Nine Years After Filing a Lawsuit, Climate Scientist Michael Mann Wants a Court to Affirm the Truth of His Science

The case raises difficult issues about free speech in an era of online misinformation and disinformation.

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Scientist Michael Mann attends the New York screening of the HBO Documentary "How To Let Go Of The World And All The Things Climate Can't Change" on June 21, 2016 in New York City. Credit: Slaven Vlasic/Getty Images for HBO
Scientist Michael Mann attends the New York screening of the HBO Documentary "How To Let Go Of The World And All The Things Climate Can't Change" on June 21, 2016 in New York City. Credit: Slaven Vlasic/Getty Images for HBO

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When Penn State climate scientist Michael Mann first threatened to sue two conservative bloggers and their publishers for defamation in 2012, they seemed to welcome the opportunity for a face-off in court.

The Competitive Enterprise Institute, an anti-regulation think tank, and National Review magazine defended their online commentaries in which they attacked Mann’s science and  compared him to Jerry Sandusky, the disgraced Penn State assistant football coach convicted of child sexual abuse. “All’s fair in love, war and political campaigns,” Rand Simberg, the CEI blogger, wrote about Mann’s threat, on his personal website. In an editorial, National Review editor Rich Lowry mused about gaining access to Mann’s files if he sued and hiring a “dedicated reporter to comb through” the material and expose Mann’s “methods and maneuverings to the world.”

That investigative project has never materialized, even though Mann’s side has produced more than 1 million documents in the defamation suit he filed, now entering its ninth year. The material includes emails, correspondence, notes, drafts and discussions with co-authors—including all the background material for his seminal 1998 and 1999 papers charting this century’s dramatic temperature rise, the so-called “Hockey Stick” graph. 


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The case centers around Mann’s seminal research into historic temperatures, nicknamed the “Hockey Stick” because of the graph’s distinctive shape. To produce it, Mann and his co-authors reconstructed temperatures from time periods before the widespread use of thermometers by using the evidence gathered from tree rings, lake and ocean sediment, ice cores and corals. The graph featured prominently in former Vice President Al Gore’s 2006 movie, “An Inconvenient Truth,” as an image that dramatically illustrated the rapid warming the Intergovernmental Panel on Climate Change concluded is “unprecedented over decades to millennia.”  

Now, with discovery in the case concluded, Mann is asking the court to rule that the conservative outlets have failed to summon any evidence to challenge the validity of his science.

In a motion for partial summary judgment filed Jan. 22 in Superior Court of the District of Columbia (the Washington, D.C. equivalent of a state trial court), Mann’s lawyers have asked the court to bar the Competitive Enterprise Institute, the National Review and their authors from using as their defense an argument that their accusations were true, or “substantially true,” and therefore could not be defamatory. 

Mann’s case raises difficult issues regarding free speech in an era of online misinformation and disinformation. If Mann prevails in his motion, the blog publishers could still win the case, mounting other defenses, including that their columns were protected by the First Amendment, an argument they have made throughout the long history of the litigation. But Mann also would gain an important victory: a ruling supporting the validity of his science.

“For years, the defendants have been boasting that they wanted to get us into court so they could question us under oath. For years they have been boasting that the documents they would subpoena from us would prove that the hockey stick research was improperly manipulated,” Mann said, through his attorneys. “They came up with nothing. And they came up with nothing because their statements were absolutely baseless, to the extent that even their own witnesses had to acknowledge that there was no fraud, no deception, no corruption, no misconduct.”

A Lightning Rod for Skeptics

The Competitive Enterprise Institute, the National Review and the bloggers have filed their own motions, calling for the judge to decide the case in their favor without proceeding to trial. The National Review’s lawyers did not respond to a query about the case. But lawyers for the blogger Mark Steyn, who is pursuing his defense separately, and for the Competitive Enterprise Institute and its author, Simberg, provided the motions in response to questions about the case.

Mann’s research has been a lightning rod for skeptics of global warming, but the National Research Council in 2006 concluded that Mann and his co-authors “accurately and honestly reported their underlying research and did not make claims that were stronger than the data could support.”

In 2009, Mann’s work came under scrutiny again when his correspondence was among more than 1,000 email exchanges among climate scientists hacked from a university server in England and posted on the Internet. Over the next two years, seven investigations by government agencies and institutions in the United Kingdom and the United States all concluded that the so-called “Climategate” emails showed no wrongdoing by the scientists. The inquiries included two probes—one by Penn State and one by the National Science Foundation inspector general—that focused specifically on Mann.

But in the world of climate denial, Mann’s science remained a target. And in July 2012, with the Sandusky sex abuse scandal roiling the Penn State campus, Simberg published a blog on the Competitive Enterprise Institute website seeking to draw a parallel between Sandusky and Mann who, Simberg wrote, “molested and tortured data in the service of politicized science.” Two days later, on July 15, 2012, Steyn picked up the theme for National Review, quoting extensively from the Simberg column, and blaming Penn State for a “whitewash” around what he called “the fraudulent climate-change ‘hockey-stick’ graph.”

