Former US Treasury Secretary calls for a carbon tax

Cheap oil has cast doubts on the future viability all kinds of green energy projects, not just electric cars, but wind and solar power too.

And with gasoline or petrol so much cheaper, consumers and industries are likely to be tempted to use much more.

One solution to limit the use of CO2 emitting fuels is by introducing a carbon tax. There's a growing campaign to do just that - and it's won the support of economist and former US Treasury Secretary Larry Summers.

We asked him if enough is being done about climate change globally.