This Scientist Fought His Attackers in Court—and Won

The climate scientist, author of the “hockey-stick graph" paper that infamously depicted a shocking rise in postindustrial average temperatures, has been battling critics for more than two decades.

In that time, a state attorney general accused him of misusing public money. The National Research Council and the university that employed him investigated his research. And conservative commentators attacked his work and his character. There were death threats.

Then last month, Mann won a 12-year legal fight and a $1 million jury verdict against the conservative bloggers who called his work fraudulent and compared him to a pedophile. The defendants have said they would appeal.

Mann’s $1 million jury award comes when public trust in science is at a low, scientific journals are retracting more papers than ever before, and researchers in a range of disciplines are scrutinizing the work of their peers and calling out what they see as errors or shoddy work in public forums.

Despite these wobbles, Mann is optimistic about both the discoveries and the integrity of how science is conducted these days.

“Science has given us remarkable advancements and achievements over the past decade," Mann said in an interview in his office at the University of Pennsylvania where he is a professor of earth and environmental science. He cited gene-editing technology, the Covid-19 vaccine and space probes landing on asteroids. “Seems to me that science is actually on a winning streak," he said.

It is also true that some areas of science are under assault, he added. “Clearly that’s true with climate and is true in a different way with Covid-19. But, we don’t see public mistrust of the science of black holes, or the science of interstellar space travel."

Mann said he feels vindicated by his court victory and hopes it will embolden other climate researchers to defend their work as vigorously as he has defended his own.

“I wasn’t going to shy away from fighting what I felt was the good fight," said Mann, 58 years old. “A lot of scientists would have sort of shunned the spotlight, retreated and withdrawn. That wasn’t in my nature."

Soft-spoken in person, Mann can be a tiger online. He spars with critics on his X account, where he has more than 220,000 followers. He punches back in frequent newspaper opinion pieces, letters to the editor, television interviews and on podcasts. In 2024 alone, he has done more than 20 interviews with major news outlets, from CNN to Le Monde. His public message is simple: The climate is changing rapidly, but it isn’t too late to save the planet.

Mann grew up in Amherst, Mass., the son of a math professor and a teacher. A self-described computer nerd in high school, he studied applied math and physics at the University of California, Berkeley, then continued his studies at Yale, where he earned a Ph.D. in geology and geophysics and became interested in using math and computers to simulate the Earth’s climate.

He entered the public spotlight in 1998 as a 33-year-old postdoctoral researcher at the University of Massachusetts, Amherst, when he and two colleagues published a paper in the journal Nature that used tree rings, ice cores and other proxy records to create a global temperature record from the present back to 1400 A.D.

That paper included what became a lightning rod for climate-change skeptics: a chart depicting a long period, beginning in 1400, of relatively stable temperatures followed by a sharp bend upward in temperatures starting in the late 1800s through the present—like a hockey stick on its side with the blade turned up.

“I’ve sort of felt like the hockey stick actually sort of overshadowed much of what we thought was most interesting in that original article," Mann said.

Perhaps because the paper was published on Earth Day in 1998—at that time, the hottest year on record—the media picked up Mann’s paper and its findings.

Mann remembers his first television appearance on CBS Nightly News after the paper was published, when he was asked several times whether the hockey stick proved that humans were causing climate warming. Mann wasn’t ready to make that statement, telling the correspondent instead that it was “strongly suggestive."

The finding was amplified when the United Nations Intergovernmental Panel on Climate Change published an updated version of the graph in its 2001 report and found that global temperatures were the warmest in 2,000 years.

Critics who didn’t believe in climate change, or thought Mann exaggerated the science to prove his point, attacked him.

In 2004, two critics disputed statistics used in the paper. They also pointed out errors in the listing of data used in the study. Mann and his co-authors issued a correction that didn’t alter the results of the paper.

Over the next eight years, Mann and his colleagues were the target of investigations by Republican lawmakers on Capitol Hill, Virginia’s Republican attorney general and officials at Pennsylvania State University, where he was a faculty member from 2005 to 2022.

In 2006, Mann’s research was confirmed by the National Research Council after a request from Congress. In 2012, the Virginia Supreme Court rejected the claim by the state attorney general, Ken Cuccinelli, and the case was dismissed. The same year, Penn State cleared Mann of research misconduct after a four-month probe.

On his office wall is a certificate from the Nobel Prize committee acknowledging his contribution to the 2007 Nobel Peace Prize along with other scientists working with the U.N.’s Intergovernmental Panel on Climate Change.

Attacks continued

In 2012, Rand Simberg, an adjunct scholar at the Competitive Enterprise Institute, a conservative think tank in Washington, D.C., compared Mann to Jerry Sandusky, the former Penn State football coach who was convicted of abusing young boys in the same year.

A separate article published a few months later by the National Review and written by conservative radio host and blogger Mark Steyn said, “Mann was the man behind the fraudulent climate-change ‘hockey-stick’ graph."

Mann had had enough.

“It’s one thing to criticize our work," he said. “It’s something else to make an actual accusation of fraud, which they did, and to compare me to a convicted child molester. I felt like I had to do something."

He sued Simberg and Steyn for defamation in Washington, D.C., Superior Court.

On Feb. 8, the jury awarded Mann $1 million in punitive damages from Steyn, $1,000 from Simberg and $1 in compensatory damages from each of them. Lawyers for Simberg and Steyn said they plan to appeal.

Simberg said he stands by his original blog post, and that he was critiquing Mann’s methods rather than the science of climate change.

“Science was on trial here, and I felt like I was the one defending it," Simberg said.

Steyn’s attorney, H. Christopher Bartolomucci, said Steyn continues to believe the statements he made are true and not defamatory.

“We believe the $1 million punitive award is grossly excessive and unconstitutional in a case where Dr. Mann had only $1 in actual damages," Bartolomucci said.

Mann’s critics, some of whom have appeared on the Opinion pages of The Wall Street Journal, have argued the case was about free speech and the right to criticize a public figure, something that Mann had become by the time Simberg and Steyn wrote their articles. Media organizations, including the Washington Post and the Reporters Committee for Freedom of the Press, submitted friend-of-the-court filings on their behalf.

For now, Mann said he can return to his research—looking at how the jet stream may be affecting summer drought and heat waves as the result of climate warming.

As for the future of the planet, Mann said it isn’t too late to prevent the worst effects of climate change. “As long as the obstacles aren’t physical or technological, but political, one can remain stubbornly optimistic," he said.

Write to Eric Niiler at eric.niiler@wsj.com