Carbon sequestration

Carbon sequestration or carbon dioxide removal (CDR) is the long-term removal, capture or sequestration of carbon dioxide from the atmosphere to slow or reverse atmospheric CO2 pollution and to mitigate or reverse global warming.

Carbon dioxide (CO₂) is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land use and agricultural practices, such as converting crop and livestock grazing 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 CO₂ using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks, bio-energy with carbon capture and storage, biochar, ocean fertilization, enhanced weathering, and direct air capture when combined with storage.

The likely need for CDR has been publicly expressed by a range of individuals and organizations involved with climate change issues, including IPCC chief Rajendra Pachauri, the UNFCCC executive secretary Christiana Figueres,^[8] and the World Watch Institute. Institutions with major programs focusing on CDR include the Lenfest Center for Sustainable Energy at the Earth Institute, Columbia University, and the Climate Decision Making Center, an international collaboration operated out of Carnegie-Mellon University’s Department of Engineering and Public Policy.

Description

Carbon sequestration is the process involved in carbon capture and the long-term storage of atmospheric carbon dioxide (CO₂) 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, which is a form of geoengineering.
• Carbon capture and storage, where carbon dioxide is removed from flue gases (e.g., at power stations) before being stored in underground reservoirs.
• Natural biogeochemical cycling of carbon between the atmosphere and reservoirs, such as by chemical weathering of rocks.

Carbon dioxide may be captured as a pure by-product in processes related to petroleum refining or from flue gases from power generation. CO₂ sequestration includes the storage part of carbon capture and storage, which refers to large-scale, artificial capture and sequestration of industrially produced CO₂ using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks.

Carbon sequestration describes long-term storage of carbon dioxide or other forms of carbon 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.

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 so on which is used by organisations as they look to reduce carbon emissions from their operations.

Biological processes

Biosequestration or carbon sequestration through biological processes affects the global carbon cycle. Examples include major climatic fluctuations, such as the Azolla event, which created the current Arctic climate. Such processes created fossil fuels, as well as clathrate and limestone. By manipulating such processes, geoengineers seek to enhance sequestration.

Peatland

Peat bogs act as a sink for carbon due to the accumulation of 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. Reforestation is the replanting of trees on marginal crop and pasture lands to incorporate carbon from atmospheric CO₂ 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, 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. Restoring all degraded forests world would capture about 205 billion tons of carbon in total (which is about 2/3rd of all carbon emissions. Still, mangroves are one of the best way to store carbon. Mangrove ecosystems are long-term carbon sinks that remove CO2 from the atmosphere and store it in their biomass for thousands of years.

In a paper published in the journal Nature Sustainability, researchers studied the net effect of continuing to build according to current practices versus increasing the amount of wood products. They concluded that if during the next 30 years new construction utilized 90% wood products that 700 million tons of carbon would be sequestered.

Urban forestry

Urban forestry 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.

Wetland restoration

Wetland soil is an important carbon sink; 14.5% of the world’s soil carbon is found in wetlands, while only 6% of the world’s land is composed of wetlands.

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 crops have larger below ground biomass fraction, which increases the SOC content. 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.

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). 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) can negatively impact other environmental concerns (increased herbicide use to control weeds not destroyed by burning).

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. Increasing soil’s carbon content can aid plant growth, increase soil organic matter (improving agricultural yield), improve soil water retention capacity and reduce fertilizer use (and the accompanying emissions of greenhouse gas nitrous oxide (N2O).As of 2016, variants of carbon farming reached hundreds of millions of hectares globally, of the nearly 5 billion hectares (1.2×1010 acres) of world farmland. Soils can contain up to five per cent carbon by weight, including decomposing plant and animal matter and biochar.

Potential sequestration alternatives to carbon farming include scrubbing CO2 from the air with machines (direct air capture); fertilizing the oceans to prompt algal blooms that after death carry carbon to the sea bottom; storing the carbon dioxide emitted by electricity generation; and crushing and spreading types of rock such as basalt that absorb atmospheric carbon. Land management techniques that can be combined with farming include planting/restoring forests, burying biochar produced by anaerobically converted biomass and restoring wetlands. (Coal beds are the remains of marshes and peatlands.)

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 fertilizers, less soil disturbance, better irrigation, and crop strains bred for locally beneficial traits and increased yields.

Replacing more energy intensive farming operations can also reduce emissions. Reduced or no-till farming 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 CO₂ to the atmosphere as it decays, reducing the net carbon reduction.^{[citation needed]}

In practice, most farming operations that incorporate post-harvest crop residues, wastes and byproducts back into the soil provide a carbon storage benefit.^{[citation needed]} This is particularly the case for practices such as field burning of stubble – rather than releasing almost all of the stored CO₂ to the atmosphere, tillage incorporates the biomass back into the soil.^{[citation needed]}

Enhancing carbon removal

All crops absorb CO₂ 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 land, which slows carbon release while returning the land to agriculture or other use.

Agricultural sequestration practices may have positive effects on soil, air, and water quality, be beneficial to wildlife, and expand food production. On degraded croplands, an increase of 1 ton of soil carbon pool may increase crop yield by 20 to 40 kilograms per hectare of wheat, 10 to 20 kg/ ha for maize, and 0.5 to 1 kg/ha for cowpeas.^{[citation needed]}

The effects of soil sequestration can be reversed. If the soil is disrupted or tillage practices are abandoned, the soil becomes a net source of greenhouse gases. Typically after 15 to 30 years 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 CO₂ 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.

Ocean-related

Iron fertilization

Ocean iron fertilization is an example of such a geoengineering technique. Iron fertilization attempts to encourage phytoplankton growth, which removes carbon from the atmosphere for at least a period of time. This technique is controversial due to limited understanding of its complete effects on the marine ecosystem, including side effects and possibly large deviations from expected behavior. Such effects potentially include release of nitrogen oxides, and disruption of the ocean’s nutrient balance.

Natural iron fertilisation events (e.g., deposition of iron-rich dust into ocean waters) can enhance carbon sequestration. Sperm whales act as agents of iron fertilisation when they transport iron from the deep ocean to the surface during prey consumption and defecation. Sperm whales have been shown to increase the levels of primary production and carbon export to the deep ocean by depositing iron rich feces into surface waters of the Southern Ocean. The iron rich feces causes phytoplankton to grow and take up more carbon from the atmosphere. When the phytoplankton dies, some of it sinks to the deep ocean and takes the atmospheric carbon with it. By reducing the abundance of sperm whales in the Southern Ocean, whaling has resulted in an extra 200,000 tonnes of carbon remaining in the atmosphere each year.

Urea fertilization

Ian Jones proposes fertilizing the ocean with urea, a nitrogen rich substance, to encourage phytoplankton growth.

Australian company Ocean Nourishment Corporation (ONC) plans to sink hundreds of tonnes of urea into the ocean to boost CO₂-absorbing phytoplankton growth as a way to combat climate change. In 2007, Sydney-based ONC completed an experiment involving 1 tonne of nitrogen in the Sulu Sea off the Philippines.

Mixing layers

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 CO₂, which limits its attractiveness.

Seaweed

Seaweed 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. In addition, Seaweed grows very fast and can theoretically be harvested and processed to generate biomethane, via Anaerobic Digestion to generate electricity, via Cogeneration/CHP or as a replacement for natural gas. 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 of CO2 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, Fucus serratus and Saccharina latissima.

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 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 is charcoal created by pyrolysis of biomass waste. The resulting material is added to a landfill or used as a soil improver to create terra preta. 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 Pg C annually).

In the soil, the carbon is unavailable for oxidation to CO₂ and consequential atmospheric release. This is one technique advocated by scientist 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. »

The mechanisms related to biochar are referred to as bio-energy with carbon storage, BECS.

Ocean storage

If CO₂ were to be injected to the ocean bottom, the pressures would be great enough for CO₂ to be in its liquid phase. The idea behind ocean injection would be to have stable, stationary pools of CO₂ at the ocean floor. The ocean could potentially hold over a thousand billion tons of CO₂. However, this avenue of sequestration isn’t being as actively pursued because of concerns about the impact on ocean life, and concerns about its stability. A biological solution can be growing seaweed that can naturally be exported to the deep ocean, sequestering significant amounts of biomass in marine sediments.

River mouths bring large quantities of nutrients and dead material from upriver into the ocean as part of the process that eventually produces fossil fuels. Transporting material such as crop waste out to sea and allowing it to sink exploits this idea to increase carbon storage. International regulations on marine dumping may restrict or prevent use of this technique.

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 fluid 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, causing an earthquake.

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 an estimated 160 Gt 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 CO₂ sequestration project which began in 1996 is called Sleipner, and is located in the North Sea where Norway’s StatoilHydro strips carbon dioxide from natural gas with amine solvents and disposed of this carbon dioxide in a deep saline aquifer. In 2000, a coal-fueled synthetic natural gas plant in Beulah, North Dakota, became the world’s first coal-using plant to capture and store carbon dioxide, at the Weyburn-Midale Carbon Dioxide Project.^{[needs update]}

CO₂ has been used extensively in enhanced crude oil recovery operations in the United States beginning in 1972. There are in excess of 10,000 wells that inject CO₂ in the state of Texas alone. The gas comes in part from anthropogenic sources, but is principally from large naturally occurring geologic formations of CO₂. It is transported to the oil-producing fields through a large network of over 5,000 kilometres (3,100 mi) of CO₂ pipelines. The use of CO₂ for enhanced oil recovery (EOR) methods in heavy oil reservoirs in the Western Canadian Sedimentary Basin (WCSB) has also been proposed. However, transport cost remains an important hurdle. An extensive CO₂ pipeline system does not yet exist in the WCSB. Athabasca oil sands mining that produces CO₂ is hundreds of kilometers north of the subsurface Heavy crude oil reservoirs that could most benefit from CO₂ 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 CO₂ can be removed from the atmosphere by chemical processes, and stored in stable carbonate mineral forms. This process is known as ‘carbon sequestration by mineral carbonation‘ or mineral sequestration. The process involves reacting carbon dioxide with abundantly available metal oxides–either magnesium oxide (MgO) or calcium oxide (CaO)–to form stable carbonates. These reactions are exothermic and occur naturally (e.g., the weathering of rock over geologic time periods).

