Carbon sequestration

Carbon sequestration is a natural process of storing carbon in a carbon pool. It plays a crucial role in effectively managing the global carbon cycle and limiting climate change by reducing the amount of carbon dioxide in the atmosphere. There are two main types of carbon sequestration: biologic and geologic.
Biologic carbon sequestration is a naturally occurring process as part of the carbon cycle. Humans can enhance it through deliberate actions and use of technology. Carbon dioxide is naturally captured from the atmosphere through biological, chemical, and physical processes. These processes can be accelerated for example through changes in land use and agricultural practices, called carbon farming. Artificial processes have also been devised to produce similar effects. This approach is called carbon capture and storage. It involves using technology to capture and sequester that is produced from human activities underground or under the sea bed.
Plants absorb carbon dioxide from the air as they grow, and bind it into biomass. However, biological stores may be temporary carbon sinks, as long-term sequestration cannot be guaranteed. Wildfires, disease, economic pressures, and changing political priorities may release the sequestered carbon back into the atmosphere.
Carbon dioxide that has been removed from the atmosphere can also be stored in the Earth's crust by injecting it underground, or in the form of insoluble carbonate salts. The latter process is called mineral sequestration. These methods are considered non-volatile because they not only remove carbon dioxide from the atmosphere but also sequester it indefinitely. This means the carbon is "locked away" for thousands to millions of years.
To enhance carbon sequestration processes in oceans the following chemical or physical technologies have been proposed: ocean fertilization, artificial upwelling, basalt storage, mineralization, deep-sea sediments, and adding bases to neutralize acids. However, none have achieved large scale application so far. Large-scale seaweed farming on the other hand is a biological process and could sequester significant amounts of carbon. The potential growth of seaweed for carbon farming would see the harvested seaweed transported to the deep ocean for long-term burial. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" on seaweed farming as a mitigation tactic.

Terminology

The term carbon sequestration has diverse meanings in the literature and media. The IPCC Sixth Assessment Report defines carbon sequestration as "The process of storing carbon in a carbon pool". Subsequently, a pool is defined as "a reservoir in the Earth system where elements, such as carbon and nitrogen, reside in various chemical forms for a period of time".
The United States Geological Survey defines carbon sequestration as follows: "Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide." Because the wording in this definition makes it very similar to the definition of carbon capture and storage, carbon sequestration is sometimes confounded with CCS.

Roles

In nature

Carbon sequestration is part of the natural carbon cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Carbon dioxide is naturally captured from the atmosphere through biological, chemical, or physical processes, and stored in long-term reservoirs.
Plants absorb carbon dioxide from the air as they grow, and bind it into biomass. However, biological stores are considered volatile carbon sinks as long-term sequestration cannot be guaranteed. Events such as wildfires or disease, economic pressures, and changing political priorities can result in the sequestered carbon being released back into the atmosphere.

In climate change mitigation and policies

Carbon sequestration, which acts as a carbon sink, helps to mitigate climate change and thus reduce harmful effects of climate change. It helps to slow the atmospheric and marine accumulation of greenhouse gases, which is mainly carbon dioxide released by burning fossil fuels.
Carbon sequestration for climate change mitigation can involve either enhancing natural carbon sinks or employing technological methods to capture and store carbon.
Within the carbon capture and storage approaches, carbon sequestration refers to the storage component. Artificial carbon storage technologies can be applied, such as gaseous storage in deep geological formations, and solid storage by reaction of CO₂ with metal oxides to produce stable carbonates.
For carbon to be sequestered artificially—that is, outside the natural processes of the carbon cycle—it must first be captured, or its release into the atmosphere must be significantly delayed or prevented. This can be achieved by incorporating carbon-rich materials into long-lasting applications, such as construction, thereby avoiding release through processes like combustion or decay. Thereafter it can be passively stored or remain productively utilized over time in a variety of ways. For instance, upon harvesting, wood can be incorporated into construction or a range of other durable products, thus sequestering its carbon over years or even centuries. In industrial production, engineers typically capture carbon dioxide from emissions from power plants or factories.
For example, in the United States, the Executive Order 13990 passed in 2021 and revoked January 2025, included several mentions of carbon sequestration via conservation and restoration of carbon sink ecosystems, such as wetlands and forests. The document emphasized the importance of farmers, landowners, and coastal communities in carbon sequestration. It directed the Treasury Department to promote conservation of carbon sinks through market based mechanisms.
Noting that the planet's carbon sequestration capacity is not unlimited, a 2025 study concluded that fully using Earth's geologic storage capacity would help limit global warming by only.

Biological carbon sequestration on land

Biological carbon sequestration is the capture and storage of the atmospheric greenhouse gas carbon dioxide by continual and enhanced biological processes. This form of carbon sequestration occurs through increased rates of photosynthesis via land-use practices such as reforestation and sustainable forest management. Land-use changes that enhance natural carbon capture have the potential to capture and store large amounts of carbon dioxide each year. These include the conservation, management, and restoration of ecosystems such as forests, peatlands, wetlands, and grasslands, in addition to carbon sequestration methods in agriculture. Methods and practices exist to enhance soil carbon sequestration in both agriculture and forestry.

