Of all the pet causes by climate skeptics, the obsession with Michael Mann has always struck me as one of the weirdest. Most of the broader public probably has no idea who Mann even is—he was one of the climatologists who created the "hockey stick" graph that used various bits of proxy data (such as tree-ring samples and ice-core measurements) to reconstruct global temperatures over the past 1,000 years. Mann and his co-authors found that the current spate of global warming is unprecedented during that time span. Hence the term "hockey stick"—the temperature graph swerves sharply upward at the end.
Mann's work is important for giving us a fuller historical picture of the Earth's climate, but the case for global warming doesn't really hinge on it. The fact that the Earth is now hotter than it has been in the past 1,000 years tells us nothing about whether human activity is currently warming the planet. Those two things are logically separate. As Potsdam oceanographer Stefan Rahmstorf has explained, the argument that greenhouse gases are heating things up was built on detection and attribution studies that look at recent temperature trends and sift through different possible culprits, such as CO2 or solar variations or volcanoes. (See here for Rahmstorf's post, "What if the hockey stick were wrong?")
And yet, for some reason, Mann has consistently remained one of the most popular targets for attacks by climate skeptics. Back when they ran Congress, Republicans held hearings that tried to discredit his work. Critics pored through those "Climategate" e-mails from East Anglia for evidence that Mann engaged in scientific misconduct. For years, skeptics have scoured through tree-ring data and other assorted curiosities in an attempt to show that the hockey stick is fatally flawed. It seems like a lot of people out there have somehow convinced themselves that if Mann can be taken down, the case for global warming will crumble.
And yet, Mann's work has held up remarkably well. Back in 2006, the National Academy of Sciences looked into all the criticisms of the hockey-stick graph, and, while the resulting report lodged a few complaints, it basically affirmed Mann's research. Other scientists have replicated his findings: The 2007 IPCC showcased a whole slew of graphs suggesting that it's currently hotter than it has been in the last millennium. Studies and reconstructions continue to get refined, and the same results keep cropping up. What's more, the independent panels that have looked into Climategate have all cleared Mann of any charges of misconduct.
Now here's one more data point. Back in May, Virginia AG Ken Cuccinelli demanded that the University of Virginia turn over a broad range of data and scientific documents associated with Mann's grant requests back when he worked there (he's now at Penn State). Cuccinelli wanted to see if Mann had committed fraud against Virginia taxpayers by working on research he knew to be wrong. And today the results are in—the judge looking at the complaint was not impressed:
Judge Paul M. Peatross Jr. ruled that Cuccinelli can investigate whether fraud has occurred in university grants, as the attorney general had contended, but ruled that Cuccinelli's subpoena failed to state a "reason to believe" that Mann had committed fraud.
Lucky for Cuccinelli, he gets to try again. The odds seem pretty slim that his next subpoena will be the one that finally takes down the hockey stick, which means Mann will probably garner yet another headline noting that he's outlasted his critics once again. But the point of Cuccinelli's hunt isn't to carefully weigh the merits of Mann's research—there are perfectly sound scientific channels for doing that. It's to turn Mann (and, by association, the entire field of climatology) into a "controversial" figure whose work somehow must be suspect if there's this much uproar about it.