A heavy gas, formula C02, that makes up 0.033% by volume of the atmosphere. It is the basic carbon source of all life, being converted to carbohydrates by *photosynthesis
. The concentration of C02
remains relatively constant despite increased burning of fossil fuels and deforestation practices. This is due to the buffering capacity of the oceans, which contain large amounts of dissolved C02
. The extreme solubility and rapid diffusion of C02
in water is a major factor in the maintenance of aquatic life.
The rate of photosynthesis can be increased by raising C02 levels. This has been put to practical use in the cultivation of some glasshouse crops. However yield increases are not as great as might be expected since increased C02
concentrations also increase stomatal closure.