I forget which graph it is now, but when I did Geology the other year we discussed global warming and its all very interesting. Oxygen isotope stages, deep sea cores etc.
If I remember correctly, as time has gone on we have seen greater extremes For example the last glacial period was the coldest it had ever been and lasted longer (not sure about the longer bit).
Wish I had saved the geology notes now
Just found this below:
http://depts.washington.edu/uwpcc/im...ess_marine.gif