Carbon sink
A carbon sink is a place or process that takes carbon, usually as carbon dioxide, out of the air and stores it. The Intergovernmental Panel on Climate Change (IPCC) describes a sink as a natural or human reservoir, in soil, the ocean or plants, where a greenhouse gas is stored.[1] Carbon sinks are part of the wider carbon cycle.
Definitions
There are two common ways of defining a sink. The IPCC glossary treats a sink as a reservoir: a store where a greenhouse gas, an aerosol or a substance that forms a greenhouse gas is kept.[1] The same glossary notes that Article 1.8 of the United Nations Framework Convention on Climate Change (UNFCCC) instead defines a sink as any process, activity or mechanism that removes such a gas from the atmosphere.[2] The IPCC uses the word "uptake" for the addition of a substance to a reservoir.[3]
Where carbon is stored
The OpenStax textbook Biology 2e lists the places where carbon is held, called carbon reservoirs. They include the atmosphere, bodies of water (mostly the oceans), ocean sediment, soil, land sediments including fossil fuels, and the Earth's interior.[4] The textbook describes the ocean itself as a major reservoir of carbon.[5]
Plants and living things
In photosynthesis, plants and other organisms turn carbon dioxide gas into organic carbon. Respiration later returns that organic carbon to the air as carbon dioxide.[6] This is why the IPCC lists plants among the places where greenhouse gases can be stored.[1]
The ocean
Carbon dioxide from the atmosphere dissolves in seawater. It combines with water to form carbonic acid, which then breaks up into carbonate and bicarbonate ions.[7]
Long-term storage
Carbon can be stored for a very long time when the remains of living things are buried deep underground and become fossilised. Volcanoes and, more recently, human emissions return this stored carbon to the carbon cycle.[8]
Natural and human-made removal
The IPCC separates natural sinks from carbon dioxide removal, which it defines as human activities that take carbon dioxide out of the atmosphere and store it lastingly in geological, land or ocean reservoirs, or in products. Carbon dioxide removal includes human efforts to strengthen biological or geochemical sinks and direct air capture and storage, but it does not include natural uptake that people did not cause.[9]
See also
References
- ↑ 1.0 1.1 1.2 "Annex I: Glossary". Global Warming of 1.5°C. Intergovernmental Panel on Climate Change. Retrieved 2026-10-20.
Sink A reservoir (natural or human, in soil, ocean, and plants) where a greenhouse gas , an aerosol or a precursor of a greenhouse gas is stored.
- ↑ "Annex I: Glossary". Global Warming of 1.5°C. Intergovernmental Panel on Climate Change. Retrieved 2026-10-20.
Note that UNFCCC Article 1.8 refers to a sink as any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere .
- ↑ "Annex I: Glossary". Global Warming of 1.5°C. Intergovernmental Panel on Climate Change. Retrieved 2026-10-20.
Uptake The addition of a substance of concern to a reservoir.
- ↑ "46.3 Biogeochemical Cycles". Biology 2e. OpenStax. Retrieved 2026-10-20.
carbon reservoirs, which include the atmosphere, bodies of liquid water (mostly oceans), ocean sediment, soil, land sediments (including fossil fuels), and the Earth's interior.
- ↑ "46.3 Biogeochemical Cycles". Biology 2e. OpenStax. Retrieved 2026-10-20.
Furthermore, the ocean itself is a major reservoir for carbon.
- ↑ "46.3 Biogeochemical Cycles". Biology 2e. OpenStax. Retrieved 2026-10-20.
Photosynthesis converts carbon dioxide gas to organic carbon, and respiration cycles the organic carbon back into carbon dioxide gas.
- ↑ "46.3 Biogeochemical Cycles". Biology 2e. OpenStax. Retrieved 2026-10-20.
Carbon dioxide (CO 2 ) from the atmosphere dissolves in water and combines with water molecules to form carbonic acid, and then it ionizes to carbonate and bicarbonate ions
- ↑ "46.3 Biogeochemical Cycles". Biology 2e. OpenStax. Retrieved 2026-10-20.
Long-term storage of organic carbon occurs when matter from living organisms is buried deep underground and becomes fossilized. Volcanic activity and, more recently, human emissions, bring this stored carbon back into the carbon cycle.
- ↑ "Annex I: Glossary". Global Warming of 1.5°C. Intergovernmental Panel on Climate Change. Retrieved 2026-10-20.
Anthropogenic activities removing CO 2 from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage, but excludes natural CO 2 uptake not directly caused by human activities.