COPENHAGEN (AFP) - For the past decade, the effort to muster an alliance of nations to fight climate change has seemed at times like a train wreck in slow motion.

In Copenhagen last week, there were moments when that crash finally -- horribly -- appeared to have happened.

The United Nations had billed December 18 2009 as the day when all countries would rally under its banner, forging a strategy to combat the greatest threat facing humanity this century.

Instead, the day will be recalled for the chaotic haggling among a select group of a couple of dozen top leaders.

They put together a non-binding deal -- essentially the lowest common-denominator -- that not only left climate action lodged in low gear but also drove a wedge in the world community.

Only by gavelling the document through a plenary session, to the fury of developing nations who said they had been ignored, was the UN able to stop the "Copenhagen Accord" from being strangled at birth.

Diplomats interviewed by AFP were appalled at the backroom circus, the crippling damage to global consensus and the failure of a two-year process to spell out ambitious targets on emissions curbs, for 2020 and 2050, that will brake global warming.

In the rush to understand the fiasco, some pointed at the nightmarish complexity of climate negotiations while others blamed the DNA of the nation-state itself.

"The biggest backlash from what has happened will be directed at the UN system, not on climate change," a European official predicted.

He and others voiced exasperation with the negotiation architecture under the UN Framework Convention on Climate Change (UNFCCC).

This 194-member arena proceeds by consensus and a sheep-and-goats division of rich and poor, which in turn has big repercussions for commitments for curbing greenhouse-gas emissions.

These rules were enshrined at the UNFCCC's birth in 1992 at the famous Rio Earth Summit and are virtually sacrosanct.

Poor countries are understandably loth to give up the privileges they have on emissions controls: their number still includes South Korea and Singapore, whose per-capita GDP is now among the highest in the world.

Then there is the mountain of complex issues, from finance for poor countries, emissions credits and verification of pledges to reporting of national emissions and the counting of forest "sinks."

These offer nearly infinite potential for foot-dragging and textual sabotage.

When the UNFCCC, and in 1997 its offshoot the Kyoto Protocol, came into being, time seemed plentiful and consensus, despite its flaws, was deemed vital.

Few people guessed that, within less than two decades, climate change would advance so quickly and so viciously as it has today, or that China, India and Brazil would become massive carbon polluters so quickly.

The end result is that the UNFCCC is like a crawling, overladen fire truck that has been told to race to quench a blaze.

"We have seen all the limits of the system in the past two weeks, in terms of unity, the endless series of interventions and points of order," the European source said.

Another question is whether nation states have it in their genes to address a worldwide challenge, for national leaders defend national interests, not the planet's.

Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change (IPCC), cautioned the talks were "an important test" of whether nations could join together to fight a common threat.

"I think if we are able to get a good agreement, this would clearly create an enormous amount of confidence in the ability of human society to be able to act on a multilateral basis," the UN's top climate scientist told AFP last week.

"If we fail, I don't think everything is lost, but certainly it will be a major setback."

Alden Meyer, with a US pressure group, the Union of Concerned Scientists, said the failure in Copenhagen "shows the fragility of the multilateral system."

"This is certainly not an efficient process that moves at lightning speed to address climate change," he said.

But, Meyer argued, the system's problems lay in a lack of political dynamism.

In the 1990 Gulf War, when the US mustered a huge coalition that ousted Saddam Hussein from Kuwait, "an alignment of nation-states combined with strong interests" showed how the UN system could be made to move.

UNFCCC chief Yvo de Boer on Saturday agreed his agency's process was "large, cumbersome and diverse."

"You could argue that it would be much more effect just to address climate change in the G20, where you've got 85 percent of the emissions around the table," he told reporters.

"That may be correct from an emissions point of view," said de Boer.

"But it's not correct from an equity or from an environmental point of view, because what you don't have around the table is the 100-odd countries that have contributed nothing to climate change, who have minuscule economies but who are on the front line of dealing with the impacts of climate change.