Carbon dioxide (CO2) is a naturally occurring gas in Earth’s atmosphere, playing a role in regulating the planet’s temperature and supporting life. Its presence is a result of various natural processes that continuously add and remove it from the atmosphere, forming a dynamic carbon cycle. Understanding these natural inputs helps clarify the complex ways CO2 interacts with Earth’s systems.
Life’s Breath and Decay
Living organisms contribute to atmospheric carbon dioxide through cellular respiration, a fundamental metabolic process. Plants, animals, and microbes convert organic matter, like glucose, into energy for their functions, releasing CO2 as a byproduct. This continuous process occurs in every cell. While plants also absorb CO2 through photosynthesis, they still respire and release CO2, especially at night.
The decomposition of organic matter also releases carbon dioxide into the atmosphere. When plants and animals die, bacteria and fungi, known as decomposers, break down their remains. As decomposers break down organic material, they respire, releasing CO2. This natural decay is a widespread source of CO2.
Earth’s Fiery Releases
Volcanic activity is a natural source of carbon dioxide. Volcanoes emit CO2 during eruptions and through continuous degassing from vents, porous rocks, and volcanic lakes. Estimates suggest that volcanoes, along with other geological processes, release approximately 280 to 360 million metric tons of CO2 per year into the atmosphere and oceans. While individual large eruptions can release significant amounts, such as Mount St. Helens venting about 10 million tons of CO2 in nine hours, volcanic emissions are generally a small fraction of overall natural carbon contributions over geological timescales.
Natural wildfires also contribute CO2 to the atmosphere. When vegetation burns, the stored carbon within plants is rapidly released as carbon dioxide. For example, in 2022, wildfires globally emitted around 5.3 billion tons of CO2. While these fires are part of the terrestrial carbon cycle, their emissions vary significantly year to year, influenced by factors like drought and climate variability.
The Ocean’s Role in Carbon Release
The ocean plays a dynamic role in the carbon cycle, both absorbing and releasing CO2. This exchange is influenced by factors like water temperature, pressure, and biological activity. When ocean waters warm, their capacity to hold dissolved CO2 decreases, leading to outgassing. This is similar to how a carbonated drink loses its fizz when it gets warm.
The solubility of CO2 in water decreases by about 3-4% for every 1°C increase in temperature. As ocean temperatures rise, more dissolved CO2 escapes into the atmosphere. While the ocean is a vast carbon reservoir and absorbs large amounts of atmospheric CO2, its ability to do so is reduced when temperatures climb, influencing the overall balance of atmospheric carbon.