can 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).
Congressional conservatives swung into action. Rep. “Smokey” Joe Barton (R-Texas), then the chairman of the House Energy and Commerce Committee, launched a formal inquiry into the work of Mann and other climate scientists in June 2005. As part of the inquiry, Barton—who believes acting on global warming is “absolute nonsense” and said in a hearing that “when it’s hot, we find shade“—enlisted George Mason University statistician Edward Wegman to produce a report on the hockey stick. (In doing so, Barton eschewed (PDF) the more traditional route of requesting (PDF) a report from the National Research Council, a branch of the National Academy of Sciences.)
The Hockey Game
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 