You can piece together a picture of the climate dating back millions of years by using ice cores, boreholes, tree rings, glacier lengths, pollen remains, ocean sediments and the orbit around the sun.

There were periods of stability and periodes of rapid change. Interglacial climates are more stable. Rapid climate changes are accompanied by transitions between glacial and interglacial periods. We are already in an interglacial climate so it's very strange the temperatur rises rather quick, it is warm already. Altough abrupt climate changes have occured before, human civilization arose during a period of relative climate stability.

Also take a look at this picture of the last 400.000 years. More carbon dioxide in the atmosphere means a higher temperature.

http://img246.imageshack.us/img246/1584/carbonte4.png

Red=CO2
Blue=Temp