They look at core samples taken from antarctica over a million years ago and try to justify the made up results they try to push on us. The earth a million years ago was nowhere climate wise what we have now and man didn't exist then. I'm amazed they call it science.Not to mention only bases on recorded history which is a fraction of what has really happened. And as far as solar output we have even less data, like maybe 50 years worth if we are lucky.