President Obama is preparing to break the deadlock in negotiations on a global deal on climate change by announcing a target for cutting US greenhouse gas emissions.

The US is the only developed country yet to propose an emissions target. Poorer nations, including most of Africa, are threatening to walk out of a UN summit in Copenhagen next month unless Mr Obama commits to an ambitious reduction.

Mr Obama may wait until the final stages of the negotiations in Copenhagen in order to achieve maximum political impact with his announcement and give other countries little opportunity to demand deeper cuts from the US.

The US delegation at pre-summit talks in Barcelona hinted that Mr Obama was considering offering a range of possible reductions rather than a single number. This would make it easier for the President to persuade Congress to pass legislation making the target legally binding.

During his election campaign, Mr Obama proposed that the US should cut emissions by 14 per cent on 2005 levels. A bill passed by the House of Representatives last summer would cut emissions by 17 per cent.

A second bill, tabled in the Senate by John Kerry, the former Democrat presidential candidate, would cut emissions by 20 per cent.

Jonathan Pershing, the lead US negotiator at the Barcelona talks, gave the clearest indication to date that America would announce a provisional target before the end of the Copenhagen summit.

He said: “Developing countries, including the US, need to make robust mid-term reductions from a set base year.” Mr Pershing added: “In the US we are moving to make a substantial contribution to a robust Copenhagen deal. We are very interested in seeing that deal move forward and we recognise that others are seeking numbers from us.” He said Mr Obama could make a political commitment to a target without waiting for the Senate to approve it.

“The executive body has authorities which are not exclusively reliant on Congress and that is a decision which has to be made.” Mr Pershing also said that the US was preparing to make a “substantial contribution” to a global fund aimed at helping developing countries adapt to climate change and pursue low-carbon economic growth.

He said the US was not expecting developing countries to cut their overall emissions but it wanted to see specific commitments from them on reducing their growth in emissions compared with the “business as usual” position.

Yvo de Boer, the UN’s senior climate change official, said the summit would achieve very little if Mr Obama failed to announce a target.

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