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How do forests and soils act as carbon sinks?

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Illustration of various geoengineering techniques to address climate change, including carbon capture and storage methods like artificial trees, industrial scrubbers, and deep ocean CO2 storage, as well as solar reflectance strategies such as sulfur aerosols, reflective crops, cloud whitening, and orbital mirrors. The scene shows these interventions applied to land, sea, and atmosphere, with labeled features explaining each process. — Geoengineering Various geoengineering proposals designed to increase solar reflectance or capture and store carbon.

Forests and soils act as critical carbon sinks by regulating the global carbon budget through the uptake and storage of atmospheric carbon dioxide (CO₂).

Forests as Carbon Sinks

Forests sequester carbon primarily through photosynthesis, where plants convert atmospheric CO₂ into biomass. This process, known as net primary production, stores approximately 55 billion metric tons of carbon annually worldwide. When plant tissue dies, it becomes litter and is eventually incorporated into the soil as humus, further extending the storage duration of that carbon.12

Soils as Carbon Sinks

Soils function as massive repositories for carbon, containing roughly three times as much carbon as all land vegetation combined. In addition to organic matter, soils in arid regions store carbon in inorganic forms, such as calcium carbonate. While soils naturally release carbon back into the atmosphere through soil respiration, they maintain a balance by continuously receiving organic matter from plant growth.12

Human activities, such as deforestation and intensive agriculture, disrupt these cycles, turning these natural sinks into sources of greenhouse gas emissions.12