"Global warming" is generally used to indicate the warming of the globe that has occurred since the mid-1800s. There is considerable scientific evidence that this warming, particularly the warming which occurred in the late 1980s into the 1990s and to present, has been augmented by human activities, particularly those that add CO2 to the atmosphere. CO2 concentration in the atmosphere has increased about 100 ppm since the mid-1800s, and this is about 100 ppm higher than the natural maximum over the past 640,000 years, as determined from measurements of CO2 in ice core bubbles.
Feel free to continue thinking that global warming is entirely natural. The scientific data does not support that line of thinking.
It was the last time it happened.
Please explain for the class how the Vikings made the world warm, how the Pilgrim caused things to get cold, and how Abe Lincoln managed to heat things up again.
It's a natural cycle.
And I'll bet the CO2 in ice core bubbles doesn't degrade one little bit being in contact with all that frozen and often liquid H2O for all that millenia, no sirree. Can you insure that those ice cores came from glaciers in which no liquid water occured in the time the CO2 was trapped?