BEIJING - Co-operation between China and the United States is crucial to successfully addressing the climate change problem, said a report released Friday that was co-produced by the U.S. energy secretary prior to his nomination.

The world's two leading emitters of greenhouse gases have long been at odds over how to handle climate change. China has insisted that developed nations bear the main responsibility for cutting emissions. But the U.S. under former President George W. Bush refused to sign an international pact requiring cuts in emissions, saying developing nations should not be exempt.

"If these two countries cannot find ways to bridge the long-standing divide on this issue, there will literally be no solution," said the report, jointly issued by the Asia Society's Center of U.S.-China Relations and the Pew Center on Global Climate Change.

It called on leaders of the countries to take immediate action and collaborate on developing technologies for clean use of coal, enhancing the use of renewable energy sources such as solar and wind, and creating new mechanisms for financing clean energy.

"We are in uncharted water that will beg an unprecedented effort from both the world at large and the United States and China in particular," the report said.

Environmentalists have welcomed steps on the part of President Barack Obama to address climate change, including the nomination of Steven Chu to the post of energy secretary. Co-chair of the project that produced Friday's report until Obama's December nomination announcement, Chu has vowed to develop clean energy sources and said scientific research is key to tackling climate change.

The global economic crisis has been an opportunity for both the U.S. and China to spur improvements in energy efficiency. A proposed U.S. stimulus package includes grants, tax breaks and loan guarantees to promote solar and wind energy development and to cut energy use in everything from government buildings to schools and homes.

China says it will subsidize investment in energy efficiency and technology as part of a 4 trillion yuan ($586 billion) stimulus package.

"China's economic development is now at a stage where the development must be sustainable and there must be protection of resources and the environment. Therefore, the issue of climate change cannot be avoided," said Liu Deshun, a professor with the Institute of Nuclear Energy and New Energy Technology at Tsinghua University in Beijing.

Secretary of State Hillary Rodham Clinton plans to address climate change on a visit to China later this month.

And China, whose leadership the report praised as "increasingly well-informed," has been winning kudos for its changing role in recent climate talks. Beijing has agreed that developing countries could help contain carbon emissions -- as long as the wealthy industrial countries gave them the needed technology and finances.

In comments to the Financial Times earlier this month, Premier Wen Jiabao said China supports the Copenhagen climate conference scheduled for late 2009, which aims to ink a global agreement on reducing emissions. But he also said it was "difficult" for China to agree to any set emission reduction target.

"This country is still at an early stage of development. Europe started its industrialization several hundred years ago, but for China, it has only been dozens of years," he told the paper.

China, which is heavily dependent on coal to fuel its growing economy, rivals the United States as the world's largest emitter of greenhouse gases. But it has said its economy should not be penalized by binding cuts in emissions of carbon dioxide and other heat-trapping gases when their per capita emissions are much below those in developed countries.