Question: The ice core records shows that levels of CO2 have gone up and down with changes in average temperature over the last few hundred thousand years. Actually, the CO2 levels lag behind the temp changes by about 800 years, so we might assume that its not the CO2 thats causeing it. Its an important principle to distinguish between what is a cause and what is an effect when observing scientific phenomena. A curious thing however is that during ice ages there is relatively little vegetation on earth - the northern hemisphere being covered with ice. So you would expect there to be MORE CO2 in the atmosphere at that time - seeing as there is less vegetation to absorb it???