From Mann's Facebook page:
Dr. Mann, a Professor and Director of the Earth System Science Center at Pennsylvania State University, has instituted this lawsuit against the two organizations, along with two of their authors, based upon their false and defamatory statements accusing him of academic fraud and comparing him to a convicted child molester, Jerry Sandusky. [...]Virginia Attorney General Ken Cuccinelli clumsy attempt at "investigating" Dr. Mann's work was laughed out of court. Mann has been contemplating a lawsuit for months and is now moving forward, so he must feel he has a much stronger legal case than science's hapless enemies.
In response to these types of accusations, the U.S. Environmental Protection Agency, the National Science Foundation and seven other organizations have conducted investigations into Dr. Mann’s work, finding any and all allegations of academic fraud to be baseless. Every investigation—and every replication of Mann’s work—has concluded that his research and conclusions were properly conducted and fairly presented.
Despite their knowledge of the results of these many investigations, the defendants have nevertheless accused Dr. Mann of academic fraud and have maliciously attacked his personal reputation with the knowingly false comparison to a child molester. The conduct of the defendants is outrageous, and Dr. Mann will be seeking judgment for both compensatory and punitive damages.