Carbon dioxide (CO2) is a naturally occurring chemical compound found throughout Earth’s atmosphere. It exists as a gas and plays a role in various planetary processes.
Understanding the Molecule
A carbon dioxide molecule is composed of one carbon atom covalently double-bonded to two oxygen atoms, represented by the chemical formula CO2. This linear arrangement defines its structure. The carbon-oxygen bonds are relatively short, measuring approximately 116.3 picometers, which is shorter than a typical single carbon-oxygen bond.
Carbon dioxide is a colorless and odorless gas at standard temperature and pressure. It is denser than air, with a density of about 1.98 kg/m³ at room temperature, which is approximately 1.53 times that of air.
While generally stable, CO2 can react with water to form carbonic acid, making it slightly acidic. This property allows it to dissolve in water, ethanol, and acetone.
Sources and Natural Pathways
Carbon dioxide is continually exchanged between the atmosphere, oceans, land, and living organisms through the carbon cycle. Natural sources of atmospheric CO2 include biological processes like respiration, decomposition of organic matter, natural wildfires, and volcanic eruptions. Oceans are a significant natural source, releasing CO2 into the atmosphere through outgassing.
The natural carbon cycle involves CO2 absorption by plants during photosynthesis, where they convert light energy, carbon dioxide, and water into sugars and oxygen. This process removes carbon from the atmosphere, storing it in plant structures and soils. Carbon is released back into the atmosphere when plants and animals decompose or respire. The ocean also absorbs CO2 from the atmosphere, and this carbon can be stored in deep ocean waters for centuries.
Human activities have significantly altered the natural balance of the carbon cycle. The primary human source of CO2 is the burning of fossil fuels for energy generation in industries, transportation, and electricity production. Deforestation also contributes to increased atmospheric CO2 by reducing this natural sink. Additionally, industrial processes like cement production release CO2.
Influence on Earth’s Climate
Carbon dioxide is a greenhouse gas, meaning it absorbs and re-emits infrared radiation. This property allows it to trap heat within Earth’s atmosphere, preventing it from escaping into space, similar to how glass walls trap heat in a greenhouse.
Without naturally occurring CO2 and other greenhouse gases, Earth’s average surface temperature would be much colder, around -18 °C (0.4 °F), making it largely uninhabitable.
Increased concentrations of atmospheric CO2, largely due to human activities, intensify this natural greenhouse effect. This leads to a rise in global average temperatures, often referred to as global warming. Since the pre-industrial era, global average temperatures have risen by approximately 1.3°C.
As the planet warms, the atmosphere can hold more water vapor, which is itself a greenhouse gas, further enhancing the warming effect.
Beyond its atmospheric influence, CO2 also affects ocean chemistry. When carbon dioxide dissolves in ocean water, it forms carbonic acid, which lowers the ocean’s pH, a process known as ocean acidification.
This increased acidity reduces the availability of carbonate ions, essential building blocks for the shells and skeletons of many marine organisms like corals, shellfish, and plankton. This can make it difficult for these organisms to build and maintain their structures, impacting marine food webs and ecosystems.