Carbon sequestration is the process of storing carbon in a
carbon pool. Carbon dioxide () is naturally captured from the
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
through biological, chemical, and physical processes.
These changes can be accelerated through changes in land use and agricultural practices, such as converting crop land into land for non-crop fast growing plants.
Artificial processes have been devised to produce similar effects,
including large-scale, artificial capture and sequestration of industrially produced using subsurface
saline aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
s, reservoirs,
ocean water, aging
oil fields, or other
carbon sink
A carbon sink is anything, natural or otherwise, that accumulates and stores some carbon-containing chemical compound for an indefinite period and thereby removes carbon dioxide () from the atmosphere.
Globally, the two most important carbon si ...
s,
bio-energy with carbon capture and storage
Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere. The carbon in the biomass comes from the greenhouse gas carbon ...
,
biochar
Biochar is the lightweight black residue, made of carbon and
ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of ...
,
enhanced weathering
Enhanced weathering is a process that aims to accelerate the natural weathering by spreading finely ground silicate rock, such as basalt, onto surfaces which speeds up chemical reactions between rocks, water, and air. It also removes carbon dioxi ...
,
direct air capture
Direct air capture (DAC) is a process of capturing carbon dioxide () directly from the ambient air (as opposed to capturing from point sources, such as a cement factory or biomass power plant) and generating a concentrated stream of for seque ...
and
water capture when combined with storage.
Forests,
kelp bed
Kelp forests are underwater areas with a high density of kelp, which covers a large part of the world's coastlines. Smaller areas of anchored kelp are called kelp beds. They are recognized as one of the most productive and dynamic ecosystems on Ea ...
s, and other forms of plant life absorb carbon dioxide from the air as they grow, and bind it into biomass. However, these biological stores are considered volatile
carbon sink
A carbon sink is anything, natural or otherwise, that accumulates and stores some carbon-containing chemical compound for an indefinite period and thereby removes carbon dioxide () from the atmosphere.
Globally, the two most important carbon si ...
s as the long-term sequestration cannot be guaranteed. For example, natural events, such as
wildfire
A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire ...
s or disease, economic pressures and changing political priorities can result in the sequestered carbon being released 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 into the subsurface, or in the form of
insoluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubil ...
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
salts (
mineral sequestration). These methods are considered non-volatile because they remove carbon from the atmosphere and sequestering it indefinitely and presumably for a considerable duration (thousands to millions of years).
Description
Carbon sequestration is the process involved in carbon capture and the long-term storage of atmospheric
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
()
[ and may refer specifically to:
* "The process of removing carbon from the atmosphere and depositing it in a reservoir." When carried out deliberately, this may also be referred to as ]carbon dioxide removal
Carbon dioxide removal (CDR), also known as negative emissions, is a process in which carbon dioxide gas () is removed from the atmosphere and sequestered for long periods of time. Similarly, greenhouse gas removal (GGR) or negative greenho ...
, which is a form of geoengineering.
* Carbon capture and storage
Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
, where carbon dioxide is removed from flue gases
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced ...
(e.g., at power station
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.
Many p ...
s) before being stored in underground reservoirs.
* Natural biogeochemical cycling
A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and the ...
of carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
between the atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
and reservoirs, such as by chemical weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement ...
of rocks.
Carbon dioxide may be captured as a pure by-product in processes related to petroleum refining
An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefi ...
or from flue gases from power generation. sequestration includes the storage part of carbon capture and storage, which refers to large-scale, artificial capture and sequestration of industrially produced using subsurface saline aquifers
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
, reservoirs, ocean water, aging oil fields, or other carbon sink
A carbon sink is anything, natural or otherwise, that accumulates and stores some carbon-containing chemical compound for an indefinite period and thereby removes carbon dioxide () from the atmosphere.
Globally, the two most important carbon si ...
s.
Carbon sequestration describes long-term storage of carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
or other forms of carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
to either mitigate or defer global warming and avoid dangerous climate change. It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases, which are released by burning fossil fuels and industrial livestock production.
Carbon dioxide is naturally captured from the atmosphere through biological, chemical or physical processes. Some artificial sequestration techniques exploit these natural processes,[ while some use entirely artificial processes.
There are three ways that this sequestration can be carried out: post-combustion capture, pre-combustion capture, and oxy-combustion. A wide variety of separation techniques are being pursued, including gas phase separation, absorption into a liquid, and adsorption on a solid, as well as hybrid processes, such as adsorption/membrane systems. These above processes basically capture carbon emitting from power plants, factories, fuel burning industries, and new generation livestock production facilities as they transition into restorative farming techniques, which is used by organizations as they look to reduce carbon emissions from their operations. Researchers, including from the ]European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
, found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to i.a. irreversible effects in terms of biodiversity loss
Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...
and soil degradation
Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession reverts the land to ...
. Additionally, the effects of af- or 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. Mackey and Dooley consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" "the major climate solution
Solution may refer to:
* Solution (chemistry), a mixture where one substance is dissolved in another
* Solution (equation), in mathematics
** Numerical solution, in numerical analysis, approximate solutions within specified error bounds
* Soluti ...
". The global annual net loss of trees is estimated to be approximately 10 billion.
Effect on climate change
Tropical deforestation leads to warming . The deforestation to prevent for climate change mitigation is the tropical deforestation. Standing tropical forests help cool the average global temperature by more than 1 °C. Researchers, including from the European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
, found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to i.a. irreversible effects in terms of biodiversity loss
Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...
and soil degradation
Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession reverts the land to ...
. Additionally, the effects of af- or 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. Mackey and Dooley consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" "the major climate solution
Solution may refer to:
* Solution (chemistry), a mixture where one substance is dissolved in another
* Solution (equation), in mathematics
** Numerical solution, in numerical analysis, approximate solutions within specified error bounds
* Soluti ...
". The global annual net loss of trees is estimated to be approximately 10 billion.
A survey by the United Nations Development Programme
The United Nations Development Programme (UNDP)french: Programme des Nations unies pour le développement, PNUD is a United Nations agency tasked with helping countries eliminate poverty and achieve sustainable economic growth and human dev ...
of public opinion on climate change found that forests and land conservation policies were the most popular solutions of climate change mitigation.
