The Earth is approx. 4.6 billion years old. We know it was much warmer in the past as that is how planets are formed. They are in fact molten rock for hundreds of millions of years. And planetary bodies change over time. The Sahara used to be a tropical forest until a change in the Earth's tilt. Jupiter's great red spot is shrinking. Mars used to have an atmosphere and a active core. So, who is to say what the "norm" is, especially over such vast amounts of time?
Now, considering the vastness of the Earth's age, we are supposed to believe that since the year 1800 humans have managed to wreck the climate of a planet that has warmed and cooled hundreds, if not thousands of times? In a 200 year period? After all the world-wide natural disasters, comet impacts, thousands of active/inactive Sun cycles, seismic upheavals and other calamities....it is man that has destroyed the planet?
Just stop.