CaO + CO₂ → CaCO₃

MgO + CO₂ → MgCO₃

Calcium and magnesium are found in nature typically as calcium and magnesium silicates (such as forsterite and serpentinite) and not as binary oxides. For forsterite and serpentine the reactions are:

Mg₂SiO₄ + 2 CO₂ → 2 MgCO₃ + SiO₂

Mg₃Si₂O₅(OH)₄+ 3 CO₂ → 3 MgCO₃ + 2 SiO₂ + 2 H₂O

The following table lists principal metal oxides of Earth’s crust. Theoretically up to 22% of this mineral mass is able to form carbonates.

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. 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.

CO₂ naturally reacts with peridotite rock in surface exposures of ophiolites, notably in Oman. It has been suggested that this process can be enhanced to carry out natural mineralisation of CO₂.

When CO₂ is dissolved in water and injected into hot basaltic rocks underground it has been shown that the CO₂ 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, 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.

Demolition concrete waste or recycled crushed concrete are also potential low cost materials for mineral carbonation as they are calcium-rich waste materials.

Electrochemical method

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.

Industrial use

Traditional cement manufacture releases large amounts of carbon dioxide, but newly developed cement types from Novacem can absorb CO₂ from ambient air during hardening. A similar technique was pioneered by TecEco, which has been producing « EcoCement » since 2002. A Canadian startup CarbonCure takes captured CO₂ and injects it into concrete as it is being mixed. Carbon Upcycling UCLA is another company that uses CO₂ 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 ash, generated by power stations could be used as sorbents for CO₂ mineral sequestration. The amount of CO₂ captured averaged 60 to 65% of the carbonaceous CO₂ and 10 to 11% of the total CO₂ emissions.

Chemical scrubbers

Various carbon dioxide scrubbing processes have been proposed to remove CO₂ from the air, usually using a variant of the Kraft process. Carbon dioxide scrubbing variants exist based on potassium carbonate, which can be used to create liquid fuels, or on sodium hydroxide. These notably include artificial trees proposed by Klaus Lackner to remove carbon dioxide from the atmosphere using chemical scrubbers.

Ocean-related

Basalt storage

Carbon dioxide sequestration in basalt involves the injecting of CO₂ into deep-sea formations. The CO₂ first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of Ca²⁺ and Mg²⁺ 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 CO₂ hydrate is denser than CO₂ in seawater, the risk of leakage is minimal. Injecting the CO₂ at depths greater than 2,700 meters (8,900 ft) ensures that the CO₂ 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 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 in 2 years, using 25 tonnes of water per tonne of CO₂.

Acid neutralisation

Carbon dioxide forms carbonic acid when dissolved in water, so ocean acidification 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). A variety of different bases have been suggested that could neutralize the acid and thus increase CO₂ absorption. For example, adding crushed limestone 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 by reaction with a volcanic silicate rock such as enstatite, effectively increasing the rate of natural weathering of these rocks to restore ocean pH.

Obstacles

Financial costs

The use of the technology would add an additional 1–5 cents of cost per kilowatt hour, according to estimate made by the Intergovernmental Panel on Climate Change. The financial costs of modern coal technology would nearly double if use of CCS technology were to be required by regulation. The cost of CCS technology differs with the different types of capture technologies being used and with the different sites that it is implemented in, but the costs tend to increase with CCS capture implementation. One study conducted predicted that with new technologies these costs could be lowered but would remain slightly higher than prices without CCS technologies.

Energy requirements

The energy requirements of sequestration processes may be significant. In one paper, sequestration consumed 25 percent of the plant’s rated 600 megawatt output capacity. After adding CO₂ capture and compression, the capacity of the coal-fired power plant is reduced to 457 MW.

Carbon dioxide removal

Carbon dioxide removal (CDR), also known as greenhouse gas removal, usually refers to human-driven methods of removing carbon dioxide from the atmosphere and sequestering it for long periods, such that more carbon dioxide is sequestered in the process than emitted. These methods are also known as negative emissions technologies, as they offset greenhouse gas emissions from practices such as the burning of fossil fuels.

CDR methods include afforestation, agricultural practices that sequester carbon in soils, bio-energy with carbon capture and storage, ocean fertilization, enhanced weathering, and direct air capture when combined with storage. To assess whether net negative emissions are achieved by a particular process, comprehensive life cycle analysis of the process must be performed.

Alternatively, some sources use the term « carbon dioxide removal » to refer to any technology that removes carbon dioxide, such as direct air capture, but can be implemented in a way that causes emissions to increase rather than decrease over the lifecycle of the process.

The IPCC‘s analysis of climate change mitigation pathways that are consistent with limiting global warming to 1.5°C found that all assessed pathways include the use of CDR to offset emissions. A 2019 consensus report by NASEM concluded that using existing CDR methods at scales that can be safely and economically deployed, there is potential to remove and sequester up to 10 gigatons of carbon dioxide per year. This would offset greenhouse gas emissions at about a fifth of the rate at which they are being produced.

Definitions

The Intergovernmental Panel on Climate Change defines CDR as:

Anthropogenic activities removing CO2 from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage, but excludes natural CO2 uptake not directly caused by human activities.

The U.S.-based National Academies of Sciences, Engineering, and Medicine (NASEM) uses the term “negative emissions technology” with a similar definition.

The concept of deliberately reducing the amount of CO2 in the atmosphere is often mistakenly classified with solar radiation management as a form of climate engineering and assumed to be intrinsically risky. In fact, CDR addresses the root cause of climate change and is part of strategies to reduce net emissions. Whether CDR would satisfy common definitions of « climate engineering » or « geoengineering » usually depends upon the scale at which it would be undertaken.^{[citation needed]}

Concepts using similar terminology

CDR can be confused with carbon capture and storage (CCS), a process in which carbon dioxide is collected from point-sources such as coal-fired power plants, whose smokestacks emit CO2 in a concentrated stream. The CO2 is then compressed and sequestered or utilized. When used to sequester the carbon from a coal-fired power plant, CCS reduces emissions from continued use of the point source, but does not reduce the amount of carbon dioxide already in the atmosphere.

Potential for reducing net emissions

Using CDR in parallel with other efforts to reduce emissions, such as deploying renewable energy, is likely to be less expensive and disruptive than using other efforts alone. A 2019 consensus study report by NASEM assessed the potential of all forms of CDR other than ocean fertilization that could be deployed safely and economically using current technologies, and estimated that they could remove up to 10 gigatons of CO2 per year if fully deployed worldwide. This is one-fifth of the 50 gigatons of CO2 emitted per year by human activities.

Some mitigation pathways propose achieving higher rates of CDR through massive deployment of one technology,, however these pathways assume that hundreds of millions of hectares of cropland are converted to growing biofuel crops. Further research in the areas of direct air capture, geologic sequestration of carbon dioxide, and carbon mineralization could potentially yield technological advancements that make higher rates of CDR economically feasible.

The possibility of large-scale future CDR deployment has been described as a moral hazard, as it could lead to a reduction in near-term efforts to mitigate climate change. The 2019 NASEM report concludes:

Any argument to delay mitigation efforts because NETs will provide a backstop drastically misrepresents their current capacities and the likely pace of research progress.

Carbon sequestration

Main article: Carbon sequestration

Forests, kelp beds, and other forms of plant life absorb carbon dioxide from the air as they grow, and bind it into biomass. As the use of plants as carbon sinks can be undone by events such as wildfires, the long-term reliability of these approaches has been questioned.

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 carbonate salts (mineral sequestration). This is because they are removing carbon from the atmosphere and sequestering it indefinitely and presumably for a considerable duration (thousands to millions of years). Carbon capture technology has yet to reach more than 33% efficiency. Furthermore, this process could be rapidly undone, for example by earthquakes or mining.^{[citation needed]}

Methods

Afforestation, reforestation, and forestry management

This section needs expansion. You can help by adding to it. (February 2020)

Bio-energy with carbon capture & storage

Bio-energy with carbon capture and storage, or BECCS, uses biomass to extract carbon dioxide from the atmosphere, and carbon capture and storage technologies to concentrate and permanently store it in deep geological formations.

BECCS is currently (as of October 2012) the only CDR technology deployed at full industrial scale, with 550 000 tonnes CO₂/year in total capacity operating, divided between three different facilities (as of January 2012).

The Imperial College London, the UK Met Office Hadley Centre for Climate Prediction and Research, the Tyndall Centre for Climate Change Research, the Walker Institute for Climate System Research, and the Grantham Institute for Climate Change issued a joint report on carbon dioxide removal technologies as part of the AVOID: Avoiding dangerous climate change research program, stating that « Overall, of the technologies studied in this report, BECCS has the greatest maturity and there are no major practical barriers to its introduction into today’s energy system. The presence of a primary product will support early deployment. »

According to the OECD, « Achieving lower concentration targets (450 ppm) depends significantly on the use of BECCS« .