Shortly afterward, the Competitive Enterprise Institute removed two sentences of the Simberg blog post, including his “molested and tortured” phrasing, as “inappropriate,” but stood by the piece after receiving Mann’s lawsuit threat. “We’re not retracting the piece, and we’re not apologizing,” the group said in a press release. And after Mann did sue, Steyn would write on his own blog that he planned to call on “an array of witnesses” to “testify to the fraud necessary to create the hockey stick.”

Despite the public bluster, the defendants’ approach in court has been conservative. They have  maintained that they didn’t have to prove that Mann’s science was a “fraud” or “deception”—the words the bloggers used. In its motion to dismiss the case, the Competitive Enterprise Institute said the burden of proof was on Mann to show that each defendant knew the statements at issue were false, or entertained serious doubts about their truth.

The defendants have presented as evidence published academic critiques by scientists who are critics of Mann, and press articles critical of Mann’s science from The Atlantic, The Wall Street Journal, The New Scientist and other publications. The defendants also submitted as evidence the “Climategate” emails.

Steyn, when questioned during his deposition in the case, admitted that at the time of his writing he had never read any of the investigations by the American agencies, which he called “that bewildering array of acronyms beginning with ‘N.'” In fact, he testified that he did not take much time at all to write the blog, but said it was informed by his years of study of global warming, which he said he believes is happening but is caused by natural cycles. He likened himself to the artist James Whistler, who once claimed that one of his paintings, although finished quickly, gained worth from his lifetime of experience. “My post… took whatever it was to write; 20, 30 minutes… but certainly a couple of decades of experience,” Steyn testified.

In his new motion, Mann argues that the defendants’ positions in the case have been weakened significantly because their own witnesses declined to testify that the Penn State scientist committed scientific misconduct or fraud.

“I’m not making a judgment on that. I’m agnostic on it,” Judith Curry, a prominent contrarian and former chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, testified when deposed by Mann’s lawyers. Instead, Curry said, she was only testifying as to “whether it’s reasonable for the general public or a journalist or a whatever to regard this as fraud.” Another defense witness, statistician Abraham Wyner of the University of Pennsylvania, testified that in his opinion, the hockey stick was “not a deception,” although he thought it misleading. Roger Pielke Jr., a political scientist at the University of Colorado, Boulder conceded during his deposition that when he blogged about allegations against Mann in 2010, he had written, “None of this rises to scientific misconduct or fraud, not even close.”

Mann’s lawyers, including John Williams, of Washington, D.C., and Peter Fontaine, of Philadelphia, argue that because the defendants have presented no evidence challenging his science, the court should bar them from using the defense that the assertions in the blogs were “substantially true,” or that his science was “substantially false.”

If the court rules in Mann’s favor, the defendants would still have a number of legal arguments to rely on, including their contention that Mann suffered no real harm. The National Review argues that it is a website operator and so, under Section 230 of the Communications Decency Act, cannot be held liable for material posted on its platform by a non-employee (Steyn had a contract with the magazine but was not full-time staff). 

The magazine and the think tank both have argued that the blogs were constitutionally protected speech, and professional journalism groups, newspapers and the American Civil Liberties Union have supported them in this argument.

Simberg’s statements “are not actionable assertions of fact that the Plaintiff engaged in literal fraud, but First Amendment-protected expressions of opinion and interpretation regarding Climategate and its aftermath,” the Competitive Enterprise Institute says in its motion to dismiss the case, filed Jan. 22.

In 2019, the U.S. Supreme Court declined to intervene on the defendants’ behalf to stop Mann’s case based on the First Amendment argument, although Justice Samuel Alito dissented, saying that the case “presents questions that go to the very heart of the constitutional guarantee of freedom of speech and freedom of the press: the protection afforded to journalists and others who use harsh language in criticizing opposing advocacy on one of the most important public is- sues of the day.”

Under First Amendment law, a public figure, which Mann is, has a high burden of proof in defamation cases. Such a plaintiff must show that the defendants acted with “actual malice,” knowing falsehood or reckless disregard for the truth. But in making the motion for a ruling on the truth of his science, Mann’s side is arguing that the underlying facts matter, regardless of what happens with the defense’s Constitutional arguments.

A ruling in Mann’s favor could have implications for anyone publishing smears based on falsehoods, giving the case, filed years before the Trump era, a new salience amid the rapid spread of dangerous and reputation-damaging conspiracy mongering and disinformation on the Internet.

“The American people are fed up with fake news and false accusations,” Mann said in a statement emailed by his lawyers, “and this case will hopefully prove that there are consequences for this type of behavior.”

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