As others have often noted, such a lawsuit runs up against the hardest standard for libel cases - New York Times v. Sullivan. Basically, if a "public figure" (which Mann essentially admits he is in paragraph 14) sues a "media defendant" (which fits most or all of the defendants here), he can't recover a penny of damages unless he proves "actual malice" - that is, he's got to prove that the person who made the statements knew they were false, or acted with "reckless disregard" as to their falsity. (The latter was important in the original case, because at least one statement printed by the Times actually was false.) Naturally, in reading the complaint, I was interested to see how Mann was going to argue that.
The answer is found in paragraph 21:
Following the publication of the CRU emails, Penn State, the University of East Anglia...and five governmental agencies...have conducted separate and independent investigations into the allegations of scientific misconduct against Dr. Mann and his colleagues. Every one of these investigations has reached the same conclusion: there is no basis to any of the allegations of scientific misconduct or manipulation of data.Paragraph 30 goes on to say that "well-respected journalists," the pop-science magazine Discover, and (drumroll) the Union of Concerned Scientists all said nasty things about Steyn, NRO, and CEI "in the wake of these attacks."
Now, as it happens, Mann attaches the offending articles from CEI and NRO. And both these articles explain briefly why they don't agree with the "independent" investigations exonerating Mann. The CEI article includes links to the sources for their belief, and Steyn makes a pretty obvious reference to the "Mike's nature trick" Climategate email.
So there you have it. If the government conducts a bunch of investigations, and you don't believe them, and you don't believe left-wing advocacy groups and an editorial in a pop-sci magazine, according to Mann you've got "actual malice." Believe the government - or get sued and pay damages. The Green left has wandered into strange territory indeed!
A few other thoughts from me. In exhibit C (NRO's response to Mann's original threat), Rich Lowry comments that discover in this case may discomfit Mann considerably. That may well be true. Truth is a defense to libel claims, so any evidence that shows Mann is a "data manipulator" is relevant, and he can be made to disgorge it.
But the defendants should still try to have this complaint dismissed before discovery begins. The complaint itself and the attached documents, it seems to me, make a good case for that - a complaint has got to state facts which, if true, entitle the plaintiff to relief. "He had actual malice" is a legal conclusion, not a fact; "the government did investigaitons and said I'm innocent" is a fact, but in light of the attachments is a "so-what?" fact. If they can't get it dismissed, they should above all things try to win on summary judgment - show the judge that Mann has no evidence to prove Steyn disbelieved (or didn't care about the truth of) what he was writing - and not be tempted by courtroom glory, that serpent's eye that charms only to destroy.
Experience has taught me to be against using trials for spectacles. If you're suing someone, you're there to get the money. If you're getting sued, you're there to not have to pay. If you're facing possible criminal charges - you're there to avoid the punishment, or as much of it as you can. You are not there to tell the world about something - there are many forums for that. If discovery turns up the kind of data that Mann is wont to refuse, well and good, but that should never become the purpose of defending the lawsuit. Litigation, civil and criminal, goes its own strange ways, and does strange things to people - shrinks them if they are not careful.
The same goes for the discovery process. It occurs to me that Mann may be playing a slightly deeper game here. To be sure, the defendants can demand documents, e-mails, etc. from him to show he manipulated data; but he can insist the defendants themselves submit to depositions. Now, really, all Steyn has to say is "I read this book and I chased links at this website and I believed them over the government" - and if Mann doesn't have proof to the contrary, he is (or ought to be) hosed.
But maybe his lawyer's planning to grill Steyn at deposition (rather than trial) on his lack of science background, to make the deposition testimony itself embarrassing ("So, you didn't graduate college? - So, you're not a statistician? - So, you just believe these guys over those? - Because they fit your ideology...?") - and leak it publicly, to make him look foolish. I haven't had to deal with the issue of whether that's forbidden in civil litigation, but I have a hard time believing a deposition from this case would stay secret if it had polemically useful material.