The only process that removes carbon dioxide from the air is photosynthesis- plants use it to make carbohydrates, proteins and fats.
Animals eat the plants and the carbon compounds are passed along to animals in a food chain.
Both plant and animal respiration put carbon dioxide into the atmosphere.
plants and animals die and decay
They are decomposed by fungi and bacteria. These decomposers release carbon dioxide back into the air by respiration and as they break down material.
Fossil fuels are burned/ combusted. This releases carbon dioxide back into the atmosphere.