"So how can scientists — or any plaintiff in a defamation case, for that matter — prove that their character has been defamed? In Weaver’s case, he pointed to the comments section of the Post’s site. In testimony to the court, he called them “crushing” — “people claimed he was a fraud; a liar; many people attacked him in phone, in shows. He did not know what to do to defend himself. All of this was based on a complete fabrication of facts,” Justice Burke wrote.
The court’s opinion even excerpted some of the comments, including this one: “Dr. Weaver is as big a hypocrite as he is a fraudster. He was front and center with his “global warming” lies and deception and should be made to repay his research monies and lose his tenure and degrees. A few centuries in jail would give him time to reflect on his part in the biggest fraud in the history of mankind. Perhaps he would settle for a 100-year sentence by giving evidence against his fellow fraudsters?”
Weaver claims he got so many negative comments that he created a “Wall of Hate” outside his office, where he posted copies of diatribes against him since 2010.
Though it doesn’t seem to have been addressed in U.S. courts yet, Weaver’s case was the first in Canada to opine on whether an online publication can be held liable for how readers react to their stories in the comments section, according to the Toronto Star. Though Justice Burke apparently accepted the Post’s argument that it removed vitriolic comments from its site, it did seem to factor into her decision to deem them defamatory. The Post had argued that they did not attack Weaver’s character."
The Thinkprogress explanation is that Weaver convinced the judge he had been defamed through drawing attention to the reaction of the commenters on the online article. It looks like the judge probably doesn't understand the concept of 'trolls' - people who express aggressive views on the internet may not genuinely hold that view, they may be expressing an exaggerated mean-spirited view simply for their own amusement.
One repercussion of this libel case is that newspapers might have to moderate online comments more vigorously, or not allow comments for certain types of article.
I believe that the National Post is going to appeal against the decision.