Al Gore savaged the US government’s “obstructing” attitude and urged delegates at the UN conference on climate change to ignore Washington if necessary to pursue the “moral imperative” of a new global regime.

“My country is principally responsible for obstructing progress here in Bali,” the former US vice-president told 2,000 of the 12,000 people attending the conference on Thursday. “[But] over the next two years the United States is going to be somewhere it is not now.”

The Bali meeting is trying to reach an agreement to start negotiations that will culminate in 2009 with a new global deal to tackle climate change. The US is due to elect a new president in November 2008 and the majority of the frontrunners have a more proactive attitude to climate change than the Bush administration.

European Union nations said they might boycott a U.S.-led climate meeting next month unless Washington compromises to achieve a deal on Bali.

‘‘No result in Bali means no Major Economies Meeting,’’ said Sigmar Gabriel, top EU environment official from Germany, referring to a series of separate climate talks initiated by President Bush in September. ‘‘This is the clear position of the EU. I do not know what we should talk about if there is no target.’’

The US invited 16 other major economies, including European countries, Japan, China and India, to discuss a program of what are expected to be nationally determined, voluntary cutbacks in greenhouse gas emissions.

Mr Gore, fresh from receiving the Nobel peace prize jointly with the UN’s Intergovernmental Panel on Climate Change, said delegates must “find the grace to navigate around this enormous obstacle, the elephant in the room that I have been undiplomatic enough to name.”

The US delegation in Bali has repeatedly said it is committed to finding a consensus and reaching a deal but numerous countries have accused it, as well as Japan, Canada and Saudi Arabia, of blocking progress.

A substantial part of Mr’s Gore’s hour-long address was a recap of material he has used on numerous occasions since making An Inconvenient Truth, his Oscar-winning film, in 2006. He described how scientists are warning of a rapidly escalating crisis unless greenhouse gas emissions are significantly reduced.

He sought to inspire the audience by telling them they had the privilege of being some of the few people in the world who can make a difference in saving “the world’s civilisation”.

“The way ahead from Bali is difficult,” he said. “The truth is that is the maximum now considered possible even here in this conference is still far short of the minimum that will really solve this process. So we have to expand the limits of what’s possible. We must have the moral imagination of humankind to see ourselves as the symbol of global civilisation.”