"All the countries in the international community are looking for more and greater leadership from the United States," U.N. Secretary-General Ban Ki-moon said after a celebration to mark the 20th anniversary of the founding of the Intergovernmental Panel on Climate Change.
Ban praised the administration of U.S. President George W. Bush for playing an "important role" in discussing how countries can minimize greenhouse gas emissions, thought to be the main reason for global warming.
But the United States has not done enough to turn talk into action, considering it is one of the biggest emitters of greenhouse gases, he said.
Emerging powers such as China and India point to the U.S. rejection of the 1997 Kyoto Protocol when arguing against making commitments on climate change. Ban told journalists in Geneva that all developed countries need to take part if emissions are to be cut by at least half by 2050.
In a report published last year, the IPCC said such a reduction would be necessary to stop global temperatures rising more than 3.6 degrees above preindustrial levels. Failure to do so will lead to severe droughts and cause massive hunger and poverty, it said.
"I think that, whoever may be elected as the president of the United States, may be in a better position to lead this process," Ban said.