SCENARIOS: What will happen at the Copenhagen climate talks?

Japan's Prime Minister Yukio Hatoyama addresses a session of the United Nations Climate Change Conference 2009 in Copenhagen December 18, 2009. World leaders worked through the early hours to try and beat a Friday deadline for a deal on cutting emissions and helping poor countries cope with the costly impact of global warming.

(Reuters) - About 120 U.N. world leaders were meeting on Friday to try to overcome barriers to a new deal to combat climate change. Following are possible scenarios for the outcome:

WHAT'S THE STRONGEST POSSIBLE OUTCOME?

A few nations still want a legally binding treaty in Copenhagen but most agree it is out of reach. A legal text would include binding deep cuts in greenhouse gas emissions for developed nations by 2020, actions by developing nations to slow their rising emissions, and a package for finance and technology to help poor nations.

WHAT SORT OF DEAL IS MORE LIKELY?

World leaders would agree what they call a "politically binding" text including targets for slowing climate change by 2020. They would also set a deadline for transforming it into a legal text -- a draft text suggests the end of 2010. They might then leave and tell environment ministers to stay in Copenhagen for a day or two to work on details, such as transfers of green technology to poor nations or a plan to slow deforestation.

WHAT HAPPENS IF THERE IS DEADLOCK?

If the meeting fails, leaders could agree to suspend the negotiations and reconvene sometime in 2010 -- a similar deadlock happened at a U.N. session in The Hague in November 2000 that then resumed in mid-2001. The next U.N. meetings are set for Bonn in mid-2010 and Mexico in November 2010.

AND IF THE MEETING COLLAPSES?

The worst scenario -- a full breakdown in talks -- could deepen mistrust between rich and poor nations and undermine confidence in the U.N. system. It would probably also halt consideration by the U.S. Senate of legislation to cap U.S. emissions -- other nations' goals might in turn unravel.

IF THERE IS A "POLITICAL" DEAL, WHAT WOULD IT SAY?

One goal, in a draft considered on Friday, is to agree to limit global warming to a maximum temperature rise of 2 Celsius above pre-industrial times. The poorest nations and small island states want a tougher ceiling of 1.5 Celsius. A big problem is that a temperature goal is vague and would not bind individual nations to act.

The draft does not include another possible target -- a bit firmer but still distant -- of halving world greenhouse gas emissions by 2050. China and India and other developing nations have opposed such a goal in the past, saying rich nations first have to make far deeper cuts in their emissions by 2020.

HOW ABOUT MONEY?

A draft suggests a fund of $100 billion a year from 2020, raised from public and private sources, to help the poor cope with climate change. And it calls for fast-start cash of $10 billion a year from 2010-12.

WHAT DO RICH NATIONS HAVE TO DO?

They would have to set deeper cuts in greenhouse gas emissions in the years until 2020. A U.N. panel of climate scientists suggested in 2007 that emissions would have to fall by between 25 and 40 percent below 1990 levels by 2020 to help avert the worst of climate change, such as more droughts, species extinctions, floods and rising seas. Industrialized nations' offers of cuts by 2020 so far range from about 14 to 18 percent.

HOW ABOUT DEVELOPING NATIONS?

They would have to commit to a "substantial deviation" to slow the rise in their greenhouse gas emissions below projected growth rates by 2020, for instance by shifting to more use of solar or wind power and away from coal-fired power plants.