Agricultural practices

Main article: Carbon farming

This section needs expansion. You can help by adding to it. (February 2020)

Wetland restoration

Main article: blue carbon

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Biochar

Biochar is created by the pyrolysis of biomass, and is under investigation as a method of carbon sequestration. Biochar is a charcoal that is used for agricultural purposes which also aids in carbon sequestration, the capture or hold of carbon. It is created using a process called pyrolysis, which is basically the act of high temperature heating biomass in an environment with low oxygen levels. What remains is a material known as char, similar to charcoal but is made through a sustainable process, thus the use of biomass. Biomass is organic matter produced by living organisms or recently living organisms, most commonly plants or plant based material. The offset of greenhouse gas (GHG) emission, if biochar were to be implemented, would be a maximum of 12%. This equates to about 106 metric tons of CO₂ equivalents. On a medium conservative level, it would be 23% less than that, at 82 metric tons. A study done by the UK Biochar Research Center has stated that, on a conservative level, biochar can store 1 gigaton of carbon per year. With greater effort in marketing and acceptance of biochar, the benefit could be the storage of 5–9 gigatons per year of carbon in biochar soils.

Enhanced weathering

Enhanced weathering is a chemical approach to remove carbon dioxide involving land- or ocean-based techniques. One example of a land-based enhanced weathering technique is in-situ carbonation of silicates. Ultramafic rock, for example, has the potential to store from hundreds to thousands of years’ worth of CO₂ emissions, according to estimates. Ocean-based techniques involve alkalinity enhancement, such as grinding, dispersing, and dissolving olivine, limestone, silicates, or calcium hydroxide to address ocean acidification and CO₂ sequestration. Enhanced weathering is considered one of the least expensive geoengineering options. One example of a research project on the feasibility of enhanced weathering is the CarbFix project in Iceland.

Direct air capture (DAC)

Carbon dioxide can be removed from ambient air through chemical processes, sequestered, and stored. Traditional modes of carbon capture such as precombustion and postcombustion CO2 capture from large point sources can help slow the rate of increase of the atmospheric CO2 concentration, but the direct removal of CO2 from the air, or direct air capture (DAC), can actually reduce the global atmospheric CO2 concentration if combined with long-term storage of CO2.

DAC relying on amine-based absorption demands significant water input. It was estimated, that to capture 3.3 Gigatonnes of CO2 a year would require 300 km³ of water, or 4% of the water used for irrigation. On the other hand, using sodium hydroxide needs far less water, but the substance itself is highly caustic and dangerous.

DAC also requires much greater energy input in comparison to traditional capture from point sources, like flue gas, due to the low concentration of CO2. The theoretical minimum energy required to extract CO2 from ambient air is about 250 kWh per tonne of CO2, while capture from natural gas and coal power plants requires respectively about 100 and 65 kWh per tonne of CO2.

Ocean fertilization

Ocean fertilization or ocean nourishment is a type of climate engineering based on the purposeful introduction of nutrients to the upper ocean to increase marine food production and to remove carbon dioxide from the atmosphere. A number of techniques, including fertilization by iron, urea and phosphorus have been proposed.

Economic issues

A crucial issue for CDR methods is their cost, which differs substantially among the different technologies: some of these are not sufficiently developed to perform cost assessments. In 2011 the American Physical Society estimated the costs for direct air capture to be $600/tonne with optimistic assumptions. A 2018 study found this estimate lowered to between $94 and $232 per tonne. The IEA Greenhouse Gas R&D Programme and Ecofys provides an estimate that 3.5 billion tonnes could be removed annually from the atmosphere with BECCS (Bio-Energy with Carbon Capture and Storage) at carbon prices as low as €50 per tonne, while a report from Biorecro and the Global Carbon Capture and Storage Institute estimates costs « below €100 » per tonne for large scale BECCS deployment.

Risks, problems and criticisms

CDR is slow to act, and requires a long-term political and engineering program to effect. CDR is even slower to take effect on acidified oceans. In a Business as usual concentration pathway, the deep ocean will remain acidified for centuries, and as a consequence many marine species are in danger of extinction.

The Special 1.5°C IPCC report was very clear about CDR: « CDR deployed at scale is unproven and reliance on such technology is a major risk in the ability to limit warming to 1.5°C. »

These objections are at least partly based on a straw man, as CDR has never been proposed as a sole solution, claiming to solve the climate crisis by itself. The Environmental Defense Fund (EDF) now favors its use in conjunction with renewable electricity, electric vehicles, and other strategies to reduce emissions.

However, the heavy reliance on CDR in the integrated assessment models currently informing climate mitigation policy has been questioned by scientists, arguing that it may well contribute to locking in high-temperature pathways.

Removal of other greenhouse gases

As of 2012, there have been proposals to research ways to remove methane, a greenhouse gas 20 times more potent than carbon dioxide, from the atmosphere.

Afforestation

Afforestation is the establishment of a forest or stand of trees (forestation) in an area where there was no previous tree cover.

Many government and non-governmental organizations directly engage in programs of afforestation to create forests, increase carbon capture.

Sometimes special tools, such as a tree planting bar, are used to make planting of trees easier and faster.^{[citation needed]}

The rate of net forest loss decreased substantially over the period 1990–2020 due to a reduction in deforestation in some countries, plus increases in forest area in others through afforestation and the natural expansion of forests.

In areas of degraded soil

In some places, forests need help to reestablish themselves because of environmental factors. For example, in arid zones, once forest cover is destroyed, the land may become dry and inhospitable for the growth of new trees. Other factors include overgrazing by livestock, especially animals such as goats, cows, and over-harvesting of forest resources. Together these may lead to desertification and the loss of topsoil; without soil, forests cannot grow until the long process of soil creation has been completed – if erosion allows this. In some tropical areas, forest cover removal may result in a duricrust or duripan that effectively seal off the soil to water penetration and root growth. In many areas, reforestation is impossible because people are using the land. In other areas, mechanical breaking up of duripans or duricrusts is necessary, careful and continued watering may be essential, and special protection, such as fencing, may be needed.

Forests to attract rain

Several new studies suggest that forests attract rain and this may explain why drought is occurring more frequently in parts of the world such as western Africa. A new study by Carol Rasmussen, NASA’s Jet Propulsion Laboratory gives the first observational evidence that the southern Amazon rain forest triggers its own rainy season using water vapor from plant leaves. The finding helps explain why deforestation in this region is linked with reduced rainfall. A study by Douglas Sheil and Daniel Murdiyarso hypothesises that forest cover plays a much greater role in determining rainfall than previously recognized. It explains how forested regions generate large-scale flows in atmospheric water vapor. Makarieva and Gorshkov have developed a hypothesis to explain how forests attract moist air and increase rainfall in area covered by trees.

Countries and regions

Australia

In Adelaide, South Australia (a city of 1.3 million as of June 2016), Premier Mike Rann (2002 to 2011) launched an urban forest initiative in 2003 to plant 3 million native trees and shrubs by 2014 on 300 project sites across the metro area. Thousands of Adelaide citizens have participated in community planting days on sites including parks, reserves, transport corridors, schools, water courses and coastline. Only Native trees were planted to ensure genetic integrity. He said the project aimed to beautify and cool the city and make it more liveable; improve air and water quality and reduce Adelaide’s greenhouse gas emissions by 600,000 tonnes of C02 a year.

Brazil

There are ongoing afforestation efforts to counter the significant deforestation of the Amazon Rainforest in Brazil. In Para, Brazil, 1 billion trees were intended to be planted to restore deforested lands by 2013.

China

China has deforested most of its historically wooded areas. China reached the point where timber yields declined far below historic levels, due to over-harvesting of trees beyond sustainable yield. Although it has set official goals for reforestation, these goals are set over an 80-year time horizon and have not been significantly met by 2008. China is trying to correct these problems by projects like the Green Wall of China, which aims to replant a great deal of forests and halt the expansion of the Gobi desert. The Green Wall of China Project has historical precedences dating back to before the Common Era. However, in pre-modern periods, government sponsored afforestation projects along the historical frontier regions were mostly for military fortification.

A law promulgated in 1981 requires that every school student over the age of 11 plants at least one tree per year. As a result, China has the highest afforestation rate of any country or region in the world, with 47,000 square kilometers of afforestation in 2008. However, the forest area per capita is still far lower than the international average.

According to Carbon Brief, China planted the largest amount of new forest out of any country between 1990 and 2015, facilitated by the country’s Grain for Green programme started in 1999, by investing more than $100bn in afforestation programmes and planting more than 35bn trees across 12 provinces. By 2015, the amount of planted forest in China covered 79m hectares.

From 2011–2016, the city Dongying in Shandong province forested over 13,800 hectares of saline soil through the Shandong Ecological Afforestation Project, which was launched with support from the World Bank. In 2017, the Saihanba Afforestation Community won the UN Champions of the Earth Award in the Inspiration and Action category for « transforming degraded land into a lush paradise ».

Europe

Europe has deforested the majority of its historical forests. The European Union (EU) has paid farmers for afforestation since 1990, offering grants to turn farmland back into forest and payments for the management of forest. Between 1993 and 1997, EU afforestation policies made possible the re-forestation of over 5,000 square kilometres of land. A second program, running between 2000 and 2006, afforested more than 1,000 square kilometres of land (precise statistics not yet available). A third such program began in 2007. Europe’s forests are growing by 8,000 square kilometres a year thanks to these programmes.

According to Food and Agriculture Organization statistics, Spain had the third fastest afforestation rate in Europe in the 1990-2005 period, after Iceland and Ireland. In those years, a total of 44,360 square kilometers were afforested, and the total forest cover rose from 13,5 to 17,9 million hectares. In 1990, forests covered 26.6% of the Spanish territory. As of 2007, that figure had risen to 36.6%. Spain today has the fifth largest forest area in the European Union.

In January 2013 the UK government set a target of 12% woodland cover in England by 2060, up from the then 10%. In Wales the National Assembly for Wales has set a target of 19% woodland cover, up from 15%. Government-backed initiatives such as the Woodland Carbon Code are intended to support this objective by encouraging corporations and landowners to create new woodland to offset their carbon emissions. Charitable groups such as Trees for Life (Scotland) also contribute to afforestation and reforestation efforts in the UK.

