What does global warming have to do with history?

During the total history of the earth (over billions of years) there have been many changes to the climate. Most of these are reasonably well understood. For instance the sun becomes 10% brighter every million years. The atmosphere originally had a much higher concentration of CO2 than today which was fortunate because with a dimmer sun there would have been no liquid water without a major greenhouse effect. The development of plant life resulted in a reduction of CO2 and a build up of fossil fuels. We are now burning those fossil fuels which is increasing the greenhouse effect but we now have a much hotter sun,

More recently there have been variations to the earths orbit and its orientation caused in part by the gravitational effects of Jupiter and Saturn. These minor variations caused major variations in earth's climate including the Ice Ages. This indicates that climate sensitivity is quite high, so that changes caused by increasing CO2 in the atmosphere are likely to be amplified rather than reduced as a result of feedback.