American climatologist  Michael Mann drew a chart  back in 1999 .   It's called "The Hockey Stick Graph" because of the way it shoots up.  There was no new information in it and it drew on agreed international temperature data.  Like Charles Darwin, Dr Mann dared to publish. His "hockey stick" still makes him a target for fossil fuel lobbyists.  So what happens when a scientist is taken on by powerful interests ?  Dr Karl asks him about the experience.