The COP26 summit in Glasgow is being billed as the biggest UN climate conference since countries secured the Paris Agreement at talks in the French capital in 2015.
However, there is no big new deal like the Paris Agreement to agree at COP26 – instead Glasgow has to deliver on the promises made six years ago and, alongside the formal UN negotiations, drive action to tackle the worsening climate crisis.
Here are some of the key areas where action is needed and where momentum and new commitments could help Glasgow be seen as a success:
Keeping 1.5C within reach
Glasgow has been billed as the last best chance to limit global warming to 1.5C in the long term.
Under the Paris Agreement, countries committed to curbing temperature rises to “well below” 2C above pre-industrial levels and to pursue efforts to limit warming to 1.5C – beyond which worsening impacts of climate change will be felt.
But, back in 2015, it was clear the emissions cuts countries had signed up to left the world far off track to meet the global temperature goals so, under the Paris deal, countries were due to bring forward more ambitious post-2020 national plans ahead of COP26.
Even with new plans many countries have brought forward, the world is nowhere near on track for the 1.5C target, and there are concerns that some countries might turn their attention to post-2030 action, when much more efforts are needed within the next ten years.
So UK officials want to see countries addressing how to close the gap between ambition and action required up to 2030, as part of the negotiated text that it is hoped will be secured by the end of the two weeks of talks.
The key to success at COP26 is delivering on a long-promised $100bn a year for 2020 to 2025 for poorer countries to develop cleanly and cope with the impacts of climate change.
It is seen as a matter of trust between developing and developed nations for donor countries to deliver on the promised private and public climate finance, and conversations will also begin on unlocking further funds after 2025.
There is pressure for finance to be split equally between efforts to cut emissions and to adapt to climate change, and also pressure to address demands on support for loss and damage caused by extreme weather and rising seas.
Coal is the dirtiest fossil fuel, and polluting coal plants need to be phased out in the next two decades to meet climate goals, according to the International Energy Agency.
The UK wants to see more momentum on ending the use of coal, and is urging developed countries and regions to commit to phasing it out by 2030, or by 2040 in the case of developing nations, and for commitments to no new plants.
Road transport accounts for a tenth of global emissions, so countries are being urged to commit to ensuring all new car and van sales are zero emission vehicles by 2035 or 2040 and put in place policies to boost uptake.
Vehicle manufacturers are also being urged to commit to selling only zero emissions vehicles by 2035 or earlier.
Healthy and restored forests can absorb and lock up vast amounts of carbon from the atmosphere, and protecting trees – along with other carbon-storing natural habitats such as peatlands – is seen as key to cutting emissions and helping communities and wildlife cope with climate change.
The pressure is on countries to take steps to halt and reverse deforestation, switch to sustainable agriculture and support efforts to protect or conserve 30% of the world’s land and oceans by 2030.
While the most significant greenhouse gas is carbon dioxide, methane – from sources including livestock, agriculture such as rice production and fossil fuel extraction – is a powerful, but short-lived climate-warming gas.
Cutting emissions of methane is seen as a key way to curb warming in the short-term.
A US and EU-led “global methane pledge” which commits countries to cut their emissions of the gas by 30% by 2030 has already garnered a number of signatures ahead of its formal launch at COP26, where it is hoped more will sign up.
The Paris rulebook
Back in the negotiations, there are still some outstanding issues about how bits of the Paris Agreement are going to work, and they need to be sorted out to make it operational and effective.
There are three issues: transparency, Article 6, and common timeframes, and negotiating them will be key to COP26.
A transparency regime would see UN-run assessments of what countries are doing on climate, but all countries need to agree to face these reviews.
Countries are meant to submit updated climate plans – or NDCs – every five years under the Paris Agreement, but there is no coherence on how long a period those plans cover.
Agreeing common timeframes will make it clearer who is doing what and help comparisons.
And then there is Article 6: the part of the Paris Agreement which covers carbon markets.
Finalising the rules on how these markets work would allow countries to buy carbon credits that fund new clean projects or protect and restore forests to cover their emissions as part of climate action.