Can the U.S. Congress impeach a chart?
In one of the more unusual scenes of the 109th Congress, a House of Representatives subcommittee did just that.
For more than 10 hours spread out over two days, Rep. Edward Whitfield, a Republican from Kentucky, swore in a dozen witnesses to provide testimony about a squiggly two-dimensional figure. They delved into its past, looking at who had sired it and what company it had kept over the years in numerous scientific publications, newspaper articles, and political documents. As in many trials, there was even false testimony, when eyewitnesses mistakenly said they had seen the accused at one scene or another.
The defendant is a temperature chart, an estimate of how the climate has changed across the Northern Hemisphere in the past millennium. It’s known as the “hockey stick” because the line representing temperature remains relatively straight through nine centuries and then arcs sharply up in the past 100 years, like the blade of a hockey stick.
That figure is one of the most scrutinized scientific graphs in recent memory. In late June, the National Research Council, the investigative arm of the National Academy of Sciences, released a 141-page assessment. The next month, a panel of statisticians convened by the Republican leaders of the House Committee on Energy and Commerce weighed in with its own 92-page analysis. Several teams of scientists in the United States and Europe have published papers either supporting or criticizing the hockey-stick curve. And in Toronto, a retired mining consultant has devoted a blog, and many of his waking hours over the past few years, to attacking the graph.
For politicians, pundits, and interest groups skeptical of the evidence for greenhouse warming, the hockey stick has become a potent symbol. They portray the research it represents as a flawed study so fundamental to climate science that its errors raise important questions about the consensus on global warming — and consequently about any proposals to limit greenhouse-gas pollution.
At one of the recent hearings, Mr. Whitfield, chairman of the House energy committee’s subcommittee on oversight and investigation, said, “Everyone has latched on to this hockey stick and almost created a panic in a way.” The Wall Street Journal, in an editorial in July, said the graph “has cropped up all over the place,” and that it was “a man-made global warming evangelist’s dream.”
For many scientists, however, the hockey-stick drama has become a nightmare, a surreal example of how the results of research can be stretched and distorted when they get politicized.
Gerald North, a professor of atmospheric sciences at Texas A&M University at College Station, served as chairman of the National Research Council committee that has investigated the hockey-stick curve. Despite finding some problems in the seven-year-old study that was the basis of the curve, the panel determined that it is basically correct in its conclusions, which have been corroborated by more-recent work. The scrutiny by Congress “is kind of a delaying tactic to find little things like this to slow down government action on greenhouse-gas limitations,” says Mr. North.
For academic researchers, the ramifications of the debate go far beyond this one graph. Republicans at the hearing saw the hockey stick as a sign of significant problems in the field of climate science, which they view as too insular to ensure that its research is reliable. They promised increased federal investigations into the way climate science is being done.
“The issues at hand concern legitimate questions about the rigor of scientific analysis, the results of which ultimately reach policy makers,” says Mr. Whitfield. “The hockey-stick story provides a clear case study into the lack of proper scrutiny.”
Birth of an Icon
Much of the recent heat over the hockey stick has focused on its main parent, Michael E. Mann, an associate professor of meteorology at Pennsylvania State University at University Park, who developed it with two colleagues. Modest in stature, Mr. Mann is not a physically imposing figure. But he is an aggressive researcher whose intensity has won him many supporters as well as detractors.
Mr. Mann has risen quickly in the world of climate science. A decade ago, he was just finishing his doctorate at Yale University and had already made a name for himself by publishing a paper in the prestigious journal Nature about the historical climate.
Since reliable thermometer records reach back only a little more than a century in most places around the globe, researchers like Mr. Mann, who are interested in earlier times, have to look for clues in other places. They often consult natural recorders of climate information, like tree rings, sediments at the bottoms of lakes, and the annual ice layers in glaciers. Each of those phenomena grows one year at a time, locking in information about annual snowfall, temperature, wind speeds, and other indications of past conditions. (Researchers call those clues to past climate “proxy records.”)
In 1996 Mr. Mann left Yale for a postdoctoral fellowship at the University of Massachusetts at Amherst to work with Raymond S. Bradley, a professor of geosciences. Mr. Mann brought an unusual set of skills with him, having spent two years pursuing a doctorate in physics before switching to climate research. He eventually combined the two interests and specialized in developing statistical techniques to find patterns in records of the past.
