Brussels - These are the main problems which negotiators face in Copenhagen from December 7-18 as they try to work out a deal on fighting climate change.
TARGETS: most of the world's major economies agreed at a Group of Eight summit in Italy in July that global warming should be kept to within 2 degrees centigrade of pre-industrial levels.
But some developing countries, especially island states which are most threatened by rising temperatures and sea levels, want a more ambitious target of 1.5 degrees.
Countries are also at odds over when emissions should be allowed to reach their maximum level, and how far they should fall by 2050.
Options for the deadline for emissions to peak include 2013, 2020 and "the next 10-20 years."
Developing countries also want rich states to accept their own, more ambitious and expensive targets. Suggestions include cuts of 25- 45 per cent by 2020 and of 80-95 per cent by 2050.
So far, the EU has pledged a 20-per-cent cut below 1990 levels by 2020, cutting further to 30 per cent if other developed states make comparable cuts. Japan has pledged a 25-per-cent cut by 2020, again based on 1990 levels.
Australia has pledged to cut 30 per cent below 2005 levels (equal to 11 per cent below 1990), Canada has pledged 20 per cent below 2005 (3 per cent below 1990), and the US is expected to target a cut of 17-20 per cent below 2005 (the same level as in 1990).
BASELINE: the Kyoto Protocol calculated its emissions reduction targets by comparing them with 1990. Since then, emissions in Europe and Russia have fallen, while emissions in other major economies have soared.
Europe and Russia therefore argue for keeping the 1990 base year. Many other nations would prefer 2005.
FINANCING: developed economies such as the United States and the European Union say that every country should contribute financially toward the effort, although rich countries would pay the most.
The EU's executive, the European Commission, has calculated that poor countries will need around 100 billion euros (148 billion dollars) per year in funding by 2020 to control climate change.
Developing nations say that the 100-billion-euro proposal is half to a third of the actual sum needed. They argue that it would not be fair to make them pay at all, since it is developed countries, with their long histories of heavy industry, who started global warming.
CARBON MARKETS: the EU currently operates a scheme encouraging industrial plants to cut emissions by making them buy permits to emit greenhouse gases. The bloc hopes that other developed economies will set up their own Emissions Trading Schemes (ETS), with the goal of creating a vast, worldwide market for emissions permits.
EU officials say this would both promote emissions reductions around the world and raise up to 38 billion euros a year for climate adaptation in poor countries.
But so far, only Australia and New Zealand are close to setting up their own cap-and-trade schemes. Plans to set up a US scheme are currently bogged down in the US Senate.
OFFSETS: the Kyoto Protocol set up a "Clean Development Mechanism" (CDM) which allowed developed states to claim credit for building climate-friendly facilities in developing states as if they had made the investment at home - so-called "offset credits."
But developed nations say that the CDM system too often allowed Western firms to pay for projects which had no impact on reducing emissions, but then claim environmental credits. Developed states seek to reform that process.
THE FUND: developing countries in the G77 want a single "mother fund," which developed countries would pay for by contributing 1 per cent of their GDP each year. The fund would fund all kinds of climate-linked projects in all parts of the world.
The US has proposed a fund to which developed and rich developing countries would contribute on a voluntary basis.
Mexico has proposed a fund to which all countries would contribute based on a common formula. The EU has proposed a similar fund using a similar formula, but managed by existing bodies such as the World Bank and regional development banks.
KYOTO OR NOT: at present, negotiators are working on two separate agreements for Copenhagen. One would update the Kyoto Protocol, which imposes emissions reduction targets on most developed economies, but not on the United States, which never ratified the protocol.
The other would update the UN's Framework Convention on Climate Change, imposing emissions targets on developed and developing countries, including the US, China and India.
TRADE: countries whose economies rely heavily on oil exports, such as Saudi Arabia, fear that their future growth will be damaged if the world agrees to switch to other fuels which do not produce so much greenhouse gas.
They therefore want compensation, known as "response measures," from the developed world for their expected loss in revenue. According to EU officials, a growing number of African nations support the OPEC stance.
FORESTRY: there is general agreement that efforts to reduce the destruction of forests, especially in the tropics, can play an important role in reducing worldwide emissions. Reducing Emissions from Deforestation and Forest Degradation (REDD) is therefore likely to be a key issue in Copenhagen.
