Renewable, energy efficient and flexible electricity sources are being adopted by policy makers and investors across the globe and this is sign of optimism in the battle against climate change, a University of Exeter energy policy expert is suggesting.

In a journal article published in Nature Energy, Professor Catherine Mitchell from the University's Energy Policy Group argues that investment in renewable electricity now outstrips that in fossil fuels, and that increasing numbers of policies to improve the efficiency of energy use and to make energy systems more flexible are pointing to a global momentum in the adoption of sustainable energy systems.

"While the world is still dependent on fossil fuels, because energy systems have long lives, it has got to the point where more than half of global electricity system investment is in renewables rather than fossil fuels investment. It is a sign that globally we have moved our public policy discourse and investor preferences from the old 'dirty' energy system to a clean one," she said.

The adoption of renewable electricity by a few countries like Denmark and Germany in the 1990s, has led to improved understanding of energy system operation and a fall in prices which has had a knock on effect. A few countries, like the UK, remain dominated by conventional energy systems but most are supporting the move to sustainable energy systems.

"They are just trying to act as good global neighbours and have realised that meeting their climate change reduction commitments is no longer as expensive as they thought, and it helps, rather than makes worse, the security of their energy systems, " added Professor Mitchell, who us based at the University's Penryn Campus in Cornwall.

While the changing discourse is welcome, Professor Mitchell stresses that the challenge of climate change has not yet been met and that policy statements need to be backed up with firm action: "The recent United Nations meeting on climate change in Paris and its agreements has led to strong support for individual country's sustainable energy policies. However, these statements need to be backed up with appropriate governance -- policies, institutions, incentives and energy system rules -- to make sure they are implemented and are successful."

Momentum is increasing towards a flexible electricity system based on renewables by Catherine Mitchell is published in Nature Energy.