On Wednesday, the big shots started arriving in Copenhagen, turning the climate change conference from a discussion among environment ministers and technocrats into a mega-summit.

On this rare occasion the leaders of the United States and Iran, China, Russia and India, Britain and Zimbabwe and almost every nation on the planet are supposed to put aside their differences and come up with a deal to stop disastrous global overheating.

That was the plan at least.

With two days to go before the end of the summit, almost two weeks of negotiations were supposed to have produced a draft committing nations to slash greenhouse gas emissions, defend tropical forests, pump billions into supporting clean development of poor nations and other measures to stall the inexorable rise of global temperatures.

Instead, the players seemed as far apart as ever.

China joined developing nations to blast the rich north for trying to wriggle out of commitments; the European Union appealed to the Chinese and Americans to raise their emissions-cutting ambitions; Africans demanded more financial help to cope with the impact of rich nations' pollution; the leftist leaders of Venezuela and Bolivia railed against western imperialism; small island states despaired at the lack of progress as rising sea levels threaten their very existence.

"This is more than just another meeting. This is a matter of life and death," said President Mohamed Nasheed of the Maldives. "We urgently need to move forward."

An aura of gloom hung over the talks as officials acknowledged that failure had become a real possibility.

"I'm disappointed with the slow pace of negotiations in the past days," admitted European Commission President Jose Manuel Barroso. Danish Minister Connie Hedegaard warned talks were on a "knife's end" before she stepped down as chairman of the talks, handing over to her prime ministers as the arrival of heads of government upgraded the status of the talks.

There was some progress Wednesday. The EU and several African nations announced they were close to an agreement on financing to help poor countries adapt agriculture, build sea defenses and take other measures to adapt to the impact of global warming, which they blame on pollution from richer nations.

There was also progress reported on a plan to protect tropical forests, ensuring they would absorb carbon dioxide from the atmosphere.

Elsewhere deep rifts remained. The U.S. and China both rejected European calls for greater emissions cuts. The EU dismissed as unrealistic developing nations' demands for an extension of the Kyoto Protocol which commits mostly rich nations to binding emission cuts without including new industrial powers like China and India.

The Kyoto deal — which has never been ratified by the U.S. — runs out in 2012 and European nations say it should be replaced with a broader global deal. Swedish Prime Minister Fredrik Reinfeldt, speaking for the EU, pointed out that the countries covered by Kyoto today represent just 27 percent of greenhouse gas emissions.

"Here I turn to the United States and China. Together you are responsible for half of the global greenhouse gas emissions," Reinfeldt told the meeting. "Together your ambitions to limit emissions will make or break the world's efforts to keep global warming below 2 degrees Celsius."

Speeches from a succession of national leaders revealed the hugely complicated nature of the talks with every one having a particular axe to grind. Even that 2 percent target was called into question by some African and island nations who said they would suffer even at that level and demanded efforts to keep increases to 1.5 or 1 degree Celsius.

Delegates complained that draft documents were growing shorter and shorter as contentious details were removed in efforts to get a deal that would leave out many of the difficult questions — perhaps setting the scene for a follow-followup summit next year.

The frustrations inside the meeting were matched by growing anger among protesters outside. Danish police, backed by reinforcements from neighboring Sweden, arrested 230 demonstrators outside the suburban Bella Center. Meanwhile some campaigners granted access to the conference took their protest inside, interrupting the meeting with shouts of "global justice now" and staging a sit-down protest in a concourse between two meeting rooms.

The United Nations' top mediator Yvo de Boer suggested that the summit-level talks could be jeopardized if there were continued security breeches.

"The incidents that have taken place today inside the conference center test my courage to continue in this way," he told a press conference. "I'm actually in a huge dilemma ... at the end of the day my responsibility is for your safety and for that of the other participants."