The most anticipated climate meeting in years will be held in the Danish capital in December. Out of those talks a broader climate pact to replace the Kyoto Protocol is expected to emerge.
But the negotiations leading up to Copenhagen are fraught with risks and pit the ambitions of rich nations against those of the developing countries, whose emissions now comprise more than half of mankind's greenhouse gas pollution.
At stake is an agreement that will mean rich nations likely spending hundreds of billions of dollars greening their economies by 2020 and helping poorer states do the same. In addition, wealthy states are expected to provide funds to allow developing nations to protect themselves against the impacts of climate change.
These core issues will be a key focus of a G20 leaders' summit in the United States on Thursday and Friday.
Following are possible outcomes for December's two-week gathering of delegates from about 190 nations.
A GOOD OUTCOME
Rich nations bound by Kyoto's first phase in 2008-12 to curb emissions from 1990 levels, pledge to make much deeper cuts by 2020.
The U.N. Climate Panel says those cuts should be in the range of 25-40 percent by 2020 from 1990 levels to limit global warming -- reductions deeper than most rich nations are considering.
Wealthy states also pledge to ramp up funding to pay for climate change adaptation and mitigation programmes as well as make it easier to transfer affordable clean-energy technology to the poorer states.
In return for concrete pledges of financial and technological support, developing nations agree to pursue their own nationally appropriate climate change mitigation, such as greater use of renewable energy, promoting energy efficiency and imposing carbon intensity targets for industry.
The nations of the world also agree on how developing countries get access to funding -- who governs any new funds emerging from Copenhagen and who decides what is funded when.
Negotiators use the Copenhagen agreement as the framework to build an expanded set of rules and regulations.
This becomes the formal replacement pact for Kyoto. Governments would then have up to two years to ratify the new pact before it enters into force on Jan 1, 2013.
A BAD OUTCOME
The talks stall. Rich nations collectively fail to pledge mid-term targets that are deemed tough enough by poorer countries or fail to agree the funding mechanisms for adaptation, mitigation and technology transfer.
The negotiations resume three to six months later but drag on for another year or two before a weak agreement is finally reached.
AN ALTERNATE OUTCOME
Developed nations extend their obligations under the Kyoto Protocol for a second phase from 2013 that could last five to eight years.
Developing nations, seeking continuity, could simply opt for this outcome or a mix of the existing protocol with parts of an emerging new agreement.
(Editing by Jan Dahinten)