Governor Arnold Schwarzenegger's key environmental adviser, Terry Tamminen, has left his post. Earlier this year, Tamminen was demoted from cabinet member to adviser. Among the key issues he promoted were greenhouse gas reductions and the hydrogen highway. The governor's office said Tamminen left the job at the beginning of August to work on special projects and the governor's reelection campaign. Some in the environmental community see Tamminen's departure as a considerable loss for clean-energy advocates. "It leaves a big hole in the governor's inner circle," said Bill Magavern, Sierra Club legislative coordinator. Tamminen has taken on the oil and automobile industries and is writing a book on alternative fuels and efficiency. Sources say his advocacy created problems for him in the governor's office. Tamminen, who will soon depart for a honeymoon, said he was unavailable for comment until mid-September.