Expressing increased optimism that an international deal on climate change can be reached in Copenhagen this month, the White House has bumped back the date President Barack Obama will attend the conference from Dec. 9 to Dec. 18.

“Based on his conversations with other leaders and the progress that has already been made to give momentum to negotiations, the President believes that continued U.S. leadership can be most productive through his participation at the end of the Copenhagen conference on December 18th rather than on December 9th,— White House Press Secretary Robert Gibbs said in a statement. “There are still outstanding issues that must be negotiated for an agreement to be reached, but this decision reflects the President’s commitment to doing all that he can to pursue a positive outcome.—

Obama had been criticized in some quarters for traveling to Copenhagen well before other world leaders, who will attend toward the end of the conference.