Wildlife activists cheer as a participant passes through a 'global warming' gate on the opening day of the climate conference in Copenhagen. (Peter Dejong/Associated Press)

The United Nations' two-week conference on climate change formally opened Monday in Copenhagen, with organizers warning diplomats that the summit was the best chance to reach an agreement to prevent dangerous levels of global warming.

The conference — which is expected to draw about 15,000 people — is aimed at reaching a new agreement on controlling greenhouse gas emissions

Climate negotiators and political leaders from 192 countries, including Canada, are attending the summit, which opened with a film about the dangers of a changing climate. The film featured images of parched deserts, rising flood waters and violent storms.

"The time for formal statements is over," UN climate chief Yvo de Boer told delegates. "The time for re-stating well-known positions is past."

"Copenhagen will only be a success [if] it delivers significant and immediate action."

The conference's first week is to be spent refining a complex draft treaty, while environment ministers and heads of state aren't due to arrive until next week, when major decisions will await.

EPA concludes greenhouse gases endanger health

Negotiations to come up with a deal to replace the Kyoto Protocol, which expires in 2012, have dragged on for the last two years, lowering expectations that a new deal will be agreed to at Copenhagen.

But three major emitters who didn't agree to Kyoto — the United States, China and India — have all come forward with recent commitments to cut greenhouse gas emissions, giving the conference a lift on its first day.

The U.S. Environmental Protection Agency also announced on Monday that it has concluded that greenhouse gas emissions are endangering Americans' health and must be regulated, a step that could allow the U.S. government to take action even without Congressional approval.

But stumbling blocks remain, particularly over how to fund a proposed $10 billion US a year plan to help developing nations adapt to climate change.

Connie Hedegaard, the Danish minister hosting the conference, urged delegates to push for an agreement.

“Political will will never be stronger," Hedegaard said. "This is our chance. If we miss this one, it could take years before we get a new better one. If we ever did.”

Canada had the dubious honour Monday of being one of the countries to win the Fossil of the Day award, which is presented by non-governmental groups at the Copenhagen conference to countries they deem laggards on the environment.

Canada has been criticized internationally for reneging on the Kyoto Protocol and refusing to sign on to a new deal limiting greenhouse gases unless developing nations are included.

Alberta Environment Minister Rob Renner said the Canadian contingent wants to influence those trying to reach an effective agreement on reducing emissions around the world.

"The folks that are giving out awards like the fossil award are not our target audience," said Renner, who is headed to the summit later this week. "They're not the group of people that we're trying to influence."

Summit comes after leak of scientists' emails

The opening of talks comes a few weeks after climate-change skeptics stole and published emails from a British university. The hackers said the emails show scientists have conspired to hide evidence that refutes the theory that man-made pollutants are behind warming temperatures.

Rajendra Pachauri, the head of the United Nations' Intergovernmental Panel on Climate Change, defended climate research and said the hacking was an attempt to derail the summit.

"The recent incident of stealing the emails of scientists at the University of East Anglia shows that some would go to the extent of carrying out illegal acts perhaps in an attempt to discredit the [panel,]" he told the conference.