Michael Mann is a climate scientist and researcher whose work has been at the center of the global warming debate for decades. After emails came to light concerning Mann’s statistical methods, two of his critics wrote scathing pieces arguing that Mann had “molested and tortured data in the service of politicized science,” and calling for “a fresh, truly independent investigation.” Despite such harsh criticism being par for the course in online commentary, Mann sued both writers and their publishers for libel.

A three-judge panel of the D.C. Court of Appeals ruled that the First Amendment didn’t prevent Mann’s libel claim from going to a jury and allowed the case to go forward. The defendants then asked the court to reconsider the implications of its decision, and Cato filed a brief supporting that request. That was two years ago, in January of 2017. In December of 2018, the Court amended two footnotes in the original opinion but didn’t alter the substance of the decision. The defendants have again requested that the court reconsider its opinion, and Cato has again filed an amicus brief in support.

Harsh words are common to the discourse of pundits and politicians alike. Op-eds and stump speeches frequently feature terms like “fraud,” “scam,” “misconduct,” and even “treason.” Whether such characterizations are apt or not is for readers and listeners to judge, but until now few imagined that using them could lead to years of litigation and a costly libel verdict. Similarly, calls for investigation and accusations of whitewashing have a long history dating back to Emile Zola’s J’accuse…! and continuing today with debates over the trials of O.J. Simpson, George Zimmerman, and many others.

If Mann’s critics committed actionable libel, then so might everyone who has voiced disagreement with such verdicts, as well as everyone who has called for politicians to be investigated for corruption, fraud, or war crimes. The court also wrongly held that merely comparing a public figure to a “notorious person” could be libelous. As we know from Godwin’s law, such comparisons are a time-honored tradition of American debate. Opinion writers in recent years have invoked colorful analogies to Timothy McVeigh, Charles Manson, and Jack the Ripper to express their displeasure with the conduct of public figures. Writers and historians concerned with the conduct of politicians have drawn parallels with Stalin, Mussolini, and, of course, the ubiquitous Hitler. Right or wrong, such language is unquestionably speech on subjects of public concern. The D.C. Court of Appeals should give this case a second (or third) look and reverse its earlier decision. It’s not an exaggeration to say that the court’s reasoning could put thousands of articles, blogposts, and even tweets under a cloud of potential liability, thereby chilling the speech that is the lifeblood of Washington politics. Cultural and political debates should be litigated in the court of public opinion, not law.