John Kerry, the former US presidential candidate and secretary of state for the Obama administration, discusses his life and career with the Observer's chief political commentator, Andrew Rawnsley. Kerry reflects on his early memories, his role in the Vietnam war and what action needs to be taken to address the issues presented by climate change. Kerry told the live audience: 'We face several life-threatening challenges … if we don’t respond very quickly, we’re inviting catastrophe to this planet'