Final answer:
Approximately one-third of the carbon dioxide released by human activities is absorbed by the oceans, while the rest remains in the atmosphere or is used by plants. Deforestation and the combustion of fossil fuels significantly influence the amount of atmospheric CO2.
Step-by-step explanation:
Currently, about one-third of the carbon dioxide (CO2) humankind releases into the atmosphere enters the oceans. The remaining carbon dioxide is either taken up by plants for photosynthesis or remains in the atmosphere. Deforestation has an impact on the absorption of CO2 as it reduces the total amount of carbon dioxide that is absorbed by plants, thereby increasing the amount of CO2 that stays in the atmosphere. The combustion of fossil fuels is a significant source of this CO2, with coal, oil, and natural gas contributing to varying degrees. The exchange of carbon between the atmosphere, the biosphere, the upper oceans, and the deep plays a critical role in the Earth's carbon cycle.