Deforestation is the second major way we increase atmospheric CO2. Felled timber releases CO2 as it burns or decays, and disturbed soils produce CO2 from burned organic matter. Forests give way largely to annual crops that store CO2 for only a season, or to cities with little vegetation at all. Human activities add appreciably to atmospheric CO2, but natural processes are fundamental in regulating the amount of CO2 in the atmosphere and elsewhere. Besides the atmosphere, Earth has several other reservoirs of CO2 including vegetation and the oceans.
Oceans constitute by far the largest reservoir, however.
Atmospheric CO2 dissolves into surface waters, and over time, ocean circulation carries it to great depths and distant locations. Eventually, biochemical processes may turn it into shells and sediments that drift toward the bottom of the oceans. Because high levels of greenhouse gases may have a significant effect on climate, vegetation, and other aspects of our lives, it is important to determine when major increases will occur. Predictions become more complicated when they take other greenhouse gases into account. While increasing CO2 is expected to be the main factor in enhancing Earth's atmospheric greenhouse, gases like methane, nitrous oxide and the CFCs almost certainly will contribute to changing climate as well.