Evidence that carbon dioxide levels have historically been much higher than current levels, and can change dramatically as a natural process of the planet's eco

Evidence that carbon dioxide levels have historically been much higher than current levels, and can change dramatically as a natural process of the planet's ecosystems, and the ice caps have dramatically expanded and shrunk to even much smaller levels than they are today, all as a matter of natural course and in relatively quick time frames? I doubt this will receive much mainstream media attention.