If “humans are responsible for all of the warming we have suffered since 1950” what caused previous warming periods? What caused cooling up until 1975?How do you explain the Medieval Warming period, long before Oil or Coal were discovered?

As you can see the Mann graph uses doctored data, which he will not release, even to a Court of Law. http://principia-scientific.org/breaking-fatal-courtroom-act-ruins-michael-hockey-stick-mann/

Rick Perry is not alone in his distrust of the rubbish science being called “Climate Science” these days.