Guardian: The decision by Barack Obama to appoint John Holdren as his chief scientific adviser deserves widespread welcome. The Harvard academic and former energy expert at the University of California, Berkeley, commands international respect among physicists, climate experts and other researchers. He is an able scientist and is also a vociferous critic of those who still deny our planet is overheating because of humanity’s industrial activities. Sceptics such as academic Bjørn Lomborg have …