Global investments in clean energy need to double by 2020 to avoid missing climate change targets, the International Energy Agency (IEA) said on Monday, calling on governments to spend more on technologies such as carbon storage and solar power.

Some $23.9 trillion in investments are required by 2020 and $140 trillion by the middle of this century, when governments aim to keep the average rise in global temperatures to below 2 degrees Celsius, the Paris-based organization said.

World nations will have to spend from now to 2050 $36 trillion more than what is currently foreseen, with China having to spend the most.

But cash-strapped governments hit by the recession may take comfort in the IEA's assessment that every additional dollar invested in clean energy can generate three dollars in future fuel savings, with total savings offsetting investments by 2025.

"Let me be straight. Our ongoing failure to realize the full potential of clean energy technology is alarming," IEA Executive Director Maria van der Hoeven said in a report.

"Continued heavy reliance on a narrow set of technologies and fossil fuels is a significant threat to energy security, stable economic growth and global welfare, as well as to the environment," she said.

The IEA said some of the technologies with the largest potential, such as carbon capture and storage (CCS), offshore wind power and concentrated solar power (CSP), were showing the least progress.

While the project pipeline is sizeable, the recession and belt-tightening in many countries, are diverting funds and slowing projects in CSP, a system that uses lenses to focus a large area of sunlight onto a small area, the body added.

The IEA cited Spain and the United States, the world leaders in the CSP technology, as examples.

Another technology with unrealized potential is carbon capture and storage, seen as the only technology to allow industrial sectors such as iron and steel factories to meet deep emissions reductions goals, the IEA said.

Governments need to enforce more stringent performance standards in the building and transport sectors to ramp up energy efficiency, it added.

Only the most mature technologies such as hydropower, biomass, onshore wind and photovoltaic power production are making sufficient progress, the IEA said.

"Low-carbon electricity generation is already competitive in many markets and will take an increasing share of generation in coming years," the report said.

In the transport sector, the IEA said government targets for electric vehicles, set at 20 million vehicles on the roads in 2020, were encouraging, but at twice the current industry planned capacity, could prove difficult to achieve.