Michael Mann Lawsuit: Verdict, Sanctions, and Settlement

Climate scientist Michael Mann’s defamation lawsuit ended in a split result that has largely turned against him. A District of Columbia jury found in February 2024 that two conservative writers had defamed him by calling his climate research fraudulent, but post-trial rulings slashed the punitive damages from $1 million to $5,000, sanctioned Mann for misleading the jury about his financial losses, and ordered him to pay hundreds of thousands of dollars in attorneys’ fees to the defendants under the D.C. Anti-SLAPP Act.

What the Writers Said

The case grew out of two blog posts published in July 2012. Rand Simberg, an adjunct scholar at the Competitive Enterprise Institute, wrote on the think tank’s blog that Mann “could be said to be the Jerry Sandusky of climate science, except for instead of molesting children, he has molested and tortured data in the service of politicized science.”¹ Simberg also accused Mann of “data manipulation” and “academic and scientific misconduct.”²

Days later, commentator Mark Steyn published a column at National Review Online referencing Simberg’s post and calling Mann “the man behind the fraudulent climate-change ‘hockey-stick’ graph, the very ringmaster of the tree-ring circus.”³

Mann argued the statements amounted to false accusations of scientific fraud. Penn State University, the National Science Foundation, and the National Academy of Sciences had already investigated his work and concluded it was “both honest and solid.”⁴ Penn State’s inquiry, triggered by the 2009 “Climategate” email leak, found “no evidence” that Mann had suppressed or falsified data.⁵

Twelve Years of Pretrial Fighting

Mann filed his complaint in October 2012 in D.C. Superior Court, naming Simberg, Steyn, the Competitive Enterprise Institute, and National Review as defendants.⁶ The defendants moved to dismiss under the D.C. Anti-SLAPP Act, which shields speech on matters of public interest from meritless litigation. They said their commentary was constitutionally protected opinion.¹

The Superior Court denied those motions in July 2013, finding Mann had shown a sufficient basis to assert actual malice given the prior investigations clearing his research.⁷ The D.C. Court of Appeals affirmed in December 2016, holding that a reasonable jury could find the statements false, defamatory, and made with actual malice.⁸ Rehearing petitions failed, and in November 2019 the U.S. Supreme Court declined to take the case. Justice Samuel Alito dissented from the denial, warning that the case raised “delicate and sensitive” questions about applying defamation law to scientific critique and that litigation costs alone could chill dissent on public issues.⁹

In July 2021, the trial court granted summary judgment to National Review and CEI as institutional defendants, narrowing the case to Simberg and Steyn as individuals.¹⁰

The 2024 Trial and Jury Verdict

The four-week trial started in January 2024 before Judge Alfred S. Irving Jr. Steyn represented himself. Judge Irving told jurors the trial was about defamation, not the validity of global warming.¹¹ Mann testified the posts cost him grant funding and research collaborations. Simberg and Steyn testified they sincerely believed what they had written; Simberg said he had relied on ClimateGate emails, peer-reviewed work by Steve McIntyre and Ross McKitrick, and a presentation by physicist Richard Muller, and that he discounted the Penn State report as conflicted and the NSF report as “infected with politics.”¹²

On February 8, 2024, the six-person jury found that both Simberg and Steyn had defamed Mann with “maliciousness, spite, ill will, vengeance or deliberate intent to harm.”¹¹ The jury awarded $1 in compensatory damages from each defendant, $1,000 in punitive damages from Simberg, and $1 million in punitive damages from Steyn.¹³ No compensatory damages beyond the nominal $1 were awarded.¹⁴

Punitive Damages Cut to $5,000

Steyn moved for judgment as a matter of law and, alternatively, for remittitur, calling the million-to-one ratio between punitive and nominal damages “mind-blowing.”¹⁴ On March 4, 2025, Judge Irving issued an omnibus order that denied the motions for judgment as a matter of law and denied Steyn’s motion for a new trial, leaving the defamation findings intact. But the judge granted remittitur, vacated Steyn’s $1 million punitive award as “grossly excessive,” and reduced it to $5,000. Simberg’s $1,000 award was untouched.¹⁵

Sanctions Against Mann for Misleading the Jury

The more damaging post-trial ruling concerned how Mann’s team had presented his damages. At trial, Mann’s attorneys showed jurors a demonstrative chart claiming he had lost $9,713,924 in grant funding because of the defamatory statements. The correct figure from discovery was $112,000.¹⁶ Mann had acknowledged under oath before trial that no evidence supported the higher figure.¹⁷

