Ministers from around the world have begun high-level talks aimed at getting a new international climate deal, with the pressure on to reach an ambitious agreement.
With parts of the UK hit by severe rain and floods that rising temperatures may have played a part in, and warnings that extreme rainfall and flooding will worsen with climate change, the British team at the United Nations talks in Paris is being urged to secure a strong and binding deal.
The European Union, which negotiates as a bloc in the talks, has said it is keen to see an ambitious agreement which limits global temperature rises to less than 2C above pre-industrial levels - and it is "open" to the lower 1.5C goal some of the most vulnerable countries say is necessary for their protection.
European ministers, including the UK's Energy and Climate Change Secretary Amber Rudd, have warned that all countries will need to compromise to secure a deal as the conference enters what some are describing as the "sharp end" of the talks.
Ministers face key sticking points including finance for poor countries to cope with climate change, a long-term goal to bring greenhouse gas emissions to zero and a review and ratchet mechanism allowing countries to revisit their climate action plans and increase ambition.
Making sure ambition can be raised is key to achieving the 2C limit - beyond which "dangerous" climate change is expected - as current pledges by countries for climate action will only put the world on a path to around 3C.
The first day of the ministerial talks took place as a study suggested carbon dioxide emission rises were stalling, and are predicted to fall slightly this year, after coal use fell in China, renewable deployment increased and there was lower growth in oil and gas demand.
But experts warned emissions had to fall to zero in coming decades to stabilise the climate, and there was only "an extremely thin chance" of curbing temperature rises to 1.5C, while even meeting the 2C goal is "very difficult".
Speaking at the opening of the high-level part of the talks, UN secretary general Ban Ki-moon reminded ministers of the political will for a deal, with more than 150 world leaders attending the first day of the summit last week and backing robust action.
Ms Rudd is one of two ministers chairing a group on increasing the action countries will take to curb emissions before 2020, when the Paris deal would kick in, as well as playing a role within the EU negotiating team on ambition for cutting emissions after the end of this decade.
But the Energy Secretary and the UK Government have faced criticism domestically for curbing measures to cut emissions including subsidies for renewables and energy efficiency, and the UK is likely to miss its EU 2020 targets for renewable energy.
Scotland's First Minister Nicola Sturgeon, who was at the talks in Paris to promote her country's climate action, said the whole EU was speaking with one voice to try to get a "solid, ambitious" agreement.
She said she did not want the focus of her visit to be on points of disagreement between Scotland and the United Kingdom governments.
But she said: "It's no secret we think some of the policy decisions taken recently, wind subsidies and withdrawing the carbon capture competition, really do run counter to what we're trying to do in terms of climate change and the move to a low carbon economy."
She said all developed countries would face increasing scrutiny on the extent to which their rhetoric on climate change is matched by policy.
Ms Sturgeon said she thought there was a mood of "cautious optimism" at the conference despite the thorny issues.
The president of the COP21 talks, French foreign minister Laurent Fabius, has brought the negotiations together under the so-called Paris Committee to make progress and facilitate compromises between the 195 countries negotiating the agreement.
Groups led by ministers will cover areas including support for countries to tackle climate change, how to differentiate between rich and poor countries in the action they will take, and the ambition of the treaty including a long-term goal to cut emissions and periodically reviewing progress.
The French have set a tough timetable, wanting a final draft of the deal by Thursday, but experience from previous negotiations suggests the talks will overrun their official finish on Friday.