Research Background:

     Carbon Dioxide, colorless, odorless, and slightly acid-tasting gas, sometimes called carbonic acid gas, the molecule of which consists of one atom of carbon joined to two atoms of oxygen (CO2). It was called "fixed air" by the Scottish chemist Joseph Black, who obtained it through the decomposition of chalk and limestone and recognized that it entered into the chemical composition of these substances. The French chemist Antoine Lavoisier proved that it is an oxide of carbon by showing that the gas obtained by the combustion of charcoal is identical in its properties with the "fixed air" obtained by Black. Carbon dioxide is about 1.5 times as dense as air. It is soluble in water, 0.9 volume of the gas dissolving in 1 volume of water at 20° C (68° F).

     Carbon dioxide is produced in a variety of ways: by combustion, or oxidation, of materials containing carbon, such as coal, wood, oil, or foods; by fermentation of sugars; and by decomposition of carbonates under the influence of heat or acids. Commercially, carbon dioxide is recovered from furnace or kiln gases; from fermentation processes; from reaction of carbonates with acids; and from reaction of steam with natural gas, a step in the commercial production of ammonia. The carbon dioxide is purified by dissolving it in a concentrated solution of alkali carbonate or ethanolamine and then heating the solution with steam. The gas is evolved and is compressed into steel cylinders.

     The atmosphere contains carbon dioxide in variable amounts, usually 3 to 4 parts per 10,000, and has been increasing by 0.4 percent a year. It is used by green plants in the process known as photosynthesis, by which carbohydrates are manufactured (see Carbon Cycle).

     Most of the recent increases in atmospheric carbon dioxide is attributed to burning of fossil fuels such as coal and natural gas, for the purpose of generating electricity for residential and industrial uses. Additional carbon dioxide comes from slash and burn farming techniques, and the clearing and burning of rainforests around the world. Because at present there are no alternatives to burning fossil fuels to generate electricity, we can anticipate that carbon dioxide in the atmosphere will continue to increase.

     There are two kinds of plants based on how they carry on photosynthesis. These are called C3 and C4 plants. C3 plants show increase growth when atmospheric carbon dioxide is increased. On the other hand, C4 plants show very little effect of increased atmospheric carbon dioxide on growth. C3 plants include winter grain crops such as wheat and barley, and plants such as cotton, cucumber, and cabbage. C4 plants include corn and sorghum and most warm season grasses.