Al Gore, the former US vice-president turned climate campaigner, has blamed the US for blocking progress at UN climate talks in the Indonesian island of Bali, but said a breakthrough was possible in the final days of the conference.
He said: "Some of the reports are worrisome, but I know from experience ... that when breakthroughs do occur, they usually happen in the last 48 hours."
"I hope there will be a change on the part of some countries, including and most importantly my own - the United States."
The newly awarded Nobel laureate told delegates at the climate conference that they can leave an "open space" in their framework and hope it will eventually be filled by the successor of George Bush, the current US president.
US obstacle
Gore said: "I am not an official and I am not bound by diplomatic niceties."
"So I am going to speak an inconvenient truth - my own country - the United States - is principally responsible for obstructing progress here in Bali."
The talks are mired over a dispute involving industrial countries and whether they should give an indication of how far they are willing to cut their own emissions.
Critical stage
According to Yvo de Boer, the UN's top climate change official, global efforts to tackle climate change could collapse "like a house of cards" unless envoys make rapid progress on a new global warming pact.
De Boer said there was less than a day to resolve key issues on a framework for combating the worst effects of climate change.
He said: "We are in an all-or-nothing situation in that if we don't manage to get the work done on the future, then the whole house of cards basically falls to pieces."
The EU, backed by developing countries, wants a reference by industrialised nations that a cut of 25-40 per cent in their emissions by 2020, compared to 1990 levels, will be a guideline for talks.
Climate talks called by Bush in Hawaii next month may be snubbed by the EU if the Bali meeting collapses.
"If we would have a failure in Bali, it would be meaningless to have the major economies meeting," said Humberto Rosa, the Portuguese secretary of state for the environment.
The
US, which is the only country not to have signed up to the Kyoto Protocol, says guidelines – although non-binding - would prejudge the outcome of future talks.
Under the Kyoto pact, 37 industrialised nations committed to curb their emissions of so-called greenhouse gases between 2008 and 2012.
The UN is calling for a successor to Kyoto by late 2009 to allow governments time to ratify the new deal by the end of 2012 and to give markets clear guidelines on how to make investments in clean energy technology.
More than 190 countries have until Friday to agree with a framework for negotiations that will culminate in a pact for tackling global warming past 2012, when pledges under the Kyoto Protocol expire.