Read here and here. Well, isn't this interesting....climate scientists don't understand the past warming; they can't explain the present global cooling; and, they have yet to predict any climate condition correctly. A climate science trifecta!
"During an event called the Palaeocene-Eocene Thermal Maximum, global temperatures rose between 5 and 9 degrees Celsius within several thousand years. The world at that time was already warmer than now with no surface ice..."We now believe that the CO2 did not cause all the warming, that there were additional factors,"."