World powers at the climate summit in Copenhagen are increasingly concerned that the talks are heading for failure and an agreement may have to wait until next year.
The US has sought concessions from emerging economic giants on emissions, while the EU expressed 'concern' at the lack of progress.
US Secretary of State Hillary Clinton, who announced that Washington would contribute to a $100bn fund to help poor nations cope with climate change, said it was 'time to take an historic step we can all be proud of.'
Speaking ahead of the arrival of President Barack Obama, she accused developing nations - without naming them - of backsliding on pledges to open their emissions controls to scrutiny.
Danish Prime Minister Lars Loekke Rasmussen, the conference chairman, declared the meeting was 'now at a critical juncture and we have now agreed on how to proceed.'
'Now we rely on the willingness of all parties to take that extra step that would enable us to make the deal that is expected of us,' he said.
It is widely believed that the next few hours will reveal whether a comprehensive agreement can be secured or if the Copenhagen summit is going to be characterised by failure.
Media focus has been on developing countries who have felt both marginalised and angered by their Danish hosts introducing new draft texts.
The question is whether compromise can be found on issues such as the date and size of emissions reductions, how that is verified, as well as the provision of finance and technology by rich nations to the poor.
Gormley warns of summit deadlock
Minister for the Environment John Gormley has said there is a real danger that the parties to the climate change summit in Copenhagen will ‘talk themselves into depression’ and become paralysed, amid continuing signs of deadlock.
He said it was time the EU highlighted its credentials and indicate that it was willing to go to a 30% cut in carbon emissions by 2020 as compared to 2005 levels, so long as there were comparable cuts from the big developed countries.
Mr Gormley said if they could harness the support of the G77 group of developing countries to come on board, and for them to persuade the other bigger members of the G77 like Brazil, India and China to make a huge effort to get a deal, then it would help introduce vital momentum in the talks which had been lacking so far.
Amid continuing tensions between the US and China over emissions levels, Mr Gormley said that between them they were responsible for half the world's carbon emissions.
He said, however, the US was still the biggest carbon emitter on the planet per capita and it was now ‘up to Washington’ to make a supreme effort and to get away from what he called the ‘stalling tactics of the Bush administration’.
'I'm surprised to see they are continuing along that vein. They must look at what the EU is doing and make a similar effort.'
Mr Gormley said there had been criticism of the Danish handling of the climate change summit and the negotiating process, but he said he was 'hopeful we can find a resolution to these difficulties.'
The key issues at the summit include how much money the developing world will receive from richer countries in order to combat the effects of climate change and to help them reduce their own emissions, and how much western countries should cut their own carbon emissions.
How a successor to the Kyoto Protocol is monitored and applied remains a sticking point.
For countries like India, China and Brazil bringing their populations out of poverty requires economic growth which in turn necessitates an increase in carbon emissions.
The US is reluctant, however, to commit to major carbon emission reductions until developing countries make clear commitments on their own reductions.
US Secretary of State Hilary Clinton told a news conference at the summit that the US now recognised that the cost of climate change for developing countries would be in the region of $100bn billion by 2020, the first time the US has put such a figure on the table.
The EU has already declared that the cost for the third world in terms of drought, rising sea levels and violent storms, as well as reducing their carbon emissions, would be in the region of €100bn.