Jury to decide on climate scientist Michael Mann's defamation suit over comparison to molester

It's been 12 years since a pair of conservative writers compared a prominent climate scientist to a convicted child molester for his depiction of global warming. Now, a jury is about to decide whether the comments were defamatory.

Closing arguments were expected Wednesday in a lawsuit brought by Michael Mann, who rose to fame for a graph first published in 1998 in the journal Nature that was dubbed the “hockey stick” for its dramatic illustration of a warming planet. Mann's graph showed average temperatures in the Northern Hemisphere changing little for 900 years until they started to rise rapidly in the 20th century.

The work brought Mann, then at Penn State but now at University of Pennsylvania, wide exposure. It was included in a report by a United Nations climate panel in 2001, and a version of it was featured in Al Gore’s Oscar-winning 2006 climate change documentary, “An Inconvenient Truth.”

It also brought him skeptics — two of whom Mann took to court for attacks that he said affected his career and reputation in the U.S. and internationally.

In 2012, the Competitive Enterprise Institute, a libertarian think tank, published a blog post by Rand Simberg that compared investigations by Penn State University — then Mann’s employer — into Mann's work as well as the case of Jerry Sandusky, a former assistant football coach who was convicted of sexually assaulting multiple children.

Mann’s research was investigated after his and other scientists’ emails were leaked in 2009 in an incident known as “Climate Gate” that brought further scrutiny of the “hockey stick” graph, with skeptics claiming Mann manipulated data. The investigations by Penn State and governmental organizations cleared Mann, but his work continued to draw attacks, particularly from conservatives.

“Mann could be said to be the Jerry Sandusky of climate science, except for instead of molesting children, he has molested and tortured data,” Simberg wrote. Another writer, Mark Steyn, later referenced Simberg's article in his own piece in National Review, calling Mann's research “fraudulent.”

Mann sued the two men and their publishers, seeking monetary damages. The case has bounced through various courts since then. In 2021, a judge dismissed the two outlets as defendants, saying they could not be held liable, but the claims against the individuals remained.

Simberg, in a statement, said the case was about “the ability of myself and others to speak freely about the most important issues of our day, whether climate change or another issue."

“If others are faced with over a decade of litigation for giving their opinions," Simberg said, “we will all suffer.”

Steyn declined to comment while the trial is ongoing, but previously said he was only stating an opinion.

Kate Cell, whose work as senior climate campaign manager at The Union of Concerned Scientists includes tracking climate disinformation, said Mann's case is well-known among other climate scientists. She said many were hoping a favorable verdict for Mann would “reduce the comfort and regularity with which those who do not accept climate change science speak, and speak very nastily, about climate scientists.”

But Mann needs to prove that the writers not only made false and defamatory statements, but acted with actual malice — a higher threshold for cases involving public figures.

Lyrissa Lidsky, a constitutional law professor at the University of Florida and an expert on defamation, said the law in defamation cases involving public figures often favors free speech rights.

“There’s a misperception that defamation is purely a contest of what’s true and what’s not true," she said. “The First Amendment gives a lot of leeway for people to say unkind, harsh things.”

The trial comes as climate change continues to be a divisive and highly partisan issue in the United States. A 2023 poll from The Associated Press-NORC Center for Public Affairs Research found that 91% of Democrats believe climate change is happening, while only 52% of Republicans do.

Many scientists have followed Mann’s case for years as misinformation about climate change has grown and many of them have themselves been subjected to attacks. Lidsky was skeptical that Mann’s case would have any broader significance, particularly on social media.

“A jury’s decision in one case about a climate scientist will not stop climate skepticism,” said Lidsky, “no matter what the outcome of the trial is.”

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