Then in 1999 an obscure young US physicist, Michael Mann, came up with a new graph like nothing seen before. Instead of the familiar rises and falls in temperature over the past 1,000 years, the line ran virtually flat, only curving up dramatically at the end in a hockey-stick shape to show recent decades as easily the hottest on record. This was just what the IPCC wanted, The Mediaeval Warming had simply been wiped from the record. When its next report came along in 2001, Mann's graph was given top billing, appearing right at the top of page one of...