A District of Columbia appeals court has given a major legal win to Michael Mann, a professor at Pennsylvania State University who studies climate change, in his defamation suits against two bloggers who compared him to Jerry Sandusky, the former coach found to have sexually assaulted numerous boys.

The three-judge panel did not rule on the merits of the case but rejected an attempt by the bloggers to have the suits thrown out on First Amendment grounds.

The bloggers and their backers have maintained that the suits are seeking to limit their ability to criticize Mann, who is widely praised by many scientists for his work demonstrating climate change, but has been a target of those who question climate change. But Mann has argued that there is a distinction between critiquing his ideas and slandering him with false statements about the integrity of his work.

The D.C. appeals court agreed with Mann.

"Tarnishing the personal integrity and reputation of a scientist important to one side may be a tactic to gain advantage in a no-holds-barred debate over global warming. That the challenged statements were made as part of such debate provides important context and requires careful parsing in light of constitutional standards," the decision says. "But if the statements assert or imply false facts that defame the individual, they do not find shelter under the First Amendment simply because they are embedded in a larger policy debate."

The decision could be important for several reasons. Mann and others who work in climate change say they face unfair personal smears by those who deny climate change, and Mann has emerged as a scholar willing to fight back on the issue. Mann -- Distinguished Professor of Atmospheric Science at Penn State -- is also a prominent figure among scientists who work on climate change.

At the same time, the case is unusual. Mann and his supporters say that his suits are consistent with the principles of academic freedom and free expression. But many media and civil liberties groups have backed the bloggers, saying that Mann's suits could endanger free expression.

The 'Hockey Stick' Paper

Mann is best known as the co-author of papers in 1998 and 1999 that showed long-term changes in global temperatures. The 1999 paper was illustrated by a chart showing the rapid increase in temperature in the 20th century -- an increase that made the graph look like a hockey stick, prompting many people to refer to the paper by that image. The papers were considered significant by many scientists in showing the accelerating speed at which the climate has warmed in the last 100 years.

In 2009, thousands of private emails of scholars with ties to the Climate Research Unit of Britain's University of East Anglia were leaked and published online. Critics of climate change said that the emails raised questions about the integrity of some of the scholars, including Mann, suggesting that these scholars were trying to manipulate the data. Those who deny climate change called the leak and its aftermath "Climategate" and demanded investigations into the work of Mann and others. Mann and others said their emails had been taken out of context and didn't mean what critics said.

The blog posts in question did not just question Mann's conclusions, but suggested that Mann and his colleagues engaged in misconduct and deception, as some climate change skeptics alleged after the 2009 leaks.

One of the bloggers sued was Rand Simberg, who in 2012 wrote on a Competitive Enterprise Institute blog a post that included this paragraph: "So it turns out that Penn State has covered up wrongdoing by one of its employees to avoid bad publicity. But I’m not talking about the appalling behavior uncovered this week by the Freeh report [on Sandusky]. No, I’m referring to another cover-up and whitewash that occurred there two years ago, before we learned how rotten and corrupt the culture at the university was. But now that we know how bad it was, perhaps it’s time that we revisit the Michael Mann affair, particularly given how much we’ve also learned about his and others' hockey-stick deceptions since. 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 that could have dire economic consequences for the nation and planet."

The other blog post, by Mark Steyn and published on National Review's website, built on the first one. Steyn wrote, "Not sure I’d have extended that metaphor all the way into the locker-room showers with quite the zeal Mr. Simberg does, but he has a point. Michael Mann was the man behind the fraudulent climate-change 'hockey stick' graph, the very ringmaster of the tree-ring circus. And, when the East Anglia emails came out, Penn State felt obliged to 'investigate' Professor Mann …. And, as with Sandusky and [the late football coach, Joe] Paterno, the college declined to find one of its star names guilty of any wrongdoing. If an institution is prepared to cover up systemic statutory rape of minors, what won’t it cover up?"

A key part of the background cited by the appeals court in its decision was that a series of independent reviews were conducted of Mann's research after the emails were leaked. And these investigations not only backed his research but found no misconduct. These investigations were conducted and released in 2010 and 2011 -- before the blog posts.

"Following disclosure of the emails and the questions raised, Penn State, the University of East Anglia and five governmental agencies -- the U.K. House of Commons Science and Technology Committee, the U.K. Secretary of State for Energy and Climate Change, the Inspector General of the U.S. Department of Commerce, the U.S. Environmental Protection Agency, and the U.S. National Science Foundation -- issued reports after conducting inquiries into the validity of the methodology and research underlying the hockey stick graph and investigating the allegations impugning the integrity of Dr. Mann’s and other climate scientists’ conduct. The inquiries that considered the science largely validated the methodology underlying the hockey stick graph. None of the investigations found any evidence of fraud, falsification, manipulation or misconduct on the part of Dr. Mann. These reports were published in 2010 and 2011."

Based in part on this record, the court said that criticisms or opinions about Mann's methodology or findings or his recommendations on what to do about climate change would all be protected by the First Amendment. But stating as fact that Mann engaged in misconduct was not, the court said.

"The law distinguishes between statements expressing ideas and false statements of fact," the decision says. "To the extent statements in appellants’ articles take issue with the soundness of Dr. Mann’s methodology and conclusions -- i.e., with ideas in a scientific or political debate -- they are protected by the First Amendment. But defamatory statements that are personal attacks on an individual’s honesty and integrity and assert or imply as fact that Dr. Mann engaged in professional misconduct and deceit to manufacture the results he desired, if false, do not enjoy constitutional protection and may be actionable."

Attacks on Professors in a Contentious Time

Henry Reichman, professor emeritus of history at California State University at East Bay and chair of the AAUP's Committee A on Academic Freedom and Tenure (of which Mann is a member), blogged that the decision was "a victory for both academic freedom and science."

Reichman wrote that the decision was important "especially given the renewed danger to climate science and academic freedom posed by the incoming Trump administration."

But an editorial in National Review said the decision undermined the First Amendment.

"Properly understood, the First Amendment provides broad protection for free expression on matters of political and scientific controversy. It protects vigorous debate not only over the merits but also over the ethics of politically controversial scientific enterprises. In particular, it protects the right of all Americans -- scientists, journalists and even bloggers -- to express caustic criticism of scientific theories that purport to resolve hot-button political controversies on matters as sweepingly consequential as the extent and cause of global warming. The court’s decision yesterday badly neglects these principles."