One mystery in environmental science is the imbalance in the "carbon dioxide budget." Considering only human activities, scientists have estimated that 1.6 billion metric tons of CO2 is added to the atmosphere every year because of deforestation (plants use CO2, and fewer plants will leave more CO2 in the atmosphere). Another 5.5 billion tons per year is put into the atmosphere because of burning fossil fuels. It is further estimated (again, considering only human activities) that the atmosphere actually takes up about 3.3 billion tons of this CO2 per year, while the oceans take up 2 billion tons per year, leaving about 1.8 billion tons of CO2 per year unaccounted for. This "missing" CO2 is assumed to be taken up by the "land." What do you think might be happening?