Wikipedia: Carbon dioxide

Carbon dioxide, or CO₂, is an atmospheric gas composed of one carbon and two oxygen atoms. In solid form it is sometimes known as [dry ice]?, since it sublimes at atmospheric pressure. As a gas it is opaque to infrared energy, and odorless and colorless.

In biochemistry it is commonly produced by animals that break down sugars with oxygen as part of their metabolism. Carbon dioxide is removed from the atmosphere by plants, that use photosynthesis of carbon dioxide and water to produce free oxygen gas and hydrocarbon plant materials.

Increases in the amount of carbon dioxide in the atmosphere as a result of burning hydrocarbons such as coal and petroleum oils has created a condition currently known as global warming, due to the decrease of energy leaving the earth.