Supporters say a top U.S. climate scientist is being subjected to a political witch-hunt to undermine his work on the threat to polar bears because of global warming. Dr. Charles Monnett, a wildlife biologist with the U.S. Bureau of Ocean Energy Management, was recently placed on administrative leave in connection with an investigation launched by the Department of Interior. U.S. officials have denied the investigation is politically motivated and claim it has nothing to do with Dr. Monnett’s scientific work. But transcripts from a session with investigators in February show Dr. Monnett has been thoroughly questioned about his studies of polar bears. Climate change experts and activists, including former Vice President Al Gore, have cited Dr. Monnett’s work. The group Public Employees for Environmental Responsibility has filed a misconduct complaint on Dr. Monnett’s behalf.