The earth has warmed and cooled many times in its history. Isn't it reasonable to expect there is a natural negative feedback mechanism, and that this negative feedback mechanism will manifest itself and return the earth to equilibrium?
Eventually, CO2 levels drop back down and the planet cools, but that's a much slower process involving things like rock erosion over millions of years. In the short term there are strong positive feedbacks...forests drying out and burning down, permafrost melting and releasing CO2 and methane, undersea methane ice destabilizing, etc.
A great book that covers the geological evidence in detail, written for laymen, is Storms of My Grandchildren by James Hansen.
This is the key thing. We're just modeling, and models aren't so trustworthy over the long term when they're based only on past experience.
yep, an it brought up and down massive civilizations. Roman Empire, Caliphates, Viking Age, Mongols, Medieval Europe/Black Death... somewhere here goes our current world order :)