EU climate chief Connie Hedegaard acknowledged Friday that "difficult and unpleasant" negotiations lay ahead with countries like India and China to agree a global framework to cut greenhouse-gas emissions.
Hedegaard played an instrumental role at UN climate talks in Durban last December in building consensus towards a legal accord that for the first time will bring all major emitters under a single legal roof.
The agreement was seen as a breakthrough, given India and China's long-held opposition to any sort of legally binding structure for emissions cuts.
Both countries fear it would stifle the economic growth needed to lift millions out of poverty and argue that a greater portion of the cuts' burden should fall on industrialised nations.
Speaking on the sidelines of a Sustainable Development Summit in New Delhi, Hedegaard said the next step was to get global consensus on a peak year for emissions and how cuts would be distributed and legally enforced.
"We've come to the point where we have to start this very difficult and very unpleasant discussion," Hedegaard said.
"Some do not dare to discuss it because they think they are harming themselves," she added -- a clear reference to India's insistence that no agreement should deprive it of its right to development.
The agreement in Durban envisaged the adoption of a global pact on emissions cuts by 2015 -- although it allows entry into force to be delayed until 2020.
After intense last-minute haggling, the term "legally binding" was rejected in favour of a compromise wording that the pact would have "legal force".
While the precise nature of that "legal force" still has to be debated, Hedegaard said simply getting countries like India to accept the concept of a legal framework was a huge step forward.
"Nobody in Europe is arguing against the need for India to have substantial growth," she said.
"But when it comes to climate change, we are mutually interdependent... and we must be equally bound.
"When the world faces big, urgent challenges... experience shows that we have to have some sort of legal framework," she said.
Critics of the Durban accord say it provides for too little, too late, citing warnings that global emissions must start to peak before 2020 to avoid average global temperatures rising by more than 2 degrees Celsius (3.6 degrees Fahrenheit) from pre-industrial levels.
According to research presented by German scientists, the world is on track for a 3.5 degrees Celsius (6.3 Fahrenheit) rise, spelling worsening droughts, floods, storms and rising sea levels for tens of millions of people.