Biological processes on land
According to the IPCC Sixth Assessment Report
The Sixth Assessment Report (AR6) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports which assess scientific, technical, and socio-economic information concerning climate change. Three ...
, 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.
Biosequestration
Biosequestration
Biosequestration or biological sequestration is the capture and storage of the atmospheric greenhouse gas carbon dioxide by continual or enhanced biological processes.
This form of carbon sequestration occurs through increased rates of photosyn ...
is the capture and storage of the atmospheric greenhouse gas carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
by continual or enhanced biological processes. This form of carbon sequestration occurs through increased rates of photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
via land-use
Land use involves the management and modification of natural environment or wilderness into built environment such as Human settlement, settlements and semi-natural habitats such as Arable land, arable fields, pastures, and managed Woodland, woo ...
practices such as reforestation
Reforestation (occasionally, reafforestation) is the natural or intentional restocking of existing forests and woodlands (forestation) that have been depleted, usually through deforestation, but also after clearcutting.
Management
A debat ...
and sustainable forest management Forest management is a branch of forestry concerned with overall administrative, legal, economic, and social aspects, as well as scientific and technical aspects, such as silviculture, protection, and forest regulation. This includes management fo ...
.
Peatland
Peat bogs
A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg ...
act as a sink for carbon because they accumulate partially decayed biomass that would otherwise continue to decay completely. There is a variance on how much the peatlands act as a carbon sink or carbon source that can be linked to varying climates in different areas of the world and different times of the year. By creating new bogs, or enhancing existing ones, the amount of carbon that is sequestered by bogs would increase.
Forestry
Afforestation is the establishment of a forest in an area where there was no previous tree cover. Proforestation Proforestation is the practice of protecting existing natural forests to foster continuous growth, carbon accumulation, and structural complexity. It is recognized as an important forest based strategy for addressing the global crises in climate and ...
is the practice of growing an existing forest
A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...
intact toward its full ecological potential. Reforestation
Reforestation (occasionally, reafforestation) is the natural or intentional restocking of existing forests and woodlands (forestation) that have been depleted, usually through deforestation, but also after clearcutting.
Management
A debat ...
is the replanting of trees on marginal crop and pasture
Pasture (from the Latin ''pastus'', past participle of ''pascere'', "to feed") is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep, or sw ...
lands to incorporate carbon from atmospheric into biomass.
For this carbon sequestration process to succeed the carbon must not return to the atmosphere from mass burning or rotting when the trees die. To this end, land allotted to the trees must not be converted to other uses and management of the frequency of disturbances might be necessary in order to avoid extreme events. Alternatively, the wood from them must itself be sequestered, e.g., via biochar
Biochar is the lightweight black residue, made of carbon and
ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of ...
, bio-energy with carbon storage ( BECS), landfill or 'stored' by use in e.g., construction. Short of growth in perpetuity, however, reforestation with long-lived trees (>100 years) will sequester carbon for substantial period and be released gradually, minimizing carbon's climate impact during the 21st century. Earth offers enough room to plant an additional 1.2 trillion trees. Planting and protecting them would offset some 10 years of CO2 emissions and sequester 205 billion tons of carbon. This approach is supported by the Trillion Tree Campaign
The Trillion Tree Campaign is a project which aims to plant one trillion trees worldwide. It seeks to repopulate the world's trees and climate change mitigation, combat climate change as a Nature-based solutions, nature-based solution. The proje ...
. Restoring all degraded forests world would capture about 205 billion tons of carbon in total, which is about two thirds of all carbon emissions. However in a study from 2022, a modest effect on carbon emissions compensation by afforestation is presented, only 1%.
In a paper published in the journal ''Nature Sustainability,'' researchers studied the net effect of construction utilizing wood products. They concluded that if during the next 30 years all new construction globally utilized 90% wood products, largely via adoption of mass timber
Engineered wood, also called mass timber, composite wood, man-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or wood veneer, veneers or b ...
in low rise
A low-rise is a building that is only a few stories tall or any building that is shorter than a high-rise, though others include the classification of mid-rise.
Definition
Emporis defines a low-rise as "an enclosed structure below 35 metres 1 ...
construction, that 700 million net tons of carbon would be sequestered per year, negating approximately 2% of annual carbon emissions in 2019. 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.
In a study published in Journal of Environmental Management researchers concluded "that coniferous and broadleaf trees can have diverse effect on soil organic carbon sequestration in soils of different age and previous land use".
Urban forestry
Urban forestry
Urban forestry is the care and management of single trees and tree populations in urban settings for the purpose of improving the urban environment. Urban forestry involves both planning and management, including the programming of care and ...
increases the amount of carbon taken up in cities by adding new tree sites and the sequestration of carbon occurs over the lifetime of the tree. It is generally practiced and maintained on smaller scales, like in cities. The results of urban forestry can have different results depending on the type of vegetation that is being used, so it can function as a sink but can also function as a source of emissions. Along with sequestration by the plants which is difficult to measure but seems to have little effect on the overall amount of carbon dioxide that is uptaken, the vegetation can have indirect effects on carbon by reducing need for energy consumption.
Wetlands
Wetland restoration involves restoring a wetland's natural biological, geological, and chemical functions through re-establishment or rehabilitation. It has also been proposed as a potential climate change mitigation strategy, with carbon sequestered this way being known as blue carbon. Wetland soil, particularly in coastal wetlands such as mangroves, sea grasses, and salt marshes, is an important carbon reservoir; 20–30% of the world's soil carbon is found in wetlands, while only 5–8% of the world's land is composed of wetlands. Studies have shown that restored wetlands can become productive sinks and many restoration projects have been enacted in the US and around the world. Aside from climate benefits, wetland restoration and conservation can help preserve biodiversity, improve water quality, and aid with flood control.
As with forests, for the sequestration process to succeed, the wetland must remain undisturbed. If it is disturbed somehow, the carbon stored in the plants and sediments will be released back into the atmosphere and the ecosystem will no longer function as a carbon sink. Additionally, some wetlands can release non- greenhouse gases, such as methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
, which could offset potential climate benefits. The amounts of CO2 sequestered by wetlands can also be difficult to measure.
