Stephen Sackur talks to Sir David King, the UK's Chief Scientific Adviser from 2000 to 2007. Five years ago he described climate change as a greater threat to the world than terrorism. Back then Sir David was a scientist trying to influence the political process from the inside; now he's out of Government, his warnings are even starker. In the run-up to the climate change summit in Copenhagen, is there a disconnect between the science and the politics of climate change?