Working with Mr. Bradley and Malcolm K. Hughes, a professor of dendrochronology at the University of Arizona, Mr. Mann combined records from disparate sources — tree rings, ice cores, and coral layers — to reconstruct what temperatures were like across the Northern Hemisphere over the past six centuries. In 1998 the three scientists published a paper in Nature that laid the foundation of the hockey-stick curve. According to their analysis, hemispheric temperatures were warmer in the late 20th century than at any other time since 1400.
Soon after their paper appeared, Phil D. Jones, a professor of environmental studies at the University of East Anglia, in England, and several colleagues used tree rings, coral layers, and glacial records to develop a 1,000-year climatic history. Their study did not specifically estimate the uncertainty of the temperature estimates, meaning they did not specify how reliable those numbers were.
Mr. Bradley remembers sitting in his office one morning when Mr. Mann came in brandishing Mr. Jones’s paper.
“Look at this,” he recalls Mr. Mann saying. “This is rubbish. You can’t do this. There isn’t enough information. There’s too much uncertainty” to go back so far.
The two talked, and Mr. Bradley said, “Why don’t we try to use the same approach we used in Nature, and see if we could push it back a bit further?”
A couple of weeks later, Mr. Mann came back surprised that his initial caution had been too strong. “There is a certain amount of skill,” he told Mr. Bradley. “We can actually say something, although there are large uncertainties.”
Mr. Mann, who doesn’t remember using the word “rubbish” about Mr. Jones’s article, gives it credit for prompting him to try to quantify the uncertainty in the earlier centuries. Before 1600, he found, the data were spotty and the statistical methods could not yield strong conclusions. But they could say something.
“Our conclusion was that even with those uncertainties and those caveats, we believe it was likely that the late-20th-century warmth was anomalous,” says Mr. Mann.
He, Mr. Bradley, and Mr. Hughes wrote up a paper titled “Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations,” and published it in 1999 in a less prominent journal, Geophysical Research Letters.
As the title suggests, the paper discussed the uncertainties and difficulties of reaching so far back in time. It concluded that “the 1990s were likely the warmest decade, and 1998 the warmest year, in at least a millennium.” But it added that more data were needed “before more confident conclusions can be reached.”
Greenhouse Poster Child
While that publication, and the temperature plot inside, made some headlines, it took a few more events to elevate the graph to the level of an icon for greenhouse warming.
First came its catchy name. The curve was christened by Jerry D. Mahlman, a former director of the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory, one of the premier U.S. research facilities devoted to forecasting weather and climate. When Mr. Mann gave a talk at the lab, Mr. Mahlman observed that the rising 20th-century temperatures on the graph resembled the blade of a hockey stick. The nickname stuck.
Then, in 2001, the graph had its coming-out party, given by a United Nations body called the Intergovernmental Panel on Climate Change, better known as the IPCC. Every five years or so, the IPCC has convened hundreds of researchers to determine the state of knowledge concerning the science of climate change and how it will affect society.
As scientists prepared the 2001 report, they looked at several studies that attempted to chart temperatures reaching back to medieval times. All of the reports reached generally similar conclusions. Mr. Mann and other authors who wrote the section on temperature changes described the millennial reconstructions and the uncertainties inherent in them.
But those caveats faded from view when leaders of the IPCC boiled down the 994-page scientific report into a 20-page synopsis. The first page of that condensed “Summary for Policy Makers” states that “new analyses of proxy data for the Northern Hemisphere indicate that the increase in temperature in the 20th century is likely to have been the largest of any century during the past 1,000 years. It is also likely that, in the Northern Hemisphere, the 1990s was the warmest decade and 1998 the warmest year.”
In small print at the bottom of the page, the authors explained that in IPCC parlance, “likely” means a conclusion that has a 66-percent to 90-percent chance of being correct. That range is a much lower standard of certainty than scientific studies usually require, but leaders of the IPCC decided that the more speculative information, when properly labeled, would be useful to include in the report.
On its own, the wording might not have attracted so much controversy. But in the first figure of the summary, the authors chose to highlight only one of the long-term temperature reconstructions: the hockey-stick curve from Mr. Mann’s group. When Sir John T. Houghton, leader of the IPCC’s scientific working group, appeared before the television cameras to unveil his committee’s long-awaited report, he had a poster behind him bearing a large image of the hockey stick.
For many in the news media and the general public, that graph appeared to be the star witness in the IPCC’s case that humans were warming the globe, when in fact that argument actually rested on a mass of other evidence unrelated to the curve.
The panel’s decision to emphasize the hockey stick so strongly “was a colossal mistake, just as it was a mistake for the climate-science-writing press to amplify it,” says Mr. Mahlman, the scientist who named the curve. “In other words, was that the smoking gun for global warming? It’s not the smoking gun. That’s the data we’ve had for the past 150 years, which is quite consistent with the expectation that the climate is continuing to warm.”
