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Michael Mann’s Hockey Stick

The climate scientist tells his story and explores the role of skepticism in science

by Rudy M. Baum
December 10, 2012 | A version of this story appeared in Volume 90, Issue 50

Credit: Columbia University Press
The Hockey Stick And The Climate Wars: Dispatches From The Front Lines, by Michael E. Mann, Columbia University Press, 2012, 395 pages, $28.95 hardcover (ISBN: 978-0-231-15254-9)
Book cover, words only: The Hockey Stick and the Climate Wars: Dispatches from the Front Lines, Michael E. Mann
Credit: Columbia University Press
The Hockey Stick And The Climate Wars: Dispatches From The Front Lines, by Michael E. Mann, Columbia University Press, 2012, 395 pages, $28.95 hardcover (ISBN: 978-0-231-15254-9)

Symbols matter—especially symbols that cut through clutter and obfuscation, ones that convey a complex concept with irrefutable simplicity.

Ask Michael E. Mann, the Pennsylvania State University climate scientist who published the graph of global temperatures over the past millennium that became known as the “hockey stick” for its distinctive shape. Climate science is complex. Arguments about the impact of human activities on Earth’s climate abound. Climate-change deniers argued for years, and many still argue, that there isn’t any evidence that Earth’s climate is changing.

The hockey stick cut through that clutter. With devastating clarity, it showed that, from about the year A.D. 1000, Earth’s temperature followed a gentle decline until the beginning of the 20th century (the shaft of the hockey stick), and then began a sharp rise that continues through today (the blade). The hockey stick says nothing about causation, but it demolishes the claim that nothing untoward is occurring in Earth’s climate.

And that made it a target, which it remains to this day. Ever since the hockey stick graph was featured prominently in the third assessment report of the Intergovernmental Panel on Climate Change (IPCC), climate-change deniers have attacked the graph and, perhaps even more vehemently, Mann’s scientific integrity. In late October, Mann filed a libel suit against two organizations: the Competitive Enterprise Institute, which posted an article on its website comparing Mann to Jerry Sandusky, the former Penn State football coach convicted of child molestation, and the National Review, which published an article that references the CEI post.

In his book “The Hockey Stick and the Climate Wars: Dispatches from the Front Lines,” Mann tells the story of how he and his coworkers developed the hockey stick graph and its place in climate science. Mann writes, “In this book, I attempt to tell the real story behind the hockey stick. I reflect on the emphasis, and indeed at times the overemphasis, that players on both sides of the climate change debate have often placed on this work. … I use my own story, more than anything else, as a vehicle for exploring broader issues regarding the role of skepticism in science, the uneasy relationship between science and politics, and the dangers that arise when special interests and those who do their bidding attempt to skew the discourse over policy-relevant areas of science.”

Mann succeeds in all of these goals and more. “The Hockey Stick” is one of the most useful books yet in explaining climate science, especially the use of paleoclimate proxy data to assess the history of Earth’s climate, which is Mann’s specialty. It also offers one of the clearest and most damning examinations of the tactics used by climate-change deniers to distort the science of climate change and smear the reputations of climate scientists.

After a brief chapter on how Mann, a physics and applied math major at the University of California, Berkeley, got into climate science, “The Hockey Stick” provides readers with a concise primer on the fundamentals of climate science:

■ Human activity has increased CO2 concentrations in the atmosphere.

■ The increase in CO2 and other trace gases produced by humans has a warming effect on Earth’s surface.

■ Thermometer measurements show that, by the mid-1990s, Earth had warmed by about 1 °F since preindustrial times.

■ Sophisticated models have been developed to investigate the causal mechanisms behind changes in Earth’s climate.

■ Only when human factors are included do those models reproduce all of the observed warming.

The case for anthropogenic climate change has only strengthened since the mid-1990s, Mann writes, but “even by the mid-1990s there was no longer reason for real scientific debate over the proposition that humans had warmed the planet and changed the climate.”

Credit: Michael Mann
More than a dozen independent temperature reconstructions (including that of Mann and coworkers) affirm the conclusion that Earth’s temperature has risen sharply in the past century.
Two graphs, known as hockey-stick graphs, show northern hemisphere temperatures between years A.D. 200 and 2000, with sharp increases between 1800 and 2000.
Credit: Michael Mann
More than a dozen independent temperature reconstructions (including that of Mann and coworkers) affirm the conclusion that Earth’s temperature has risen sharply in the past century.

