Under an ominous shadow cast by the US presidential election, the world's nations gather in Morocco Monday to flesh out a landmark climate deal that promises to save humanity from itself.
The just-activated Paris Agreement, inked in the French capital last December, is the first treaty binding all countries, rich and poor, to halt global warming, caused mainly by the burning of coal, oil and gas.
"It is now the roadmap in the fight against climate change," said Manuel Pulgar-Vidal, Peru's former environment minister and head of climate and energy for green group WWF.
But as 15,000 negotiators, CEOs and activists from 196 nations gathered in Marrakesh settle in for the 12-day UN talks, all eyes are on the United States, where voting Tuesday could thrust climate denier Donald Trump into the White House.
When it comes to global warming, the stakes could hardly be higher, President Barack Obama 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.
The most immediate task is "finishing the rulebook" for the complex accord, said Laurence Tubiana, France's top climate negotiator for the Paris talks.
Concretely, that means working through scores of still-contentious issues, including how to measure and track each nation's CO2 emissions; disbursing hundreds of billions of dollars in financing in a way that reassures both rich and recipient nations; setting criteria for compensating poor countries devastated by climate-fuelled storms, droughts or floods.
"COP22 is really a COP of implementation and action," lead US negotiator Jonathan Pershing told journalists in a teleconference, using the acronym for the annual Conference of the Parties climate meet.
By informal consensus, 2018 is the target for working through these issues.
- 'Plug the gap' -
2018 is also the next high-stakes rendezvous in the ongoing talks when nations can further narrow the so-called "emissions gap" between their carbon-cutting pledges and the level of reductions needed to keep the planet from dangerously overheating.
That gap is still huge, and getting bigger every year.
On current trends, the Earth will heat up about three degrees Celsius (5.4 degrees Fahrenheit) above the pre-industrial era benchmark, a sure recipe for climate catastrophe, according to scientists.
The Paris Agreement calls for capping global warming at under 2.0C (3.6F), and even 1.5C (2.7F) if possible -- a hugely daunting challenge.
"We have to plug that gap," Tubiana told AFP. "The big battle of the next two years is how to get countries to increase their ambition."
Negotiators will be buoyed by a raft of encouraging signs.
New figures show that renewable energy attracted record investment of 300 billion dollars (270 billion euros) in 2015, outstripping fossil fuels.
Installed capacity of solar, wind and hydro also, for the first time, overtook carbon-intensive coal, which is in sharp decline.
A separate international agreement inked last month ensures the phase out of potent, manmade greenhouse gases known as HFCs, potentially shaving 0.5C (0.9F) off global temperatures by the end of the century.
Businesses -- ever-more present at the UN climate forum -- have also become crucial drivers of change, motivated by the need to anticipate the rapid shift to a low- or zero-carbon global economy.
At the same time, however, climate scientists are sending up red flags.
After two successive record-breaking years, 2016 is shaping up to be the hottest ever registered.
And still-climbing concentrations of CO2 in the atmosphere passed a critical -- if symbolic -- threshold of 400 parts per million in 2015.
"If we don't start taking additional action now," warned UN Environment Programme head Erik Solheim, "we will grieve over the avoidable human tragedy."
Ministers -- including US Secretary of State John Kerry -- will join the November 7-18 talks on November 15 to lend political impetus.
Marrakesh, Morocco | AFP