WASHINGTON – A Republican-led federal probe of climate scientists at the National Oceanic and Atmospheric Administration found no evidence that they manipulated data, after leaked e-mails in 2009 sparked the "climategate" controversy.

The investigation was conducted by the inspector general of the Commerce Department. It reviewed the 1,073 leaked messages, particularly the 289 that were exchanged with NOAA scientists, and interviewed NOAA chief Jane Lubchenco and her staff about them.

"We did not find any evidence that NOAA inappropriately manipulated data," the inspector general concluded in a recent report. It also cleared Lucbhenco for testifying before Congress that the e-mails did not weaken the science of climate change.

The probe was requested by Sen. James Inhofe of Oklahoma, the top Republican on the environment committee, who has called global warming "the greatest hoax ever perpetrated on the American people."

The e-mails were stolen in late 2009 from the Climatic Research Unit at Britain's University of East Anglia. Inhofe and other climate change skeptics suggested it was proof of a conspiracy to corroborate a near-unanimous consensus among scientists that the earth is warming due in part to human activities.

The investigation is the latest in a series of prior probes that exonerated the scientists of any misconduct. They were also cleared by Pennsylvania State University, the InterAcademy Council, National Research Council and the British House of Commons.

The "climategate" controversy is believed to have weakened the prospects for a comprehensive energy and climate change bill in the Senate, after the House passed a version in the summer of 2009.

"None of the investigations have found any evidence to question the ethics of our scientists or raise doubts about NOAA’s understanding of climate change science," said Mary Glackin, the agency's deputy undersecretary for operations, according to the New York Times.

The results may have arrived at an important time as the Obama administration battles with the GOP-led House over the extent to which the Environmental Protection Agency should regulate greenhouse gas emissions.

While Republicans have introduced measures curtailing the ability of the EPA to limit pollution, the Commerce Department's investigation may boost Democrats' efforts to persuade the public that carbon emissions are having a dangerous impact on the planet.