About 120 U.N. world leaders are aiming to try to end deadlock at a U.N. climate summit in Copenhagen that is meant to agree a new deal on Friday for fighting global warming.
Following are possible scenarios:
WHAT'S THE STRONGEST POSSIBLE OUTCOME?
The most robust would be legal texts including deep cuts in greenhouse gas emissions by developed nations by 2020, actions by developing nations to slow their rising emissions, and a package for finance and technology to help poor nations. Almost all nations reckon that a legal text is out of reach.
WHAT SORT OF DEAL IS MORE LIKELY?
World leaders could agree only what they call a "politically binding" text and try to set a deadline for transforming it into a full legal text sometime in 2010.
IF THERE IS A DEAL, WHAT WOULD IT SAY?
The easiest global goal would be 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 limit of 1.5 Celsius. A big problem is that a temperature goal does not bind individual nations to act.
A slightly firmer, but still distant, target is to agree to at least to halve world greenhouse gas emissions by 2050. But 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.
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.
HOW ABOUT MONEY TO HELP THE POOR?
The latest text is blank on the amounts to be committed. The United Nations wants to raise at least $10 billion a year from 2010-2012 in new funds to help kickstart a deal to help developing nations. Many nations also speak of raising the amount to $100 billion a year from 2020 to help the poor.
WHAT HAPPENS IF THE TALKS FAIL?
One option if the talks end in deadlock is to "suspend" the meeting and reconvene sometime in 2010 -- a similar deadlock happened at talks in The Hague in November 2000. 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.