The rising popularity of using coal to generate electricity is putting the world on the "wrong path" to delivering clean energy economically.
Electricity is set to increasingly power the world's economies in the 21st century, rivalling oil as the dominant source of energy, but while electricity's share of global energy demand had doubled in the past 40 years, a report by the International Energy Agency (IEA) said most power generation is not low-carbon.
The "unrelenting rise" in coal use, without technology to capture and store carbon emissions permanently underground, is incompatible with keeping global temperatures from rising by more than 2°C and risking dangerous climate change, the report said.
Maria van der Hoeven, executive director of the IEA said: "Electricity is going to play a defining role in the first half of this century as the energy carrier that increasingly powers economic growth and development.
"While this offers many opportunities, it does not solve all our problems; indeed, it creates many new challenges. We must get it right, but we're on the wrong path at the moment.
"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. A radical change of course at the global level is long overdue."
Clean energy deployment has rallied in poorer countries over the past year making up for declines in the industrialised world, but the level of progress is bleak, the IEA said.
Trillions of pounds more will be needed than previously estimated to secure a global low-carbon energy system and the longer the world waits the more expensive it will become, the report warned, saying managing the transformation is the only way to ensure the world meets goals on energy security and tackling climate change economically.
The report found that an extra £26 trillion in investment would be needed to secure a clean energy system by 2050, up from £21 trillion in the last such analysis by the IEA.
But this represented only a small portion of global economic output and would be offset by £68 trillion in fuel savings, the IEA said. In part the increase shows that the longer the world waits, the more expensive the transition will be.
The report also found that natural gas can in the short term both replace coal and support the use of variable renewable energy sources such as wind, but in the medium to long term, it must be "seen for what it is – a transitional fuel, not a low-carbon solution", unless coupled with carbon capture and storage, the report warned.
The Energy Technology Perspectives 2014 report set out three scenarios, including one which would take the actions needed to keep temperature rises to no more than 2°C with a concerted effort to drastically reduce reliance on fossil fuels.
Electricity generation accounts for 40 per cent of primary energy use and carbon emissions from energy, but the report by the IEA said cost effective, practical solutions could increase efficiency, control demand and decarbonise almost all electricity by 2050.
Deployment of variable renewables such as wind is growing, and in some cases is becoming competitive with fossil fuels but balancing supply and demand needs to be actively managed.
Technology to allow storage of electricity could play multiple roles in the energy system but it is not, on its own, a game changer.
And electricity could be key to weaning the transport sector off oil, replacing combustion engines with electric vehicles, but not all regions are ready to make that leap, the study said.