AS Advent begins around the world, for lobbyists, campaigners, and negotiators, the first week in December marks crunch time at the annual UN climate-change summit.

The 18th Conference Of the Parties (COP18), meets this year in the fossil-fuel-loving capital of Qatar, Doha. Its object is to try and make progress on curbing the harmful carbon emissions that contribute to climate change.

Minds have been focused this year by the extreme weather events around the world, from severe droughts in the American south and the Sahel region of Africa, to the unseasonally catastrophic flooding in the Philippines, and the Superstorm Sandy, which caused devastation across the Caribbean and on America's East Coast.

At last year's summit in Durban, South Africa, all 196 nations agreed to draw up, by 2015, a new global agreement to tackle climate change, which would come into force by 2020.

Here in Doha, policy-makers have been negotiating four main areas.

The first is to start work on the global treaty agreed in Durban, known as the Durban Platform. The parties must have this in place by 2015 at the latest.

The second is to agree what countries will be doing between now and 2020 - a crucial period, as scientists are warning that the planet must stop increasing carbon emissions by 2017 to avoid catastrophe. To do this, parties are negotiating an extension of the Kyoto Protocol, the only legally binding global climate treaty, in which developed countries, such as those in the EU and Australia, have signed up to reduce their emissions.

The third is to agree what measures will be taken by countries not covered by the Kyoto Protocol, which is everyone else. These include developed countries that have opted out of Kyoto, such as the United States and Japan, and developing countries that have become major emitters, such as China and India.

The fourth plank of the negotiations is that of climate finance. In 2010, developed countries agreed to create a fund which would distribute $100 billion a year to developing nations, to help them adapt to the impacts of climate change, such as flooding in Bangladesh and droughts in Africa. It would also help them to develop in a low-carbon way using modern technology and renewable energy.

Although this Green Climate Fund has been established, it is currently an empty pot, and needs developed countries to start filing it with cash.

So, there is plenty of work for decision-makers to get through. On Wednesday, Government ministers from around the world will arrive at the talks to hammer out the final details, before the summit closes in the early hours of Saturday morning.

Mohamed Adow, Christian Aid's senior climate-justice adviser, is at the talks. "This is an important transition year for the planet and for the UN climate negotiations. It's important that the work of the last 20 years is not lost and is incorporated into the new Durban Platform.

"Crucially, it needs to be built upon what the science is telling us is required to avoid the planet warming by more than 2 degrees Celsius above pre-industrial levels. We've already seen what is happening to the climate around the world in recent years, and that is at just 0.8 degrees of warming.

"We can't allow the new agreement to be dictated by simply what governments offer to do. If that happens, climate change we've already seen will get worse, and the poorest people in the world will suffer the most."

Joe Ware works in the Christian Aid communications department.