Agriculture
Compared to natural vegetation, cropland soils are depleted in soil organic carbon (SOC). When a soil is converted from natural land or semi natural land, such as forests, woodlands, grasslands, steppes and savannas, the SOC content in the soil reduces by about 30–40%. This loss is due to the removal of plant material containing carbon, in terms of harvests. When the land use changes, the carbon in the soil will either increase or decrease, this change will continue until the soil reaches a new equilibrium. Deviations from this equilibrium can also be affected by variated climate. The decreasing of SOC content can be counteracted by increasing the carbon input, this can be done with several strategies, e.g. leave harvest residues on the field, use manure as fertiliser or include perennial crops in the rotation. Perennial crop Perennial crops are crops that – unlike annual crops – don't need to be replanted each year. After harvest, they automatically grow back. Many fruit and nut crops are naturally perennial, however there is also a growing movement to create perenn ...
s have larger below ground biomass fraction, which increases the SOC content. Perennial crops reduce the need for tillage
Tillage is the agricultural preparation of soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shoveling, picking, mattock work, hoein ...
and thus help mitigate soil erosion, and may help increase soil organic matter. Globally, soils are estimated to contain >8,580 gigatons of organic carbon, about ten times the amount in the atmosphere and much more than in vegetation. Researchers have found that rising temperatures can lead to population booms in soil microbes, converting stored carbon into carbon dioxide. In laboratory experiments fungi-rich soils released less carbon dioxide when heated than other soils.
Modification of agricultural practices is a recognized method of carbon sequestration as soil can act as an effective carbon sink offsetting as much as 20% of 2010 carbon dioxide emissions annually. (See No-till
No-till farming (also known as zero tillage or direct drilling) is an agricultural technique for growing crops or pasture without disturbing the soil through tillage. No-till farming decreases the amount of soil erosion tillage causes in certai ...
). Restoration of organic farming and earthworms may entirely offset CO2 annual carbon excess of 4 Gt per year and drawdown the residual atmospheric excess. (See Compost).
Carbon emission reduction methods in agriculture can be grouped into two categories: reducing and/or displacing emissions and enhancing carbon removal. Some of these reductions involve increasing the efficiency of farm operations (e.g. more fuel-efficient equipment) while some involve interruptions in the natural carbon cycle. Also, some effective techniques (such as the elimination of stubble burning
Stubble burning is the practice of intentionally setting fire to the straw stubble that remains after grains, such as rice and wheat, have been harvested. The technique is still widespread today.
Effects
The burning of stubble has both positi ...
) can negatively impact other environmental concerns (increased herbicide use to control weeds not destroyed by burning).
As enforcement of forest protection may not sufficiently address the drivers behind deforestation – the largest of which being the production of beef in the case of the Amazon rainforest – it may also need policies. These could effectively ban and/or progressively discourage deforestation-associated trade via e.g. product information requirements, satellite monitoring like the Global Forest Watch
Global Forest Watch (GFW) is an open-source web application to monitor global forests in near real-time. GFW is an initiative of the World Resources Institute (WRI), with partners including Google, USAID, the University of Maryland (UMD), Esri, V ...
, related eco-tariff
An eco-tariff, also known as an environmental tariff or carbon tariff, is a trade barrier erected for the purpose of reducing pollution and improving the environment. These trade barriers may take the form of import or export taxes on products t ...
s, and product certifications.
Carbon farming
Bamboo farming
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.
Deep soil
Soils hold four times the amount of carbon stored in the atmosphere. About half of this is found deep within soils. About 90% of this deep soil C is stabilized by mineral-organic associations.
Reducing emissions
Increasing yields and efficiency generally reduces emissions as well, since more food results from the same or less effort. Techniques include more accurate use of fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s, less soil disturbance, better irrigation
Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...
, and crop strains bred for locally beneficial traits and increased yields.
Replacing more energy intensive farming
Intensive agriculture, also known as intensive farming (as opposed to extensive farming), conventional, or industrial agriculture, is a type of agriculture, both of crop plants and of animals, with higher levels of input and output per unit of ...
operations can also reduce emissions. Reduced or no-till farming
No-till farming (also known as zero tillage or direct drilling) is an agricultural technique for growing crops or pasture without disturbing the soil through tillage. No-till farming decreases the amount of soil erosion tillage causes in certai ...
requires less machine use and burns correspondingly less fuel per acre. However, no-till usually increases use of weed-control chemicals and the residue now left on the soil surface is more likely to release its to the atmosphere as it decays, reducing the net carbon reduction.
In practice, most farming operations that incorporate post-harvest crop residues, wastes and byproducts back into the soil provide a carbon storage benefit. This is particularly the case for practices such as field burning of stubble – rather than releasing almost all of the stored to the atmosphere, tillage incorporates the biomass back into the soil.
Enhancing carbon removal
All crops absorb during growth and release it after harvest. The goal of agricultural carbon removal is to use the crop and its relation to the carbon cycle to permanently sequester carbon within the soil. This is done by selecting farming methods that return biomass to the soil and enhance the conditions in which the carbon within the plants will be reduced to its elemental nature and stored in a stable state. Methods for accomplishing this include:
* Use cover crops such as grasses and weeds as temporary cover between planting seasons
* Concentrate livestock in small paddocks for days at a time so they graze lightly but evenly. This encourages roots to grow deeper into the soil. Stock also till the soil with their hooves, grinding old grass and manures into the soil.
* Cover bare paddocks with hay or dead vegetation. This protects soil from the sun and allows the soil to hold more water and be more attractive to carbon-capturing microbes.[
* Restore degraded, marginal, and abandoned land, which slows carbon release while returning the land to agriculture or other use. Degraded land with low soil carbon pool have particularly high potential to store soil C which can be farther enhanced by proper selection of vegetation.
Agricultural sequestration practices may have positive effects on ]soil
Soil, also commonly referred to as earth or dirt
Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty.
Common types of dirt include:
* Debri ...
