Nearly 200 countries will meet in Doha, Qatar, next week to work for a new climate deal to curb the greenhouse gas emissions that scientists say are warming the planet, raising sea levels and disrupting weather patterns.
The new deal should be signed by 2015 and come into force by 2020.
Delegates will also discuss an extension to the 1997 Kyoto Protocol, the world's current climate pact, which expires at the end of this year.
Most countries agreed last year to extend the protocol, but they have yet to agree on whether it should last for five or eight years, or on the level of various nations' emissions cuts under the pact.
The United States anyway never ratified the Kyoto deal. Japan, Russia and Canada did, but have signalled they will not sign up to any further emissions cuts in an extension.
Following are details of the protocol.
WHAT IS THE KYOTO PROTOCOL?
It is an international agreement that comes under the United Nations Framework Convention on Climate Change (UNFCCC). It was agreed by governments at a 1997 U.N. conference in Kyoto, Japan.
It sets binding targets for 37 industrialised countries and the European Union for reducing greenhouse gas emissions by an average of 5.2 per cent from 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 have ratified the pact.
IS IT LEGALLY BINDING?
It had legal force from February 2005, when it represented 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 countries and would cost U.S. jobs.
The protocol has a number of provisions to ensure regular reporting and measurement of emissions by developed countries. 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 to 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 tradable carbon offsets, and Joint Implementation (JI).
JI projects can also earn tradable offsets from emission reduction projects. The offsets can be sold to other developed nations bound by the protocol.
GREENHOUSE GASES COVERED
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 and N2O mainly from fertiliser use. The other three are man-made gases used in industry and household appliances.
WHAT SHOULD BE DECIDED IN DOHA?
The length of an extension should be finalised. The European Union favours an eight-year "commitment period" so that emissions cuts are made right up to the launch of a new deal in 2020.
Other nations, including island states, prefer a five-year period. They say a longer one would delay action by the United States, China, Japan and Russia, which will not be signing up to any cuts during the extension period.
The European Union, Australia and some smaller nations, together covering around 14 percent of global emissions, have committed to more cuts under a Kyoto extension.
To avoid a legal gap after Kyoto expires on December 31, the Doha conference must formally amend the Protocol so that its second period can come into effect on January 1.
A procedure to increase emissions cut pledges under the second commitment period should also be agreed on.
Green groups say developed countries should increase their 2020 emissions cut pledges so that they cut their combined greenhouse gas emissions by 25 to 40 percent.
Countries are also under pressure to close some loopholes in the current protocol that damage its environmental integrity, and to improve existing market mechanisms.
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