COP21 refers to a key UN climate change summit taking place in Paris from the end of this month, tasked with producing a climate rescue pact.
Among fossil fuels, natural gas, the least carbon-intensive, is the only one expected to see its share rise, the IEA report added.
"Where it replaces more carbon-intensive fuels or backs up the integration of renewables, natural gas is a good fit for a gradually decarbonising energy system," the IEA said.
As demand for oil picks up, the oil price is expected to recover gradually to reach US$80 per barrel in 2020, the IEA said. In the following two decades oil demand is likely to level off as governments continue to reduce subsidies and there is further momentum towards energy efficiency and alternative energy sources.
With less than three weeks to go before the crucial COP21 conference, the IEA said an ongoing policy shift was not enough to avoid the worst effects of climate change.
"There are unmistakeable signs that the much-needed global energy transition is underway, but not yet at a pace that leads to a lasting reversal of the trend of rising CO2 emissions," it said.
The world still needed a "clear and credible vision of long-term decarbonisation" to combat climate change.