In just 12 months, global warming has been elevated to the great challenge of our time, a cause for public and celebrities alike, a Nobel-winning issue and a headache for politicians of every rank.

In a vast report, the UN's Intergovernmental Panel on Climate Change (IPCC), issued its grimmest scientific assessment yet.

Its prose lacked varnish, was riddled with jargon impenetrable to the outsider and admitted to areas of doubt or uncertainty -- but this honesty made the findings all the more terrifying.

Its verdict: global warming is a fact. Humans bear inescapable responsibility for it, thanks to the uncontrolled burning of fossil fuels.

Climate climate change is already visible, in the form of shrinking glaciers and snow cover, and misery for millions lies just decades away. On current trends, said the IPCC, drought, floods, rising sea levels and more violent storms will lead to hunger, disease and homelessness. No country will escape damage.

The IPCC's Fourth Assessment Report provided a jolt of fear that translated into a surge of public awareness -- and drought, floods or storms, in North America, Australia, South Asia and eastern Europe, also played their part.

The Arctic's summer sea ice shrank to its lowest recorded extent, and for the first time in history, ships were for a while able to travel through the Canadian Northwest Passage, the legendary trans-Arctic link between the Pacific and Europe.

At the G8 summit in June, President George W. Bush, facing accusations of indifference, joined other rich countries in vowing to pursue "substantial" cuts in carbon emissions and "seriously consider" Europe's aim of halving this pollution by 2050.

In July, the Live Earth concerts girdling the globe enlisted musicians and actors to a cause that for years had been the lonely fight of greens.

In September, UN Secretary General Ban Ki-moon nailed climate change to the mast of his tenure by staging an unprecedented summit.

"The time for doubt has passed," said Ban. "What we do about it will define us, our era, and ultimately the global legacy we leave for future generations."

That same week, Bush launched a US initiative gathering 16 countries that together account for around 80 percent of global emissions.

In November, climate change ascended into the pantheon of Nobel issues, as former US vice president Al Gore and the IPCC were awarded the 2007 peace award.

And in December came the climate meeting in Bali.

There, 190 nations under the UN Framework Convention on Climate Change (UNFCCC) agreed to launch negotiations leading to a new treaty for slashing emissions and helping poor countries most exposed to climate change.

But, with its extraordinary scenes of stonewalling and finger-pointing, the Bali marathon also exposed the inconvenient truth about climate change.

Everyone agrees that climate change is a danger. Indeed, many experts say it is coming upon us much faster and more viciously than was thought possible just a few years ago.

But with trillions of dollars at stake to curb fossil-fuel pollution, switch to clean energy and shore up the defences of developing countries, there is absolutely no agreement as to who should pay the bill.

Should it be the rich countries, which got prosperous by gorging on cheap oil, gas and coal and thus are to blame for today's warming?

Or should it be China and India and other emerging giants that will be responsible for the even greater problems of tomorrow?

Bali was in essence about negotiations for launching negotiations.

For the next two years, while the clock ticks for Earth's climate system, officials will haggle over a treaty of fiendish complexity that may not even see daylight if Bush's successor objects to Kyoto Protocol-style emissions curbs.

Ordinary people may wonder why, if an arsonist has set fire to the town, the local council has chosen to spend the next two years squabbling over a long-term programme about how to tackle the blaze.

"We are struggling to keep our heads above water on this issue. The gap between the need for action and political rhetoric is growing," says Bill Hare, of the Potsdam Institute for Climate Research near Berlin.

Hare admits that the failure touches at the very heart of the nation-state basis for planetary governance.

In other words, if the UN system, moving at tortoise pace because of the need for consensus, cannot tackle this urgent global problem, it may not have a future at all.

"Maybe it does raise that question. But we don't have time to solve that problem while simultaneously trying to solve the climate crisis," said Hare. "We have what we have, and have to work with it."

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