How do we decide what's 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. Sir Martin Rees is used to considering the biggest of canvases as one of the world's leading astrophysicists but recently he's 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? Show less