The reason for this difference is not entirely understood, but several factors are thought to be involved.
One possibility is that changes in ocean circulation cause more CO2 to be absorbed by the ocean during ice ages. When the ocean is cold, it can hold more dissolved CO2. As the Earth's climate warms and oceans become warmer, they release some of this stored CO2, leading to higher atmospheric CO2 levels.
Another possibility is that changes in plant growth lead to lower CO2 levels during ice ages. Plants absorb CO2 from the atmosphere as they grow, and they store this carbon in their leaves, stems, and roots. When plants die, this carbon is released back into the atmosphere. During ice ages, plant growth is slower, and more carbon is stored in plants, leading to lower atmospheric CO2 levels.
Changes in the amount of dust in the atmosphere may also cause variations in atmospheric CO2. Dust can act as a catalyst for chemical reactions that remove CO2 from the atmosphere. During ice ages, there is more dust in the atmosphere, which may explain why CO2 levels are lower.
The precise mechanisms that cause CO2 levels to vary during ice ages are still a topic of scientific research. However, it is clear from ice core data that these fluctuations occur regularly and that they are linked to changes in Earth's climate.
