IEA published its third annual mid-term renewable market report, which shows total combined output from renewable energy resources in 2013 was on par with electricity from natural gas.
By 2020, renewable energy generation should account for 26 percent of total electricity output, but annual growth in new renewable power begins to stabilize next year.
IEA Executive Director Maria van der Hoeven said renewable energy resources are a "necessary" part of global energy security measures, though policy and regulatory uncertainty puts new low-carbon power generation at risk.
"This calls for a serious reflection on market design needed to achieve a more sustainable world energy mix," she said in a statement Thursday.
Renewable energy in economies outside of North American and Europe are the largest source of growth through 2020, but they only meet 35 percent of the electricity needs. Because some of those economies, notably China, are growing faster than the rest of the work, IEA said this trend illustrates the role fossil fuels continue to play in the global marketplace.
"Just when [renewables] are becoming a cost-competitive option in an increasing number of cases, policy and regulatory uncertainty is rising in some key markets," van der Hoeven said.