More than 190 countries are meeting in Doha, Qatar, from November 26 to December 7 to make progress on a new deal to fight climate change, due to be agreed by 2015 and come into force in 2020.
The current emissions-cutting pact, the Kyoto Protocol, commits most developed states to binding targets for cutting emissions but expires at the end of this year. It may be extended for a period of five or eight years, but several industrialized countries have already said they will not sign up to further emission cuts.
Following are the negotiating positions of the some of the biggest greenhouse gas emitters ahead of the U.N. meeting:
China (26.2 percent of global carbon dioxide emissions from energy consumption in 2010)
* Has made a voluntary pledge to reduce its "carbon intensity" - carbon dioxide emissions per unit of economic growth - by 40-45 percent from 2005 levels by 2020. Has also announced pilot emissions trading programs in seven provinces.
* Would prefer the Kyoto Protocol to be extended for five years as it considers rich nations' current ambition levels too low, and would not like them to be locked in for as long as eight years.
* Wants a new deal to be based on the principle of "common but differentiated responsibility" (CBDR), meaning that developed nations who were historically responsible for climate change should make the deepest emissions cuts and bear most of the costs of fighting global warming.
* Has called on poorer nations to make their own voluntary cuts in exchange for technological and financial support.
United States (17.6 percent)
* Never ratified the Kyoto Protocol because it excluded rapidly emerging economies such as China and India and Washington said it could hurt the U.S. economy.
* President Barack Obama has promised to cut emissions by 17 percent from 2005 levels by 2020. Unlikely to increase this pledge, which has not been ratified by the Senate.
* Washington says rapidly emerging economies such as China and India should also make ambitious and legally binding emissions cuts.
* Wants other developing countries to pledge voluntary emissions cuts.
* Has committed itself to "providing continuity in climate finance" after 2012, and to a global target of developed countries providing $100 billion a year by 2020 to help the developing world use clean energy and adapt to climate change.
India (5.3 percent)
* Plans to reduce its carbon intensity by 20-25 percent from 2005 levels.
* Like China, wants developed nations to undertake more ambitious cuts under a Kyoto Protocol extension.
Russia (5.1 percent)
* Has made a voluntary pledge to cut emissions by 15-25 percent below 1990 levels by 2020 - but this still represents a rise from current depressed levels.
* Ratified Kyoto in 2005 but will not sign up to new cuts in an extension as it finds the current pact ineffective.
Japan (3.7 percent)
* Has pledged to reduce emissions by 25 percent from 1990 levels by 2020 if other big emitters make ambitious goals.
* Will not sign up to any new cuts under an extension of Kyoto. An impending election on December 16 is likely to mean Japan will pay little attention to Doha.
* Has committed $15 billion to promote clean energy in the developing world in 2010-12, half the overall total of the "Fast Start" scheme, but has made no new pledges for 2013 onwards.
European Union (12.4 percent)
* Has pledged to cut emissions by 20 percent from 1990 levels by 2020. A more ambitious cut of 30 percent is almost certainly off the table.
* Has committed over $9.23 billion in Fast Start funds, but has made no new pledges for 2013 onwards.
* One of the few parties to have committed itself to an extension of Kyoto. Wants it to last for eight years to ensure cuts continue until a wider global climate deal is in place.
Canada (1.7 percent)
* Withdrew from the Kyoto Protocol last December, saying it would be liable to huge financial penalties under the treaty.
* Before pulling out, had pledged to match the U.S. goal of a 17 percent cut in emissions from 2005 levels by 2020.
Brazil (1.4 percent)
* Intends to cut emissions by between 36.1 and 38.9 percent from "business as usual" levels: the path that emissions would follow if nothing were done.
* Member of the BASIC negotiating group, also including South Africa, India and China.
* Says the number of countries signing up to a Kyoto extension is less important than the principle that developed nations must pledge more ambitious cuts because they have a greater historic responsibility for climate change.
* Ideally wants rich nations to cut emissions by 25-40 percent from 1990 levels by 2020, but would prefer the current level of ambition to no action at all.
Source for share of 2010 carbon emissions: US Energy Information Administration, www.eia.gov