The world’s governments are about to meet in Paris to discuss a global agreement on how to reduce carbon dioxide emissions and avoid the threat of dangerous climate change.

You may have seen this in the news.

Read on if you would like to understand a bit more about a meeting that will define this century.

This meeting is known as COP21. What is COP21?

It’s a meeting convened by the UN of those who are involved in the process of reducing human CO2 emissions.

In UN jargon: The 21st Session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC).

It’s also the eleventh meeting of those parties who signed the Kyoto Protocol, a former smaller-scale climate accord which only involves industrialised nations.

Why is it happening now?

They actually happen once a year. This is the 21st such meeting.

There have also been ongoing ‘negotiating sessions’ throughout the year, and draft agreements are now fairly ready for the big diplomatic push.

It won’t all happen in Paris.

Last year COP20 was held in Lima, and the year before that COP 19 was in Warsaw.

Previous commitments run out in 2020, so by 2015 the pressure is on.

Is this one the big one then?

After 21 attempts you may well wonder this. And weren't we told that COP15 in Copenhagen was the big one back in 2009?

Part of the reason COP21 is grabbing the world’s media attention is a new mandate given by the Intergovernmental Panel on Climate Change (IPCC) with its Fifth Assessment Report. This gives a far stronger scientific base for action and stresses the urgency of a deal.

Recent COPs have also been laying the groundwork for Paris, for instance calling on governments to get ready their own national commitments for COP21.

So what are we aiming for?

Officially: “adoption of a universal agreement that will provide a framework for transition towards low-carbon societies and economies able to withstand climate change”.

The hope is that this can be achieved by keeping atmospheric warming within the much discussed 2°C limit (compared with the pre-industrial era of ~1850). We’re currently on track for about 5°C.

Both attenuation (reducing greenhouse gas emissions) and the adaptation of societies to an already changing climate are on the table

This year ‘climate finance’ has come to the fore, especially finance for the developing world to adapt to climate change. A major hope is that the Green Climate Fund – a fund that is gearing up to wield $100 billion annually – will become institutionalised and attract private sector investment.

Will it work?

Delegates are drawing optimism from a few things. The highest profile is an announcement from China and the USA who have agreed to work together on ambitious emission cuts to combat climate change. This was independent of the UNFCCC process.

Additionally, thanks to some recent COPs in Durban and Warsaw, there is now a clear timetable and institutional framework. This means that negotiations should be less frantic than they were in Copenhagen in 2009.

Furthermore, by now the case for action is grasped by governments, the private sector and the public. Nine out of ten Europeans consider climate change to be a serious problem.

Nations have already submitted measures (Intended Nationally Determined Contributions, or INDCs), which go a long way towards the goal already.

And finally, because this is a legal agreement, courts of justice should be able to hold nations to account.

Why wouldn’t it work?

Decisions can only be made with unanimous agreements. This has seriously compromised outcomes in the past, most significantly with the Kyoto accords.

Copenhagen was deemed a failure because, among other things, it did not properly link the development agenda with the climate change one. However the emergence of the Green Climate Fund this time may change this.

The INDCs still fall short of a 2°C limit, currently predicted to only reach about 2.7°C.

Who is going to call the shots?

There will be 195 nation states along with the EU.

40,000 people are expected in total, which will be the largest diplomatic event France has ever hosted.

World leaders have left the diplomacy to ministers and civil servants at most previous COPs. However, the “high-level segment” towards the end of this conference will see world leaders say their bit. They have the power to tell their negotiators to agree with each other.

As ever, the US, China and the EU are likely to call some significant shots. However, now with the bigger profile of developing nations perhaps countries like India and Brazil will have louder voices.

Why are only governments making these important decisions?

The UN’s Framework Convention on Climate Change was adopted in 1992 to coordinate member states’ action on climate change as it was evident that no one country can solve the problem alone.

It has been suggested that a more polycentric climate governance system would be more effective, with groups such as cities, businesses and regions working together.

In Paris there will be NGOs, lobby groups and business organisations present too.

It’s also a chance for civilian action. Copenhagen saw 80,000 people on the streets, and record-breaking rallies are already being planned for Paris.

What goes on behind those closed doors?

Over the conference the delegates will argue about the clauses and sub-clauses in the draft agreement which have not yet been agreed upon. This will happen in small group sessions and in plenaries.

And by the time the world leaders arrive it should be ready to ratify.

At least, that’s the plan.