CO2

Carbon dioxide, CO2, is a colorless, non-flammable gas consisting of one carbon atom bonded to two oxygen atoms. It is a naturally occurring component of Earth’s atmosphere and a central part of the carbon cycle. Its concentration is about 420 parts per million by volume in recent years, a level elevated from preindustrial times due to human activities.

CO2 is produced by respiration, decomposition, volcanic activity, and various industrial processes, including fossil fuel combustion and cement production. It is also used commercially in beverage carbonation, chemical synthesis (such as urea production), fire suppression systems, and oil recovery. The gas dissolves in water, forming carbonic acid, which influences ocean chemistry and pH.

In the atmosphere, CO2 is a greenhouse gas. It absorbs infrared radiation, helping to maintain the natural greenhouse effect. However, sustained increases in atmospheric CO2 from human activities enhance this effect and contribute to climate change. CO2 has a relatively long atmospheric lifetime, allowing it to circulate among the atmosphere, oceans, and terrestrial ecosystems over decades to centuries.

Health and safety considerations depend on concentration. At typical ambient levels, CO2 is not acutely toxic, but high concentrations in confined spaces can reduce oxygen availability and cause asphyxiation. Monitoring, reducing emissions, and increasing carbon sinks are central to climate policy and environmental management, reflecting both the natural role and anthropogenic impact of CO2.