Final answer:
Carbon is added to the atmosphere through photosynthesis, respiration, and the burning of fossil fuels.
Step-by-step explanation:
Carbon is added to the atmosphere by several processes, one of which is photosynthesis. During photosynthesis, plants take in carbon dioxide from the atmosphere and convert it into glucose, releasing oxygen as a byproduct.
Another process that adds carbon to the atmosphere is the respiration of living organisms. Through respiration, organisms release carbon dioxide back into the atmosphere as a waste product.
Additionally, the burning of fossil fuels by humans also contributes to the increase of carbon dioxide in the atmosphere. Fossil fuels, such as coal, oil, and natural gas, are made from the remains of ancient plants and animals that stored carbon in their bodies millions of years ago.