Stripped Naked
In the wake of the IPCC report, the paparazzi of the climate-change debate swarmed around the suddenly famous hockey stick. Environmental groups and some government reports pictured the curve in an overly flattering light, while skeptics of greenhouse warming showed it in the harshest glare possible, distorting its features for their own purposes.
“Advocates on both sides of the climate-change debate at various times have misrepresented the results for their own purposes,” says Mr. Mann.
One common tactic used by both sides is to disrobe the curve, taking off the error bars that indicate how much uncertainty there is in the figure. The airbrushing makes the hockey stick look much more definitive than it really is. In 2001 the federal government’s U.S. National Assessment of the Potential Consequences of Climate Variability and Change showed the stripped version of the hockey stick as part of a report on how climate change would affect the United States. (In a caption, the report described only part of the uncertainty in the graph.)
Those who doubt that humans are warming the climate substantially also often print the curve without its error bars, and then disingenuously attack it for being inaccurate. The editorial page of The Wall Street Journal recently published a naked copy of the hockey stick as part of a critique of it.
“That was very misleading, in fact downright dishonest,” says Texas A&M’s Mr. North.
After the IPCC made the hockey stick the poster child for global warming, the graph became a prime target for people opposed to the Kyoto Protocol, the international agreement that requires industrialized nations to reduce their emissions of carbon dioxide. The United States signed the treaty, but the Senate has not ratified it.
The American Petroleum Institute provided funds for research that criticized the hockey stick, and Sen. James M. Inhofe, a Republican from Oklahoma, took shots at the curve from the floor of the Senate.
In Toronto, a businessman who worked in the mining industry was motivated to scrutinize the mathematics behind the graph. Stephen McIntyre, working with Ross McKitrick, an associate professor of economics at the University of Guelph, in Ontario, eventually found what he considered to be flaws that shattered the hockey stick. He started a blog (http://www.climateaudit.org) documenting his criticisms and was flown to Washington, where he presented his work to Congressional staff members, the Competitive Enterprise Institute, and others.
As part of his campaign, Mr. McIntyre charged that Mr. Mann had denied him access to the fundamental data and computer codes needed to replicate his work. Mr. Mann and his colleagues started their own blog (http://www.realclimate.org) in part to respond to comments made by critics such as Mr. McIntyre.
When The Wall Street Journal wrote about Mr. McIntyre’s efforts in February 2005, Mr. Whitfield and Rep. Joe Barton, a Republican from Texas who is chairman of the House energy committee, sent letters to Mr. Mann and his colleagues requesting detailed information about not only the hockey stick but also every other study they had ever conducted. The two congressmen said they intended to resolve questions surrounding the hockey stick and the independence of the IPCC process, considering that Mr. Mann had played a role in writing the chapter that included his work.
But the committee had held only one hearing on climate change science since 1995, and many people saw the letters as an effort to intimidate Mr. Mann and other climate researchers. Sherwood L. Boehlert, a Republican from New York and chairman of the House Science Committee, wrote a letter to Mr. Barton “to express my strenuous objections to what I see as the misguided and illegitimate investigation.”
Instead of requesting a study by the National Research Council, as Mr. Boehlert and the head of the National Academy of Sciences suggested, Mr. Barton and Mr. Whitfield asked three academic statistics specialists to look over the hockey-stick curve. Mr. Boehlert, meanwhile, asked the National Research Council to convene a panel to assess the state of knowledge about temperatures over the past millennium and to put the work of Mr. Mann and his colleagues into context.
Combat in Congress
The two studies set the stage for a duel of science and politics.
The National Research Council panel led by Mr. North issued its report in late June. It reached a nuanced conclusion, finding validity in some of the statistical criticisms of the hockey stick made by Mr. McIntyre and others. It also stated that there were larger uncertainties in the early part of the millennium than the original hockey-stick study had estimated.
But on the whole, the panel agreed with the main, tentative conclusion of the 1999 paper and subsequent ones. “The committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period of the preceding millennium,” it stated in its report. The review panel had less confidence in the specific statements that the 1990s were the warmest decade and 1998 the warmest year of the millennium.
By contrast, the report prepared for Mr. Barton’s House energy committee sharply assailed the work of Mr. Mann. The committee released its report early to The Wall Street Journal, which published its naked version of the curve in its July 14 editorial.
