How many ways can carbon dioxide return to the atmosphere?
Carbon Dioxide is a gas it is always part of the atmosphere. However Carbon Dioxide gas can be removed and returned to the atmosphere.
Plants use Carbon Dioxide as one of the two main reactants in the process of photosynthesis. Photosynthesis removes Carbon Dioxide from the atmosphere turning the Carbon into Carbohydrates, such as cellulose found in wood.
Cellular Respiration, burning coal, wood, gasoline, turn the Carbon-based molecules back into Carbon Dioxide and water. These Oxidation reactions return the Carbon Dioxide to the atmosphere.
A full description of various ways carbon dioxide is returned to atmosphere can be summarised in the image below of carbon cycle.