Global warming issue 'on par with slavery'

Dealing with climate change is a moral issue on a par with ending slavery, the world's most celebrated climate scientist, James Hansen, of Nasa, believes. Dr Hansen, who heads Nasa's Goddard Institute of Space Studies, will be making the slavery comparison in his acceptance speech for the Edinburgh Medal next Tuesday, when he will also be calling for a global tax on all carbon emissions. Nothing less will do, he will argue, so urgent is the challenge which climate change presents for future generations.