The committee’s panel, led by Edward J. Wegman, a professor of information technology and applied statistics at George Mason University, found fault with the statistics used by Mr. Mann and his colleagues. “The paucity of data in the more remote past makes the hottest-in-a-millennium claims essentially unverifiable,” concluded the panel.
At the same time, it charged that paleoclimate researchers were too inbred to provide sufficiently independent reviews of new work. In particular, the panel recommended that paleoclimate researchers consult more with mainstream statistical academics.
At the first hearing, Mr. Barton, the committee chairman, characterized the report as calling Mr. Mann’s work “flat wrong.” A week later, he announced at the second hearing that he would request more scrutiny of climate science on a number of levels. The oversight was warranted, he said, because of the costs associated with combating greenhouse warming: “I really do want to make sure that these models are independently reviewed and the science is accurate.”
He said he would request that the National Research Council convene scientists who do not conduct climate research, to assess whether the field needed to be broadened. He has also asked the U.S. Government Accountability Office to examine policies on data sharing among scientists whose work is supported by federal funds.
Some scientists welcomed that suggestion. Hans von Storch, a professor of meteorology at the University of Hamburg and director of the Institute for Coastal Research, in Geesthacht, Germany, says: “We must be open about the data we are using. The journals must insist on open documentation, and the funding organizations must insist on that as well.”
Other researchers were skeptical about the practicality of some of the proposals raised by Republicans on Mr. Whitfield’s subcommittee, such as including more statistical experts in climate studies. Many climate researchers already collaborate with such experts, the scientists say, and it would be costly to archive computer programs, as has been suggested.
“We’re as open as our money and resources allow us to be,” says John R. Christy, a professor of atmospheric science at the University of Alabama at Huntsville.
Texas A&M’s Mr. North says Mr. Wegman and Mr. Barton are wrong in thinking that climate science is so cozy a field that researchers cannot truly review each other’s work. “They make it sound like a love nest — well, it isn’t,” he says. “If you know anything about science, it’s more like a contact sport.”
Mr. Bradley notes that even though he has published with Mr. Jones and Mr. Mann, he disagrees with some of their recent work together in which they have pushed the temperature record back 2,000 years. “I don’t buy any of that, frankly,” he says. “I think there’s too much uncertainty.”
At the Congressional hearing, Democrats objected to the focus on Mr. Mann’s first efforts while ignoring more-recent work that they say has corroborated his findings and the mass of other evidence related to climate change. Henry A. Waxman, Democrat of California, said, “This committee is doing what the deniers of global warming would have us do: ignore all the important questions and divert ourselves to a ridiculous effort to discredit a climate scientist and two studies he published eight years ago.”
The strategy, he charged, was to cast doubt on all climate-change research. “It’s back to the tactics of the tobacco industry,” he says, “manufacture doubt to delay action on an urgent problem.”
Mistaken Identity
For some members of the House energy committee, the hockey stick has become something of a boogeyman, a dangerous figure they see lurking in all corners even when it isn’t present.
Representative Barton and others repeatedly claimed that Mr. Mann’s curve was in An Inconvenient Truth, the movie and book about Al Gore’s slide show on global warming. While there is a graph shaped like a hockey stick in the book and the movie, the data do not come from Mr. Mann but from a different study, of glaciers.
At another point in the hearings, Mr. Whitfield said the hockey-stick curve was so influential that it was a cornerstone of the Kyoto Protocol, the international agreement to limit carbon emissions. “The Kyoto arguments were primarily based upon this new chart,” he said, before another committee member pointed out that the graph had been published after the protocol was adopted.
For those who study science policy, the hearings were a textbook example of how politics and climate science have grown intertwined. “The problem is that the science is so irrevocably politicized,” says Daniel Sarewitz, director of the Consortium on Science, Policy, and Outcomes at Arizona State University. “What seems to be a debate about science isn’t really about science at all.”
“I’m so discouraged by the whole situation,” he adds.
Roger A. Pielke Jr., a professor of environmental studies at the University of Colorado at Boulder, faults the scientific establishment for making the hockey stick into an icon. “If the case for climate change is broad and deep, which I think it is,” he says, “then the IPCC was wrong in choosing to let the hockey stick stand for a lot of that symbolically.”
In that sense, it was not surprising that the debate over the science would venture from the world of research into partisan terrain. “It’s really kind of sad, but it’s the perfect case study,” says Mr. Pielke, who studies the intersection of politics, policy, and science. Regarding the recent Congressional attention, he says, “the whole purpose of the hearing, as far as I could tell, was to wage a political battle through the science of the hockey stick.”
http://chronicle.com Section: Research & Publishing Volume 53, Issue 3, Page A10