A British panel on Wednesday exonerated the scientists caught up in the controversy known as Climategate of charges that they had manipulated their research to support preconceived ideas about global warming.
But the panel also rebuked the scientists for several aspects of their behavior, especially their reluctance to release computer files supporting their scientific work. And it declared that a chart they produced in 1999 about past climate was “misleading.”
The new report is the last in a series of investigations of leading British and American climate researchers, prompted by the release of a cache of e-mail messages that cast doubt on their conduct and raised fresh public controversy over the science of global warming.
All five investigations have come down largely on the side of the climate researchers, rejecting a number of criticisms raised by global-warming skeptics. Still, mainstream climate science has not emerged from the turmoil unscathed.
Some polls suggest that the recent controversy has eroded public support for action on climate change, complicating the politics of that issue in Washington and other world capitals. And leading climate researchers have come in for criticism of their deportment, of their episodic reluctance to share data with climate skeptics, and for not always responding well to critical analysis of their work.
“The e-mails don’t at all change the fundamental tenets of the science,” said Roger Pielke Jr., a professor of environmental studies at the University of Colorado. “But they changed the notion that people could blindly trust one authoritative group, when it turns out they’re just like everybody else.”
The researcher at the center of the controversy was Phil Jones, a leading climatologist who had headed the Climatic Research Unit of a British university, the University of East Anglia. He had stepped down temporarily pending results of the inquiry, but was reinstated on Wednesday to a job resembling his old one.
The university solicited and paid for the new report, which climate skeptics assailed. “This is another example of the establishment circling the wagons and defending their position,” said Myron Ebell, director of energy and climate change policy at the Competitive Enterprise Institute in Washington.
The Climatic Research Unit, often referred to as C.R.U., has played a leading role in efforts to understand the earth’s past climate. Embarrassing e-mail messages sent by Dr. Jones and other scientists were purloined from a computer at the university in November and posted to the Internet, prompting a round of accusations.
Some of the scientists were forced to admit to poor behavior, such as chortling about the death of one climate skeptic. But were the researchers guilty of any scientific misconduct?
“On the specific allegations made against the behavior of C.R.U. scientists, we find that their rigor and honesty as scientists are not in doubt,” said the new report, led by Muir Russell, a retired British civil servant and educator.
The University of East Anglia welcomed the findings on Wednesday, declaring that an unjust attack on its scientists had been found spurious. Dr. Jones — who had said he considered suicide after the e-mail messages emerged — issued a more muted statement, saying he needed time to reflect. “We have maintained all along that our science is honest and sound, and this has been vindicated now by three different independent external bodies,” Dr. Jones said.
Last week, the second of two reviews at Pennsylvania State University exonerated Michael Mann, a scientist there who was also a focus of the controversy.
The latest report was by no means a complete vindication. Echoing the findings of an earlier report by a parliamentary committee in London, the reviewers criticized the scientists at the Climatic Research Unit for consistently “failing to display the proper degree of openness” in responding to demands for backup data and other information under Britain’s public-record laws.
On one of the most serious issues raised by the e-mail messages, the Russell panel did find some cause for complaint, but it did not issue the robust condemnation sought by climate skeptics.
The issue involved a graphic for a 1999 United Nations report, comparing recent temperatures with those of the past. Dr. Jones wrote an e-mail message saying he had used a “trick” to “hide” a problem in the data. After the e-mail messages came out, Dr. Jones said he had meant “trick” only in the sense of a clever maneuver.
The Russell panel concluded that the data procedure he used was acceptable in principle, but should have been described more fully, and his failure to do so had produced a “misleading” graphic.
The issue involved an effort to reconstruct the climate history of the past several thousand years using indirect indicators like the size of tree rings and the growth rate of corals. The C.R.U. researchers, leaders in that type of work, were trying in 1999 to produce a long-term temperature chart that could be used in a United Nations publication.
But they were dogged by a problem: since around 1960, for mysterious reasons, trees have stopped responding to temperature increases in the same way they apparently did in previous centuries. If plotted on a chart, tree rings from 1960 forward appear to show declining temperatures, something that scientists know from thermometer readings is not accurate.
Most scientific papers have dealt with this problem by ending their charts in 1960 or by grafting modern thermometer measurements onto the historical reconstructions. In the 1999 chart, the C.R.U. researchers chose the latter course for one especially significant line on their graph. This technique was what Dr. Jones characterized as a “trick.”
The recent season of controversy included close scrutiny of the Intergovernmental Panel on Climate Change, the United Nations body that produces a major review of climate science every few years.
The Russell panel found little reason to question the advice that the British scientists had given to the climate panel, or the conclusions of that body. The panel declared in 2007 that the earth was warming and that human activity was the major reason.
But small errors in the 2007 report keep coming to light. A review issued earlier this week by the Netherlands Environmental Assessment Agency found several, including a case in which the panel overstated the potential impact of global warming on fish catches.
The Netherlands agency also found that the climate change panel had tended to emphasize the negative effects of global warming while playing down positive ones, like greater tree growth in northern climates. It recommended better balance and a greater emphasis on fact-checking.
“The idea that these things could be perfect is a fallacy,” said Gavin Schmidt, a climate researcher at Columbia University. Christopher B. Field, an ecologist at the Carnegie Institution for Science and a leader in the United Nations climate body, said he foresaw an opportunity “to really do a better job in characterizing what we know and what we don’t know” in the group’s next report, due in 2014.
Yet another evaluation of the panel’s work is under way, with results due in August.
Dr. Pielke, who is largely persuaded by the mainstream consensus on climate change, has criticized both climate skeptics and the scientific community for the tone of their debate.
“It has been dominated for a number of years by people at the poles — the most activist scientists emphasizing alarm, versus the most ardent skeptics saying we don’t have to do anything,” Dr. Pielke said. “This recent controversy has opened the eyes of a lot of people to a much richer tapestry of views on climate policy that are out there, which I think is a good thing.”
