Washington  - Efforts to tackle global warming will amount to nothing unless the United States and China, the world's largest- polluters, can work out an agreement to cut emissions, according to a report issued by a panel of US-Chinese experts Monday.

The group, led by by the Asia Society and the US-based Pew Centre on Global Change, both non-governmental organizations, laid out a "roadmap" for the two countries to beef up climate-change cooperation. It urged presidents Barack Obama and Hu Jintao to hold a summit as soon as possible to begin the process.

China's deputy ambassador to the US, Xie Feng, who attended the report's release, said it offered "new and inspirational thinking" on how the two often-time rivals could cooperate in the future. He said China "takes seriously" its role in cutting global emissions.

While no member of Obama's administration present, the panel was co-chaired by Steven Chu until he was nominated to become Obama's energy secretary. Richard Holbrooke, now Obama's special envoy to Pakistan and Afghanistan, led the Asia Society before accepting his new role.

The report, compiled with the help of dozens of experts over one year, made clear that no other group of countries - including Europe - could make any serious progress toward reducing the greenhouse-gas emissions blamed for global warming.

"Without the United States and China, it doesn't really matter what Europe does. That's the reality," said Orville Schell, director of the Asia Society's Centre on US-China Relations.

The call comes as talks on a new global climate deal enter a crucial phase. Governments have resolved to agree on a new treaty to replace the Kyoto Protocol - the world's first climate treaty - by the end of the year.

The US never ratified the Kyoto treaty, in part because the pact demanded no emissions reductions from emerging economies like China and India. The role of developing countries has again proven a key stumbling block in the new round of negotiations.

"If the US and China can't find a way to collaborate and get in the game, then there is no game," Schell warned.

Together, China and the United States emit about half of the world's man-made greenhouse gases. The panel warned that as China continues to grow, it could potentially out-pollute the entire world unless it can build its economy around clean energy alternatives.

Xie said that would require help from the US, especially by expanding technological cooperation that would give China access to the latest renewable energy alternatives.

China and the United States have shared a complex relationship over the years, forging strong economic ties but clashing over human rights as well as China's currency policy.

Former president George W Bush began a "strategic economic dialogue" with China led by then-treasury secretary Henry Paulson, which included collaboration on energy policy but focussed little on climate change.

The Obama administration has signalled a sharp shift in US climate policy - promising to cut greenhouse-gas emissions 80 per cent by 2050 - but offered few clues as to how it might manage the bilateral relationship with China.

Obama's Treasury Secretary Timothy Geithner last month said he believed China was manipulating its currency. That was denied by the Chinese central bank, which said Geithner was making excuses for the US-caused financial crisis.

The Pew-Asia Society panel suggested that a successful climate treaty could pave the way for closer cooperation between the two countries in other areas. (dpa)