, air, and water quality, be beneficial to wildlife
Wildlife refers to undomesticated animal species, but has come to include all organisms that grow or live wild in an area without being introduced by humans. Wildlife was also synonymous to game: those birds and mammals that were hunted ...
, and expand food production
The food industry is a complex, global network of diverse businesses that supplies most of the food consumed by the world's population. The food industry today has become highly diversified, with manufacturing ranging from small, traditiona ...
. On degraded croplands
A farm (also called an agricultural holding) is an area of land that is devoted primarily to agricultural processes with the primary objective of producing food and other crops; it is the basic facility in food production. The name is used f ...
, an increase of 1 ton of soil carbon pool may increase crop yield by 20 to 40 kilograms per hectare of wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
, 10 to 20 kg/ ha for maize, and 0.5 to 1 kg/ha for cowpeas
The cowpea (''Vigna unguiculata'') is an annual herbaceous legume from the genus ''Vigna''. Its tolerance for sandy soil and low rainfall have made it an important crop in the semiarid regions across Africa and Asia. It requires very few input ...
.
The effects of soil sequestration can be reversed. If the soil is disrupted or intensive tillage practices are used, the soil becomes a net source of greenhouse gases. Typically after several decades of sequestration, soil becomes saturated and ceases to absorb carbon. This implies that there is a global limit to the amount of carbon that soil can hold.
Many factors affect the costs of carbon sequestration including soil quality, transaction costs and various externalities such as leakage and unforeseen environmental damage. Because reduction of atmospheric is a long-term concern, farmers can be reluctant to adopt more expensive agricultural techniques when there is not a clear crop, soil, or economic benefit. Governments such as Australia and New Zealand are considering allowing farmers to sell carbon credits once they document that they have sufficiently increased soil carbon content.[
]
Physical processes
Biomass-related
Bio-energy with carbon capture and storage
Bio-energy with carbon capture and storage (BECCS) refers to biomass in power stations
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.
Many po ...
and boilers that use carbon capture and storage. The carbon sequestered by the biomass would be captured and stored, thus removing carbon dioxide from the atmosphere.
Burial
Burying biomass (such as trees) directly, mimics the natural processes that created fossil fuels.
Biochar burial
Biochar
Biochar is the lightweight black residue, made of carbon and
ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of ...
is charcoal created by pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
of biomass waste. The resulting material is added to a landfill or used as a soil improver to create terra preta
''Terra preta'' (, locally , literally "black soil" in Portuguese) is a type of very dark, fertile anthropogenic soil ( anthrosol) found in the Amazon Basin. It is also known as "Amazonian dark earth" or "Indian black earth". In Portuguese its f ...
. Addition of pyrogenic organic carbon (biochar) is a novel strategy to increase the soil-C stock for the long-term and to mitigate global-warming by offsetting the atmospheric C (up to 9.5 Gigatons C annually).
In the soil, the carbon is unavailable for oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
to and consequential atmospheric release. This is one technique advocated by scientist
A scientist is a person who conducts scientific research to advance knowledge in an area of the natural sciences.
In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosoph ...
James Lovelock, creator of the Gaia hypothesis. According to Simon Shackley, "people are talking more about something in the range of one to two billion tonnes a year." However concerns have been raised about Biochar potentially accelerating release of the carbon already present in the soil.
The mechanisms related to biochar are referred to as bio-energy with carbon storage, BECS.
Geological sequestration
Geological sequestration refers to the storage of CO2 underground in depleted oil and gas reservoirs, saline formations, or deep, un-minable coal beds.
Once CO2 is captured from a point source, such as a cement factory, it would be compressed to ≈100 bar so that it would be a supercritical fluid. In this form, the CO2 would be easy to transport via pipeline to the place of storage. The CO2 would then be injected deep underground, typically around 1 km, where it would be stable for hundreds to millions of years. At these storage conditions, the density of supercritical CO2 is 600 to 800 kg / m3.
The important parameters in determining a good site for carbon storage are: rock porosity, rock permeability, absence of faults, and geometry of rock layers. The medium in which the CO2 is to be stored ideally has a high porosity and permeability, such as sandstone or limestone. Sandstone can have a permeability ranging from 1 to 10−5 Darcy, and can have a porosity as high as ≈30%. The porous rock must be capped by a layer of low permeability which acts as a seal, or caprock, for the CO2. Shale is an example of a very good caprock, with a permeability of 10−5 to 10−9 Darcy. Once injected, the CO2 plume will rise via buoyant forces, since it is less dense than its surroundings. Once it encounters a caprock, it will spread laterally until it encounters a gap. If there are fault planes near the injection zone, there is a possibility the CO2 could migrate along the fault to the surface, leaking into the atmosphere, which would be potentially dangerous to life in the surrounding area. Another danger related to carbon sequestration is induced seismicity. If the injection of CO2 creates pressures that are too high underground, the formation will fracture, potentially causing an earthquake.[Smit, Berend; Reimer, Jeffrey A.; Oldenburg, Curtis M.; Bourg, Ian C. (2014). ''Introduction to Carbon Capture and Sequestration''. London: Imperial College Press. .]
While trapped in a rock formation, CO2 can be in the supercritical fluid phase or dissolve in groundwater/brine. It can also react with minerals in the geologic formation to precipitate carbonates. See CarbFix.
Worldwide storage capacity in oil and gas reservoirs is estimated to be 675–900 Gt CO2, and in un-minable coal seams is estimated to be 15–200 Gt CO2. Deep saline formations have the largest capacity, which is estimated to be 1,000–10,000 Gt CO2. In the US, there is estimated to be at least 2,600 Gt and at most 22,000 Gt total CO2 storage capacity.
There are a number of large-scale carbon capture and sequestration projects that have demonstrated the viability and safety of this method of carbon storage, which are summarized here by the Global CCS Institute. The dominant monitoring technique is seismic imaging, where vibrations are generated that propagate through the subsurface. The geologic structure can be imaged from the refracted/reflected waves.
