Sir Martin Rees - UK Astronomer Royal

How do we decide what is important? How do we balance the personal priorities of the here and now, with the big picture challenges that will determine the future of human civilisation? Stephen Sackur's guest is used to considering the biggest of canvases. Martin Rees is one of the world's leading astrophysicists, but recently he has been gazing into the future of our own planet. The next century, he says, will determine humanity's long term destiny - so, are the prospects good or grim?