Over the last 540 Million years, over what is termed the phanerozoic, life evolved that is large enough to see in the fossil record with the unaided eye. During this time there have been fluctuations in temperature and carbon dioxide and also five mass extinctions most of which at least are related mainly to these changes.
“Where does carbon dioxide fit into the picture?...not as neatly as you might think. CO2 and temperature levels do not show a strong correlation.......we find the climate changing for reasons we don’t fully understand.” Patrick Moore
3. The Albedo effect:- If the Earth is frozen then much more sunlight is reflected. Therefore the same levels of CO2 and/or solar strength will not necessarily result in the same temperature produced when comparing different time periods in the record separated by millions of years.
4.Reduced silicate weathering:- The levels of CO2 naturally build up slowly during ice ages due to the reduced silicate weathering from rocks (which otherwise removes CO2 from the atmosphere). Since the land is covered in ice the rocks are not exposed to the atmosphere. Higher levels of CO2 over longer periods of time that would show up in the record are required to get out of the ice age due to the increased albedo effect.
(This combination of the albedo effect and reduced silicate weathering results in a hysteresis loop effect. This further complicates the temperature and CO2 records.)