The predicted three percent fall in energy-related CO2 pollution compared with a year earlier would be the steepest drop in 40 years, chief IEA economist Fatih Birol said at a press conference in Bangkok.

The global carbon output up to now has on average grown three percent annually, he added.

Birol said this silver-lining drop in carbon pollution was a "unique window of opportunity" for the world to put itself on a path to limit the increase in global temperatures to two degrees Celsius (3.6 degrees Fahrenheit), the scientific threshold for dangerous global warming.

The recession-driven fall would lead to CO2 emissions in 2020 being five percent lower than the IEA forecast from just a year ago, even if no further action is taken to curb global warming, he added.

The IEA estimate is part of its World Energy Outlook report, an excerpt of which was released at UN climate talks under way in the Thai capital.

It outlined how steeply countries would have to cut their energy-related carbon emissions over the next 20 years in order fix the concentration of carbon dioxide in the atmosphere at a level that would ensure the two-degree threshold is not crossed.

That level, measured in parts per million, is 450 ppm, according to a benchmark scientific report issued in 2007 by the UN Intergovernmental Panel on Climate Change (IPCC).

"This gives us a chance to make real progress toward a clean-energy future, but only if the right policies are put in place promptly," said IEA executive director Nobuo Tanaka in a statement.

"Every year of delay adds an extra 500 billion dollars (340 billion euros) to the investment needed between 2010 and 2030 in the energy sector," he warned.

Energy production accounts for about 65 percent of the world's greenhouse gas emissions, according to the IEA.

The climate talks under the UN Framework Convention on Climate Change (UNFCCC) have been stymied for months, and are running out of time to deliver a new global climate treaty at a December conference in Copenhagen.

Rich and poor nations are divided over how to share the burden of cutting greenhouse gases, and who is going to pay for it.

Developed nations are willing to take the lead, but expect emerging giants such as Brazil, India and China to commit to mitigation measures as well -- pledges these countries have fiercely resisted.

Rich nations created the problem and should bear the brunt of the responsibility to fix it, the developing countries say.

"Continuing the current energy policies would have catastrophic consequences for the climate," said UNFCCC chief Yvo de Boer. "This is a unique opportunity... to transition the global energy system."

In Stockholm, Brazil's president urged the United States, China and others to do their share to reduce greenhouse gases so that the key Copenhagen summit could be a success.

"If we solve a little bit the US issue, and Obama tries to convince his Congress and the Senate" to accept more ambitious climate objectives, "then things can advance," Brazilian President Luiz Ignacio Lula da Silva said.

The IEA's Tanaka confirmed that China had overtaken the United States as the world's top carbon polluter in 2007, adding that "it will be the same in the future."

While it has not announced an emission reductions target, if China fulfils its energy efficiency plans it would account for a quarter of the global effort needed by 2020 under the IEA scenario for stabilising CO2 levels, he said.

"It would put China at the forefront of the fight against climate change," Birol told AFP.

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