Copenhagen

At the opening of the mammoth 12-day conference, Danish Prime Minister Lars Lokke Rasmussen urged 15,000 negotiators from 192 nations to hammer out a "strong and ambitious" deal.

"Differences can be overcome if the political will is present. And I believe it is," Rasmussen said.

The opening ceremonies featured a short film depicting a child's apocalyptic nightmare of climate change - a grim warning of the price of failure if world leaders don't clinch a political deal by December 18.

Some 110 world leaders - including US President Barack Obama - have already agreed to attend the conference's closing summit.

US position

Obama's chief UN negotiator, Jonathan Pershing, outlined the US position on day one of the conference, saying the Obama administration was making an "unprecedented level of effort."

Coinciding with the opening day of the conference, the US Environmental Protection Agency issued a landmark ruling that the greenhouse gas emissions blamed for global warming represent a danger to public health and can be regulated under existing US laws.

The ruling marks a major shift from the position taken by former president George W. Bush's administration. And for the first time, the US is willing to put a target on the table in Copenhagen, saying it plans to cut carbon dioxide emissions to 17 percent of 2005 levels by 2020. The US says it is also prepared to provide financial support to help the world's poorest countries achieve their climate change goals.

"But to succeed, we need a global effort," Pershing said.

In the run-up to the conference, analysts have stressed the deep gap between the demands of developing countries and the willingness of richer nations to share the burden of curbing the emissions blamed for global warming.

Email scandal

The head of the United Nations' panel of climate scientists, Rajendra Pachauri, was also on hand Monday to defend scientific findings on global warming after hacked emails from a British university led sceptics to claim that researchers had exaggerated the threat. He said the hack was an attempt to undermine the work of the Intergovernmental Panel on Climate Change (IPCC).

"Given the wide-ranging nature of change that is likely to be taken in hand, some naturally find it inconvenient to accept its inevitability," Pachauri said.

"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 IPCC."

Saudi Arabia's top climate negotiator Mohammed al-Sabban, said that his country's trust in climate science had been "shaken" by the leaked emails. He called for an "independent" international investigation, claiming that the IPCC was unqualified to carry it out. Saudi Arabia is oil cartel OPEC's leading producer and exporter.

In its landmark publication, the IPCC declared that the evidence of global warming was "uneqivocal" and that action was needed to avoid more intense heatwaves, floods and loss of the Greenland ice sheet, which could mean a sea level rise of 7 meters over centuries.

Public scrutiny

Organizers and delegates were reminded of the intense public interest in events in Copenhagen when they were handed an online petition signed by 10 million people around the world demanding that leaders sign up to a "fair, ambitious and binding" climate treaty. The petition is an initiative of TckTckTck, an umbrella organization of 226 environmental groups.

Hopes are high that, with so many world leaders in attendance and pledges to curb emissions by the biggest polluters (China, the US, Russia and India), an effective deal can be reached.

"The clock has ticked down to zero. After two years of negotiations, the time has come to deliver," said Yvo de Boer, the head of the UN Climate Change Secretariat.

Merkel "mildly optimistic"

Speaking to public broadcaster ZDF on Monday, German Chancellor Angela Merkel said that she was only "mildly optimistic" about the outcome of the conference. She said that negotiators should agree to limit global warming to two degrees Celsius by 2050, adding that many countries' offers of action need to be improved.

"The aim of this conference must be an international commitment to the limiting of global warming to two degrees by 2050, and for that, all must step up (their offers), in particular countries like China and India that don't yet recognize this two degree aim," Merkel said.

dc/dpa/Reuters/afp/ap

Editor: Susan Houlton