Pennsylvania State University (Penn State) climate scientist Michael Mann has been cleared of research misconduct following an inquiry by the Office of the Inspector General (OIG) at the National Science Foundation (NSF). The OIG agreed with the conclusions of a previous investigation by the university last year that "cleared [Mann] of any wrongdoing" and has now closed the case.

The charges against Mann stem from information in e-mail messages that were allegedly hacked from a University of East Anglia server and released early in 2009. Sceptics of human-influenced climate change charged that the "Climategate" documents indicated falsification and destruction of data, misuse of privileged information, and serious deviation from accepted research practices by Mann and other climatologists. Mann is best known for the widely accepted “hockey-stick graph” showing the recent surge in temperatures caused by climate change.

In July 2010 a panel assigned by Penn State cleared Mann of research misconduct and, as a matter of routine, sent a copy of its report to the OIG, which then requested additional information from the university and Mann to "review the report for fairness and accuracy". Each US federal agency has an OIG that provides independent oversight of the agency's programmes and operations and Mann says the interview with the Inspector General's office covered a range of issues related to "false allegations that had been made by climate-change deniers regarding the stolen e-mails."

On 15 August the OIG released its findings, which exonerated Mann and agreed with the conclusion reached by the university panel. "Lacking any evidence of research misconduct, as defined under the NSF Research Misconduct Regulation, we are closing the investigation with no further action," the OIG report says.

"I guess this is about the seventh investigation now that has confirmed that there is absolutely no evidence of impropriety either for me or any of my climate scientist colleagues," Mann told "It should be the final nail in the coffin given the unimpeachability of the NSF Office of the Inspector General. But unfortunately, many of our detractors will simply conclude that the imagined conspiracy runs wider and deeper."

Narrow questions

The decision, however, will likely not end more inquiries into the internal workings of the climate-change community. David Schnare, director of the Environmental Law Center at the American Tradition Institute (ATI) says that the NSF report "focused on a very narrow question and does not address a variety of questions about Mr Mann's activities that remain unexamined not only by NSF but by the other bodies that have looked into these matters".

The ATI, a conservative group that focuses on environmental issues, has called on the University of Virginia – where Mann worked from 1999 to 2005 – to release documents, including those not covered by the Freedom of Information act. "The policy debate associated with climate change requires more than a few pronouncements claiming to be based on science," Schnare adds. "To understand the validity and strength of the science, we need to understand the potential biases of the scientific work."

On 23 August the University of Virginia released 3800 pages of e-mails, yet Mann takes strong exception to efforts to release more documents. "I hope that the University of Virginia will respect the privacy issues of not just me but the 30-plus other scientists who are involved and fully defend the exemptions that exist in the law to protect scientists from fossil-fuel industry hired guns engaging in fishing expeditions intended to embarrass, smear and malign honest scientists," he says.