SCENARIOS: U.N. talks descend into chaos; possible exits

COPENHAGEN (Reuters) - U.N. climate talks descended into chaos on Saturday after some developing nations rejected a plan for fighting global warming championed by U.S. President Barack Obama.

Saturday had been intended as a day celebrating a new U.N. accord after two years of negotiations culminated in a summit on Friday but, after a stormy all-night session, the 193-nation meeting was at risk of unraveling.

Some delegates said it risked becoming like the stalled Doha round on world trade talks. One Saudi delegate said it was without doubt "the worst plenary I have ever attended."

Developing nations including Venezuela and Tuvalu said they could not accept a text originally agreed by the United States, China, India, Brazil and South Africa as the blueprint of a wider U.N. plan to fight climate change.

They said the plan was worked out without their approval and that its goals of limiting global warming to a 2 Celsius temperature rise, alongside a $100 billion a year in aid from 2020, were inadequate.

The embarrassing deadlock casts a shadow over a U.N. process that demands unanimity to get decisions made and has to reconcile the radically different climate policies of OPEC oil exporters, worried about a shift to renewable energy, or tropical island states who fear rising sea levels.

Tempers flared during the session, held after most of 120 visiting world leaders had left. A Sudanese delegate even compared developed nations' policies to the Holocaust, saying global warming was killing people in Africa.

Danish Prime Minister Lars Lokke Rasmussen suspended the session after daybreak to consult lawyers on a possible way out. Options include:

1) Opponents of the plan back down and allow the deal to pass -- there is no formal vote but each state has an effective veto by objecting. This looks unlikely because several states have so vehemently opposed the accord.

British Environment Minister Ed Miliband, however, warned delegates that the plan would have to be endorsed to unlock funds outlined in the deal, including $30 billion in quick-start aid from 2010-12, rising to $100 billion a year from 2020.

2) The plan is downgraded to a "miscellaneous document" -- with less legal weight than the planned "Copenhagen Accord." That might still let its backers go ahead with the plan, but would limit their ability to control targets such as limiting a rise in world temperatures to 2 Celsius over pre-industrial times.

Apart from the original five nations supporting the scheme, European Union states, Japan and groups representing small island states, least developed nations and African countries spoke in favor of the plan during the overnight session.

3) In case of deadlock, the meeting could simply be adjourned without a decision and delegates agree to meet again sometime in 2010. That would leave the U.N. process largely rudderless because some other decisions due in Copenhagen are meant to guide the process.