The first large-scale sequestration project which began in 1996 is called Sleipner, and is located in the North Sea
The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
where Norway's StatoilHydro
Equinor ASA (formerly Statoil and StatoilHydro) is a Norwegian state-owned multinational energy company headquartered in Stavanger. It is primarily a petroleum company, operating in 36 countries with additional investments in renewable energy. I ...
strips carbon dioxide from natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
with amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen
Hydrogen is the chemical element wi ...
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s and disposed of this carbon dioxide in a deep saline aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
. In 2000, a coal-fueled synthetic natural gas
Substitute natural gas (SNG), or synthetic natural gas, is a fuel gas (predominantly methane, CH4) that can be produced from fossil fuels such as lignite coal, oil shale, or from biofuels (when it is named bio-SNG) or using electricity with power- ...
plant in Beulah, North Dakota
Beulah is a city in Mercer County, North Dakota, United States. The population was 3,058 at the 2020 census. Beulah is home to the Dakota Gasification Company. It is near the largest lignite mine in the United States, owned by North American ...
, became the world's first coal-using plant to capture and store carbon dioxide, at the Weyburn-Midale Carbon Dioxide Project
The Weyburn-Midale Carbon Dioxide Project (or IEA GHG Weyburn-Midale Monitoring and Storage Project) is, as of 2008, the world's largest carbon capture and storage project.Allan Casey, ''Carbon Cemetery'', Canadian Geographic Magazine, Jan/Feb 2 ...
. Several other sequestration projects have followed. The Energy Impact Center
The Energy Impact Center is an American research institute based in Washington, D.C. It primarily advocates for the expansion of nuclear power as a clean energy solution to climate change. The organization's research into nuclear power has led it ...
launched the OPEN100 project in February 2020, which is the world's first open-source blueprint for the design, construction and financing of a small, standard, pressurized water reactor. In September 2020, the US Department of Energy
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United States. ...
awarded $72 million in federal funding to support the development and advancement of carbon capture technologies.
has been used extensively in enhanced crude oil
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
recovery operations in the United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
beginning in 1972.[ There are in excess of 10,000 wells that inject in the state of ]Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
alone. The gas comes in part from anthropogenic sources, but is principally from large naturally occurring geologic formations of . It is transported to the oil-producing fields through a large network of over of pipelines. The use of for enhanced oil recovery (EOR) methods in heavy oil reservoirs in the Western Canadian Sedimentary Basin
The Western Canadian Sedimentary Basin (WCSB) underlies of Western Canada including southwestern Manitoba, southern Saskatchewan, Alberta, northeastern British Columbia and the southwest corner of the Northwest Territories. This vast sedimentary ...
(WCSB) has also been proposed. However, transport cost remains an important hurdle. An extensive pipeline system does not yet exist in the WCSB. Athabasca oil sands mining that produces is hundreds of kilometers north of the subsurface Heavy crude oil
Heavy crude oil (or extra heavy crude oil) is highly-viscous oil that cannot easily flow from production wells under normal reservoir conditions.
It is referred to as "heavy" because its density or specific gravity is higher than that of light cru ...
reservoirs that could most benefit from injection.
Chemical processes
Developed in the Netherlands, an electrocatalysis by a copper complex helps reduce carbon dioxide to oxalic acid; This conversion uses carbon dioxide as a feedstock to generate oxalic acid.
Mineral carbonation
Carbon, in the form of can be removed from the atmosphere by chemical processes, and stored in stable carbonate mineral
Carbonate minerals are those minerals containing the carbonate ion, .
Carbonate divisions Anhydrous carbonates
*Calcite group: trigonal
** Calcite CaCO3
** Gaspéite (Ni,Mg,Fe2+)CO3
** Magnesite MgCO3
** Otavite CdCO3
**Rhodochrosite MnCO3
** ...
forms. This process (-to-stone) is known as "carbon sequestration by mineral carbonation
Carbonation is the chemical reaction of carbon dioxide to give carbonates, bicarbonates, and carbonic acid. In chemistry, the term is sometimes used in place of carboxylation, which refers to the formation of carboxylic acids.
In inorganic ch ...
" or mineral sequestration. The process involves reacting carbon dioxide with abundantly available metal oxides – either magnesium oxide
Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
(MgO) or calcium oxide
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ...
(CaO) – to form stable carbonates. These reactions are exothermic and occur naturally (e.g., the weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
of rock over geologic time periods).
:CaO + →
:MgO + →
Calcium and magnesium are found in nature typically as calcium and magnesium silicates
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name i ...
(such as forsterite
Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthorh ...
and serpentinite
Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''se ...
) and not as binary oxides. For forsterite and serpentine the reactions are:
: + 2 → 2 +
:+ 3 → 3 + 2 + 2
The following table lists principal metal oxides of Earth's crust. Theoretically up to 22% of this mineral mass is able to form carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
s.
These reactions are slightly more favorable at low temperatures. This process occurs naturally over geologic time frames and is responsible for much of the Earth's surface limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
. The reaction rate can be made faster however, by reacting at higher temperatures and/or pressures, although this method requires some additional energy. Alternatively, the mineral could be milled to increase its surface area, and exposed to water and constant abrasion to remove the inert Silica as could be achieved naturally by dumping Olivine in the high energy surf of beaches. Experiments suggest the weathering process is reasonably quick (one year) given porous basaltic rocks.
naturally reacts with peridotite rock in surface exposures of ophiolite
An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.
The Greek word ὄφις, ''ophis'' (''snake'') is found ...
s, notably in Oman
Oman ( ; ar, عُمَان ' ), officially the Sultanate of Oman ( ar, سلْطنةُ عُمان ), is an Arabian country located in southwestern Asia. It is situated on the southeastern coast of the Arabian Peninsula, and spans the mouth of t ...
. It has been suggested that this process can be enhanced to carry out natural mineralisation of .
When is dissolved in water and injected into hot basaltic rocks underground it has been shown that the reacts with the basalt to form solid carbonate minerals. A test plant in Iceland started up in October 2017, extracting up to 50 tons of CO2 a year from the atmosphere and storing it underground in basaltic rock.
Researchers from British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
, developed a low cost process for the production of magnesite, also known as magnesium carbonate, which can sequester CO2 from the air, or at the point of air pollution, e.g. at a power plant. The crystals are naturally occurring, but accumulation is usually very slow.
