Laurent Fabius told African delegates at UN climate talks in Bonn that "we know the politics in the US Whether we like it or not, if it comes to the Congress, they will refuse."
If negotiators follow his plan, that would exclude an international treaty that has legally-binding limits on greenhouse gas emissions something some countries still insist on but which would have no chance of being ratified by the Republican-controlled Congress.
Those pushing for a legally binding deal in Paris include the 28-nation European Union and small island nations who fear being wiped out by rising seas.
Amjad Abdulla, a Maldives delegate who is the chief negotiator for the small-island group, said while the group still wants a binding agreement, "I think it's important that we get everyone on board. We are still looking into options."
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The Obama administration has pledged to reduce US emissions by 26-28 per cent below 2005 levels by 2025.
Peruvian Environment Minister Manuel Pulgar-Vidal said he was "completely sure that we will have an agreement in Paris," despite the complex political situation in the US Jennifer Morgan, a climate policy expert at the World Resources Institute, said it was encouraging that Fabius was raising the legal issue now so it can be dealt with before the Paris conference.
Negotiators also need to decide how to differentiate between what rich and poor countries should do to fight climate change, and how to verify that countries are doing what they say they would.