Last summer, when Louis J. Freeh’s commission came out with a withering report on Penn State’s failure to protect children from Jerry Sandusky, most commentators wrote about the effects on the school’s football program, or about child abuse. But a few drew a direct parallel between Sandusky and a Penn State meteorology and geosciences professor, Michael E. Mann ‘98PhD. Mann has never been accused of child abuse. He studies, among other things, the way the climate has behaved for the last 2,000 years.

“Mann could be said to be the Jerry Sandusky of climate science,” wrote Rand Simberg in a blog post for the Competitive Enterprise Institute, “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.”

The National Review Online’s Mark Steyn excerpted the post, weighed in approvingly, and took it to a bigger audience. Wrote Steyn, “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.”

A few days later, the Chronicle of Higher Education published a blog post by Peter W. Wood, president of the nonprofit advocacy group the National Association of Scholars, comparing Penn State’s handling of the Sandusky affair to the university’s finding that allegations of scientific wrongdoing by Mann were unfounded.

Given the inventively biting rhetoric of the political campaign against climate science, it’s not surprising that Mann was compared to Sandusky. What’s surprising is that invective at this level didn’t show up sooner.

Michael Mann is the scientist whose research produced, in 1999, the iconic and alarming “hockey stick” graph of average annual temperatures in the Northern Hemisphere over the past thousand years. He is also the US scientist most affected by the 2009 “E-mailgate,” when climate contrarians hacked into a group of scientists’ e-mails, took them out of context, and made them a cause célèbre.

Mann recently wrote a book about his experiences, The Hockey Stick and the Climate Wars. Over the last 15 years, as his research has gained prominence, he has been called a liar, a charlatan, and a scumbag. His critics have demanded his arrest. Blogger Marc Morano called for Mann and other scientists to be publicly flogged. Morano’s former boss, Rush Limbaugh, said they should be drawn and quartered.

Mann has found his office girded with police tape as a crime scene. He has received threats to himself and his family. He has been the focus of lawsuits seeking the public release of his e-mails. Mann is, arguably, the nation’s most hated climate scientist.

“I’ve been at the center of these attacks more than most others,” he says. “I think the intention is to make an example of me.”

Other climate scientists have faced attacks, too, including Benjamin Santer, a climate researcher at Lawrence Livermore National Laboratory in California, whose research showed the “human fingerprint” on the changing climate. But climate contrarians have a particular interest in Mann, Santer believes, because they think if they can bring him down, they can claim they dismantled the entire theory of climate change. “You go after the things that are important, that are iconic, that are visual, visceral, powerful, and easily interpretable,” Santer says, referring to Mann’s work and the hockey stick graph in particular. “And if you can’t attack the underlying science, you go after the scientist.”

State College, Pennsylvania, home of Penn State, is what Hollywood imagines in a college town. Tucked into a leafy valley in central Pennsylvania, the Penn State campus is a mix of neo-classical buildings and boxy, modern ones. On a Saturday morning, Mann and I make our way to a coffee house on the edge of State College’s small, bustling downtown. We’re here because of a phone call I’d made to him two years earlier.

On the eve of the 2010 midterm elections, it was clear Republicans would retake the US House of Representatives and possibly the Senate. Climate scientists worried that this meant another spate of hearings, similar to others under the GOP, in which their research would be misinterpreted and their attempts to answer cut off. Congressional hearings, as anyone who has been can attest to, are not about gathering information but about building an argument.

I interviewed Mann for the first time, by phone. He was calm and careful in his responses, and at the end of the interview, I asked whether he ever got angry. Most people who talk regularly to the press don’t admit to basic emotions and will deflect such a question. Mann waited a beat, but then he said: “Yes, I get mad. Many of us do. You’ll be seeing more scientists speaking out.”

Shortly afterwards, Mann put me in touch with colleagues who had just formed the Climate Science Rapid Response Team, an online ‘matchmaker’ for journalists and others seeking laymen’s explanations of climate phenomena and scientists specializing in the issues. At professional conferences and universities, panels and courses cropped up—their audiences often filled to overflowing—to teach scientists how to talk about their research in ways nonscientists would understand. Scientists and bloggers also formed a Climate Science Legal Defense Fund to help climatologists who face legal challenges from contrarian groups.

Fighting back has made Mann, who is not very good at hiding his feelings, even more of a target. “He fights back hard,” says Santer. “For him, it’s not just retreating to your office and closing the door but trying to mobilize friends, colleagues, and fighting back legally. To draw a line in the sand and say, ‘You are wrong and you claim these untrue things about me and my research’—that takes guts.”

Mann himself began his career, 20 years ago, more skeptical than some of his colleagues about what the evidence showed regarding the human impact on the climate. Now 47, bald and with flecks of gray in his goatee, he has become, as he puts it, an “accidental public figure.”

