The future of the Kyoto Protocol on climate change is largely in the hands of the world's biggest contributors to greenhouse gas emissions. BBC News Online looks at how much they emit, what are they doing about it and where they stand on Kyoto.
The US emits more, absolutely and per head, than any other country - although it also produces more wealth. When Kyoto was agreed, the US signed and committed to reducing its emissions by 6%. But since then it has pulled out of the agreement and its carbon dioxide emissions have increased to more than 15% above 1990 levels.
For the agreement to become a legally binding treaty, it had to be ratified by countries which together were responsible for at least 55% of the total 1990 emissions reported by the industrialised countries and emerging economies which made commitments to reduce their emissions under the protocol.
As the US accounted for 36.1% of those emissions, this 55% target was much harder to achieve without its participation.
But 141 countries banded together and the protocol came into force in February 2005.
President George W Bush said in March 2001 that the US would not ratify Kyoto because he thought it would damage the US economy and because it did not yet require developing countries to cut their emissions.
He says he backs improvements in energy efficiency through voluntary emissions reductions - rather than imposed targets - and through the development of cleaner technologies.
All 15 European Union states ratified the Kyoto deal in May 2002. The protocol's most enthusiastic supporter, the EU has pressured countries such as Russia, Japan and Canada to ratify Kyoto so that it could come into force without the commitment of the US.
The EU has continually argued for a rigorous application of Kyoto, wanting to limit the use of so-called "flexibility mechanisms" which allow countries to partially meet their emissions reduction targets by paying for improvements in other countries.
The EU has also opposed widespread use of forests and other carbon "sinks" to absorb pollution - but gave substantial ground on the issue at talks in Bonn in 2001.
However, despite its tough stance on Kyoto, the EU is some way off its own target. It pledged to bring total greenhouse gas emissions to 8% below 1990s levels by 2008-2012, but by 2002 they had dropped only 2.9% - and CO2 emissions had risen slightly. Only four EU countries are on track to achieve their own targets.
China is the world's second biggest emitter of greenhouse gases, but as a developing country is not yet required to reduce its emissions.
With China accounting for a fifth of the world's population, increases in its emissions could dwarf any cuts made by the industrialised countries.
The average Chinese person consumes only 10-15% of the energy an average US citizen uses, but with the economy developing at high speed many analysts expect China's total emissions to overtake America's by mid-century.
Fossil fuels play a major role - China is the world's biggest coal producer and oil consumption has doubled in the last 20 years. The country faced power cuts in 2004 as soaring growth outstripped electricity generation.
However, although no UN figures are available, analysts say there is evidence to back up Chinese claims of a reduction in emissions during the late 1990s, largely due to increased efficiency and slower economic growth.
China's leaders recognise that climate change could devastate their society and ratified the Kyoto Protocol in 2002. In 2004 Beijing announced plans to generate 10% of its power from renewable sources by 2010.
But it is far from clear whether the country would ever agree to internationally-imposed emissions restrictions.
Russia ratified the Kyoto Protocol in November 2004 - the crucial moment making the treaty legally binding.
Russia's entry was vital, because the protocol had to be ratified by nations accounting for at least 55% of greenhouse gas emissions to become valid.
This target was only met after Russia joined.
Russia's economy has shrunk so drastically since 1990 that industrial activity has dropped, leaving emissions reduced by about 35% and well below the level allowed under Kyoto.
In the short-term, Russia stands to gain billions of dollars through emissions trading - selling its unused emissions entitlement to developed countries which want to emit more than the protocol allows them to.
It says the money would be used for energy efficiency projects. Committing to keep emissions low could, however, bring Russia economic costs in the longer term.
A major world economic power, Japan is a leading member of Kyoto, committed to cutting emissions. It was responsible for 8.5% of emissions in 1990 and its support for the agreement has been critical in the absence of US participation.
Although previously reluctant to ratify the protocol unless the US also committed, Japan ratified it in June 2002.
It committed to reduce emissions by 6% from 1990 levels, but 2002 figures showed total greenhouse gas emissions had risen 11% above the baseline figure.
The country recognises that its economy could benefit from the Kyoto agreement, as Japanese companies could capture markets for new, clean technology.
Developing countries like India are not obliged to make any cuts in greenhouse emissions under Kyoto. But as they raise living standards their emissions will increase. India's emissions are estimated to have risen by more than 50% in the 1990s, although the country has only submitted emissions figures to the UN for one year, 1994.
India recognises that many of its one billion people will be vulnerable to the effects of climate change and ratified the Kyoto Protocol in August 2002.
But with India's economy and population, like China's, continuing to grow, it is clear that the thorny issue of developing country emissions commitments will have to be tackled soon in future rounds of negotiations.