Answer:
Plants play a large factor in fluctuating levels of CO2 within the atmosphere. Plants, through photosynthesis, convert CO2 gas into sugars and O2 gas powered through sunlight. In different seasons, the plants become active or deactivate and can undergo different amounts of photosynthesis. For example, during the winter, CO2 is very high, as many plants are not undergoing photosynthesis and cannot convert the CO2 into O2. But in spring, CO2 is drastically lowered as they are far more active in converting the atmospheric gas.
As we know the Earth is on a tilt. So when Earth revolves around the sun we rotate also. Making it so that as we spin, one hemisphere will get the most sunlight. Therefore that hemisphere will have summer at that time. So for example say that the Northern hemisphere is getting the most sunlight right now, so that hemisphere is now going to have summer. While the Northern hemisphere has summer that means that the Southern Hemisphere is having winter. But also as we rotate then at one time the Northern will have fall and the southern will have spring. Or visa versa. Climate mostly moves with the sunlight and depends on the area.