How do humans affect the carbon cycle?
Humans are increasingly burning fossil fuels, consequently there are more carbon dioxide emissions. In addition, we take part in deforestation (where trees are cut down), meaning once again CO2 levels increase.
Cutting down trees and overharvesting plants means less photosynthesis occurs, subsequently, less oxygen is being release and less Co2 levels are being absorbed. Overall, human activity causes more carbon emissions.
Adding more carbon, as CO2, to the atmosphere and thereby strengthening the natural greenhouse effect.
Human burning of fossil fuels is essentially shifting carbon that has been stored for millions of years in geological reservoirs to the atmospheric reservoir. This is increasing the CO2 concentration in the atmosphere that is resulting in more heat being trapped in the atmosphere. This in turn, is warming the planet.