A major disagreement is what to do with the Kyoto Protocol, the world's main climate pact, which binds nearly 40 industrialised nations to emissions targets until end-2012.
Poorer nations want the Kyoto Protocol's emissions cut targets for rich countries extended into a second period. Many developed nations say the pact is out of date and that the world needs a new one that binds all major emitters.
Following are details of the Kyoto Protocol, which is at the heart of the climate talks in Durban, South Africa, from November 28 to December 9.
What is the Kyoto Protocol?
It is an international agreement that comes under the United Nations Framework Convention on Climate Change. It was agreed by governments at a 1997 UN conference in Kyoto, Japan.
It sets binding targets for 37 industrialised countries and the European community for reducing greenhouse gas emissions by an average of five per cent against 1990 levels from 2008-2012.
Developing nations do not have binding emissions targets but are encouraged to take voluntary steps to curb the growth of carbon dioxide (CO2) pollution from power stations, cars and industry and other greenhouse gases.
A total of 193 Parties (192 States and 1 regional economic integration organization) have ratified the pact.
Is it legally binding?
It had legal force from February 2005. It represents 63.7 percent of developed nations' total emissions.
The United States, the world's second-largest greenhouse gas emitter after China, did not ratify the treaty, saying it wrongly omitted developing nations.
The protocol has a number of provisions to ensure regular reporting and measurement of emissions by developed countries to ensure compliance. Regular reviews of the protocol and specialist panels advising on compliance and technical matters are also included.
The protocol also includes several market mechanisms that have helped drive clean energy investment in developing nations and between developed countries bound by Kyoto.
These are the Clean Development Mechanism, in which investors in clean energy projects in poorer nations can earn tradeable carbon offsets, and Joint Implementation (JI).
JI projects can also earn tradeable offsets from emission reduction projects. The offsets can be sold to other developed nations bound by the protocol.
Greenhouse gases under Kyoto
National targets cover emissions of the six main greenhouse gases carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O); hydrofluorocarbons (HFCs); perfluorocarbons (PFCs); and sulphur hexafluoride (SF6).
CO2 comes from burning fossil fuels and deforestation, methane from deforestation and agriculture, N2O is mainly from fertiliser use and the remaining three are man-made gases used in industry and household appliances.
What should happen next?
Well before the end of the first commitment period of the Kyoto Protocol in 2012, a new international framework needs to have been negotiated and ratified to deliver the stringent emission reductions. That has not happened.
Climate change conferences in Copenhagen in 2009 and Cancun in 2010 ended without a plan for a new global deal . Delegates have low expectations for progress in Durban, saying the likely outcome would perhaps be a political agreement to extend Kyoto but not include binding emissions cuts.
(Sources: UNFCCC, Reuters)
(For more on Kyoto: here ) (Editing by Yoko Nishikawa)