UNITED NATIONS, Dec. 4 (Xinhua) -- Just days before the UN conference on climate change in Copenhagen, there have been recent "several signs of optimism" with over 100 world leaders and 15,000 people expected to attend, said here on Friday Janos Pasztor, director of the UN secretary-general's Climate Change Support team.

    "For more than 2 years, the secretary-general has been urging heads of state to own the climate change issue as a strategic priority; a priority for the security and prosperity of their nations and for the world," Pasztor said in a press conference at the UN headquarters in New York.

    "Head of state involvement is crucial for successful outcome in Copenhagen," he said.

    Welcoming the recent goal by U.S. President Barack Obama to cut greenhouse gas emissions to 17 percent from 2005 levels by 2020, in addition to his participation in the conference, Pasztor said UN Secretary-general Ban Ki-moon "believes that the full engagement of the U.S. in the multilateral process can help propelglobal action."

    On Tuesday, Ban said in an address to the Women's International Forum at the UN headquarters in New York that "such high-level attendance is a game-changer."

    "From all corners of the globe, we now see uNPRecedented momentum for governments to act quickly and decisively," Ban said. "I am optimistic Copenhagen can be a success."

    World governments are seeking to agree to a successor to the Kyoto Protocol, the 1997 treaty that committed 37 industrialized states to cutting emissions by an average of 5 percent against 1990 levels over the period from 2008 to 2012.