Global warming and cancer are the starting points for some of this year's most enlightened, original and, yes, upbeat science books of 2011.  This year a new star emerged in the constellation of great science writers, with Siddhartha Mukherjee's "biography of cancer", The Emperor of all Maladies (Fourth Estate, ?9.99 ?9.49). Mukherjee's gripping narrative is littered with pioneers, maveric