As we entered the 21st century, the world was guzzling oil, coal and gas like never before. Despite fears of 'peak oil', Professor Iain Stewart discovers that while huge technological advances are helping extend the life of existing oilfields, new unconventional oil and gas supplies like shale gas and tar sands are extending the hydrocarbon age well into the 21st century. Given there's plenty of fossil fuels still in the ground, the spectre of climate change has forced many to ask can we really afford to burn what's left? In this concluding episode, Iain Stewart argues we face a stark choice. Do we continue feed our addiction - suck Planet Oil dry - and risk catastrophic climate change, or do we go hell for leather for alternative energy sources; nuclear, renewables, to make the transition from our fossil fuel past to a low carbon future. In which case, how do we make that shift?