There are growing indications the deadline for the historic global agreement on climate change will continue into Saturday.

A new draft of the Paris Agreement, originally expected on Thursday afternoon, has been pushed back several hours as negotiators at the summit, known as COP21, continue to wrangle over the major issues that still cause divisions.

Talks president, the French foreign minister Laurent Fabius, said the latest draft being circulated Thursday evening would be close to the final accord that should be signed sometime this weekend. But other parties to negotiations have said there may be further drafts.

At a longer than expected plenary session on Wednesday night, involving ministers from 195 countries, there was a high volume of criticism, suggesting many of the big gaps are still a long way from resolution.

However, there was general acceptance among delegates that the 29-page text provided a strong basis for an agreement, which raised optimism of a meaningful solution.

The big issues include how much funding developed countries are willing to pay poorer countries to respond to climate change, as well as finding a workable solution to ensure every country in the world increases its commitment to lower emissions and meet the long-term target of keeping global temperatures to well either below 2 degrees, or 1.5 degrees, above in preindustrial levels.

The other big obstacle is "differentiation". In the past developing countries like India and China did not have to cut emissions. But now the US and others are trying to put pressure on them to present ambitious long-term goals that include emissions tracking and reductions.

A well-placed source said differentiation remained the stumbling block as it affected all aspects of the agreement. If progress was achieved on this matter, said the source, it would allow progress on other key areas, such as ambition and transparency.

Professor John Sweeney of NUI Maynooth, and An Taisce, said the talks were at the "crunch point" now but added the difficulties were "not impossible".

Like many others in attendance, he said the atmosphere at this summit had been calmer than at previous UN climate conferences. The French Presidency has been widely praised for its handling of the process.

“The fault lines are the ones that have always existed, namely the unwillingness of the developed world to take responsibility on a common but differentiated basis,” said Prof Sweeney.

“Secondly, the unwillingness of the developed countries to ensure that when they receive funds they are properly monitored and spent wisely. That has been a stumbling block in the past.”

Green Party leader Eamon Ryan said his sense was that the summit would run on until Saturday at least but said he was reasonably optimistic of a positive outcome.

“My expectation is that there will be a deal and there is a chance it could be a good deal.

“That is significant because us at home particularly we have to change our tack and not be left behind.”

He said the big issues for him were more ambition in terms of reducing carbon emissions; better mechanism to check people were doing what they said they were doing; and climate justice, ensuring that poor people were not being penalised by climate change policies.

Dr Cara Augustenburg, chair of Friends of the Earth Ireland, agreed that the differentiation issue needed to be resolved.

“I am concerned that some of the least developed countries are not willing to move towards renewables and are more interested in the finances.

“I am also concerned that developed countries not willing to pay to help the less developed countries,” she said.

David Healy of Oxfam Ireland said that food security and climate inequality were two key issues that needed to be reflected in the text.

“Oxfam launched a report last week on extreme carbon inequality. What that showed was the top ten per cent highest emitting individuals in the planet are emitting half the pollution, half the greenhouse gases,” he said.

Dr Lorna Gold of Trócaire also identified those two issues.

“From our point of view there are two main issues. The first one is the removal of the problematic language around the safeguarding of food production and distribution. We should instead have strong language around food security .

“We know that the issues… are about access to food.

The other issue is human rights. We see this is really weak in the current text,” she said.

Ed Cameron is a Dublin-born spokesman for We Mean Business, a group advocating leadership for business in climate change. He said there were difficulties but that the process was moving towards agreement.

“We are dealing with the typical rhythm of the COP,” he said but said there were very positive signs.

He pointed to Brazil breaking a taboo by making a commitment to reduce emissions even though it is an emerging economy. He said he was encouraged by the commitment of China to mobilise finance and scale up on renewables as well as the leadership role shown by the US.

Praising the stewardship of the French, he said there was a commitment of a five-year review cycle, good language on finance and measures to protect vulnerable and marginalised communities.

“We need a long term goal. Business makes investment based on decades.

"We need a clear steer that their commitment is not based on electoral cycles but is a long term commitment until the end of the century," said Mr Cameron.

Concern's Alexander Carnwath puts the focus on another big matter of disagreement, money for poor countries to adapt to climate change.

“We have resilience projects around the world where some of the poorest people are experiencing the worst effects of climate change. That is happening now.

“These people are going to experience more and more of that due to locked-in warming. It is imperative that this agreement deliver the support that is required for poor countries. They are among the least that has contributed to climate change,” he said.