Concrete is a promising destination of captured carbon dioxide. Several advantages that concrete offers include, but not limited to: a source of plenty of calcium due to its substantial production all over the world; a thermodynamically stable condition for carbon dioxide to be stored as calcium carbonates; and its long-term capability of storing carbon dioxide as a material widely used in infrastructure
Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and priv ...
. Demolished concrete waste or recycled concrete could be also used aside from newly produced concrete. Studies at HeidelbergCement
HeidelbergCement is a German multinational building materials company headquartered in Heidelberg, Germany. It is a DAX corporation and is one of the largest building materials companies in the world. On 1 July 2016, HeidelbergCement AG complet ...
show that carbon sequestration can turn those demolished and recycled concrete into
supplementary cementitious material
which acts as a secondary binder in tandem with Portland cement, for a new butch of concrete production.
Electrochemistry
Another method uses a liquid metal catalyst and an electrolyte liquid into which CO2 is dissolved. The CO2 then converts into solid flakes of carbon. This method is done at room temperature. In 2022, the team updated its work to operate at a lower temperature, and operate more quickly and with fewer steps.
Industrial use
Traditional cement manufacture releases large amounts of carbon dioxide, but newly developed cement types from Novacem can absorb from ambient air during hardening. A similar technique was pioneered by TecEco, which has been producing "EcoCement" since 2002. Canadian startup CarbonCure Technologies
CarbonCure Technologies is a manufacturer of carbon removal and utilization technologies that inject captured carbon dioxide into concrete. It was founded in 2012 by Rob Niven, and the company headquarters are in Halifax, Nova Scotia.
Technology ...
takes captured CO2 and injects it into concrete as it is being mixed. Carbon Upcycling UCLA is another company that uses in concrete. Their concrete product is called CO2NCRETE, a concrete that hardens faster and is more eco-friendly than traditional concrete.
In Estonia, oil shale
Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...
ash
Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...
, generated by power stations could be used as sorbent
A sorbent is a material used to absorb or adsorb liquids or gases. Examples include:
*A material similar to molecular sieve material, which acts by adsorption (attracting molecules to its surface). It has a large internal surface area and good th ...
s for mineral sequestration. The amount of captured averaged 60 to 65% of the carbonaceous and 10 to 11% of the total emissions.
Chemical scrubbers
Various carbon dioxide scrubbing processes have been proposed to remove from the air, usually using a variant of the Kraft process
The kraft process (also known as kraft pulping or sulfate process) is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibres, the main component of paper. The kraft process involves treatment of wood chip ...
. Carbon dioxide scrubbing variants exist based on potassium carbonate
Potassium carbonate is the inorganic compound with the formula K2 CO3. It is a white salt, which is soluble in water. It is deliquescent, often appearing as a damp or wet solid. Potassium carbonate is mainly used in the production of soap and gl ...
, which can be used to create liquid fuels, or on sodium hydroxide. These notably include artificial trees proposed by Klaus Lackner
Klaus S. Lackner is the Founding Director of the Center for Negative Carbon Emissions (CNCE) and a professor in School of Sustainable Engineering and the Built Environment at Arizona State University. He is scientific advisor to Carbon Collect ...
to remove carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
from the atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
using chemical scrubbers.
Sequestration techniques in oceans
Seaweed farming
Seaweed
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
grow in shallow and coastal areas, and capture significant amounts of carbon that can be transported to the deep ocean by oceanic mechanisms; seaweed reaching the deep ocean sequester carbon and prevent it from exchanging with the atmosphere over millennia. Growing seaweed offshore with the purpose of sinking the seaweed in the depths of the sea to sequester carbon is under research. In addition, seaweed grows very fast and can theoretically be harvested and processed to generate biomethane
Renewable natural gas (RNG), also known as sustainable natural gas (SNG) or biomethane, is a biogas which has been upgraded to a quality similar to fossil natural gas and having a methane concentration of 90% or greater. By increasing the concentr ...
, via anaerobic digestion
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to Waste management, manage waste or to produce fuels. Mu ...
to generate electricity, via cogeneration/CHP or as a replacement for natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
. One study suggested that if seaweed farms covered 9% of the ocean they could produce enough biomethane to supply Earth's equivalent demand for fossil fuel energy, remove 53 gigatonnes
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...
of per year from the atmosphere and sustainably produce 200 kg per year of fish, per person, for 10 billion people. Ideal species for such farming and conversion include ''Laminaria digitata
''Laminaria digitata'' is a large brown alga in the family Laminariaceae, also known by the common name oarweed. It is found in the sublittoral zone of the northern Atlantic Ocean.
Description
''Laminaria digitata'' is a tough, leathery, dark ...
'', ''Fucus serratus
''Fucus serratus'' is a seaweed of the north Atlantic Ocean, known as toothed wrack or serrated wrack.
Description and reproduction
''Fucus serratus'' is a robust alga, olive-brown in colour and similar to '' Fucus vesiculosus'' and ''Fucus spi ...
'' and ''Saccharina latissima
''Saccharina latissima'' is a brown alga (class Phaeophyceae), of the family Laminariaceae. It is known by the common names sugar kelp, sea belt, and Devil's apron, and is one of the species known to Japanese cuisine as kombu. It is found in the ...
''.
Ocean fertilisation
Artificial upwelling
Artificial upwelling or downwelling is an approach that would change the mixing layers of the ocean. Encouraging various ocean layers to mix can move nutrients and dissolved gases around, offering avenues for geoengineering. Mixing may be achieved by placing large vertical pipes in the oceans to pump nutrient rich water to the surface, triggering blooms of algae, which store carbon when they grow and export carbon when they die. This produces results somewhat similar to iron fertilization. One side-effect is a short-term rise in , which limits its attractiveness.
Mixing layers involve transporting the denser and colder deep ocean water
Deep ocean water (DOW) is the name for cold, salty water found deep below the surface of Earth's oceans. Ocean water differs in temperature and salinity. Warm surface water is generally saltier than the cooler deep or polar waters; in polar regio ...
to the surface mixed layer
The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, surface heat fluxes, or processes such as evaporat ...
