US state department officials were so convinced that the Copenhagen climate change summit was heading for collapse that they crafted a "talks fail" speech for Barack Obama.

Jonathan Pershing, who helped lead talks at Copenhagen, instead sketched out a future path for negotiations dominated by the world's largest polluters such as China, the US, India, Brazil and South Africa, who signed up to a deal in the final hours of the summit. That would represent a realignment of the way the international community has dealt with climate change over the last two decades.

"It is impossible to imagine a global agreement in place that doesn't essentially have a global buy-in. There aren't other institutions beside the UN that have that," Pershing said. "But it is also impossible to imagine a negotiation of enormous complexity where you have a table of 192 countries involved in all the detail."

Pershing said the flaws in the UN process, which demands consensus among the international community, were exposed at Copenhagen. "The meeting itself was at best chaotic," he said, in a talk at the Centre for Strategic and International Studies in Washington. "We met mostly overnight. It seemed like we didn't sleep for two weeks. It seemed a funny way to do things, and it showed."

The lack of confidence in the UN extends to the $30bn (£18.5bn) global fund, which will be mobilised over the next three years to help poor countries adapt to climate change. "I am not sure that any of us are particularly confident that the UN managing the near-term financing is the right way to go," he said.

Pershing did not exclude the UN from future negotiations. But he repeatedly credited the group of leading economies headed by America for moving forward on the talks. He suggested the larger forum offered by the UN was instead important for countries such as Cuba or the small islands which risk annihilation by climate change to air their grievances.

"We are going to have a very very difficult time moving forward and it will be a combination of small and larger process[es]," he said.

The first test of the accord agreed by the US, China, India, South Africa, and Brazil arrives on 31 January, the deadline for countries to commit officially to actions to halt global warming.

Here too Pershing indicated that the focus would be far narrower in scope that the UN's all-inclusive approach.

"We expect that there will be significant actions recorded by major countries," he said. "We are not really worried what Chad does. We are not really worried about what Haiti says it is going to do about greenhouse gas emissions. We just hope they recover from the earthquake."