Environmental lobby group, the World Wide Fund For Nature, says the world's energy could be renewable by 2050.
This view contrasts with that of the International Energy Agency, which has repeatedly warned of growing use of fossil fuel, especially coal, despite worries about its greenhouse gas emissions.
But the lobby group says research commissioned from the consultancy Ecofys shows this is wrong. It says that by 2050, power, transport, industrial and domestic energy needs could be met with only isolated residual uses of fossil and nuclear fuels.
It says energy-efficient buildings, vehicles and industry would help meet this goal, as would greater use of electricity that is renewably generated and well managed via so-called smart grids.