Forestry

Forests are an important part of the global carbon cycle because trees and plants absorb carbon dioxide through photosynthesis. Therefore, they play an important role in climate change mitigation. By removing the greenhouse gas CO₂ from the air, forests function as terrestrial carbon sinks, meaning they store large amounts of carbon in the form of biomass, encompassing roots, stems, branches, and leaves. By doing so, forests sequester approximately 25% of human carbon emissions annually, playing a critical role in Earth's climate. Throughout their lifespan, trees continue to sequester carbon, storing atmospheric CO₂ long-term. Sustainable forest management, afforestation, reforestation are therefore important contributions to climate change mitigation.
An important consideration in such efforts is that forests can turn from sinks to carbon sources. In 2019 forests took up a third less carbon than they did in the 1990s, due to higher temperatures, droughts and deforestation. National-scale forest inventory data also shows trends from 1999 to 2020 that some forests were already approaching climate thresholds shifting them from carbon sinks to carbon sources. The typical tropical forest may become a carbon source by the 2060s.
Researchers have found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the latter leads to irreversible effects in terms of biodiversity loss and soil degradation. Furthermore, the probability that legacy carbon will be released from soil is higher in a younger boreal forest. In particular, boreal forests have been noted to support the growth of Armillaria, which is a root pathogen that breaks down compounds necessary for wood integrity, increasing the likelihood of carbon release. Global greenhouse gas emissions caused by damage to tropical rainforests may have been substantially underestimated until around 2019. Additionally, the effects of afforestation and reforestation will be farther in the future than keeping existing forests intact. It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation. Therefore, scientists consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" to be "the major climate solution".
The planting of trees on marginal crop and pasture lands helps to incorporate carbon from atmospheric into biomass. For this carbon sequestration process to succeed the carbon must not return to the atmosphere from biomass burning or rotting when the trees die. Several species of Ficus such as Ficus wakefieldii have been observed to sequester atmospheric CO₂ as calcium oxalate in the presence of oxalotrophic bacteria and fungi, which catabolize the oxalate, which produces calcium carbonate. The calcium carbonate is precipitated throughout the tree, which also alkalinizes the surrounding soil. These species are current candidates for carbon sequestration in agroforestry. This Calcium-oxalate fixation process was first observed in the Iroko tree, which can sequester up to a ton of calcium carbonate in the soil over its lifespan. Also Cacti, such as the Saguaro, transfer carbon from the biological cycle to the geological cycle by forming the mineral calcium carbonate.
Earth offers enough room to plant an additional 0.9 billion ha of tree canopy cover, although this estimate has been criticized, and the true area that has a net cooling effect on the climate when accounting for biophysical feedbacks like albedo is 20-80% lower. Planting and protecting these trees would sequester 205 billion tons of carbon if the trees survive future climate stress to reach maturity. To put this number into perspective, this is about 20 years of current global carbon emissions . This level of sequestration would represent about 25% of the atmosphere's carbon pool in 2019.
Life expectancy of forests varies throughout the world, influenced by tree species, site conditions, and natural disturbance patterns. In some forests, carbon may be stored for centuries, while in other forests, carbon is released with frequent stand replacing fires. Forests that are harvested prior to stand replacing events allow for the retention of carbon in manufactured forest products such as lumber. However, only a portion of the carbon removed from logged forests ends up as durable goods and buildings. The remainder ends up as sawmill by-products such as pulp, paper, and pallets. If all new construction globally utilized 90% wood products, largely via adoption of mass timber in low rise construction, this could sequester 700 million net tons of carbon per year. This is in addition to the elimination of carbon emissions from the displaced construction material such as steel or concrete, which are carbon-intense to produce.
A meta-analysis found that mixed species plantations would increase carbon storage alongside other benefits of diversifying planted forests.
Although a bamboo forest stores less total carbon than a mature forest of trees, a bamboo plantation sequesters carbon at a much faster rate than a mature forest or a tree plantation. Therefore, the farming of bamboo timber may have significant carbon sequestration potential.
The Food and Agriculture Organization reported that: "The total carbon stock in forests decreased from 668 gigatonnes in 1990 to 662 gigatonnes in 2020". In Canada's boreal forests as much as 80% of the total carbon is stored in the soils as dead organic matter.
The IPCC Sixth Assessment Report says: "Secondary forest regrowth and restoration of degraded forests and non-forest ecosystems can play a large role in carbon sequestration with high resilience to disturbances and additional benefits such as enhanced biodiversity."
Impacts on temperature are affected by the location of the forest. For example, reforestation in boreal or subarctic regions has less impact on climate. This is because it substitutes a high-albedo, snow-dominated region with a lower-albedo forest canopy. By contrast, tropical reforestation projects lead to a positive change such as the formation of clouds. These clouds then reflect the sunlight, lowering temperatures.
Planting trees in tropical climates with wet seasons has another advantage. In such a setting, trees grow more quickly because they can grow year-round. Trees in tropical climates have, on average, larger, brighter, and more abundant leaves than non-tropical climates. A study of the girth of 70,000 trees across Africa has shown that tropical forests fix more carbon dioxide pollution than previously realized. The research suggested almost one-fifth of fossil fuel emissions are absorbed by forests across Africa, Amazonia and Asia. Simon Lewis stated, "Tropical forest trees are absorbing about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of change."