5. If forests serve as important sinks for greenhouse gases, describe how past ice ages might have affected the concentration levels of carbon dioxide in the atmosphere.

Forests and other green plants uses carbon dioxide in photosynthesis thus lowering its amount in the atmosphere. In assumption, we can claim that in the ice ages, the low level temperatures may have caused the carbon dioxide levels to neutralize over these phenomenons, also to note that there were less oxygen-breathing organisms and higher carbon-dioxide dependent performing photosynthesis.