Calculating Existential Threat - Lord Martin Rees

Which is scarier: nuclear war or robots? Asteroid impact or climate change? Martin Rees is the founder of The Centre for the Study of Existential Risk at Cambridge University. He joins the program to talk about how to calculate the probability of threats to humanity, and what we should be sweating.

He's also the Astronomer Royal of the United Kingdom, and the author of "On The Future: Prospects for Humanity."