. As the ocean temperature decreases with depth, more carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
and other compounds are able to dissolve in the deeper layers. This can be induced by reversing the oceanic carbon cycle
The oceanic carbon cycle (or marine carbon cycle) is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many inte ...
through the use of large vertical pipes serving as ocean pumps, or a mixer array. When the nutrient rich deep ocean water is moved to the surface, algae bloom
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompasse ...
occurs, resulting in a decrease in carbon dioxide due to carbon intake from phytoplankton and other photosynthetic eukaryotic
Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
organisms
In biology, an organism () is any life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), taxonomy into groups such as Multicellular o ...
. The transfer of heat between the layers will also cause seawater from the mixed layer to sink and absorb more carbon dioxide. This method has not gained much traction as algae bloom harms marine ecosystems
Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the su ...
by blocking sunlight and releasing harmful toxins into the ocean. The sudden increase in carbon dioxide on the surface level will also temporarily decrease the pH of the seawater, impairing the growth of coral reefs
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
Co ...
. The production of carbonic acid through the dissolution of carbon dioxide in seawater hinders marine biogenic calcification
Marine biogenic calcification is the process by which marine organisms such as oysters and clams form calcium carbonate. Seawater is full of dissolved compounds, ions and nutrients that organisms can use for energy and, in the case of calcificatio ...
and causes major disruptions to the oceanic food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...
.
Basalt storage
Carbon dioxide sequestration in basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
involves the injecting of into deep-sea formations. The first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of and ions forming stable carbonate minerals.
Underwater basalt offers a good alternative to other forms of oceanic carbon storage because it has a number of trapping measures to ensure added protection against leakage. These measures include "geochemical, sediment, gravitational and hydrate formation." Because hydrate is denser than in seawater, the risk of leakage is minimal. Injecting the at depths greater than ensures that the has a greater density than seawater, causing it to sink.
One possible injection site is Juan de Fuca plate. Researchers at the Lamont–Doherty Earth Observatory
The Lamont–Doherty Earth Observatory (LDEO) is the scientific research center of the Columbia Climate School, and a unit of The Earth Institute at Columbia University. It focuses on climate and earth sciences and is located on a 189-acre (64 ...
found that this plate at the western coast of the United States has a possible storage capacity of 208 gigatons. This could cover the entire current U.S. carbon emissions for over 100 years.
This process is undergoing tests as part of the CarbFix project, resulting in 95% of the injected 250 tonnes of CO2 to solidify into calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
in two years, using 25 tonnes of water per tonne of CO2.
Mineralization and deep sea sediments
Similar to mineralization processes that takes place within rocks, mineralization can also occur under the sea. The rate of dissolution of carbon dioxide from atmosphere to oceanic regions relies upon the circulation period of the ocean and buffering ability of subducting
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
surface water. Researches have demonstrated that the carbon dioxide marine storage at several kilometers deep could be viable for up to 500 years, but is dependent on injection site and conditions. Several studies have shown that although it may fix carbon dioxide effect, carbon dioxide may be released back to the atmosphere over time. However, this is unlikely for at least a few more centuries. The neutralization of CaCO3, or balancing the concentration of CaCO3 on the seafloor, land and in the ocean, can be measured on a timescale of thousands of years. More specifically, the predicted time is 1700 years for ocean and approximately 5000 to 6000 years for land. Further, the dissolution time for CaCO3 can be improved by injecting near or downstream of the storage site.
In addition to carbon mineralization, another proposal is deep sea sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
injection. It injects liquid carbon at least 3000 m below the surface directly into ocean sediments to generate carbon dioxide hydrate. Two regions are defined for exploration: the negative buoyancy zone (NBZ), which is the region between liquid carbon dioxide denser than surrounding water and where liquid carbon dioxide has neutral buoyancy, and hydrate formation zone (HFZ), which typically has low temperatures and high pressures. Several research models have shown that the optimal depth of injection requires consideration of intrinsic permeability and any changes in liquid carbon dioxide permeability for optimal storage. The formation of hydrates decreases liquid carbon dioxide permeability, and injection below HFZ is more energetically favored than within the HFZ. If the NBZ is a greater column of water than the HFZ, the injection should happen below the HFZ and directly to the NBZ. In this case, liquid carbon dioxide will sink to the NBZ and be stored below the buoyancy and hydrate cap. Carbon dioxide leakage can occur if there is dissolution into pore fluid or via molecular diffusion
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of ...
. However, this occurs over thousands of years.
Adding bases to neutralize acids
Carbon dioxide forms carbonic acid when dissolved in water, so ocean acidification
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
is a significant consequence of elevated carbon dioxide levels, and limits the rate at which it can be absorbed into the ocean (the solubility pump
In oceanic biogeochemistry, the solubility pump is a physico-chemical process that transports carbon as dissolved inorganic carbon (DIC) from the ocean's surface to its interior.
Overview
The solubility pump is driven by the coincidence of tw ...
). A variety of different bases have been suggested that could neutralize the acid and thus increase absorption. For example, adding crushed limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
to oceans enhances the absorption of carbon dioxide. Another approach is to add sodium hydroxide to oceans which is produced by electrolysis of salt water or brine, while eliminating the waste hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
by reaction with a volcanic silicate rock such as enstatite, effectively increasing the rate of natural weathering of these rocks to restore ocean pH.
Single-step carbon sequestration and storage
Single-step carbon sequestration and storage is a saline water-based mineralization technology extracting carbon dioxide from seawater and storing it in the form of solid minerals.
Abandoned ideas
Direct deep-sea carbon dioxide injection
It was once suggested that CO2 could be stored in the oceans by direct injection into the deep ocean and storing it there for some centuries. At the time, this proposal was called "ocean storage" but more precisely it was known as "direct deep-sea carbon dioxide injection
Direct deep-sea carbon dioxide injection was a (now abandoned) technology proposal with the aim to remove carbon dioxide from the atmosphere by direct injection into the deep ocean and storing it there for some centuries. If carbon dioxide was to ...
