Carbon dioxide (CO₂) is a nontoxic, odorless, and colorless gas present in trace concentrations in the atmosphere. The molecule is linear with a central carbon atom doubly bonded to two oxygen atoms (O=C=O). Natural sources of CO₂ include volcanic outgassing, animal respiration, biomass decay, and oceanic evaporation. Removal processes include photosynthesis and dissolution into the oceans.

CO₂ is a long-lived gas, with an atmospheric lifetime of more than one hundred years. It is a natural greenhouse gas and plays an important role in regulating Earth's climate. Like water vapor, CO₂ traps outgoing infrared radiation emitted by Earth into space. By absorbing this energy, the atmosphere warms the earth, a process known as the natural greenhouse effect. Without carbon dioxide and water in the atmosphere, the earth's average surface temperature would be below 0°F, turning oceans into ice and dramatically altering life as it is...