It is produced by combustion of wood and other organic materials and fossil fuels such as coal, peat, petroleum and natural gas. Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread, beer and wine making. It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals, including humans. Plants, algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a waste product.CO2 is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration. Carbon dioxide is odorless at normally encountered concentrations, however, at high concentrations, it has a sharp and acidic odor.As the source of available carbon in the carbon cycle, atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena. It is present in deposits of petroleum and natural gas. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, ice caps, glaciers and seawater. Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. The current concentration is about 0.04% -410 ppm- by volume, having risen from pre-industrial levels of 280 ppm.

It occurs naturally in Earth's atmosphere as a trace gas. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms. Carbon dioxide: Carbon dioxide -chemical formula CO2- is a colorless gas with a density about 60% higher than that of dry air.

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