Mann’s lawyers argued the jury was never meant to rely on the $9.7 million figure for pecuniary damages, that the grant data served as a proxy for reputational harm, and that the defendants could have challenged the numbers on cross.¹⁸ Judge Irving rejected the explanation, writing that it “strained credulity” and that the only plausible reason for the inflated chart was that Mann and his team wanted the jury to see the inflated number and hoped it would go unchallenged.¹⁶

In March 2025 the judge sanctioned Mann and his trial attorneys, Peter Fontaine of Cozen O’Connor and John Williams of Harty Williams, for “bad-faith trial misconduct,” finding by “clear and convincing evidence” that the attorneys “knowingly made a false statement of fact to the Court” and that Mann “knowingly participated in the falsehood.”¹⁹ Both attorneys denied any intent to deceive. Fontaine said neither lawyer intended to mislead the court or jury; Williams said the team had caught errors in the grant data and tried to correct them.¹⁸ Mann posted on social media that he was “confident neither I nor my lawyers did anything wrong during the trial.”²⁰

In January 2026, Judge Irving denied reconsideration and finalized sanctions of $16,762.82 payable to one defendant and $11,404.80 to the other.²¹

Anti-SLAPP Fee Awards Against Mann

The larger financial hit came from the D.C. Anti-SLAPP Act. In January 2025, the court ordered Mann to pay $530,820.21 in attorneys’ fees and costs to National Review, tied to the 2021 dismissal of claims against the organization.¹¹

In May 2025, Judge Irving ordered Mann to pay another $477,350.80 in attorneys’ fees to CEI and Simberg, finding they were “presumptively entitled to attorneys’ fees” under the statute after their successful appeal, and that “any other conclusion would be untenable under the terms of the statute.” Mann said the fee award “was not correctly decided” and said he would seek further review.²⁰

Settlement With National Review

In October 2025, Mann and National Review settled. Mann agreed to drop all claims against the publication and dismiss his pending appeals; in exchange, National Review forgave the $530,820.21 fee judgment and any accrued interest. The agreement stated it was not an admission of liability by either side and did not affect claims involving CEI, Simberg, or Steyn.²²

Where Things Stand

As of early 2026, the jury’s finding that Simberg and Steyn defamed Mann still stands. The judge denied their motions for judgment as a matter of law, so the defamation verdict has not been undone. The money has moved the other way. Steyn’s punitive damages sit at $5,000, Simberg’s at $1,000. Mann owes CEI and Simberg $477,350.80 in anti-SLAPP fees and roughly $28,000 in sanctions, while the National Review settlement erased the $530,820.21 fee award on that side of the case. Mann has said he plans to challenge the fee awards, and further proceedings involving Simberg and Steyn remain possible.¹⁶

1
FindLaw. Mann v. Competitive Enterprise Institute
2
Legal Planet. Why Michael Manns Defamation Suit Against Climate Denialists Is the Right Move
3
Rutgers Institute for Information Policy and Law. One Manns Assault on the First Amendment Continues
4
Penn State University. Iconic Graph at Center of Climate Debate
5
Nature. Penn State Clears Michael Mann
6
Competitive Enterprise Institute. Michael E. Mann v. National Review and CEI et al.
7
Columbia Law School Climate Change Blog. D.C. Court Affirms Michael Manns Right to Proceed in Defamation Lawsuit
8
ACLU of the District of Columbia. Mann v. National Review
9
Supreme Court of the United States. National Review, Inc. v. Mann, Alito Dissent
10
WRAL. Climate Scientist Awarded More Than $1 Million in Lawsuit Against Conservative Writers Who Defamed His Work
11
First Amendment Center at MTSU. Jury Awards Climate Scientist Mann $1 Million in Defamation Lawsuit
12
Media Law Resource Center. Mann v. Simberg, Omnibus Post-Trial Order
13
The Guardian. US Climate Scientist Michael Mann Wins $1M in Defamation Lawsuit
14
Schaerr Jaffe LLP. Defendant Mark Steyns Renewed Motion for Judgment as a Matter of Law
15
Sabin Center for Climate Change Law. Mann v. Simberg, Court Order on Post-Trial Motions
16
Reason – Volokh Conspiracy. Sanctions Award to Defendants in Mann v. Steyn Defamation Case
17
Legal Newsline. Judge Says Climate Scientist Misled Jury, Orders Penalty
18
DeSmog. Climate Scientist Michael Mann Fights New Court Penalties in 2024 Defamation Trial
19
Sabin Center for Climate Change Law. Mann v. Simberg, Sanctions Order
20
The Daily Pennsylvanian. Penn Michael Mann Additional Fees Defamation Trial Update
21
Sabin Center for Climate Change Law. Mann v. National Review, Inc., Case Documents
22
Michael Mann Website. Mann-National Review Settlement and Release Agreement