The institute in Oakland revealed its inquiry into the widening controversy in a terse statement posted on Wednesday on its website, hours after the San Francisco Chronicle said it was discontinuing an online blog that Gleick had been writing for the newspaper.

"The Board of Directors of the Pacific Institute is deeply concerned and is actively reviewing information about the recent events involving its president ... and documents pertaining to the Heartland Institute," the board statement said.

Gleick himself went public about the matter on Monday with a statement confessing that he had posed as someone else to obtain internal memos from the Heartland Institute, a think tank that argues skeptic positions, among them that climate change is not caused by human activity and that health hazards from tobacco have been exaggerated.

"My judgment was blinded by my frustration with the ongoing efforts - often anonymous, well-funded, and coordinated - to attack climate science and scientists ... and by the lack of transparency of the organizations involved," Gleick wrote in the statement, carried on the Huffington Post website.

Even before his mea culpa, Gleick, a renowned authority on global freshwater issues and winner of a MacArthur "genius" grant, had resigned last Thursday as chairman of the American Geophysical Union's Task Force on Scientific Ethics.

HARSH DEBATE

The scandal illustrates the increasingly harsh tone in the public and political debate over global warming, despite the consensus among mainstream scientists that rising levels of heat-trapping "greenhouse" gases, primarily caused by human activity, are altering the Earth's climate.

Heartland is among a group of skeptic organizations that have written extensively about the so-called Climategate case in which thousands of climate scientists' emails were hacked via the University of East Anglia in Britain.

The initial batch of those emails was made public in 2009 and a second set in December 2011 as a major climate conference was getting under way in Durban, South Africa.

Heartland cited those emails in claiming that the scientists who wrote them were trying to cover up evidence that cast doubt on human-caused climate change. Five separate investigations later found no wrongdoing on the part of the scientists. The source of the hacking was never identified.

Gleick has admitted that he obtained various internal Heartland documents - including a fundraising plan, a meeting agenda and a budget - by soliciting them under someone else's name, then forwarding them anonymously to members of the media and other climate scientists.

One of those lists dozens of major U.S. corporations from a wide range of industries as donors to the Heartland Institute, among them tobacco and energy companies. Another lists consultants Heartland has paid, one of them hired to devise a "climate education project" for public school children.

LUMINARY?

In a written statement on Monday, Heartland Institute President Joseph Bast acknowledged that all of the documents Gleick circulated were authentic except one, titled "2012 Heartland Climate Strategy," which Bast called a forged memo.

Gleick said he did not alter any Heartland document and said he received this document anonymously in the mail and that it provided the impetus for him to use a false identity in requesting additional records from Heartland in a bid to verify its source.

Bast said release of the allegedly forged document had damaged Heartland's reputation, and he threatened legal action. "Gleick's crime was a serious one," he wrote.

"The documents he admits stealing contained personal information about Heartland staff members, donors, and allies, the release of which has violated their privacy and endangered their personal safety," Bast said.

The incident has raised concern among climatologists that scientific credibility might be tarnished.

"We think it unfortunate that this has the potential to deflect the conversation away from the scientific consensus that the climate change is taking place," said Christine McEntee, executive director of the American Geophysical Union.

It also raised ethical questions for journalists. Alana Nguyen, executive producer of the San Francisco Chronicle's website, said the newspaper had discontinued Gleick's unpaid blog because it was part of a feature reserved for local "luminaries."

"We decide who is a luminary," she said. "That kind of admission is something that affects your reputation in the community, and we strive to have people with a good reputation in the community."

(Additional reporting by Deborah Zabarenko; Editing by Steve Gorman, Tim Gaynor and Sandra Maler)

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