Beijing will raise the stakes in the race to agree a global climate change treaty by using a summit of world leaders in New York today to announce that China, the biggest emitter of greenhouse gases, is ready to take new measures to cut pollution.

Although more than 100 leaders will attend today's conference, the focus will be on China's premier, Hu Jintao, and US President Barack Obama, who together may hold the fate of the treaty in their hands.

Officials in Beijing indicated last night that Mr Hu would arrive in Manhattan this morning ready to unveil "important" plans for reducing China's carbon dioxide emissions, which could break the deadlock in negotiations. While he is not expected to commit China to emissions reduction targets, an acceptance of intensity targets, which aim to reduce the amount of carbon dioxide emitted per unit of industrial production, would be a big step forward.

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The UN has called the summit to try to build momentum towards achieving a new deal on cutting emissions at talks in Copenhagen in December. Scientists are calling for an ambitious target for reducing the greenhouse gases which cause climate change, as a successor to the Kyoto protocol.

But with time running out before the talks in Denmark, there are fears that not enough progress is being made to reach a new deal. China's move could kick-start talks, but may also leave Mr Obama having to shoulder the blame if the Copenhagen conference ends in failure. A Bill, backed by Mr Obama and proposing a "cap-and-trade" system to cut CO2 output in the US, has been passed by the House of Representatives but is stuck in the Senate.

America is the world's second-biggest polluter after China.

Yvo de Boer, the UN's leading climate official, confirmed that China was poised to offer a potential breakthrough and said he expected Beijing to become the "world leader" in tackling climate change. He said the package of measures expected from President Hu would take Chinese emissions "very significantly away from where they would have been and are".

About 70 per cent of China's energy is produced from coal. With her industrial capacity and urbanisation still growing, the country's energy needs are being met by the opening of a new coal-fired power station every week. China's CO2 emissions from fossil fuels soared by 129 per cent between 1990 and 2005.

Exactly how big an impact today's announcement by China will have on the talks depends on what detail Mr Hu offers. According to reports from Beijing, he intends to be fairly specific, offering for the first time some numeric framework for what China intends to do. China is traditionally wary of signing up to multilateral, binding treaties, but Mr Hu could deliver a strong political message of his willingness to tackle the problem of global warming.

"We want to give the world a strong, clear signal, especially ahead of the Copenhagen summit, that we are sincere and committed," said Zhang Haibin, a professor of environmental politics at Beijing University and an adviser to the government.

Today's gathering, hosted by the UN secretary general, Ban Ki-Moon, will feature a parade of heads of government, Mr Obama included, calling for progress before the Copenhagen talks. Yet the impasse in Washington will be on everyone's mind.

It is hard to imagine Mr Obama travelling to Denmark and signing a comprehensive pact without action having first been taken in the Senate. Yet for the moment, all the Senate's political energies are focused on the President's controversial healthcare proposals.

It is the scant progress being made in America that may have prompted Gordon Brown to make an impassioned plea for progress in an article published yesterday by the US magazine Newsweek. World leaders must go to Copenhagen to avert the "grave danger" of the treaty negotiations falling apart, he argued.

"Securing an agreement in Copenhagen will require world leaders to bridge our remaining differences and seize these opportunities," the Prime Minister added. "If we miss this opportunity, there will be no second chance sometime in the future, no later way to undo the catastrophic damage to the environment we will cause."

The message was echoed in New York yesterday by the Climate Change Secretary, Ed Miliband, who warned that the world was facing a "make or break" opportunity. Many countries, including China, were "working hard to defy the odds" to agree a treaty, he said, expressing hope that the US political hold-up could be overcome. Although he said the "constellation of the stars" made reaching a pact difficult, he added: "I actually think this will be the best chance for some years to come."

That the negotiations may boil down largely to what China and the US can deliver was acknowledged last week by Mr Ban. China is by far the biggest of the emerging industrial nations, with India next. China and America are responsible for 40 per cent of the world's greenhouse gas emissions.

"China and the US will be the two key countries which can make a great impact to this negotiation," Mr Ban said, adding that presidents Obama and Hu and other leaders should "publicly commit to sealing a deal in Copenhagen".

Any significant step forward by China will rob the US Senate of one of its principal arguments for dragging its feet. Conservative politicians on Capitol Hill have repeatedly asserted that it would be unfair for America to take the leap into a system that might impede her economic growth if developing countries such as China were allowed to get away with doing virtually nothing.

Mr Hu is expected precisely to counter that charge.