BEIJING - Ties between the United States and China could be transformed by cooperation on climate change, House of Representatives Speaker Nancy Pelosi said, linking environmental concerns to human rights and the rule of law.

Pelosi told an audience in the Chinese capital on Tuesday that the two nations -- the world's top emitters of greenhouse gases -- must work together to fight global warming.

China and the United States can and must confront the challenge of climate change together, she said at a meeting organized by the American Chamber of Commerce in Beijing.

I think that this climate change crisis is a game-changer in the U.S.-China relationship. It is an opportunity that we cannot miss.

Pelosi was speaking during a visit to China with a group of U.S. lawmakers examining how the two powers can cooperate better while governments seek to agree on a new global treaty on fighting global warming from greenhouse gases.

But Pelosi, a Democrat well known as a critic of China over human rights and its rule in Tibet, also obliquely linked that concern to rights concerns, calling it a matter of environmental justice.

Fighting global warming would require political transparency, rule of law and accountability, Pelosi told the audience, which included former Chinese Foreign Minister Li Zhaoxing and its current ambassador to Washington, Zhou Wenzhong.

Pelosi, however, did not mention specific human rights issues in her speech.

Whether Washington and Beijing can agree on how each will help contain greenhouse gas emissions will be crucial to negotiations aimed at striking a new treaty by the end of the year in Copenhagen.

While the two sides have struck up-beat notes since President Barack Obama took office, much still divides them. Many U.S. lawmakers want China to make firm commitments to contain its growing greenhouse gas output before they back any deal.

Pelosi's visit comes on the heels of the House Energy and Commerce Committee approving a climate change bill on Thursday that would cut U.S. emissions of carbon dioxide, the main greenhouse gas from human activity, by 17 percent from 2005 levels by the year 2020.

But Beijing has said that in a new climate change pact all developed countries should agree to cut their greenhouse gas emissions by a much steeper 40 percent by 2020 from 1990 levels.

As the world's biggest emitter of these gases, China also faces pressure to begin cutting them soon. But it says developing nations should not accept mandatory emissions caps to solve a problem caused over the centuries by wealthy countries, which still have much higher per capita emissions.

Global warming Climate change Nancy Pelosi Climate