Humans affect the carbon cycle through the exhalation of carbon dioxide, the burning of fossil fuels, deforestation and other poor agricultural practices. Burning fossil fuels and deforestation leads to a disruption in the balance of the carbon cycle.
The natural amount of carbon dioxide exhaled by humans is utilized in the carbon cycle by vegetation to produce oxygen. When a surplus of fossil fuels are burned, a large amount of carbon dioxide is released into the air. Deforestation reduces the amount of vegetation that can reduce the atmosphere's carbon dioxide levels and creates less habitable soil for new growth. Carbon dioxide builds up due to the overuse of fossil fuels and an increasing lack of vegetation.