These are the players -- nations and alliances -- that could make or break the chance of making deal by the December 11 deadline for the end of the talks:
CHINA
The world's top carbon polluter since 2007, China has made substantial commitments to curb greenhouse gas output, pledging to peak emissions around 2030, if not sooner. Unlike other developing nations, notably India, China favours the early implementation of a system for monitoring progress on countries' carbon-cutting pledges.
POTENTIAL DEAL BREAKERS: China has joined the mainly rich-country club of climate finance donors, but insists it does not want this voluntary role to be inscribed in the Paris agreement. Only rich nations should have a finance obligation, it insists.
THE UNITED STATES
Working around a Republican-dominated Congress hostile to action on climate change, President Barack Obama's administration has used its executive authority to curb emissions in industry, the energy sector and from vehicles. Like Beijing, Washington favours a periodic review of country pledges, which are currently not enough to meet the UN target of capping global warming under two degrees Celsius from pre-industrial levels.
POTENTIAL DEAL BREAKERS: The United States insists that the concept of "differentiated responsibilities" for rich and developing nations -- enshrined in the 1992 climate convention -- is out of date and has no place in a new accord. Backed by the European Union, the United States is also wary of efforts by developing countries to make rich ones pay "loss and damage" for climate change harms -- this is too close, it says, to liability for compensation.
INDIA
Number two in terms of in population, and number four in emissions behind China, the United States and European Union, India has dug its heels in on a number of key issues. Along with other developing countries, New Delhi insists that any deal must make it clear that nations which industrialised first must lead the fight against global warming.
POTENTIAL DEAL BREAKERS: New Delhi says it cannot reduce its carbon output or boost renewables without guarantees of financial aid and green technology. It also opposes language in the core agreement calling for "decarbonisation" of the world economy. With 300,000 people still bereft of electricity, India cannot afford to foreswear coal, environment minister Prakash Javadekar has said. He has also called a proposal for reviewing carbon-cutting pledges in 2017/18 -- two years before they go into effect -- "absolutely ridiculous".
VULNERABLE NATIONS
Forty-three nations home to a billion people particularly exposed to rising seas, superstorms and expanding deserts, have banded together under the Climate Vulnerable Forum to push for key demands.
POTENTIAL DEAL BREAKERS: The bloc insists that half of the promised $100 billion per year in climate finance from 2020 must come from governments, and seeks assurances that the amount will increase over time. Calling it an existential issue, the group -- which includes Bangladesh, the Philippines, small island states and poor nations in Africa -- wants the 2 degree C target lowered to 1.5 degrees.
SAUDI ARABIA
Saudi Arabia is regarded as a potential obstacle to a deal in Paris. While other countries seek to move away from fossil fuels, Riyadh has called for sustained investment in oil output capacity, on which its economy is largely based.
