More than a hundred countries have backed an ambitious new climate deal that could see levels of greenhouse gas emission cuts reviewed and ramped up every five years.
Ministers from 195 countries are at a United Nations climate summit in Paris, which aims to secure a new deal to curb global temperature rises and prevent dangerous climate change.
As the talks enter their final days, the European Union and 79 African, Caribbean and Pacific (ACP) states have agreed they want to see a legally binding, ambitious and fair deal that sets out a long-term goal to tackle climate change which matches the science.
Crucially, the grouping that accounts for more than half the countries at the talks is backing a five-yearly review system which would see nations look at their pledges on cutting emissions and tackling climate change - and enhance the action they are taking where appropriate.
This regular review and ratchet mechanism, to prevent low levels of effort on tackling emission being locked into the agreement, is seen as a key element for those wanting an ambitious deal, with hopes the first review could take place before 2020 when the Paris agreement will kick in.
Making sure ambition can be raised is key to achieving a 2C limit to global temperature rises - beyond which "dangerous" climate change is expected - or the more stringent 1.5C many countries have backed.
This is because the current pledges by countries for climate action they will take up to 2030 will only put the world on a path to almost 3C.
Campaigners say the review mechanism is vital to the deal.
Mohamed Adow, Christian Aid's senior climate adviser, said: "This would make the Paris deal not just revolutionary but also evolutionary.
"It would mean it evolves to keep pace with the falling costs of renewable energy and other changes in the geopolitical landscape."
A new version of the text of the draft agreement is expected today, which it is hoped will make further progress on sticking points, including a long-term goal for the climate, the review mechanism and finance to help developing countries cope with climate change and develop cleanly.
But it comes amid fears that some countries are using the negotiations process to slow down progress so an unambitious deal is finalised in the last hours of the conference.
Meanwhile the "Basic" group of countries, Brazil, South Africa, India and China, are also calling for a legally binding and ambitious deal, and calling on rich countries to "substantially scale up" finance from the promised 100 billion US dollars (£67 billion) in private and public funding a year by 2020.
They also call for developed countries to take more action on tackling climate change before 2020.