Alpine and Subalpine regions have undergone a lot of deforestation and then forestation in the last 300 years. Out of this has emerged much practical experience. One example is the clustered group, which is a method to bring in stable age mixed tree communities.

India

According to the NASA study, China and India have led in increasing the Earth’s greenery over the past two decades. In 1950 around 40.48 million hectares was covered by forest. In 1980 it increased to 67.47 million hectares and in 2006 it was found to be 69 million hectares. 23% of India is covered by forest. In 2018, the total forest and tree cover in India increased to 24.39% or 8,02,088 km². The forests of India are grouped into 5 major categories and 16 types based on biophysical criteria. 38% of the forest is categorized as subtropical dry deciduous and 30% as tropical moist deciduous and other smaller groups. Only local species are planted in an area. Trees bearing fruits are preferred wherever possible due to their function as a food source.

In 2019, Indians Planted 220 Million trees in a Single day in the Indian state of Uttar Pradesh.

On Thursday, 29 August 2019, Prime Minister of India Mr. Narendra Modi released ₹47, 436 crores (over 6.6 Bn USD) to various states for compulsory afforestation activities. The funds can be used for treatment of catchment areas, assisted natural generation, forest management, wildlife protection and management, relocation of villages from protected areas, managing human-wildlife conflicts, training and awareness generation, supply of wood saving devices and allied activities. Increasing the tree cover would help in creating additional carbon sink to meet the nation’s Intended Nationally Determined Contribution (INDC) of 2.5 to 3 billion tonnes of carbon dioxide equivalent through additional forest and tree cover by the year 2030 – part of India’s efforts to combat climate change. The Maharashtra government planted almost 20,000,000 saplings in the entire state, and will pledge to plant another 30,000,000 next year. According to The Telegraph, the Indian government has attributed $6.2 billion for tree-planting in order to increase “forestation in line with agreements made at the Paris climate change summit in 2015.” The Indian government has also passed the CAMPA (Compensatory Afforestation Fund Management and Planning Authority) law, which will allow about 40 thousand crores rupees (almost $6 Billion) will go to Indian states for planting trees.

Iran

Iran is considered a low forest cover region of the world with present cover approximating seven percent of the land area. This is a value reduced by an estimated six million hectares of virgin forest, which includes oak, almond and pistachio. Due to soil substrates, it is difficult to achieve afforestation on a large scale compared to other temperate areas endowed with more fertile and less rocky and arid soil conditions. Consequently, most of the afforestation is conducted with non-native species, leading to habitat destruction for native flora and fauna, and resulting in an accelerated loss of biodiversity. ^{[page needed]}

Israel

With over 240 million planted trees, Israel is one of only two countries that entered the 21st century with a net gain in the number of trees, due to massive afforestation efforts. Most Israeli forests are the product of a major afforestation campaign by the Jewish National Fund (JNF).^{[citation needed]}

Critics argue that many JNF lands inside the West Bank were illegally confiscated from Palestinian refugees, and that the JNF furthermore should not be involved with lands in the West Bank. Shaul Ephraim Cohen has claimed that trees have been planted to restrict Bedouin herding. Susan Nathan wrote that forests were planted on the site of abandoned Arab villages after the 1948 war.

Since 2009, the JNF has provided the Palestinian Authority with 3,000 tree seedlings for a forested area being developed on the edge of the new city of Rawabi, north of Ramallah.

Japan

In Japan, demand for timber increased due to the construction of steelmaking fuel and large-scale castles in the Middle Ages, and forest resources decreased. As a result, forests have been planted to prevent timber resources and floods, and the Edo Shogunate enacted a law called the Liushan system, restricting the logging of timber and planting trees. The afforestation project that started after the reconstruction after World War II when large areas of forest were clear-cut for timber and to create pastures to attract immigrant farmers. A new management plan for the forests of Japan was instated after many pastures were abandoned and there was a recognized decline of old growth and secondary forests.

North Africa

Many African countries that border the Sahara desert are cooperating on the Great Green Wall project. The $8-billion project intends to restore 100 million hectares of degraded land by 2030.

Also in North Africa, the Sahara Forest Project coupled with the Seawater greenhouse has been proposed. Some projects have also been launched in countries as Senegal to revert desertification. As of 2010, African leaders are discussing the combining of national resources to increase effectiveness. In addition, other projects as the Keita Project in Niger have been launched in the past, and have been able to locally revert damage done by desertification. See Development aid#Effectiveness

Turkey

As Turkey was deforested over the past few thousand years some authors refer to the restoration of these forests as « afforestation » and some « reforestation ». In Turkish « ağaçlandırma » can mean either of these or « forestation ». So for readability the process is all described in Reforestation#Turkey.

United States

The United States is roughly one-third covered in forest and woodland.^{[citation needed]} Nevertheless, areas in the US were subject to significant tree planting. In the 1800s people moving westward encountered the Great Plains – land with fertile soil, a growing population and a demand for timber but with few trees to supply it. So tree planting was encouraged along homesteads. Arbor Day was founded in 1872 by Julius Sterling Morton in Nebraska City, Nebraska. By the 1930s the Dust Bowl environmental disaster signified a reason for significant new tree cover. Public works programs under the New Deal saw the planting of 18,000 miles of windbreaks stretching from North Dakota to Texas to fight soil erosion (see Great Plains Shelterbelt).

At their summit in Copenhagen in 2009, organised by the UK based The Climate Group, leaders of subnational governments – states, regions and provinces – unanimously supported a recommendation by Premier Rann to plant one billion trees across their varied jurisdictions. The initiative was strongly supported by leaders present including Quebec Premier Jean Charest, California Governor Arnold Schwarzenegger and Scottish First Minister Alex Salmond. At a subsequent meeting in Rio de Janeiro in June 2012, The Climate Group announced that it had already received commitments by member governments to plant more than 500 million trees.

Criticism

The use of afforestation as strategy of conservation of forest biomes is seen as a menace to the conservation of natural grassland and savanna biomes, as the ideal would be the reforestation of areas where forest occurs naturally.

Reforestation

Reforestation (occasionally, Reafforestation) is the natural or intentional restocking of existing forests and woodlands (forestation) that have been depleted, usually through deforestation. Reforestation can be used to rectify the effects of deforestation or improve the quality of human life by soaking up pollution and dust from the air, rebuilding natural habitats and ecosystems, mitigating global warming since forests facilitate biosequestration of atmospheric carbon dioxide, and harvesting for resources, particularly timber, but also non-timber forest products. In the beginning of the 21st century more attention is given to the ability of reforestation to mitigate climate change as one of the best methods to do it.

Management

A debated issue in managed reforestation is whether or not the succeeding forest will have the same biodiversity as the original forest. If the forest is replaced with only one species of tree and all other vegetation is prevented from growing back, a monoculture forest similar to agricultural crops would be the result. However, most reforestation involves the planting of different selections of seedlings taken from the area, often of multiple species. Another important factor is the natural regeneration of a wide variety of plant and animal species that can occur on a clear cut. In some areas the suppression of forest fires for hundreds of years has resulted in large single aged and single species forest stands. The logging of small clear cuts and/or prescribed burning actually increases the biodiversity in these areas by creating a greater variety of tree stand ages and species.

For harvesting

Reforestation need not be only used for recovery of accidentally destroyed forests. In some countries, such as Finland, many of the forests are managed by the wood products and pulp and paper industry. In such an arrangement, like other crops, trees are planted to replace those that have been cut. The Finnish Forest Act from 1996 obliges the forest to be replanted after felling. In such circumstances, the industry can cut the trees in a way to allow easier reforestation. The wood products industry systematically replaces many of the trees it cuts, employing large numbers of summer workers for tree planting work. For example, in 2010, Weyerhaeuser reported planting 50 million seedlings. However replanting an old-growth forest with a plantation is not replacing the old with the same characteristics in the new.

In just 20 years, a teak plantation in Costa Rica can produce up to about 400 m³ of wood per hectare. As the natural teak forests of Asia become more scarce or difficult to obtain, the prices commanded by plantation-grown teak grows higher every year. Other species, such as mahogany, grow more slowly than teak in Tropical America but are also extremely valuable. Faster growers include pine, eucalyptus, and Gmelina.

Reforestation, if several indigenous species are used, can provide other benefits in addition to financial returns, including restoration of the soil, rejuvenation of local flora and fauna, and the capturing and sequestering of 38 tons of carbon dioxide per hectare per year.

The reestablishment of forests is not just simple tree planting. Forests are made up of a community of species and they build dead organic matter into soils over time. A major tree-planting program could enhance the local climate and reduce the demands of burning large amounts of fossil fuels for cooling in the summer.

For climate change mitigation

Forests are an important part of the global carbon cycle because trees and plants absorb carbon dioxide through photosynthesis. By removing this greenhouse gas from the air, forests function as terrestrial carbon sinks, meaning they store large amounts of carbon. At any time, forests account for as much as double the amount of carbon in the atmosphere. Forests remove around three billion tons of carbon every year. This amounts to about 30% of anthropogenic all carbon dioxide emissions. Therefore, an increase in the overall forest cover around the world would mitigate global warming.

At the beginning of the 21st century, interest in reforestation grew over its potential to mitigate climate change. Even without displacing agriculture and cities, earth can sustain almost one billion hectares of new forests. This would remove 25% of carbon dioxide from the atmosphere and reduce its concentration to levels that existed in the early 20th century. A temperature rise of 1.5 degrees would reduce the area suitable for forests by 20% by the year 2050, because some tropical areas will become too hot. The countries that have the most forest-ready land are: Russia, Canada, Brazil, Australia, United States and China.