". However, the interest in this avenue of carbon storage has much reduced since about 2001 because of concerns about the unknown impacts on marine life[IPCC, 2005]
IPCC Special Report on Carbon Dioxide Capture and Storage
Prepared by Working Group III of the Intergovernmental Panel on Climate Change etz, B., O. Davidson, H. C. de Coninck, M. Loos, and L. A. Meyer (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 442 pp. , high costs and concerns about its stability or permanence. The "IPCC Special Report on Carbon Dioxide Capture and Storage" in 2005 did include this technology as an option. However, the IPCC Fifth Assessment Report in 2014 no longer mentioned the term "ocean storage" in its report on climate change mitigation methods. The most recent IPCC Sixth Assessment Report
The Sixth Assessment Report (AR6) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports which assess scientific, technical, and socio-economic information concerning climate change. Three ...
in 2022 also no longer includes any mention of "ocean storage" in its "Carbon Dioxide Removal taxonomy".[IPCC (2022]
Chapter 12: Cross sectoral perspectives
i
Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
Cost
Cost of the sequestration (not including capture and transport) varies but is below US$10 per tonne in some cases where onshore storage is available. For example Carbfix cost is around US$25 per tonne of CO2. A 2020 report estimated sequestration in forests (so including capture) at US$35 for small quantities to US$280 per tonne for 10% of the total required to keep to 1.5 C warming. But there is risk of forest fires releasing the carbon.
Researchers have raised the concern that the use of carbon offsets – such as by maintaining forests, reforestation or carbon capture – as well as renewable energy certificates allow polluting companies a business-as-usual approach to continue releasing greenhouse gases and for being, inappropriately trusted, untried techno-fixes. This also includes the 2022 IPCC report on climate change criticized for containing "a lot of pipe dreams", relying on large negative emissions technologies. A review of studies by the Stanford Solutions Project concluded that relying on Carbon capture and storage/utilization (CCS/U) is a dangerous distraction, with it (in most and large-scale cases) being expensive, increasing air pollution
Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different typ ...
and mining, inefficient and unlikely to be deployable at the scale required in time.
Applications in climate change policies
United States
Starting in the mid-late 2010s, many pieces of US climate and environment policy have sought to make use of the climate change mitigation potential of carbon sequestration. Many of these policies involve either conservation of carbon sink ecosystems, such as forests and wetlands, or encouraging agricultural and land use practices designed to increase carbon sequestration such as carbon farming
Carbon farming is a name for a variety of agricultural methods aimed at sequestering atmospheric carbon into the soil and in crop roots, wood and leaves. The aim of carbon farming is to increase the rate at which carbon is sequestered into soil ...
or agroforestry, often through financial incentivization for farmers and landowners.
The ''Executive Order on Tackling the Climate Crisis at Home and Abroad,'' signed by president Joe Biden on January 27, 2021, includes several mentions of carbon sequestration via conservation and restoration of carbon sink ecosystems, such as wetlands and forests. These include emphasizing the importance of farmers, landowners, and coastal communities in carbon sequestration, directing the Treasury Department to promote conservation of carbon sinks through market based mechanisms, and directing the Department of the Interior to collaborate with other agencies to create a Civilian Climate Corps to increase carbon sequestration in agriculture, among other things.
Several pieces of legislation introduced in the 116th and 117th Congresses, including the ''Climate Stewardship Act of 2019,'' the ''Ocean Based Climate Solutions Act of 2020'', the ''Healthy Soil, Resilient Farmers Act of 2020'', and the ''Healthy Soils Healthy Climate Act of 2020'', have sought to increase carbon sequestration on private and public lands through financial incentivization.
Several state governments, including California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
, Maryland
Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
, and New York, have passed versions of a carbon farming
Carbon farming is a name for a variety of agricultural methods aimed at sequestering atmospheric carbon into the soil and in crop roots, wood and leaves. The aim of carbon farming is to increase the rate at which carbon is sequestered into soil ...
tax credit, which seek to improve soil health and increase carbon sequestration by offering financial assistance and incentives for farmers who practice regenerative agriculture
Regenerative agriculture is a conservation and rehabilitation approach to food and farming systems. It focuses on topsoil regeneration, increasing biodiversity, improving the water cycle, enhancing ecosystem services, supporting biosequestration, ...
, carbon farming, and other climate change mitigation practices. The California Healthy Soils Program is estimated to have resulted in 109,809 metric tons of CO2 being sequestered annually on average.
The White House and USDA are reportedly developing plans to use $30 billion in funds from the Commodity Credit Corporation
The Commodity Credit Corporation (CCC) is a wholly owned United States government corporation that was created in 1933 to "stabilize, support, and protect farm income and prices" (federally chartered by the CCC Charter Act of 1948 (P.L. 80-806) ...
(CCC) for the creation of a carbon bank program, which would involve giving carbon credits to farmers and landowners in return for adopting carbon sequestration practices, which they could then sell in a cap and trade market.
Some environmental activists and politicians have criticized carbon capture, and storage or sequestration (CCS) as a false solution to the climate crisis. They cite the role of the fossil fuel industry in origins of the technology and in lobbying for CCS focused legislation and argue that it would allow the industry to "greenwash" itself by funding and engaging in things such as tree planting campaigns without significantly cutting their carbon emissions.
See also
* Bio-energy with carbon capture and storage
Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere. The carbon in the biomass comes from the greenhouse gas carbon ...
* Blue carbon
* Carbon storage in the North Sea
Carbon storage in the North Sea (also known as carbon sequestration in the North Sea) includes programmes being run by several Northern European countries to capture carbon (in the form of carbon dioxide, ), and store it under the North Sea in e ...
* Repurposing offshore drilling rigs for storing carbon
References
External links
Carbon Sequestration Leadership Forum
International carbon capture and storage initiative.
UK Carbon Capture and Storage Consortium
Overview of the UK academic consortium focused on researching issues related to Carbon Capture and Storage.
Carbon Capture & Sequestration Technologies
MIT program covers carbon capture and storage (CCS)
{{DEFAULTSORT:Carbon Sequestration
Forestry and the environment
Emissions reduction
Sustainable food system
Carbon dioxide removal