Bit by bit, the world’s governments have started bringing forward new pledges for reducing greenhouse gas emissions after 2020. They will be collated in time for the Paris climate summit at the end of this year – and the negotiation of a new climate change deal.

But do these new promises, known as Intended Nationally Determined Contributions or INDCs, have any legal force? What will happen if countries don’t deliver? In the wake of previous failures to reach a global deal for tackling emissions, are we really about to see a “legally binding global climate agreement” for emissions reductions after 2020 – or another fudge?

In theory, the world’s governments are already legally committed to tackling climate change. The United Nations Framework Convention on Climate Change (UNFCCC) treaty – negotiated more than two decades ago – commits its signatories to stabilising greenhouse gas concentrations in the atmosphere at a level that would “prevent dangerous anthropogenic interference in the climate system”.

That promise is legally binding. It’s also pretty unenforceable – as it doesn’t say what it means for any governments, collectively or individually, or on what timeline.

According to observers, an additional commitment to limit global temperature rise to below 2°C above pre-industrial levels – a generally agreed benchmark for “dangerous” climate change – is likely to be folded into any agreement reached in Paris. But again, it’s rather hard to convert this aim into legal commitments for specific countries.

Paris is likely to produce some kind of legal deal. After failing to reach consensus in Copenhagen in 2009, negotiators finally agreed in 2011 to create “a protocol, another legal instrument or an agreed outcome with legal force” by the end of this year.

But it’s not clear yet what this will mean in practice. It could lead to a new treaty, or a protocol (a formal amendment to the UNFCCC treaty), or one or a series of Conference of Parties (COP) ‘decisions’. Treaties and protocols are legally binding but require ratification by member state governments – a long process which doesn’t always happen. COP decisions have some legal force, but are not binding in the same way.

In any case, a legally binding deal doesn’t necessarily mean legally binding emissions targets. Dr Harro van Asselt of the Stockholm Environment Institute tells Road to Paris:

“The ‘agreed outcome with legal force’ language was inserted last minute in Durban to bridge the differences between the EU and India … However, the problem is that not all countries would like to have everything included under such a ‘legally binding deal’ … One key question is whether INDCs [country proposals for reducing emissions after 2020] are part of the ‘legally binding’ part, or whether they are agreed through other means (e.g. COP decision or Appendix or – as some have suggested – informal documents)”

Promises to reduce emissions may not be included in the legally binding part of the deal. Even if they are, the details of the language also make a big difference. Academic director of the Institute for European Studies Professor Sebastian Oberthür suggests the Paris summit could, at the least, result in some procedural obligations – for countries to report on their emissions, or the measures used to achieve them. Negotiators may also agree on an obligation to “submit” pledges to reduce emissions, to “make best efforts” to achieve them, or to “implement” them – but are less likely to agree to an obligation to “achieve” them, he says.

Similarly, it is extremely unlikely that pledges rich countries have made in the international negotiations to transfer $100 billion to poorer countries by 2020, or to support them in adapting to climate change, will be legally binding under the new deal.

The world has agreed to legally binding emissions targets in the past. The Kyoto Protocol, negotiated in 1997, set emissions targets for richer countries up until 2012. The Protocol included systems for monitoring, reporting and verification and promised “consequences” for countries that didn’t comply.

But, in practice, the deal proved to be toothless. Most notably, Canada failed to comply with its commitments under the Kyoto protocol, and then withdrew from it entirely, without suffering any penalties.

Under the new system, countries are proposing their own emissions reductions targets – a ‘bottom-up’ rather than a ‘top-down’ approach. Ultimately, this may be more effective than the top-down approach, because it encourages countries to embed the promises in their own legislation. Director of the Strathclyde Centre for Environmental Law and Governance Dr Francesco Sindico points to legal action taken by green NGO Friends of the Earth against Canada’s failure to deliver on its Kyoto Protocol emissions targets in 2008. The legal challenge failed – but would probably have stood more chance of being successful if Canada had put the pledge in its national legislation, he says.

Other commentators argue that non-legally binding targets will encourage greater ambition, and greater buy-in. Politically, it is particularly unlikely that major emitters China and the USA will agree to legally binding targets.

The Paris deal could still retain some aspects of a top-down system – for example processes to assess and review emissions pledges countries submit. Negotiators haven’t yet agreed on what that might look like, however.

One theme that frequently emerges is the increasing complexity of the whole process. Dr Van Asselt argues that international climate law is in a state of “existential flux” – with the formal treaty architecture that have dominated international climate co-operation giving way to more complex, less clear-cut structures. Voluntary pledges, bilateral negotiations and agreements and civil society are all playing an increasingly important role in driving emissions reductions.

In five years time, we could be paying just as much attention to city Mayors’ agreements to reduce emissions, or to industry-led agreements, as to the UNFCCC process, argues Dr Sindico.

The simple question of whether the international climate process imposes sanctions to force countries to tackle climate change could soon start to look rather out of date. But the lack of those sanctions also means there’s a big question over how fast the world is going to reduce emissions.