An extra episode in our climate season: we talk to Sir David King, former Chief Scientific Advisor to the British government, about what's now known about the scale of the threat and the urgency of the need for action. What has happened since the Paris agreement? What is the Chinese government most afraid of? What is the meaning of Extinction Rebellion? And is it time to start talking about refreezing the poles to repair the damage already done?
David talks to Martin Rees about how we should evaluate the greatest threats facing the human species in the twenty-first century. Does the biggest danger come from bio-terror or bio-error, climate change, nuclear war or AI? And what prospects does space travel provide for a post-human future?