Releasing its biennial "Energy Technology Perspectives" report in Seoul, the agency said electricity would increasingly power the world's economies in the decades to come, rivalling oil as the dominant energy carrier.
Surging electricity demand posed serious challenges, said IEA executive director Maria van der Hoeven.
"Growing use of coal globally is overshadowing progress in renewable energy deployment, and the emissions intensity of the electricity system has not changed in 20 years despite some progress in some regions," Van der Hoeven told reporters in the South Korean capital.
The agency said an additional USD 44 trillion in investment was needed to secure a "clean-energy future" by 2050, compared to the USD 36 trillion it had estimated in its 2012 report.
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"The increase partly shows something the IEA has said for some time: the longer we wait, the more expensive it becomes to transform our energy system," Van der Hoeven said.
While the deployment of clean energy technology in emerging economies has rallied over the past year - making up for declines in the industrialised world - the overall picture remains bleak, according to the report's lead author David Elzinga.
It also pointed out that the USD 44 trillion figure would be more than offset by an estimated USD 115 trillion in resulting fuel savings.