As described in Politico:
[T]he lawsuit may well be dismissed down the road. But the longer it continues, the more likely it becomes that Mann will eventually prevail, either by forcing an expensive settlement or by prevailing in court and winning a substantial penalty from the defendants. ... It's doubtful that could survive either outcome. Small magazines often lose money and only rarely manage to break even. They certainly don't have substantial legal budgets, let alone cash to cover an expensive payout. Indeed, in 2005, Buckley said the magazine had lost $25 million over 50 years.
Two lessons, maybe:
1) Opinion is protected speech as long as it can't be subject to a "truth test" in the real world. I'd say a comparison of someone's scientific research to serial child molestation is a degree of defamation that can be "truthed."
2) If you don't have deep pockets, the very prospect of a libel suit can discourage you from speaking your mind. A big lawsuit might destroy a small publication.
Full disclosure: I think climate change is happening, and I question the motives of those who deny it.