The four major strategies are:

• Increase the amount of forested land through reforestation
• Increase density of existing forests at a stand and landscape scale
• Expand the use of forest products that sustainably replace fossil-fuel emissions
• Reduce carbon emissions caused by deforestation and degradation

Implementing the first strategy is supported by many organizations around the world. For example, in China, the Jane Goodall Institute, through their Shanghai Roots & Shoots division, launched the Million Tree Project in Kulun Qi, Inner Mongolia to plant one million trees. China used 2.4 billion hectares of new forest to offset 21% of Chinese fossil fuel emissions in 2000. In Java, Indonesia newlywed couples give whoever is conducting their wedding 5 seedlings. Each divorcing couple gives 25 seedlings to whoever divorces them. Costa Rica doubled its forest cover in 30 years using its system of grants and other payments for environmental services, including compensation for landowners. These payments are funded through international donations and nationwide taxes.

The second strategy has to do with selecting species for tree-planting. In theory, planting any kind of tree to produce more forest cover would absorb more carbon dioxide from the atmosphere. However, a genetically modified variant might grow much faster than unmodified specimens. Some of these cultivars are under development. Such fast-growing trees would be planted for harvest and can absorb carbon dioxide faster than slower-growing trees.

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 (fixing more carbon) 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. »

As of 2008 1.3 billion hectares of tropical regions were deforested every year. Reducing this would reduce the amount of planting needed to achieve a given degree of mitigation.

Methods

Using existing trees and roots

Planting new trees often leads to up to 90% of seedlings failing. However, even in deforested areas, existing root systems often exist. Growth can be accelerated by pruning and coppicing where a few branches of new shoots are cut and often used for charcoal, itself a major driver of deforestation. Since new seeds are not planted, it is cheaper. Additionally, they are much more likely to survive as their root systems already exist and can tap into groundwater during harsher seasons with no rain. While this method has existed for centuries, it is now sometimes referred to as Farmer-managed natural regeneration.

Financial incentives

This section needs to be updated. Please update this article to reflect recent events or newly available information. (October 2019)

Some incentives for reforestation can be as simple as a financial compensation. Streck and Scholz (2006) explain how a group of scientists from various institutions have developed a compensated reduction of deforestation approach which would reward developing countries that disrupt any further act of deforestation. Countries that participate and take the option to reduce their emissions from deforestation during a committed period of time would receive financial compensation for the carbon dioxide emissions that they avoided. To raise the payments, the host country would issue government bonds or negotiate some kind of loan with a financial institution that would want to take part in the compensation promised to the other country. The funds received by the country could be invested to help find alternatives to the extensive cutdown of forests. This whole process of cutting emissions would be voluntary, but once the country has agreed to lower their emissions they would be obligated to reduce their emissions. However, if a country was not able to meet their obligation, their target would get added to their next commitment period. The authors of these proposals see this as a solely government-to-government agreement; private entities would not participate in the compensation trades.

Implementation

Global

The 2020 World Economic Forum, held in Davos, announced the creation of the Trillion Tree Campaign, which is an initiative aiming to plant 1 trillion trees across the globe. The implementation can have big environmental and societal benefits but needs to be tailored to local conditions.

Sub-Saharan Africa

One plan in this region involves planting a nine-mile width of trees on the Southern Border of the Sahara Desert for stopping its expansion to the south. The Great Green Wall initiative is a pan-African proposal to « green » the continent from west to east in order to battle desertification. It aims at tackling poverty (through employment of workers required for the project) and the degradation of soils in the Sahel-Saharan region, focusing on a strip of land that is 15 km (9 mi) wide and 7,500 km (4,750 mi) long from Dakar to Djibouti. As of May 2020, 21 countries join the project, many of them are directly affected by the expansion of the Sahara desert that happening for 1,000 years, but recently was accelerated by climate change. It should create 10 millions green jobs by 2030.

In 2019, Ethiopia begun a massive tree planting campaign « Green Legacy » with a target to plant 4 billion trees in 1 year. In 1 day only, over 350 million trees were planted.

Costa Rica

Through reforestation and environmental conservation, Costa Rica doubled its forest cover in 30 years.

Costa Rica has a long-standing commitment to the environment. The country is now one of the leaders of sustainability, biodiversity, and other protections. It wants to be completely fossil fuel free by 2050. The country has generated all of its electric power from renewable sources for three years as of 2019. It has committed to be carbon-free and plastic-free by 2021.

As of 2019, half of the country’s land surface is covered with forests. They absorb a huge amount of carbon dioxide, combating climate change.

In the 1940s, more than 75% of the country was covered in mostly tropical rainforests and other indigenous woodlands. Between the 1940s and 1980s, extensive, uncontrolled logging led to severe deforestation. By 1983, only 26% of the country had forest cover. Realizing the devastation, policymakers took a stand. Through a continued environmental focus they were able to turn things around to the point that today forest cover has increased to 52%, 2 times more than 1983 levels.

An honorable world leader for ecotourism and conservation, Costa Rica has pioneered the development of payments for environmental services. Costa Rica’s extensive system of environmental protection has been encouraging conservation and reforestation of the land by providing grants for environmental services. The system is not just advanced for its time but is also unparalleled in the world. It received great international attention.

The country has established programs to compensate landowners for reforestation. These payments are funded through international donations and nationwide taxes. The initiative is helping to protect the forests in the country.

« Robert Blasiak, a research fellow at the University of Tokyo, said: « Taking a closer look at what Costa Rica has accomplished in the past 30 years may be just the impetus needed to spur real change on a global scale. »

« Costa Rican President Carlos Alvarado has called the climate crisis « the greatest task of our generation »; one that his country is strongly committed to excel in. »

Canada

Natural Resources Canada (The Department of Natural Resources) states that the national forest cover was decreased by 0.34% from 1990 to 2015, and Canada has the lowest deforestation rate in the world. The forest industry is one of the main industries in Canada, which contributes about 7% of Canadian economy, and about 9% of the forests on earth are in Canada. Therefore, Canada has many policies and laws to commit to sustainable forest management. For example, 94% of Canadian forests are public land, and the government obligates planting trees after harvesting to public forests.

China

In China, extensive replanting programs have existed since the 1970s, which have had overall success. The forest cover has increased from 12% of China’s land area to 16%. ^{[self-published source?]} However, specific programs have had limited success. The « Green Wall of China, » an attempt to limit the expansion of the Gobi Desert, is planned to be 2,800 miles (4,500 km) long and to be completed in 2050. China plans to plant 26 billion trees in the next decade; that is, two trees for every Chinese citizen per year. China requires that students older than 11 years old plant one tree a year until their high school graduation.

Between 2013 and 2018, China planted 338,000 square kilometres of forests, at a cost of $82.88 billion. By 2018, 21.7% of China’s territory was covered by forests, a figure the government wants to increase to 26% by 2035. The total area of China is 9,596,961 square kilometres (see China), so 412,669 square kilometres more needs to be planted. According to the government’s plan, by 2050, 30% of China’s territory should be covered by forests.

In 2017, the Saihanba Afforestation Community won the UN Champions of the Earth Award in the Inspiration and Action category for their successful reforestation efforts, which began upon discovering the survival of a single tree.

Germany

The first historically proven successful method of afforestation with coniferous seeds on a large scale was developed in 1368 by the Nuremberg councillor and merchant Peter Stromer (around 1315-1388) in the Nuremberg Reichswald. This forest area thus became the first artificial forest in the world and Stromer the « father of forest culture ».^{[citation needed]}

Reforestation is required as part of the federal forest law. 31% of Germany is forested, according to the second forest inventory of 2001–2003. The size of the forest area in Germany increased between the first and the second forest inventory due to forestation of degenerated bogs and agricultural areas.

India

Jadav Payeng had received national awards for reforestation efforts, known as the « Molai forest« . He planted 1400 hectares of forest on the bank of river Brahmaputra alone. There are active reforestation efforts throughout the country. In 2016, India more than 50 million trees were planted in Uttar Pradesh and in 2017, more than 66 million trees were planted in Madhya Pradesh. In addition to this and individual efforts, there are startup companies, such as Afforest, that are being created over the country working on reforestation.

Ireland

In 2019 the government of Ireland decided to plant 440 million trees by 2040. The decision is part of the government’s plan to make Ireland carbon neutral by 2050 with renewable energy, land use change and carbon tax.

Israel

Since 1948, large reforestation and afforestation projects were accomplished in Israel. 240 million trees have been planted. The carbon sequestration rate in these forests is similar to the European temperate forests.

Japan

The Ministry of Agriculture, Forestry and Fishery explain that about two-thirds of Japanese land is covered with forests, and it was almost unchanged from 1966 to 2012. Japan needs to reduce 26% of green house gas emission from 2013 by 2030 to accomplish Paris Agreement and is trying to reduce 2% of them by forestry.

Mass environmental and human-body pollution along with relating deforestation, water pollution, smoke damage, and loss of soils caused by mining operations in Ashio, Tochigi became the first environmental social issue in Japan, efforts by Shōzō Tanaka had grown to large campaigns against copper operation. This led to the creation of ‘Watarase Yusuichi Pond’, to settle the pollution which is a Ramsar site today. Reforestation was conducted as a part of afforestation due to inabilities of self-recovering by the natural land itself due to serious soil pollution and loss of woods consequence in loss of soils for plants to grow, thus needing artificial efforts involving introducing of healthy soils from outside. Starting from around 1897, about 50% of once bald mountains are now back to green.

Lebanon

For thousands of years, Lebanon was covered by forests, one particular species of interest, Cedrus libani was exceptionally valuable and was almost eliminated due to lumbering operations. Virtually every ancient culture that shared the Mediterranean Sea harvested these trees from the Phoenicians who used cedar, pine and juniper to build their famous boats to the Romans, who cut them down for lime-burning kilns, to early in the 20th century when the Ottomans used much of the remaining cedar forests of Lebanon as fuel in steam trains. Despite two millennia of deforestation, forests in Lebanon still cover 13.6% of the country, and other wooded lands represent 11%.

