CO2 is the chemical formula for carbon dioxide, which contains one atom of carbon and two atoms of oxygen. It is a heavy, odorless gas formed during respiration and by the decomposition of organic substances. Plants absorb carbon dioxide from the air during the process known as photosynthesis.
The formula CO2 is often used instead of the full name. Carbon dioxide is produced by the decay of organic materials and the combustion of wood and fossil fuels such as coal, petroleum and natural gas. Volcanoes, hot springs and geysers also emit carbon dioxide. Over time, environmentalists have focused more on the harmful effects of carbon dioxide on the Earth's atmosphere.