Hi Louie,

Scientists have examined all the past causes of climate change, including volcanoes( usually more likely to cause global cooling than warming), shifts in the earth's axis,magnetic fields, solar irradiation( Milankovich cycles), asteroids and any other potential causes and found them to be essentially stable. BTW, geophysicists tell us that heat rising from the earth's core almost never varies.

The only change in CO2 production and global warming has occurred with the increase in human industrial activity and marches in a near one to one correspondence for over 150 years.