The report said professor Michael Mann did not seriously deviate from accepted academic practices for proposing, conducting or reporting research.
The university inquiry in February dismissed three related allegations and recommended further investigation on a fourth. A five-member panel of professors dismissed that allegation outright in the report Thursday.
Mann has long been criticized by skeptics of man-made global warming theories. The review came after computer hackers obtained messages between U.S. and British scientists in November after emails were stolen from a server at the Climatic Research Unit of the University of East Anglia in Great Britain and posted on the Internet.The review also noted that Mann's work on the the Intergovernmental Panel on Climate Change received recognition (along with several hundred other scientists) in the form of the 2007 Nobel Peace Prize.
"Clearly, Dr. Mann's reporting of his research has been successful and judged to be outstanding by his peers. This would have been impossible had his activities in reporting his work been outside of accepted practices in his field," the report said.
Reacting to the news, Francesca Grifo from the Union of Concerned Scientists said the Penn State report "shows that universities and scientists have effective systems in place to police themselves," Grifo said. He added that the report should put the final coda on further investigations of Mann's work.
Virginia Attorney General Ken Cuccinelli had earlier pressed the University of Virginia, Mann's former employer, to obtain documents connected to Mann's employment at the school. UVA rejected Cuccinelli's demand.
"Michael Mann has been exonerated by multiple investigations," Grifo said in a statement. "It's clear that the Virginia attorney general's inquiry is baseless. This is another sad episode in a long history of politicians attacking scientists whose findings don't match their worldview."
Brian Gottstein, a spokesman for the Virgina D.A., said the office "will address any arguments that the University of Virginia has posed when we file our court brief on July 13. We do not intend to address issues outside of the courtroom."
Nonetheless, Mann said he was pleased that the final phase of the university's investigation had concluded by clearing him of any wrongdoing.
"These latest findings should finally put to rest the baseless allegations against me and my research," he said.
The Associated Press contributed to this report.