The distinguished climatologist James Hansen (b. 1941) is an example of a leading scientist who has had the moral courage to speak out against politicians’ failure to act effectively against global warming. He was trained in astrophysics and became an authority on planetary atmospherics, working for NASA for many years. He developed global circulation models that have been used to analyse greenhouse effects and the human role in rising temperatures (pioneering work used by the IPCC). From about 2007 he has been a robust critic of the coal industry and of politicians who accepted money from fossil-fuel interests and encouraged climate change denial. He was arrested in 1911 and 1913 for joining protests outside the White House against the Keystone pipeline plan to bring oil from Canada to the lower US. He eventually left NASA because (he claimed) they tried to gag his more political statements and has since worked for the Earth Institute at Columbia. He has courageous continued his activism against climate change despite being demonised in many quarters.