Michael Mann says he is being targeted as part of a well-funded campaign to discredit climate science research. AP

A prominent climatologist at the center of a libel battle with deniers of man-made global warming said Sunday that he was being targeted as part of a “well-funded” campaign to silence and discredit the “entire environmental movement.”

Speaking to Al Jazeera America just days after a court ruled that his defamation lawsuit against the libertarian think tank Competitive Enterprise Institute (CEI) and conservative news magazine National Review could proceed, Michael Mann, director of the Earth System Science Center at Pennsylvania State University, accused his detractors of resorting to old allegations that had been disproved time and time again.

On Thursday, a judge for the D.C. Superior Court ruled in favor of the scientist, denying a motion to dismiss the libel suit.

Mann sued the parties for defamation in 2012, after the CEI published and National Review republished statements accusing Mann of academic fraud and comparing him to convicted child molester and former Penn State assistant football coach Jerry Sandusky, as the CEI’s Rand Simberg put it, “except that 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.”

Judge Frederick H. Weisberg found that while “opinions and rhetorical hyperbole” are protected speech under the First Amendment, statements that call into question a scientist’s work could be understood as factual assertions that go to the “heart of scientific integrity.”

“To state as a fact that a scientist dishonestly molests or tortures data to serve a political agenda would have a strong likelihood of damaging his reputation within his profession, which is the very essence of defamation,” he said.

The CEI and National Review immediately filed an appeal and were supported by the American Civil Liberties Union, which filed an amicus brief.

Sam Kazman, general counsel for the CEI, maintains that the statements reflect an opinion. “The basis for those opinions must be looked at in context, of which is laid out in the blog post that is in question.”

He added that the basis for the original allegations came from the belief that Penn State University was found to have whitewashed Sandusky’s misdeeds. “Based on that, we thought there should be a reinvestigation as well.”

But Mann told Al Jazeera that accusations made by his detractors had already been roundly rejected by the scientific community, stemmed largely from groups with a vested interest with the fossil-fuel industry and were part of a larger, ongoing effort to discredit climate-change research.

“The tactics climate-change deniers employ is based on the idea that if they can discredit one prominent scientist, they can discredit the entire environmental movement. They’re also trying to serve notice to other scientists who think about speaking out,” he said.

Mann’s lawyer John B. Williams added that the invidious nature of some comments from climate-change deniers was “sidetracking the real debate, which is science-based.”

“We're hoping that we can dispense with the invective and get to the issue, which is science,” Williams told Al Jazeera. “It's unfortunate because most scientists wear lab coats, and when they're attacked, they go back into the lab. Michael Mann is the one scientist who has consistently spoken out.”

Mann became a target for climate-change deniers in 1999, when he published the “hockey stick” chart showing rising global temperatures. The graph, spanning 1,000 years and with a distinctive hockey-stick-like bend, depicted an abrupt rise in temperatures beginning around 1900, lending credence to the now almost universally accepted view that humans have influenced climate change.

Since then, Mann has been subject to frequent attacks by climate-change skeptics and those who oppose government attempts to reduce carbon emissions. He has documented his experiences in his book “The Hockey Stick and the Climate Wars.”

In 2009, Mann was among several scientists who had their private emails leaked in a scandal that came to be known as Climategate. More than 1,000 emails and documents were distributed, all belonging to scientists working at the University of East Anglia’s (UEA) Climatic Research Unit (CRU).

Those targeted and their supporters say the documents were cherry-picked in order to discredit them and the notion that global warming is caused by people.

Mann said that despite attempts to smear his research, several investigations by scientific authorities, including the National Academy of Sciences, have cleared him of any wrongdoing, finding no evidence of fraud or data manipulation.

“These allegations have been reviewed by the highest scientific authorities in the land. None of them found any evidence of impropriety. And yet they continue to be laundered by climate-change deniers,” he told Al Jazeera.

In fact, he said, the most recent report by the U.N. Intergovernmental Panel on Climate Change made an even stronger conclusion than his, finding that the recent warmth is unprecedented for at least the past 1,400 years.

Mann added that, given the numerous investigations from scientific authorities that cleared him, the CEI and National Review should have known that the statements they were making were baseless.

Williams told Al Jazeera that Mann’s detractors have deep ties to the fossil-fuel industry and are “largely funded by oil interests and anti-regulatory interests.”

Kazman said that his organization accepts funding from a broad range of groups in the U.S., except the U.S. government. “We take funding from groups representing different issues such as free-market and anti-regulation matters. That goes for groups supporting global-warming alarmism.”

But the group’s controversial stance on climate change has caused some of its sponsors to distance themselves. In 2007, ExxonMobil announced in a Wall Street Journal interview that it would no longer provide the think tank with funding because the oil giant had shifted its stance on climate change and now accepted the science behind global warming.

To be successful in the libel case, Manning’s legal team will have to show that the statements were published with “actual malice” toward a public figure, meaning the publisher made the statements with knowledge of their falsity and “reckless disregard for their truth.”

Arthur Spitzer, D.C.-area legal director for the ACLU, said Mann still has to prove his case after the latest ruling. “The judge did not say Professor Mann will win,” he added.