This would be the steepest drop in CO2 emissions for 40 years, chief IEA economist Fatih Birol said, adding that... average annual growth in global carbon output until now has been 3 percent.
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, the threshold for dangerous global warming.
The recession-driven fall would lead to CO2 emissions in 2020 being 5 percent lower than the IEA forecast from 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 Bangkok.
The talks 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 will pay for it.
At the same time, aid agencies said the rise in Asian weather disasters should serve as a wake-up call for negotiators to intensify their efforts.
Pointing to recent typhoons, floods and droughts in Asia, World Vision and the Red Cross said poor nations like the Philippines and Vietnam will be the ones to suffer most if world leaders fail to reach a climate pact by the end of the year.