Half of the world's energy needs in 2050 could be met by renewables and improved efficiency, a study claims.

It said alternative energy sources, such as wind and solar, could provide nearly 70% of the world's electricity and 65% of global heat demand. Following a "business as usual" scenario would see demand for energy double by 2050, the authors warned. The study, by the German Aerospace Center, was commissioned by Greenpeace and Europe's Renewable Energy Council.

The report, Energy Revolution: A Sustainable World Energy Outlook, provided a "roadmap" for meeting future energy needs without fuelling climate change, said Sven Teske from Greenpeace International.

"We have shown that the world can have safe, robust renewable energy, that we can achieve the efficiencies needed and we can do all of this while enjoying global economic growth," he said. He added that the strategy outlined in the report showed that it was economically feasible to cut global carbon dioxide (CO2) emissions by almost 50% over the next 43 years.

The report calls for ageing fossil fuel and nuclear power plants to be replaced by renewable generation when they reach the end of their operational lives.