Law No. 558, which was ratified by the Lebanese Parliament on April 19, 1996, aims to protect and expand existing forests, classifying all forests of cedar, fir, high juniper (juniperus excelsa), evergreen cypress (cupressus sempervirens) and other trees, whether diverse or homogeneous, whether state-owned or not as conserved forests.

Since 2011, more than 600,000 trees, including cedars and other native species, have been planted throughout Lebanon as part of the Lebanon Reforestation Initiative, which aims to restore Lebanon’s native forests. Projects financed locally and by international charity are performing extensive reforestation of cedar being carried out in the Mediterranean region, particularly in Lebanon and Turkey, where over 50 million young cedars are being planted annually.

The Lebanon Reforestation Initiative has been working since 2012 with tree nurseries throughout Lebanon to help grow stronger tree seedlings that are better suited to survive once planted.

Pakistan

The Billion Tree Tsunami was launched in 2014 by planting 1 billion trees, by the government of Khyber Pakhtunkhwa (KPK) and Imran Khan, Pakistan, as a response to the challenge of global warming. Pakistan’s Billion Tree Tsunami restored 350,000 hectares of forests and degraded land to surpass its Bonn Challenge commitment.

In 2018, Pakistan’s prime minister declared that the country will plant 10 billion trees in the next five years.

In 2020, the Pakistani government launched an initiative to hire 63,600 laborers to plant trees in the northern Punjab region, with indigenous species such as acacia, mulberry and moringa. This initiative was meant to alleviate unemployment caused by lockdowns to mitigate the spread of COVID-19.

Turkey

Of the country’s 78 million hectares of land in total the Ministry of Agriculture and Forestry aims to increase Turkey’s forest cover to 30% by 2023.

4000 years ago Anatolia was 60% to 70% forested. Although the flora of Turkey remains more biodiverse than many European countries deforestation occurred during both prehistoric and historic times, including the Roman and Ottoman periods.

Since the first forest code of 1937 the official government definition of ‘forest’ has varied. According to the current definition 21 million hectares are forested, an increase of about 1 million hectares over the past 30 years, but only about half is ‘productive’. However, according to the United Nations Food and Agriculture Organization definition of forest about 12 million hectares was forested in 2015, about 15% of the land surface.

The amount of greenhouse gas emissions by Turkey removed by forests is very uncertain. As of 2019 however a new assessment is being made with the help of satellites and new soil measurements and better information should be available by 2020.

According to the World Resources Institute « Atlas of Forest Landscape Restoration Opportunities » 50 million hectares are potential forest land, a similar area to the ancient Anatolian forest mentioned above. This could help limit climate change in Turkey. To help preserve the biodiversity of Turkey more sustainable forestry has been suggested. Improved rangeland management is also needed.

National Forestation Day is on 11 November but, according to the agriculture and forestry trade union although volunteers planted a record number of trees in 2019, most had died by 2020 in part due to lack of rainfall.

United States

It is the stated goal of the US Forest Service to manage forest resources sustainably. This includes reforestation after timber harvest, among other programs.

United States Department of Agriculture (USDA) data shows that forest occupied about 46% of total U.S. land in 1630 (when European settlers began to arrive in large numbers), but had decreased to 34% by 1910. After 1910, forest area has remained almost constant although U.S. population has increased substantially. In the late 19th century the U.S. Forest Service was established in part to address the concern of natural disasters due to deforestation, and new reforestation programs and federal laws such as The Knutson-Vandenberg Act (1930) were implemented. The U.S. Forest Service states that human-directed reforestation is required to support natural regeneration and the agency engages in ongoing research into effective ways to restore forests.

As for the year 2020, United States of America plant 2.5 billion trees per year. At the beginning of the year 2020, a bill that will increase the number to 3.3 billion, was proposed by the Republican Party, after President Donald Trump joined the Trillion Tree Campaign.

Organizations

Ecosia is a non-profit organisation based in Berlin, Germany that has planted over 100 million trees worldwide as of July 2020.

Trees for the Future has assisted more than 170,000 families, in 6,800 villages of Asia, Africa and the Americas, to plant over 35 million trees.

Ecologi is an organisation that has its members pay a monthly fee to offset their carbon emissions, primarily through tree planting. As well as this they work to promote sustainability and low carbon alternatives. So far over 2 million trees have been planted through Ecologi.

Wangari Maathai, 2004 Nobel Peace Prize recipient, founded the Green Belt Movement which planted over 47 million trees to restore the Kenyan environment.

Shanghai Roots & Shoots, a division of the Jane Goodall Institute, launched The Million Tree Project in Kulun Qi, Inner Mongolia to plant one million trees to stop desertification and alleviate global warming.

Team Trees was a 2019 fundraiser with an initiative to plant 20 million trees. The initiative was started by American YouTubers MrBeast and Mark Rober, and was mostly supported by YouTubers. The Arbor Day Foundation will work with its local partners around the world to plant one tree for each dollar they raise.

Companies

Many companies are trying to achieve carbon offsets by Nature-based solutions like reforestation, including mangrove forests and soil restoration. Among them Microsoft, Eni. Increasing the forest cover of Earth by 25% will offset the human emissions in the latest 20 years. In any case it will be necessary to pull from the atmosphere the CO2 that already have been emitted. However, it can work only if the companies will stop to pump new emissions to the atmosphere and stop deforestation.

Related concepts

A similar concept, afforestation, refers to the process of restoring and recreating areas of woodlands or forests that may have existed long ago but were deforested or otherwise removed at some point in the past or lacked it naturally (e.g., natural grasslands). Sometimes the term « re-afforestation » is used to distinguish between the original forest cover and the later re-growth of forest to an area.^{[citation needed]} Special tools, e.g. tree planting bars, are used to make planting of trees easier and faster.

Another alternative strategy, proforestation, is similar as it can be used to counteract the negative environmental and ecological effects of deforestation through growing an existing forest intact to its full ecological potential.

Criticisms

Reforestation competes with other land uses, such as food production, livestock grazing, and living space, for further economic growth.^{[citation needed]} Reforestation often has the tendency to create large fuel loads, resulting in significantly hotter combustion than fires involving low brush or grasses.^{[citation needed]} Reforestation can divert large amounts of water from other activities.^{[citation needed]} Reforesting sometimes results in extensive canopy creation that prevents growth of diverse vegetation in the shadowed areas and generating soil conditions that hamper other types of vegetation. Trees used in some reforesting efforts (e.g., Eucalyptus globulus) tend to extract large amounts of moisture from the soil, preventing the growth of other plants.

There is also the risk that, through a forest fire or insect outbreak, much of the stored carbon in a reforested area could make its way back to the atmosphere. Reduced harvesting rates and fire suppression have caused an increase in the forest biomass in the western United States over the past century. This causes an increase of about a factor of four in the frequency of fires due to longer and hotter dry seasons.

Bio-energy with carbon capture and storage

Bio-energy 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 dioxide (CO₂) which is extracted from the atmosphere by when the biomass grows. Energy is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods. Some of the carbon in the biomass is converted to CO₂ or biochar which can then be stored by geologic sequestration or land application, respectively, enabling carbon dioxide removal and making BECCS a negative emissions technology.

The IPCC Fifth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), suggests a potential range of negative emissions from BECCS of 0 to 22 gigatonnes per year. As of 2019, five facilities around the world were actively using BECCS technologies and were capturing approximately 1.5 million tonnes per year of CO₂. Wide deployment of BECCS is constrained by cost and availability of biomass.

Negative emission

The main appeal of BECCS is in its ability to result in negative emissions of CO₂. The capture of carbon dioxide from bioenergy sources effectively removes CO₂ from the atmosphere.

Bio-energy is derived from biomass which is a renewable energy source and serves as a carbon sink during its growth. During industrial processes, the biomass combusted or processed re-releases the CO₂ into the atmosphere. The process thus results in a net zero emission of CO₂, though this may be positively or negatively altered depending on the carbon emissions associated with biomass growth, transport and processing, see below under environmental considerations. Carbon capture and storage (CCS) technology serves to intercept the release of CO₂ into the atmosphere and redirect it into geological storage locations. CO₂ with a biomass origin is not only released from biomass fuelled power plants, but also during the production of pulp used to make paper and in the production of biofuels such as biogas and bioethanol. The BECCS technology can also be employed on such industrial processes.

BECCS technologies trap carbon dioxide in geologic formations in a semi-permanent way, whereas a tree stores its carbon only during its lifetime. The IPCC report on CCS technology projected that more than 99% of carbon dioxide stored through geologic sequestration is likely to stay in place for more than 1000 years. While other types of carbon sinks such as the ocean, trees and soil may involve the risk of adverse feedback loops at increased temperatures, BECCS technology is likely to provide a better permanence by storing CO₂ in geological formations.

Industrial processes have released too much CO₂ to be absorbed by conventional sinks such as trees and soil to reach low emission targets. In addition to the presently accumulated emissions, there will be significant additional emissions during this century, even in the most ambitious low-emission scenarios. BECCS has therefore been suggested as a technology to reverse the emission trend and create a global system of net negative emissions. This implies that the emissions would not only be zero, but negative, so that not only the emissions, but the absolute amount of CO₂ in the atmosphere would be reduced.

Application

Cost

The IPCC states that estimations for BECCS cost range from $60-$250 per ton of CO₂.

Research by Rau et al. (2018) estimates that electrogeochemical methods of combining saline water electrolysis with mineral weathering powered by non-fossil fuel-derived electricity could, on average, increase both energy generation and CO₂ removal by more than 50 times relative to BECCS, at equivalent or even lower cost, but further research is needed to develop such methods.

