Prime Minister John Key returns home this morning from the Copenhagen climate change conference saying a binding agreement could be concluded in Mexico next year but that the negotiating process has to change.

"It's progress, but there is a lot more to be done if we are going to achieve the outcome that we need," he said last night from Los Angeles.

"There is a lesson to come out of Copenhagen and that is that trying to build uniform consensus across 193 countries on such a complex issue is not going to work. It is not the right process."

Mr Key said he was more upbeat now about what the summit had achieved than when he left it.

"When we left the conference it was easy to think that we had not achieved a hell of a lot. I think 24 hours on I actually feel there is the makings of a deal there."

But he said developing countries had to be more realistic in their demands of developed countries.

"Small countries like Bolivia and Sudan can jump up and down and stamp their feet but they are irrelevant when it comes to solving the challenge of climate change.

There would be no credible response to climate change without the United States and China, coupled with Brazil, India, South Africa and the European Union, the PM said.

Labour MP Charles Chauvel, who was also in Copenhagen, described the summit as "neither a resounding failure nor a major milestone on the road to curbing greenhouse gas emissions".

Green MP Jeanette Fitzsimons, who was at the summit, called it a "disgrace and a tragedy for humanity".

Mr Key said the conference had been dominated either by process or by very small countries demanding things that were never going to be acceptable to the developed world, namely limiting the rise in world temperatures to 1.5C (instead of 2C) and wanting much more than US$100 billion in the aid fund for developing countries.

The summit was organised to reach agreement about what follows the Kyoto Protocol, a treaty to cut the carbon emissions of developed countries between 2008 and 2012.

The gathering involved two weeks of talks by 193 countries, including 110 leaders in the later stages.

The Copenhagen Accord was finally reached after the leaders of the US, China, India, Brazil and South Africa negotiated privately to get an agreed text, which was then put to the other 188 nations.

There has been criticism of the role of the five powers but Mr Key defended them, saying that when the Government leaders arrived, there was no agreed text and they had been "standing at the edge of it all completely failing".

"When you put it in that context, there was no option but to get the five big players that have the most skin in the game and get them to nail a deal. It is just the practical reality of it."

Mr Key said that as a result of what happened at Copenhagen, he believed that the order of the next set of negotiations in Mexico would change.

"I think what you are going to see is a different approach - starting in the reverse order than we had at Copenhagen. I think you will see those large emitters getting in a group, building a text that they are comfortable with, building support that they are comfortable with so that a deal can be done."

Mr Key was critical of the pressure some developing nations had put on developed countries, particularly their demands for a bigger mitigation fund for them.

The developing countries would have to decide whether to accept the US$100 billion a year by 2020 being offered "or risk that there is no money available".

"$100 billion may not be enough but it is a good start. I think you will see some of the African countries taking a more modified position."

New Zealand supports a binding post-Kyoto agreement, with financial penalties for countries that do not meet their targets, and a new organisation set up to monitor the eventual treaty.

The New Zealand negotiating team at Copenhagen got agreement to rule changes for measuring forestry, but they will not be definite unless a binding treaty is achieved.