"I knew ultimately I'd be vindicated by a fair review of the facts," Mann said. "Now we can all hopefully get back to doing research."
This case is unusual in that the investigation was prompted by calls and e-mail from university alumni, state and local politicians, and others, according to a draft of the report. Usually, universities launch scientific fraud investigations only when specific charges are brought by a colleague.
A draft of the report released Thursday concluded that "the Investigatory Committee after careful review of all available evidence, determined that there is no substance to the allegations against Dr. Michael E. Mann, professor, Department of Meteorology, Pennsylvania State University."
Mann is best known for advancing the use of tree rings, ice cores, corals, and other indirect measures to reconstruct the global climate over the last millennium. His graphs tracing global temperature history have been dubbed the "hockey stick" because the temperatures appear to rise sharply during the last century.
According to the report, the panelists decided that without any formal charges against Mann, they would have to use the various complaints to "synthesize" allegations against him. They came up with four categories:
Falsifying or suppressing data.
Deleting, concealing, or otherwise destroying e-mail associated with a report by the Intergovernmental Panel on Climate Change, the main international scientific group charged with informing policy.
Misusing privileged or confidential information.
Deviating from accepted practices within the academic community.
The e-mail message that has surfaced most often in public criticism of Mann was written by colleague Phil Jones at East Anglia University. Jones referred to a "trick" Mann had used in a published paper to display some of his data. The panel concluded that this referred not to any attempted deception but to a technique for displaying data graphically.
Jones also wrote of an attempt to "hide the decline" which critics say refers to a decline in global temperatures. But read in context, Jones was clearly referring to a particular type of tree-ring datum used not by Mann but another researcher.
The initial Penn State inquiry relied on an interview with Mann as well as several prominent scientists, including Texas A&M climatologist Gerald North, who headed a 2006 panel investigating Mann's work for the National Academy of Sciences
In February, a report of the university's initial inquiry cleared Mann on the charges of falsification, concealing data, and misusing privileged information. But the panelists felt they didn't have enough evidence to determine whether Mann deviated from accepted practices. Another panel was assembled to investigate this last charge.
As reported Thursday, that investigation focused on stolen e-mail messages suggesting that Mann refused to share some of his partially processed data, and that he forwarded an unpublished paper without the author's specific permission.
The panelists interviewed a number of scientists inside and outside Penn State, including MIT's Richard Lindzen, an outspoken critic of Mann and his work.
Mann said the raw data he used were all publicly available. He said there was only one group that requested more data than he was unwilling to send - led by Toronto businessman and minerals consultant Stephen McIntyre.
Mann said he initially tried to accommodate their requests though he felt McIntyre was harassing him without making a good-faith effort to check or reproduce his work.
In response to another charge, Mann admitted to forwarding an unpublished paper by a close colleague because he assumed the author of the paper wouldn't mind.
After studying the e-mail messages and conducting a number of interviews, the Penn State panelists came to the unanimous conclusion that none of this "deviated from standard practice" in climatology.
Penn State's clearing of Mann was "absolutely no surprise," said Caspar Ammann, a climate researcher at the National Center for Atmospheric Research (NCAR) in Colorado. Ammann said in 2002 he set out to reproduce Mann's "hockey stick" graph and found the data he needed were all publicly available.
Not only was Ammann able to reproduce the graph showing unusual warming in the 20th century, but he also said Mann's was not the first such graph to show this.
Ammann said that Mann and McIntyre disagreed over the methods used to center the data, but the end result was a hockey stick either way.
MIT's Lindzen said he still believed Mann committed misconduct. "The fact that he didn't reveal data unless forced to - that's not exactly normal," he said. Of the panel's concessions, he said: "I find it peculiar but not altogether surprising. Institutions tend to try and defend people."
Nearly all climate scientists have been sympathetic to Mann and the other English researchers whose private e-mail messages were exposed. Some have wondered why the "scandal" isn't centered on the illegal hacking of private e-mail.
Authorities have not revealed who was responsible for the stolen e-mail.
Several climate researchers have also expressed surprise at the way Climategate inflated the importance of Mann's work as evidence for climate change. Mann himself says it's just one of many lines of evidence.
In an interview earlier this year, Texas A&M's Gerald North said he would remain concerned about global climate change even if all the researchers deriving "hockey stick" graphs turned out to be wrong. Climate models, he said, are becoming increasingly convincing. And it's becoming harder to ignore the retreat of glaciers and shrinkage of sea ice.
The large-scale pattern of warming is what makes human-generated greenhouse gases a more likely cause than changes in the sun, said NCAR's Ammann. Solar changes tend to heat the upper atmosphere, while greenhouse warming tends to heat the oceans and lower atmosphere, leaving the upper atmosphere colder. And that, he said, is exactly the pattern that scientists are observing.
Contact staff writer Faye Flam
at 215-854-4977 or firstname.lastname@example.org.