Technology

Main article: Carbon capture and storage

The main technology for CO₂ capture from biotic sources generally employs the same technology as carbon dioxide capture from conventional fossil fuel sources.^{[citation needed]} Broadly, three different types of technologies exist: post-combustion, pre-combustion, and oxy-fuel combustion.

Oxy-combustion

Oxy‐fuel combustion has been a common process in the glass, cement and steel industries. It is also a promising technological approach for CCS. In oxy‐fuel combustion, the main difference from conventional air firing is that the fuel is burned in a mixture of O₂ and recycled flue gas. The O₂ is produced by an air separation unit (ASU), which removes the atmospheric N₂ from the oxidizer stream. By removing the N₂ upstream of the process, a flue gas with a high concentration of CO₂ and water vapor is produced, which eliminates the need for a post‐combustion capture plant. The water vapor can be removed by condensation, leaving a product stream of relatively high‐purity CO₂ which, after subsequent purification and dehydration, can be pumped to a geological storage site.

Key challenges of BECCS implementation using oxy-combustion are associated with the combustion process. For the high volatile content biomass, the mill temperature has to be kept at a low temperature to reduce the risk of fire and explosion. In addition, the flame temperature is lower. Therefore, the concentration of oxygen needs to be increased up to 27-30%.

Pre-combustion

« Pre-combustion carbon capture » describes processes that capture CO₂ before generating energy. This is often accomplished in five operating stages: oxygen generation, syngas generation, CO₂ separation, CO₂ compression, and power generation. The fuel first goes through a gasification process by reacting with oxygen to form a stream of CO and H₂, which is syngas. The products will then go through a water-gas shift reactor to form CO₂ and H₂. The CO₂ that is produced will then be captured, and the H₂, which is a clean source, will be used for combustion to generate energy. The process of gasification combined with syngas production is called Integrated Gasification Combined Cycle (IGCC). An Air Separation Unit (ASU) can serve as the oxygen source, but some research has found that with the same flue gas, oxygen gasification is only slightly better than air gasification. Both have a thermal efficiency of roughly 70% using coal as the fuel source. Thus, the use of an ASU is not really necessary in pre-combustion.

Biomass is considered « sulfur-free » as a fuel for the pre-combustion capture. However, there are other trace elements in biomass combustion such as K and Na that could accumulate in the system and finally cause the degradation of the mechanical parts. Thus, further developments of the separation techniques for those trace elements are needed. And also, after the gasification process, CO₂ takes up to 13% – 15.3% by mass in the syngas stream for biomass sources, while it is only 1.7% – 4.4% for coal. This limit the conversion of CO to CO₂ in the water gas shift, and the production rate for H₂ will decrease accordingly. However, the thermal efficiency of the pre-combustion capture using biomass resembles that of coal which is around 62% – 100%. Some research found that using a dry system instead of a biomass/water slurry fuel feed was more thermally efficient and practical for biomass.

Post-combustion

In addition to pre-combustion and oxy-fuel combustion technologies, post-combustion is a promising technology which can be used to extract CO₂ emission from biomass fuel resources. During the process, CO₂ is separated from the other gases in the flue gas stream after the biomass fuel is burnt and undergo separation process. Because it has the ability to be retrofitted to some existing power plants such as steam boilers or other newly built power stations, post-combustion technology is considered as a better option than pre-combustion technology. According to the fact sheets U.S. CONSUMPTION OF BIO-ENERGY WITH CARBON CAPTURE AND STORAGE released in March 2018, the efficiency of post-combustion technology is expected to be 95% while pre-combustion and oxy-combustion capture CO2 at an efficient rate of 85% and 87.5% respectively.

Development for current post-combustion technologies has not been entirely done due to several problems. One of the major concerns using this technology to capture carbon dioxide is the parasitic energy consumption. If the capacity of the unit is designed to be small, the heat loss to the surrounding is great enough to cause to many negative consequences. Another challenge of post-combustion carbon capture is how to deal with the mixture’s components in the flue gases from initial biomass materials after combustion. The mixture consists of a high amount of alkali metals, halogens, acidic elements, and transition metals which might have negative impacts on the efficiency of the process. Thus, the choice of specific solvents and how to manage the solvent process should be carefully designed and operated.

Biomass feedstocks

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See also: bioenergy

Biomass sources used in BECCS include agricultural residues & waste, forestry residue & waste, industrial & municipal wastes, and energy crops specifically grown for use as fuel. Current BECCS projects capture CO₂ from ethanol bio-refinery plants and municipal solid waste (MSW) recycling center.

Current projects

Up to date, there have been 23 BECCS projects around the world, with the majority in North America and Europe. Today, there are only 6 projects in operation, capturing CO₂ from ethanol bio-refinery plants and MSW recycling centers.

5 BECSS projects have been canceled due to the difficulty of obtaining the permission as well as their economic viability. The canceled projects include: the White Rose CCS Project at Selby, UK can capture about 2 MtCO₂/year from Drax power station and store CO₂ at the Bunter Sandstone. The Rufiji Cluster project at Tanzania plan to capture around 5.0-7.0 MtCO₂/year and store CO₂ at the Saline Aquifer. The Greenville project at Ohio, USA has capacity of capturing 1 MtCO₂/year. The Wallula project was planned to capture 0.75 MtCO₂/year at Washington, USA. Finally, the CO₂ Sink project at Ketzin, Germany.

At ethanol plants

Illinois Industrial Carbon Capture and Storage (IL-CCS) is one of the milestones, being the first industrial-scaled BECCS project, in the early 21st century. Located in Decatur, Illinois, USA, IL-CCS captures CO₂ from Archer Daniels Midland (ADM) ethanol plant. The captured CO₂ is then injected under the deep saline formation at Mount Simon Sandstone. IL-CCS consists of 2 phases. The first being a pilot project which was implemented from 11/2011 to 11/2014. Phase 1 has a capital cost of around 84 million US dollars. Over the 3-year period, the technology successfully captured and sequestered 1million tonne of CO₂ from the ADM plant to the aquifer. No leaking of CO₂ from the injection zone was found during this period. The project is still being monitored for future reference. The success of phase 1 motivated the deployment of phase 2, bringing IL-CCS (and BECCS) to industrial scale. Phase 2 has been in operation since 11/2017 and also use the same injection zone at Mount Simon Sandstone as phase 1. The capital cost for second phase is about 208 million US dollars including 141 million US dollar fund from the Department of Energy. Phase 2 has capturing capacity about 3 time larger than the pilot project (phase 1). Annually, IL-CCS can capture mourned 1 million tonne of CO₂. With the largest of capturing capacity, IL-CCS is currently the largest BECCS project in the world.

In addition to the IL-CCS project, there are about three more projects that capture CO₂ from the ethanol plant at smaller scales. For example, Arkalon at Kansas, USA can capture 0.18-0.29 MtCO₂/yr, OCAP at Netherlands can capture about 0.1-0.3 MtCO₂/yr, and Husky Energy at Canada can capture 0.09-0.1 MtCO₂/yr.

At MSW recycling centers

Beside capturing CO₂ from the ethanol plants, currently, there are 2 models in Europe are designed to capture CO₂ from the processing of Municipal Solid Waste. The Klemetsrud Plant at Oslo, Norway use biogenic municipal solid waste to generate 175 GWh and capture 315 Ktonne of CO₂ each year. It uses absorption technology with Aker Solution Advanced Amine solvent as a CO₂ capture unit. Similarly, the ARV Duiven at Netherlands uses the same technology, but it captures less CO₂ than the previous model. ARV Duiven generates around 126 GWh and only capture 50 Ktonne of CO₂ each year.

Techno-economics of BECCS and the TESBiC Project

The largest and most detailed techno-economic assessment of BECCS was carried out by cmcl innovations and the TESBiC group (Techno-Economic Study of Biomass to CCS) in 2012. This project recommended the most promising set of biomass fueled power generation technologies coupled with carbon capture and storage (CCS). The project outcomes lead to a detailed “biomass CCS roadmap” for the U.K..

Challenges

Environmental considerations

Some of the environmental considerations and other concerns about the widespread implementation of BECCS are similar to those of CCS. However, much of the critique towards CCS is that it may strengthen the dependency on depletable fossil fuels and environmentally invasive coal mining. This is not the case with BECCS, as it relies on renewable biomass. There are however other considerations which involve BECCS and these concerns are related to the possible increased use of biofuels. Biomass production is subject to a range of sustainability constraints, such as: scarcity of arable land and fresh water, loss of biodiversity, competition with food production, deforestation and scarcity of phosphorus. It is important to make sure that biomass is used in a way that maximizes both energy and climate benefits. There has been criticism to some suggested BECCS deployment scenarios, where there would be a very heavy reliance on increased biomass input.

Large areas of land would be required to operate BECCS on an industrial scale. To remove 10 billion tons of CO₂, upwards of 300 million hectares of land area (larger than India) would be required. As a result, BECCS risks using land that could be better suited to agriculture and food production, especially in developing countries.

These systems may have other negative side effects. There is however presently no need to expand the use of biofuels in energy or industry applications to allow for BECCS deployment. There is already today considerable emissions from point sources of biomass derived CO₂, which could be utilized for BECCS. Though, in possible future bio-energy system upscaling scenarios, this may be an important consideration.

Upscaling BECCS would require a sustainable supply of biomass – one that does not challenge our land, water, and food security. Using bio-energy crops as feedstock will not only cause sustainability concerns but also require the use of more fertilizer leading to soil contamination and water pollution.^{[citation needed]} Moreover, crop yield is generally subjected to climate condition, i.e. the supply of this bio-feedstock can be hard to control. Bioenergy sector must also expand to meet the supply level of biomass. Expanding bioenergy would require technical and economic development accordingly.

