Carbon is one the the bricks of life. It is a vital element in organic life. Carbon has four bonding electrons. Hence the double bond of oxygen.
Carbon dioxide (click here) in earth's atmosphere is considered a trace gas currently occurring at an average concentration of about 385 parts per million by volume or 582 parts per million by mass. The mass of the Earth atmosphere is 5.14×1018 kg, so the total mass of atmospheric carbon dioxide is 3.0×1015 kg (3,000 gigatonnes). Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the Northern Hemisphere. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay (see graph at right). Concentrations also vary considerably on a regional basis: in urban areas it is generally higher and indoors it can reach 10 times the background atmospheric concentration.
From the same webpage as above. This is the negative feedback loop of Earth's oceans. The oceans is where the majority of Earth's oxygen comes from, so why have we allowed such saturation of our oceans with carbon dioxide that when dissolved with sea water forms carbonic acid?
There is about 50 times as much carbon dissolved in the oceans in the form of CO2 and CO2 hydration products as exists in the atmosphere. The oceans act as an enormous carbon sink, having "absorbed about one-third of all human-generated CO2 emissions to date." Generally, gas solubility decreases as water temperature increases. Accordingly the ability of the oceans to absorb carbon dioxide from the atmosphere decreases as ocean temperatures rise.
Most of the CO2 taken up by the ocean forms carbonic acid. Some is consumed in photosynthesis by organisms in the water, and a small proportion of that sinks and leaves the carbon cycle. There is considerable concern that as a result of increased CO2 in the atmosphere the acidity of seawater has been increasing and may adversely affect organisms living in the water. In particular, with increasing acidity, the availability of carbonates for forming shells decreases.
