Next year holds a big dream: by its end, the world will have forged a treaty in Copenhagen to shrink global warming from mankind-threatening juggernaut to manageable problem.
Unprecedented in scale and complexity, this accord, due to take effect from 2012, will rein in the greenhouse gases that stoke global warming and throw a lifeline to poor countries exposed to mutated weather patterns.
But realising this vision will now require extraordinary effort.
Climate change became the buzzword of 2007, when UN scientists published a bible-sized report spelling out perils from rising seas, drought, flood and storms, an achievement that earned them, with green guru Al Gore, the Nobel Peace Prize.
In 2008, the issue began to fade and almost vanished completely when the world financial crisis struck.
Compared with demands to muster trillions of dollars and save millions of jobs, climate change suddenly looked to many politicians like a threat beyond the horizon.
Global warming only made its return to the world agenda towards year's end.
Barack Obama, newly elected, promised to bulldoze President George W.
Bush's controversial climate policies. He vowed to set binding caps to drive down US emissions of greenhouse gases and stage a return to the global arena after eight years of isolation.
The European Union overcame internal feuding on the cost of going green by agreeing to slash emissions by 20 percent before 2020 over 1990, and spur energy efficiency and renewable sources.
That accord, at a fraught summit in Brussels last week, breathed life into talks in Poznan.
Just before dawn on Saturday, the 192-member UN Framework Convention on Climate Change (UNFCCC) approved a work programme for negotiations leading up to the Copenhagen Treaty.
The stage is now set for a 12-month haggle focussing on this question: who should restrain their carbon emissions, by how much and by when?
Should the burden be shouldered just by rich countries, historically to blame for global warming?
Or should emerging giants such as China and India -- already massive polluters and set to be the big problem for decades to come -- break new ground by joining advanced economies in committing to binding emissions goals of some kind?
In exchange for these or other concessions, developing countries will set down hefty demands for help. Inventive solutions will be essential.
Underpinning it all is money: the cost of easing addiction to cheap, dirty fossil fuels and shoring up defences against climate change.
'I can pretend that it's not the case, but we all know that it is,' UNFCCC chief Yvo de Boer admitted, as he reflected on the financial heart of the quid pro quo.
With storm clouds over the world economy, the outlook for Copenhagen is not good, judging by the time-worn principle that an economic crisis always trumps an environmental problem.
'Remember, this is a political exercise,' said Tim Wirth, a former Democratic US senator who led climate negotiations under Bill Clinton.
'The people making these decisions have got to get elected. It is not scientists and environmentalists that are making these decisions.'
Greens have argued for decades that the link between economic growth and polluting fossil fuels must be smashed and this has found powerful backers in Obama and UN chief Ban Ki-moon.
Ban called for a 'Green New Deal' in which a chunk of the billions earmarked for reviving the world economy would leverage the switch to a job-creating, low-carbon future.
And he said he may hold a special summit during the UN General Assembly in September to give an extra push to the climate talks.
So many hopes are riding on Obama. But the next US president has just months to prove his credentials on climate change before the Copenhagen showdown, while at the same tackle the US economic crisis and juggle with powerful lobbies.
British economist Nicholas Stern, author of the 2006 Stern Review on the costs of climate change, said 2009 demanded boldness.
The world had the chance to make a historic shift, he argued in Poznan.
'We can actually lay the foundations over the next two years for the low-carbon growth which will be the sustaining growth of the future,' Stern said.
But, he added: 'I don't take any of this for granted. The human race has an incredibly well developed capacity to screw up, and we may miss this chance.'