Actually, knowing what happened thousands of years ago proves more against Man Made Climate Change than anything.
We know there were floods, an ice age, and other catastrophic events.
No one is really arguing that. What some are simply saying is that Billy Bob's Dodge Ram, Carnegie's steel factories, Coal burning and Vanderbilt's railroads are NOT the reason for these natural events - cooling, warming, volcanos, weather patterns, whatever. These are cyclical events that have been happening since we could observe it.
The technology to be able to see things that happened before the industrial revolution, if anything, proves they are natural and cyclical. Big trucks and 727's had nothing to do with great weather pattern changes in 3rd century China - which we know happened (Great Flood). Or an uncanny hail storm that proceeded (and helped fuel) the French Revolution.
Man is very arrogant in how powerful he thinks he is. But Mother Nature thinks its hilarious.