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.
"California's most damaging earthquakes of the past 150 years, such as the 1906 “San Francisco” earthquake, have occurred on faults in the San Andreas fault system."
