HOW MUCH MORE CAN WE BURN?
Sticking with the IPCC’s best guesses, keeping within the two-degree global warming range means we can (maybe) ‘afford’ to liberate a maximum of 400 billion more tonnes of fossil-fuel carbon from oil, natural gas and coal. And ‘afford’ is a euphemism because we really are engaging in high-stakes gambling from here forward.

Optimistic assessments of conventional global oil reserves total 270 billion tonnes of carbon. Gas: carbon totalling 500 billion tonnes. Coal? A staggering 3500 billion tonnes of carbon.

What this means is that if we are to keep the planet out of the red zone, some oil will have to stay in the ground, along with most of the gas and nearly all of the coal.

Conclusion? Don’t worry about fossil fuels running out; we can’t afford to burn them until they do. The global energy economy needs to switch to renewables quickly, and in the meantime we all need to extract more bang from each kilo of liberated carbon.