This quote says it all:
" Mann has proven adept over his career at making controversial, no, fraudulent adjustments .. to the raw data. "

For more detail see:
wattsupwiththat.com/2019/08/22/breaki...

Good comments on:
powerlineblog.com/archives/2019/08/mi...
eg.
Michael Mann “belongs in the state pen, not Penn State.” Dr. Tim Ball

Mann’s “hockey stick” graph purported to show sudden and unprecedented 20th century warming.
Mann sued Ball for libel in 2011 and chose British Columbia as the locale.
The court in British Columbia has dismissed Mann’s lawsuit with prejudice, and assessed costs against him.

Dr. Ball asserted a truth defense. He argued that the hockey stick was a deliberate fraud, something that could be proved if one had access to the data and calculations, in particular the R2 regression analysis, underlying it. Mann refused to produce these documents. He was ordered to produce them by the court and given a deadline. He still refused to produce them, so the court dismissed his case.
An appeal- No court in North America will allow a libel case to proceed where the plaintiff refuses to produce the documents that may show whether the statements made about him were true or false.
(My comment- dismiss with prejudice- the court tells Mann, your accusation of libel is not acknowledged, do not bring it again)