Climate-change deniers like to compare themselves to great scientists like Galileo or Darwin who challenged the scientific orthodoxy of their times—the current orthodoxy being, of course, the belief that humans are altering Earth’s climate. Skepticism, they maintain, is central to science. “True skepticism, however,” Mann writes, “demands that one subject all sides of a scientific contention or dispute to equal scrutiny and weigh the totality of evidence without prejudice. That should not be conflated with contrarianism or denialism, which is a kind of one-sided skepticism that entails simply rejecting evidence that challenges one’s preconceptions. Unfortunately, the term skeptic has at times been coopted by those who are not skeptics at all, but are instead contrarians or deniers, predisposed to the indiscriminate rejection of evidence supporting a human influence on climate.”

Mann goes into considerable detail on the work that led to the hockey stick. It is a nontrivial statistical challenge to merge the various paleoclimate proxy data into a meaningful set of comparable temperature points, and Mann does a good job of leading the reader through the concepts involved. It is worthwhile to note that “The Hockey Stick” is an intellectually sophisticated examination of climate science, with more than 100 pages of notes at the back of the book. These extensive notes are a strength and a weakness of the book. Many of the notes are literature references that I am sure Mann included to provide scientific rigor to his arguments, but the casual reader will find them superfluous. Other notes, however, offer important insights and additional detail on the issues being discussed in the text. So you find yourself flipping back and forth between the text and the notes, sometimes finding important ­nuggets and other times being frustrated.

In subsequent chapters, Mann examines the origins of climate-change denial and identifies many of the major figures in the denialist camp; the IPCC and how its reports, which draw deniers’ scorn, are prepared; the politics of climate change; and the chorus of attacks on the hockey stick. Mann is a thorough scholar, and he chronicles the climate-change wars from the mid-1990s on in great detail. By 2007, he writes, “climate science was on somewhat of a winning streak.” By the time the IPCC’s fourth assessment report was published in the summer of that year, Mann maintains, the four main pillars of climate-change denial had been toppled or were crumbling badly.

To the consternation of many climate scientists, however, the denialist camp continued its campaign. “For every talking point that was refuted, two more would be offered,” Mann observes. “Moreover, the same arguments were eventually recycled, no matter how many times they were refuted in the peer reviewed literature. Whether or not a talking point is scientifically or even logically defensible is immaterial. If it has misinformed or confused an appreciable number of observers, it has served its purpose in manufacturing doubt or confusion.”

And worse was yet to come. Losing on the science, denialists turned to attacking the integrity of climate scientists. “With no scientific leg to stand on, manufactured claims of incompetence and malfeasance, ladened with innuendo and vilification, have emerged as the denialist weapon of choice,” Mann writes. He provides numerous examples of these tactics at work, culminating in the episode that became known as “climategate,” in which tens of thousands of e-mails between climate scientists were hacked from a server at the University of East Anglia’s Climate Research Unit and selectively leaked to the media.

Mann, who was one of the principal climate scientists to have his e-mails distributed by the still-unknown hacker, writes: “Imagine how unpleasant it might be to have your private e-mails, text messages, or phone conversations mined by your worst enemy for anything that, taken out of context, could be used to make you look bad. Then imagine what it would be like to be expected to defend each and every instance of sloppy word choice or ambiguous phrasing that could be found. This is the position in which climate scientists ... found themselves.”

Mann does an excellent job of examining the climategate matter and how climate scientists tried to counter the assault. He provides clear evidence that a “professional climate change denial machine” drives the climate wars and that, for too long, a professional media driven by notions of “balance” gave the deniers far too much credibility.

In the book’s penultimate chapter, “Fighting Back,” Mann posits that the tide may have turned. All investigations of the climategate affair exonerated the climate scientists whose e-mails were hacked and posted. Not satisfied with those results, newly elected Virginia Attorney General Kenneth T. Cuccinelli II (R) launched an investigation of Mann’s work while he was an assistant professor at the University of Virginia, demanding that the university turn over all of Mann’s e-mails and other documents to ascertain whether fraud had been committed in the course of Mann’s research. Cuccinelli’s effort provoked a bipartisan outcry over academic freedom and was eventually rebuffed by the courts (C&EN, Sept. 6, 2010, page 56).

As Mann writes: “The climategate and Cuccinelli affairs might have had the desired short-term effect of generating further controversy over climate change. Both appear to have been long-term tactical errors by the climate change denial machine, however. Relying on stolen e-mails and the questionable use of political office to achieve their ends, these twin assaults were such an atrocity that they’d finally, to quote one colleague, awakened a ‘sleeping bear.’ No longer would scientists stand by watching one of their own being attacked.”

Mann ends “The Hockey Stick” on a relatively optimistic note. He believes that many scientists are now fully engaged in what they recognize is a war. And, although he notes that “the scientific community is … ill-equipped to deal with direct assaults on its integrity,” he also believes that progress is being made in informing the public about the reality and consequences of climate change. “The Hockey Stick and the Climate Wars” is an important contribution to furthering that understanding.

Rudy M. Baum is C&EN editor-at-large.


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