U.N. Secretary-General Ban Ki-moon opened the annual General Assembly in New York City Wednesday with a call for nations to cooperate on global problems such as climate change, disarmament and poverty.

Mr. Ban addressed leaders of the 192-member states that climate change is humanity's greatest challenge, one day after he convened a summit on the issue.

U.S. President Barack Obama is set to make his maiden address to the gathering Wednesday.  He is expected to tell world leaders that the United States alone can not solve global problems.

In portions of Mr. Obama's speech released in advance of his address, he says for leaders who "used to chastise America for acting alone in the world", it is time for a true "global response to global challenges," including climate change, terrorism, endless conflicts and poverty.

Officials hope to make progress toward a global climate treaty that governments plan to finalize during a December meeting in Denmark.