A legally binding agreement on cutting greenhouse gas emissions is no longer a realistic goal for next month’s Copenhagen summit, the UN Secretary-General says.

According to Ban Ki Moon such an agreement will not be signed next month and the most likely outcome is voluntary targets, which countries could announce but then ignore.

He said that several key countries were not ready to sign up to binding targets and that the best the world could hope for from the summit would be “political commitments”. Mr Ban said he hoped that they would be legally binding within a year but would be dependent on each country.

His comments, made in London, marked a significant retreat from the UN’s previous plan for a new treaty to be signed at Copenhagen to replace the Kyoto Protocol, which expires in 2012. Mr Ban said: “It may be realistic if we think Copenhagen will not be the final word on all these matters. But if we agree on a strong politically binding commitment that will be, I think, a reasonable success. Then the post-Copenhagen negotiations will continue so that we have a legally binding agreement as soon as possible.

“Each and every country has their own domestic constraints when they go back — no country will be totally free, that is the difficulty. It is a very complex process including verification systems, targets and money. It is not an easy task. That is why I am saying Copenhagen is not the final word.”

Mr Ban also said that developed nations would have to increase the amount that they paid to poorer countries to help them to adapt to climate change. Asked whether he believed that the European Union’s proposal of a fund of up to $50 billion of public money a year would be sufficient, he said: “As we go into the future, I think that should be scaled up.”

He said that generous funding needed to be agreed to build trust among developing countries, which have accused richer nations of creating climate change but leaving them to face the consequences. “We should admit that there are some suspicions and distrust, particularly on the part of developing countries.”

He also suggested that the global target for limiting the temperature increase to 2C above pre-industrial levels might have to be adjusted because it could still result in sea-level rises inundating many small islands. “These small-island developing countries say that it should be a maximum of 1.5C. For them it’s a matter of life and death.”

Mr Ban said that he was working closely with members of the US Senate, which is debating proposed legislation on cutting carbon dioxide emissions. He also suggested that President Obama and other world leaders needed to be present at the end of the Copenhagen summit to ensure an ambitious political agreement. “The urgency and importance of the work requires political leadership. I would expect many leaders will come.”

Mr Ban was speaking as 50 African countries boycotted UN meetings on climate change in Barcelona. They accused developed nations of settingweak targets for cutting emissions. The African countries said that they would not discuss how developing countries could reduce their emissions until there were more stretching commitments from richer nations. “I don’t think we can get to a result in the way we’re going now,” said Kamel Djemouai, the Algerian negotiator who chairs the Africa group.

The Intergovernmental Panel on Climate Change said that developed countries should reduce emissions by 25 to 40 per cent from 1990 levels by 2020, but the targets announced have fallen short.

Anders Turesson, the chief delegate from Sweden, which holds the EU presidency, said that while EU leaders shared the Africans’ concern about the low level of pledges, their tactic of limiting the discussion to emission targets was unproductive.

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