Like most climatologists, Mann sought to “let the science speak for itself.” Anything else seemed like advocacy, which scientists largely eschew. “I started out as a scientist who didn’t really believe there was much of a role for a scientist to play in public policy,” he says, over coffee. “How my thinking has evolved has come through being a direct witness to these attacks. It’s awakened me to the war being waged against science and climate scientists by those with an axe to grind. And if scientists don’t push back, we’re ceding ground to those interests.”

Pushing back, to Mann, would involve “advocating for the proposition that policy should be informed by an objective assessment of the science.” But to critics like Morano, Mann is a glaring example of someone whose politics have shaped his research and who is spearheading a massive effort to dupe the American people. “The ‘climate con’ to which I refer is a lavishly funded climate machine that is lobbying for laws and uses every bit of data or new study to proclaim ‘it’s worse than we thought’ or we must act now,” Morano wrote in an e-mail. “Man-made global warming fears are a grand political narrative, not science.” Morano, the communications director of the advocacy group CFACT (Committee for a Constructive Tomorrow), has a BA in political science and has worked as a journalist and national television reporter and producer. He continued: “Mann is the embodiment of everything that is wrong with climate science today. He is a hardcore political activist, very thin skinned, does not take criticism well at all, and he surrounds himself within his own little world of supportive warmist activists.”

Mann doesn’t like the word “skeptic” to describe Morano and others campaigning against him. He and other scientists point out that science encourages skepticism, asking pointed questions and looking for evidence again and again. “So much of climate denial comes from ideology,” Mann says, his voice hardening. “If you’re only voicing skepticism about science that goes against your ideology, then that’s not true skepticism.”

Mann came to his own views on climate, he says, through his research. The second of three sons of a math professor at the University of Massachusetts–Amherst and a stay-at-home mom, Mann studied physics and applied math at the University of California–Berkeley before coming to Yale in 1989 to earn a PhD in physics.

From childhood, he had been interested in what he calls “big picture science”: questions related to the origins of the universe and fundamental theoretical physics questions. After finishing his coursework at Yale, he was on a track to study semiconductor devices. But they didn’t seem to address those questions. So he opened Yale’s course catalog and found that Barry Saltzman, in the department of geology and geophysics, was applying physics to understand the Earth’s climate. After meeting with Saltzman, Mann began work in geology and geophysics, and by the early 1990s, he was deep into paleoclimate research, the study of the planet’s climate in the geologic past.

At the time, climate science “was just coming of age,” Mann has written. By the mid-1990s, the United Nations Intergovernmental Panel on Climate Change had determined through its review of the research that there was “a discernible human influence on climate.” The questions that climate scientists debated at the time were the scale of human influence and if it was indeed detectable. Saltzman was initially skeptical. Other eminent scientists, such as NASA’s James Hansen, had concluded the evidence was already in.

“I was cautious,” Mann recalls. “I felt that Hansen was too far out on a limb.”

Mann thought that scientists had perhaps not given enough consideration to the naturally occurring variability of the Earth’s climate over time—an argument that most climate contrarians now use. He began researching variability in the Northern Hemisphere over increasingly long periods of time: first a century, then from 1400 to the present, and finally, in the postdoctoral project that yielded the hockey stick, for the last millennium.

Recorded temperature using thermometers extends back about 140 years. To gather climate information deeper in the past, climatologists work to reconstruct past temperatures by using so-called proxy data. Among these are tree rings (their size indicates growth rates, and trees grow faster in warmer weather), and the proportions of different oxygen isotopes (which are affected by temperature) in corals and ice cores.

In 1999, Mann produced a paper with two other scientists; it relied on multiple kinds of proxy data to reconstruct climate in the past and to identify events that could have produced temperature anomalies, such as large volcanic eruptions. Published in Geophysical Research Letters and entitled “Northern Hemisphere Temperatures during the Past Millennium: Inferences, Uncertainties, and Limitations,” it came with many caveats. Still, the reconstruction of temperatures indicated an anomalous rise in temperature through the latter half of the twentieth century compared with previous centuries, and suggested that the 1990s “were likely the warmest decade and 1998 likely the warmest year of the millennium,” Mann writes.

Mann has written that it was a colleague who first noted the graph’s resemblance to a hockey stick lying flat: the first 900 years of data form a squiggly but consistent line, akin to the stick’s handle, before temperatures shoot up at the beginning of the twentieth century, like the blade. The graph became an icon, summing up a millennium of climate history in a simple, easily grasped image. The study was featured prominently in a 2001 UN report, and since then, the reaction to it has been widespread and unrelenting among climate contrarians.

Over the next decade, articles appeared periodically with the intention of pointing out fatal errors in Mann’s work, usually by scholars and organizations funded by fossil fuel companies. In the meantime, Mann says, more than a dozen other studies using different mixes and types of data, such as borehole temperatures in Antarctica, have validated his findings. The basic hockey stick pattern has been reproduced several times over, creating what Mann calls “a veritable hockey league” (see charts, above).

