World leaders release draft climate change agreement - but can what they want to achieve be done?

French ministers, led by foreign minister Laurent Fabius, have published a 29-page draft of the possible agreement which might come out of the UN’s COP21 climate meeting in Paris.

The text has been painstakingly whittled down over the course of the past week, with various subcommittees working through disagreements on the various sections.

Everything from greenhouse gas targets to finance has been on the agenda.

Today’s draft text still contains a lot of square brackets, signifying options that remain for negotiators and politicians in the next few days. These are the points of contention that will need to be debated in order to create the final deal.

There are no huge surprises in the latest text - the French have been careful to avoid the shocks in the negotiation process that ended up derailing the Copenhagen climate talks in 2009.

But there is still something striking: The draft text still contains an option for delegates to agree to a maximum increase in global temperatures of no more than 1.5C by the end of the century.

This has raised a lot of happy eyebrows by environmentalists. It is far more ambitious than the 2C target that scientists say we must stay below in order to avoid the most dangerous effects of climate change.

That was the dream goal for many at the conference, and it was already a very ambitious target.

Before the Paris meeting, countries had come up with voluntary plans on how they would individually reduce their emissions over the coming decades and, combining those promises, the world would still have warmed by 2.7C by the end of the century.

That’s better than the 3-5C trajectory we are on if we do nothing, but still not anywhere near the magic 2C target.

You can see, therefore, why having a 1.5C target still on the table at this late stage in the Paris meeting has caused such a fuss.

The draft text doesn’t specify how the world might achieve a 1.5C target but we can assume it would imply much more aggressive action in cutting emissions and developing clean technology than anyone has volunteered so far.

Scientists have cautiously welcomed the draft text.

Prof Joanna Haigh, an atmospheric physicist at Imperial College London, said the inclusion of a 1.5C option in the draft agreement was "remarkable", as is, she said, the ambitious proposed mitigation pathway of 70 to 95 per cent cuts by 2050, leading to zero carbon emissions by the latter half of the century.

"Perhaps some of these more ambitious options will not reach the final document, but the fact that these targets are being seriously discussed is hugely positive," she added.

Dr Matthew Watson of the University of Bristol, said any agreement to keep warming below 1.5C had significant consequences not stated in the draft text.

For Prof Chris Rapley, a climate scientist at University College London, the idea that 1.5C was an option at this stage revealed a "fundamental shift" in the tone and content of the negotiations.

"Now that nations have declared their voluntary emissions reductions commitments, the focus has turned to ramping up ambition. This is an historic change, and may at last herald the beginning of ‘the Greatest Collective Action in History’," he added.

Delegates will now work overnight for the next few days to whittle down the draft text further, reducing the number of square brackets and (hopefully) coming to compromises about the uncertain parts of the agreement.

They officially have two more days to finalise a COP21 deal and, perhaps in the biggest surprise of all to everyone at the Paris meeting, there seems to be a slim chance that the delegates will actually make that deadline.