitive Enterprise Institute (CEI), both free-market think tanks that have been heavily funded by ExxonMobil and other oil interests. They were also asked to meet with Sen. James Inhofe (R-Okla.), who has called climate change "the greatest hoax ever perpetrated on the American people."
The targets of McIntyre's audits were less enthralled. "I wouldn't send him anything," Mann emailed CRU head Phil Jones in February 2004. "I have no idea what he's up to, but you can be sure it falls into the 'no good' category...There is no reason to give them any data, in my opinion, and I think we do so at our own peril!"
In February 2005, McIntyre and McKitrick published (PDF) another critique of the hockey-stick chart in the more-respected Geophysical Research Letters. They argued, essentially, that the chart underestimates the uncertainties about historical temperatures and relies on proxy data that they believe are "no more informative about the distant past than a table of random numbers."
McIntyre isn't alone in his skepticism about proxy data—in fact, it's at the heart of the climate debate. Recorded temperature measurements only go back about 160 years, so scientists use data from tree rings, ice cores, and coral to reconstruct what the climate was like before that. For two millennia, those data sets align to show swings of about one degree Fahrenheit in either direction. But then, in the 1960s, some tree-ring data diverge (PDF) and suggest declining temperatures—even as actual temperatures show a dramatic rise. No one knows quite why this is; some researchers suggest the trees may actually be showing the stress from human activities. This divergence is one reason that many skeptics argue against using temperature reconstructions in climate change research.
McIntyre's paper made headlines. A few days after publication, he was featured in a front-page piece in the Wall Street Journal that pitted (PDF) his hockey-stick critique against the whole of global warming science, saying he had "helped to reopen the debate."*
Few scientists will ever get that kind of coverage for their life's work, let alone for a single article on someone else's research. But McIntyre's critique came at a time when those seeking to block action on climate change were on the defensive—many had been pilloried for their ties to industry (PDF) and right-wing think tanks, and public opinion was turning toward action on climate change. At this pivotal moment, reopening the debate was just what the skeptics, and their industry backers, needed. McIntyre and McKitrick were flown to Washington for another briefing with the Marshall Institute and CEI (PDF).
600 years of temperature data can't be wrong. Or can it?
MICHAEL MANN'S hockey-stick graph shows average temperatures over the past 1,000 years based on "proxy data" reconstructions from tree rings, ice cores, sediment, coral, and some instrumental data. The last 600 years of Mann's proxy data are shown below in blue. Actual temperatures, starting in the 1850s, are shown in red. (The darker trend lines are based on 40-year averages.) Both sets of data show a sharp temperature spike after the Industrial Revolution and a slight dip in the 1960s followed by a continued rise in recorded temperatures. Other climatologists have done their own studies of historic climate variations, and there is much debate over the fact that some of those studies—specifically those focusing on certain sets of tree-ring data—suggest that modern temperatures are continuing to decline.
In a slideshow meant to highlight GMU's investigations for Congress (PDF), a Wegman staffer noted that Barton's office warned Wegman's group to expect criticism and told them to have "thick skins." Barton's staff also provided the group with reams of reading material—particularly troubling, considering that none of the statisticians, she said, had "any real expertise in paleoclimate reconstruction." Wegman's group also consulted McIntyre in its evaluation of Mann's study, but it never reached out to Mann.
When it was released in July 2006, the Wegman report (PDF) essentially agreed with McIntyre, citing statistical problems with the hockey stick and accusing climate scientists of uncritically reinforcing each other's work. Years later, Barton and other skeptics still tout the document as proof that the hockey stick is broken (even though GMU is currently investigating allegations that Wegman may have lifted portions of the report from a previously published book).
Meanwhile, about five months after Barton commissioned Wegman for the report, the House Committee on Science asked (PDF) the National Academy of Sciences to prepare a formal report on the hockey stick. The review concluded (PDF) that while some uncertainties "have been underestimated," there was nevertheless "an array of evidence" supporting the main conclusion of Mann's work.
* Clarification: The original Wall Street Journal article referred to a report by researcher Hans von Storch, not McIntyre’s specifically: "Reports such as [von Storch's] helped to reopen the debate, even to outsiders."
Kate Sheppard was a staff reporter in Mother Jones' Washington bureau from 2009 to 2013. She is now a senior reporter and the energy and environment editor at The Huffington Post. She can be reached by email at kate (dot) sheppard (at) huffingtonpost (dot) com and you can follow her on Twitter @kate_sheppard.