
Delegates from the world's top 16 polluting nations are meeting in Washington to discuss ways of tackling climate change.
The meeting was called by US President George Bush, who said he is looking for a show of leadership on climate change.
Representatives will draft national measures for curbing emissions and seek agreement on long-term objectives.
Critics are concerned that the meeting might be used to press for voluntary rather than binding emission cuts.
Many scientists say political action is falling behind what is needed to avert lasting damage to Earth's climate.
The two days of talks will be chaired by Secretary of State Condoleezza Rice. President Bush will address the meeting on Friday.
Representatives from Australia, Britain, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, South Korea, Mexico, Russia, South Africa and the US will attend.
Together they account for more than 90% of global greenhouse-gas emissions.
Delegates will seek agreement on long-term global goals, as well as "nationally defined mid-term goals and strategies, and sector-based approaches for improving energy security and reducing greenhouse gas emissions," the White House said in a statement.
Representatives from the EU and the UN Framework Convention on Climate Change (UNFCCC) will also attend.
Critics of the meeting fear it could dilute attempts to reach a global agreement through the UN in the next two years.
A UNFCCC meeting later this year will aim to set a roadmap for negotiations to tighten a mandatory clamp on carbon gas after 2012, when current commitments under Kyoto Protocol run out.
However, UNFCCC leader Yvo de Boer said US officials had repeatedly pledged that Mr Bush's initiative would feed back into the UN process.