Diplomats from 196 nations will flesh out the planet-saving plan inked in the French capital last December.

“We have made possible what everyone said was impossible,” said French environment minister Segolene Royal at the opening ceremony, in which she handed over stewardship of the climate forum to Moroccan foreign minister Salaheddine Mezouar.

Royal announced that 100 countries have ratified the Paris Agreement, which entered into force last Friday, a record time for an international treaty.

Amid growing alarm at the gathering pace of climate change and its impacts -- rising sea, deadly storms, drought and wildfires -- the world’s nations have moved quickly over the last year to tackle the still-growing problem.

But as 15,000 negotiators, CEOs and activists settle in for the 12-day talks, all eyes are on the United States, where voting on Tuesday could thrust Trump into the White House.

When it comes to global warming, the stakes could hardly be higher, President Barack Obama has warned.

“All the progress we’ve made on climate change” -- including the Paris pact, decades in the making -- “is going to be on the ballot,” he told TV talk show host Bill Maher on Friday.

The Republican candidate cannot carry out his threat to “cancel” the still-fragile accord, but a Trump victory could cripple it, experts here agree.

Democratic opponent Hillary Clinton has vowed to uphold Obama’s domestic energy policies and international climate commitments.

In Marrakesh, front-line diplomats must roll up their sleeves and work through scores of procedural issues that will make the difference between success and failure.

They have informally set 2018 as the deadline for laying that groundwork, Royal told journalists the day before the talks opened.