A Pennsylvania State University committee Wednesday cleared climate researcher Michael Mann of professional-misconduct charges but said it would further investigate whether the scientist "deviated from accepted practices."
The inquiry was prompted by events in November, when hackers exposed more than 1,000 e-mail messages exchanged among climate scientists, many of which were sent to and from Mann.
No formal allegations were made against Mann, but the university decided to launch the inquiry after a flood of public complaints and accusations against the climatologist.
Mann is best known for using tree rings and other indirect measures to reconstruct Earth's climate over centuries past. Those reconstructions showed temperatures shooting upward in the 20th century in a graph that became known as the "hockey stick."
Wednesday's report, though welcomed by Mann, did not satisfy his critics, who immediately called the university's investigation a "whitewash."
The university panel was chaired by vice president for research Henry C. Foley, but neither he nor his three co-authors would comment on the report or explain why they were calling for a further investigation.
The hacking incident occurred days before world leaders convened in Copenhagen to work out a treaty for curbing carbon emissions.
A number of individuals read through the e-mail messages, picking out alleged examples of misconduct by Mann and others. These were used in blogs, op-eds and other public forums to discredit the consensus view in the field that human-generated greenhouse gases were becoming a major contributor to climate change.
The issue became known as "climategate."
The e-mail message that has most often been held up as evidence against Mann was written by a colleague. It referred to a "trick" Mann used 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.
University spokesman Bill Mahon said Penn State had received a torrent of complaints from people outside the university who were concerned that something inappropriate had happened.
Many of the complaints were anonymous e-mail, said Mahon, from "folks who have no facts -- more along the lines of, 'Fire Michael Mann, he's a horrible person.'"
After sifting through the e-mail, the panel divided the allegations into four categories:
• Falsifying or suppressing data.
• Deleting, concealing, or otherwise destroying e-mail associated with a report by the Intergovernmental Panel on Climate Change.
• Misusing privileged or confidential information.
• Deviating from accepted practices within the academic community.
The panelists concluded that there was "no credible evidence" to charge Mann on any of the first three allegations, but they did not have enough information to draw a conclusion on the fourth. The report did not explain what was meant by "deviating from accepted practices," though it questioned whether the statements in the exposed e-mail sullied the reputation of the university or of science in general.
Spokesman Mahon said the panel was making no specific charges. "It wasn't indicating there was any guilt or lack of guilt. ... We think we need more information."
The fourth complaint will be investigated by five prominent Penn State scientists: a computer scientist, a physicist, a biologist and two anthropologists.
Mann said he was pleased with the report. "They absolved me of any wrongdoing on the three serious counts," he said. He added that he wasn't sure what the final charge meant or why he had not been cleared of it.
"Maybe they felt it would be more appropriate for a panel of my peers, rather than a group of administrators," he said.
Some are calling into question the panel's conclusion. The Commonwealth Foundation, a conservative group, took out a full-page ad in the student newspaper, Mahon said. "They suggested the inquiry was dishonest and the results were a whitewash."
Within hours of the release of the report, Fox News columnist Steve Milloy issued a statement calling Penn State's inquiry a whitewash.
"Comically, the report explains at length how the use of the word 'trick' can mean a 'clever device,'" wrote Milloy, who authors the Web site junkscience.com. "The report ignores that it was a 'trick ... to hide the decline.'"
Others have pointed out that the phrase "hide the decline" was used by a different researcher, not Mann, to refer to an apparent decline in temperatures reflected in a certain type of tree ring, not to a decline in global temperatures or anything Mann used in his data.
In 2006, Mann's work was reviewed by a panel assembled by the National Academy of Science, following allegations against the statistical methods he used to graph global temperatures. That report found no evidence of misconduct.
Most climate scientists have defended Mann. Michael Oppenheimer, a climatologist at Princeton University, called Mann a good scientist and an honest one. "The only lack of integrity in this case is on the part of those who stole the e-mails," he said.
Explore further: Most of Hawaii's coral recover from mass bleaching