“The hockey stick was the least interesting of the research we did,” he adds, with a small laugh; originally, it was the role played by events like volanic eruptions that drove the research. “You could take away the hockey stick, because so much research now points to the climate changing.”

But climate contrarians in Congress began homing in on Mann during the Bush administration. In 2005, then-chair of the House of Representatives Energy and Commerce Committee, Representative Joe Barton (R-TX), sent a letter to Mann, his coauthors, and two other scientists, informing them that he was launching an investigation into the hockey stick study because of “methodological flaws and data errors.”

Despite an outcry from the scientific community, media, and Republicans such as Senator John McCain (R-AZ) that he was harassing scientists, Barton commissioned a report on Mann’s 1999 study. The report criticized the hockey stick paper—only to become mired later in allegations of plagiarism and misconduct.

The brushfire that keeps flaring for Mann and other climatologists, however, is the E-mailgate scandal.

On November 17, 2009, Mann awoke to find out that private correspondence he and other scientists had sent to the University of East Anglia’s Climatic Research Unit in the United Kingdom had been hacked and individual phrases disseminated in a way that implied they had falsified their findings. Climate contrarians focused on the words “trick” and “hide the decline”—which some said indicated that Mann had erased data that had shown a decline in twentieth-century temperatures. This was the smoking gun proving climate change was a hoax, critics asserted. The media, for their part, lapped it up.

The reality is different. The e-mail with the words “trick” and “hide the decline” was sent by Phil Jones, head of East Anglia’s Climatic Research Unit. It read, “I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (i.e. 1981 onwards) and from 1961 for Keith’s to hide the decline.”

The “trick” Jones was referring to was Mann’s decision to show two kinds of data on the same chart—data from temperature proxies (like the tree rings) and actual temperature data (from thermometers). This was a trick in the sense of a clever move, not a deception: all the data were labeled, so readers could see where the proxy data end and the temperature records begin.

As for “hide the decline,” Jones wasn’t referring to declines in temperature; he was referring to a drop seen in certain types of tree-ring data after 1960. And he wasn’t referring to Mann’s work—but to that of another scientist, Keith Briffa of the University of East Anglia. Pre-1960, Briffa’s tree-ring density records track the temperature records. Post-1960, there is a decline in the response of certain trees to temperature (possibly due to pollution): the actual recorded temperatures are consistently higher than what the tree-ring data would predict. The temperature records are the more important and reliable data, so Briffa had to discard the tree-ring “decline” records. But the decline wasn’t hidden. It was clearly discussed and labeled in Briffa’s paper. And Mann’s paper didn’t rely on any of those data.

Since then, a half dozen independent inquiries in the United States and United Kingdom have cleared the climatologists involved of scientific wrongdoing.

As scientific consensus grew around the idea that climate change is happening and human activity is the main cause of it, the resistance to climate science turned sharper and marshaled millions of dollars behind it. Petrochemical interests have funded think tanks, politicians, and legal groups that seek to take apart the science and the scientists.

Over the last several years, a growing core of scientists has pushed back. In 2010, 255 members of the National Academy of Sciences issued a public letter that called “for an end to McCarthy-like threats of criminal prosecution against our colleagues based on innuendo and guilt by association, the harassment of scientists by politicians seeking distractions to avoid taking action, and the outright lies being spread about them.”

Mann was among the first to throw off the gloves—at Congressional hearings, in the media, on the Internet, and in court. His book The Hockey Stick and the Climate Wars explains his research and maps in detail the network of political and economic interests fighting climate science. He has intervened in litigation that was aimed at disclosing still more of his e-mails, and the cases so far have been resolved in his favor. He has also sued the Competitive Enterprise Institute and the National Review for damages in connection with articles accusing him of fraud and comparing him to Jerry Sandusky. (The National Review responded with the headline “Get Lost.”) He takes to the airwaves, Twitter, and Facebook to weigh in on the latest important research published and the latest attack on science.

Some of Mann’s allies have suggested that perhaps he should tone it down. It’s a suggestion he brushes off. “I would say calmly to them,” he says, “that they haven’t walked a mile in my moccasins.”

He adds: “This isn’t just an academic discussion we’re having. There are real implications about the kind of world we are leaving for our children. It’s an ethical issue, and we ignore it at our peril.”

In August 2010, the Federal Bureau of Investigation sealed off Mann’s office after he got a letter with a mysterious white powder in it. The FBI lab found it was cornmeal. But it arrived amidst a regular flow of hate mail and death threats, including an e-mail that read, “You and your colleagues who have promoted this scandal ought to be shot, quartered, and fed to the pigs along with your whole damn families.”

The anonymity of the Internet lets such rage seep through. Face to face, Mann says he gets something else: people who come up to him in the supermarket, people he doesn’t even know, who tell him they want to thank him for his work.

He takes even more hope from the next generation of scientists. “I think the idea that the attacks would have a chilling effect is backfiring,” he says. “I can’t count how many postdocs and students who have told me that they see public participation as part of their roles as scientists. And that’s something our generation didn’t have.”