The 12-day huddle under the UN Framework Convention on Climate Change (UNFCCC) means that, after 18 months of swapping visions, the process will at last get down to the details.
Little more than six months are left before the "Bali Road Map," launched in Indonesia in 2006, reaches its supposed destination at a Copenhagen summit: an accord that will transform global warming from a monster into a manageable problem.
On the table is a small mountain of paper whose notable feature is curly brackets, denoting discord among scores of submissions.
Despite the sprawling range of proposals, UNFCCC Executive Secretary Yvo de Boer said he hoped that the draft will be endorsed as a workable basis for talks over the coming months.
"There will be a negotiating text on the table for the first time," he told AFP. "I hope it will be well received, that it will be seen as a balanced representation of the different ideas that countries have come with."
The big goal is to slash emissions of greenhouse gases by 2050 compared to 1990 levels.
But that's where consensus largely ends.
In their proposals, many developing countries say rich countries, which bear historical responsibility for today's warming, should take the lead by cutting their emissions by 25-40 percent by 2020.
China has led the charge, demanding a cut of "at least" 40 percent.
But only the European Union, which has set its own reduction of 20 percent by 2020, deepened to 30 percent if other advanced economies play ball, is anywhere near such a figure.
After eight long years of vilification, the United States is now being warmly embraced in the climate arena as Barack Obama bulldozes George W. Bush's policies.
But Washington is also warning that the world cannot expect miracles.
A bill put before Congress would cut US emissions by 17 percent by 2020 over 2005 levels using a cap-and-trade system of the kind Bush loathed.
This approach would translate to a reduction of only four percent compared to the 1990 benchmark, but it would also ratchet up to 83 percent by 2050, the top US climate change negotiator, Todd Stern, said in Paris last week.
"We are jumping as high as the political system will tolerate," said Stern, characterising China's demand of a 40 percent cut by 2020 as “not realistic.”
Just as unresolved is what the emerging giant countries should do.
China is now the world's No. 1 polluter, and Brazil and India have also leapt up the emission ranks as their economies have grown.
Yet all refuse binding emissions targets of the kind that apply only to rich countries under the Kyoto Protocol, the UNFCCC treaty to be superseded from 2013 by the Copenhagen accord.