The American scientist who produced the "hockey stick graph" showing a sharp rise in global warming was largely cleared of misconduct by an academic investigation today.

The board of inquiry at Pennsylvania State University said it found no evidence that Michael Mann, a leading climatologist, had suppressed or falsified data, tried to destroy data or emails, or misused information. It will convene a second panel to investigate whether he had violated academic practices, including those governing exchanges between scholars.

The university ordered the investigation by three senior faculty members after Mann's name appeared in more than 375 of the hacked emails from the University of East Anglia's climate research unit. Climate change sceptics jumped on one email which describes Mann's solution to a problem as a "trick", a shorthand among scientists and mathematicians, as evidence of an effort to distort data.

The panel dismissed the charge. "The so-called 'trick' was nothing more than a statistical method used to bring two or more different kinds of data sets together in a legitimate fashion by a technique that has been reviewed by a broad array of peers in the field," the panel said.

It also cleared Mann of purposely hiding or destroying email relating to an IPCC climate change report.

It said it found nothing to support the charge that Mann had conspired with like-minded scholars to block competing scholars.

Mann said he was pleased with the decision. "After a thorough review, the independent Penn State committee found no evidence to support any of the allegations against me. Three of the four allegations have been dismissed completely," he said. "Even though no evidence to substantiate the fourth allegation was found, the university administrators thought it best to convene a separate committee of distinguished scientists to resolve any remaining questions about academic procedures. This is very much the vindication I expected since I am confident I have done nothing wrong."

Environmental organisations also welcomed the decision, saying the controversy over the climate hack had been a dangerous distraction.

"This is a step in the right direction that should help us move past the manufactured controversy over the stolen emails," said Peter Frumhoff, director of climate policy at the Union of Concerned Scientists. "The truth is that global warming is here, it's dangerous, and it is already affecting us."

But Mann has become a favourite target of climate change deniers because of the powerful image of his hockey stick graph, which shows a sharp rise in average global temperature in the 20th century – and they are unlikely to stop now. The graph assembled data from hundreds of studies of past temperatures using tree rings, lake sediment, and glacier ice cores. It was first published in 1998.