Guardian: If you were casting for a film about a policy academic in Whitehall, and Nicholas Stern auditioned, you would reject him on the grounds that he looked so much like a cliche that he would be a caricature. If you were casting for the rock star of the modern climate change movement, on the other hand, he would be the last man in the world you would choose. Middle-aged, soberly suited, grey and compact, he speaks softly in the fastidious register of academia, comprised of paragraphs constructed …