Carbon dioxide is released to the environment through 3 main processes:
Inorganic carbon dioxide in the atmosphere is converted by plants into simple carbohydrates, which are then used to produce more complex substances. Animals eat the plants and are then eaten by other animals. When these life forms die, they decay, breaking down into, among many other things, carbon dioxide, which returns to the atmosphere. Plants and animals also release carbon dioxide during respiration. Plants will help remove carbon dioxide in the air, it then makes use of it to photosynthesise and the whole cycle will repeat again. Also, fossil fuels which are burnt or combusted release carbon dioxide to the environment.