The Paris Climate Conference is underway. This is the 21st Conference of the Parties (COP21) to the 1992 UN Framework Convention on Climate Change (UNFCCC) to which 195 states are signatories and, like previous COPs, it has been hailed as the most important climate conference in history. This is because previous climate summits have so far failed to confront a challenge that is now getting out of hand.

Atmospheric concentrations of carbon dioxide have risen past 400 parts per million, the highest for many millions of years. Global average temperatures have surged by 1°C since the industrial revolution, and if emissions continue unabated, we are on track for up to 5°C. Unfortunately we are still rapidly burning our 'carbon budget', the amount of carbon dioxide that can be emitted to maintain a safe climate. This could be spent in as little as 25 years, after which at least 2°C warming becomes inevitable, and many changes become irreversible (including the melting of the Greenland ice sheet).

So the seriousness of the challenge and the urgency of a response could not be clearer. 

The hope is that COP21 in Paris will finally come to grips with the issue. There have been significant COPs since the first in Berlin in 1995, including COP3 in Kyoto, where the Kyoto Protocol was agreed, and COP13 in Bali, when Australia finally ratified the Kyoto Protocol. But in addition to 'good' COPs there have been 'bad' COPs, with COP15 in Copenhagen in 2009 considered to have been not so wonderful.

The Copenhagen COP attracted criticism for many reasons, among which was the fact the resulting agreement, the Copenhagen Accord, was not legally binding. However it was significant because it included a definition of dangerous climate change (+2°C) and it set in motion a process for states to pledge emissions cuts. So far 183 nations have submitted pledges, and, if fully implemented, they could hold global warming to 2.7°C. This is not remotely 'safe' but is a world of difference away from the 5°C or more that we currently are on track to experience. Australia’s post 2020 target is widely judged to be inadequate in meeting the 2°C commitment, and Australia does not currently have effective policies in place to reduce emissions at the scale and pace required.

There has been extensive speculation as to what obligations the Paris Agreement might contain. Understandably, this has mostly focused on what the agreement will do substantively to address climate change. But just as interesting as the substance, indeed perhaps more so to international lawyers, is what form or style the agreement will take. Will it be a fully-fledged, legally binding treaty? Or will it be similar to the non-binding Copenhagen Accord? Or could it comprise something in-between?

We should not assume an agreement that is legally binding is necessarily good and one that is not is necessarily bad. The Kyoto Protocol is legally binding but delivered minimal global emissions reductions. And there are non-binding, or hybrid options that combine binding and non-binding efforts that could be more effective at delivering emission reductions.

At COP17 in Durban, the UNFCCC parties agreed that in Paris they would settle 'a protocol, another legal instrument or an agreed outcome with legal force under the UNFCCC applicable to all parties'. This goal has been interpreted in different ways by different states. US Secretary of State John Kerry, for instance, has said the Paris Agreement will not be a treaty. But what Kerry meant is that the US would like a text that meets the description of an 'executive agreement' under US constitutional law, allowing the President to sign it without going to the Senate, a step that would be required if it were a treaty. Nonetheless for the purposes of the 1969 Vienna Convention on the Law of Treaties, such an agreement could still be a binding treaty satisfying other parties, including the EU.

As Australia's Ambassador for the Environment, Peter Woolcott has explained, the old Kyoto approach of top down targets in a binding treaty is no longer fit for purpose, and the only way forward is to have a process which 'allows us to build action over time to keep within the 2 degree guard rail through a regular periodic process that prompts States to revisit and update their national mitigation efforts through five-year cycles'.

Beyond these issues as to formal status, there are fascinating questions as to what mix of obligations the Paris Agreement may contain.

The draft text reveals a spectrum of views on how stringent those obligations should be, and the mix between pledging, reporting and monitoring obligations, and obligations to cut emissions.

This text recognises the urgent threat of climate change, and includes a commitment to keep temperature rises below 2°C or 1.5°C (the latter would be safer, but we no longer have a hope of meeting it). There is a provision (containing lots of bracketed text) setting out the overall objective to reduce emissions; one of the options is to achieve carbon neutrality, a goal which both the Australian Government and Opposition support, although they disagree on the timing for achieving it.

The draft also obliges all parties to have targets and to implement them. To meet US constitutional requirements, it seems likely states will agree that the targets themselves are not obligatory, but there would be a legally binding obligation to pledge them and to have plans to implement them. The draft also includes a provision requiring targets to be set for five year periods, with each target to be stronger than the last, and justified in terms of being a fair contribution to the 2°C objective. There is to be a regular stocktake of individual and collective action, and a system of transparency to ensure that states do not make empty promises.

If you want to see what rising temperatures means for Australia, the CSIRO has developed a handy tool showing where climate change is effectively moving your home (if you live in Melbourne you are on the move to Dubbo; if in Sydney, then Brisbane; if in Darwin you are heading to a climate currently found nowhere on earth). Unmitigated climate is likely to cause unmanageable levels of economic disruption to most states and cause cascading national security threats. And carbon dioxide is not only warming the planet, it is also driving ocean acidification as the seas draw down carbon (if left uncontained, heat and acidification will cause the ocean food chain to collapse).

The Paris Agreement will not itself fix the climate crisis. Indeed it will studiously avoid confronting the central question; how to set and divvy up the global carbon budget. But it is hoped that Paris will mark a break from the past and finally set in motion a collective process that is up to the task of meeting this unprecedented global challenge.

Photo by Mustafa Yalcin/Anadolu Agency