By Richard Black
Environment correspondent, BBC News website
Climate protestors in New York are demanding further cuts
The global recession and a range of government policies are likely to bring the biggest annual fall in the world's carbon dioxide emissions in 40 years.
The International Energy Agency (IEA) estimates that global CO2 emissions will fall by more than 2% during 2009.
Measures such as emissions trading have complemented the drop in emissions as economic activity has declined.
The news comes as leaders gather at the UN for a day of climate talks convened by Secretary-General Ban Ki-moon.
The anticipated fall in emissions is larger than that seen during the recession of the early 1980s.
The close relationship between GDP and carbon emissions is well documented, so many commentators were expecting that the recession might cause emissions to drop.
But the size of the fall has come as something of a surprise.
The IEA estimates that the recession is responsible for about three-quarters of the fall.
As well as curtailing the business sector's energy use by applying a general economic brake, the straitened circumstances have reportedly led to deferments on investment in new fossil fuel plants.
The remaining quarter of the reduction comes from policies designed to curb CO2 production, according to the IEA.
The EU's Emissions Trading Scheme is one cited by the agency; others are improvements to vehicle fuel efficiency in the US, and China's economy-wide drive to increase energy efficiency.
The full findings will be documented in the IEA's annual World Energy Outlook, to be published in November.
This week sees two significant summits - a special session for heads of government at the UN in New York, and a G20 meeting in Pittsburgh that may unlock new proposals on financing poorer countries' transitions to a low-carbon economy.
One of the main stumbling blocks in the process of trying to agree a new UN climate treaty has been the reluctance of some industrialised countries, in particular the US, to pledge emission cuts big enough to placate developing countries.
The IEA suggests its findings show that emissions can be cut more easily than some governments have assumed.