Technical challenges

A challenge for applying BECCS technology, as with other carbon capture and storage technologies, is to find suitable geographic locations to build combustion plant and to sequester captured CO₂. If biomass sources are not close by the combustion unit, transporting biomass emits CO₂ offsetting the amount of CO₂ captured by BECCS. BECCS also face technical concerns about efficiency of burning biomass. While each type of biomass has a different heating value, biomass in general is a low-quality fuel. Thermal conversion of biomass typically has a efficiency of 20-27%. For comparison, coal-fired plants have an efficiency of about 37%.

BECCS also faces a question whether the process is actually energy positive. Low energy conversion efficiency, energy-intensive biomass supply, combined with the energy required to power the CO₂ capture and storage unit impose energy penalty on the system. This might lead to a low power generation efficiency.

Potential solutions

Alternative biomass sources

Agricultural and forestry residues

Globally, 14 Gt of forestry residue and 4.4 Gt residues from crop production (mainly barley, wheat, corn, sugarcane and rice) are generated every year. This is a significant amount of biomass which can be combusted to generate 26 EJ/year and achieve a 2.8 Gt of negative CO₂ emission through BECCS. Utilizing residues for carbon capture will provide social and economic benefits to rural communities. Using waste from crops and forestry is a way to avoid the ecological and social challenges of BECCS.

Municipal solid waste

Municipal solid waste(MSW) is one of the newly developed sources of biomass. Two current BECCS plants are using MSW as feedstocks. Waste collected from daily life is recycled via incineration waste treatment process. Waste goes through high temperature thermal treatment and the heat generated from combusting organic part of waste is used to generate electricity. CO₂emitted from this process is captured through absorption using MEA. For every 1 kg of waste combusted, 0.7 kg of negative CO₂emission is achieved. Utilizing solid waste also have other environmental benefits.

Co-firing coal with biomass

As of 2017 there were roughly 250 cofiring plants in the world, including 40 in the US. Studies showed that by mixing coal with biomass, we could reduce the amount of CO2 emitted. The concentration of CO2 in the flue gas is an important key to determine the efficiency of CO2 capture technology. The concentration of CO2 in the flue gas from the co-firing power plant is roughly the same as coal plant, about 15% [1]. ^{[page needed]} This means that we can reduce our reliance on fossil fuel.

Even though co-firing will have some energy penalty, it still offers higher net efficiency than the biomass combustion plants. Co-firing biomass with coal will result more energy production with less input material. Currently,^[when?] the modern 500 MW coal power plant can take up to 15% biomass without changing the component of the steam boiler. ^{[page needed]} This promising potential allows co-firing power plant become more favorable^[vague] than dedicated bio-electricity.

It is estimated that by replacing 25% of coal with biomass at existing power plant in China and the U.S, we can reduce emission by 1Gt per year.^{[citation needed]} The amount of negative CO2 emitted depends on the composition of coal and biomass. 10% biomass can reduce 0.5 Gt CO2 per year and with 16% biomass can achieve zero emission.^{[citation needed]} Direct-cofiring (20% biomass) give us negative emission of -26 kg CO2/MWh (from 93 kg CO2/MWh).^{[citation needed]}

Biomass cofiring with coal has efficiency near those of coal combustion. Cofiring can be easily applied to existing coal-fired power plant at low cost.^{[citation needed]} The implementation of co-firing power plant on the global scale is still a challenge. The biomass resources have to meet strictly the sustainability criteria and the co-firing project would need the support in term of economic and policy from the governments.

Even though co-firing plant may be an immediate contribution to solving the global warming and climate change issues, co-firing still has some challenges that need to consider. Due to the moisture content of biomass, it will affect the calorific value of the combustor. In addition, high volatile biomass would highly influence the reaction rate and the temperature of the reactor; especially, it may lead to the explosion of furnace.

Instead of co-firing, full conversion from coal to biomass of one or more generating units in a plant may be preferred.

Policy

Based on the current Kyoto Protocol agreement, carbon capture and storage projects are not applicable as an emission reduction tool to be used for the Clean Development Mechanism (CDM) or for Joint Implementation (JI) projects. Recognising CCS technologies as an emission reduction tool is vital for the implementation of such plants as there is no other financial motivation for the implementation of such systems. There has been growing support to have fossil CCS and BECCS included in the protocol. Accounting studies on how this can be implemented, including BECCS, have also been done.

European Union

There are some future policies that give incentives to use bioenergy such as Renewable Energy Directive (RED) and Fuel Quality Directive (FQD), which require 20% of total energy consumption to be based on biomass, bioliquids and biogas by 2020.

United Kingdom

In 2018 the Committee on Climate Change recommended that aviation biofuels should provide up to 10% of total aviation fuel demand by 2050, and that all aviation biofuels should be produced with CCS as soon as the technology is available.

United States

In February, 2018, US congress significantly increased and extended the section 45Q tax credit for sequestration of carbon oxides. This has been a top priority of carbon capture and sequestration (CCS) supporters for several years. It increased $25.70 to $50 tax credit per tonnes of CO₂ for secure geological storage and $15.30 to $35 tax credit per tonne of CO₂ used in enhanced oil recovery.

Public perception

Limited studies have investigated public perceptions of BECCS. Of those studies, most originate from developed countries in the northern hemisphere and therefore may not represent a worldwide view.

In a 2018 study involving online panel respondents from the United Kingdom, United States, Australia, and New Zealand, respondents showed little prior awareness of BECCS technologies. Measures of respondents perceptions suggest that the public associate BECCS with a balance of both positive and negative attributes. Across the four countries, 45% of the respondents indicated they would support small scale trials of BECCS, whereas only 21% were opposed. BECCS was moderately preferred among other methods of Carbon dioxide removal like Direct air capture or Enhanced weathering, and greatly preferred over methods of Solar radiation management.

Future outlook

The examples and perspective in this section deal primarily with United States and the United Kingdom and do not represent a worldwide view of the subject. You may improve this section, discuss the issue on the talk page, or create a new section, as appropriate. (June 2019) (Learn how and when to remove this template message)

United Kingdom

In February 2019 the pilot of a BECCS facility went into operation at Drax power station in North Yorkshire, England. The aim is to capture one tonne a day of CO2 from its wood combustion generation.

United States

In the 2014 AMPERE modeling project, based on 8 different integrated assessment models, the future deployment of BECCS is predicted to help meet the US emissions budget for the future 2 °C scenario in the Paris Agreement. In the middle of the 21st century, the scale of the BECCS deployment ranges from 0 Mt to 1100 Mt CO₂per year. And by the end of the century, the deployment ranges from 720 Mt to 7500 Mt CO₂per year, while most of the models predict the scale to be within 1000 Mt to 3000 Mt by 2100. A research group from Stanford University has modeled the technical potential of BECCS in the US in the year 2020. According to their calculations, about one-third of the potential biomass production in total is located close enough to the geological storage site, which results in a CO₂capturing capability of 110 Mt – 120 Mt.

Ocean fertilization

Ocean fertilization or ocean nourishment is a type of climate engineering based on the purposeful introduction of nutrients to the upper ocean to increase marine food production and to remove carbon dioxide from the atmosphere. A number of techniques, including fertilization by iron, urea and phosphorus have been proposed.

History

John Martin, director of the Moss Landing Marine Laboratories, hypothesized that the low levels of phytoplankton in these regions are due to a lack of iron. In 1989 he tested this hypothesis (known as the Iron Hypothesis) by an experiment using samples of clean water from Antarctica. Iron was added to some of these samples. After several days the phytoplankton in the samples with iron fertilization grew much more than in the untreated samples. This led Martin to speculate that increased iron concentrations in the oceans could partly explain past ice ages.

IRONEX I

This experiment was followed by a larger field experiment (IRONEX I) where 445 kg of iron was added to a patch of ocean near the Galápagos Islands. The levels of phytoplankton increased three times in the experimental area. The success of this experiment and others led to proposals to use this technique to remove carbon dioxide from the atmosphere.

EisenEx

In 2000 and 2004, iron sulfate was discharged from the EisenEx. 10 to 20 percent of the resulting algal bloom died and sank to the sea floor.

Commercial projects

Planktos was a US company that abandoned its plans to conduct 6 iron fertilization cruises from 2007 to 2009, each of which would have dissolved up to 100 tons of iron over a 10,000 km² area of ocean. Their ship Weatherbird II was refused entry to the port of Las Palmas in the Canary Islands where it was to take on provisions and scientific equipment.

In 2007 commercial companies such as Climos and GreenSea Ventures and the Australian-based Ocean Nourishment Corporation, planned to engage in fertilization projects. These companies invited green co-sponsors to finance their activities in return for provision of carbon credits to offset investors’ CO₂ emissions.

LOHAFEX

LOHAFEX was an experiment initiated by the German Federal Ministry of Research and carried out by the German Alfred Wegener Institute (AWI) in 2009 to study fertilization in the South Atlantic. India was also involved.

As part of the experiment, the German research vessel Polarstern deposited 6 tons of ferrous sulfate in an area of 300 square kilometers. It was expected that the material would distribute through the upper 15 metres (49 ft) of water and trigger an algal bloom. A significant part of the carbon dioxide dissolved in sea water would then be bound by the emerging bloom and sink to the ocean floor.

The Federal Environment Ministry called for the experiment to halt, partly because environmentalists predicted damage to marine plants. Others predicted long-term effects that would not be detectable during short-term observation or that this would encourage large-scale ecosystem manipulation.

2012

A 2012 study deposited iron fertilizer in an eddy near Antarctica. The resulting algal bloom sent a significant amount of carbon into the deep ocean, where it was expected to remain for centuries to millennia. The eddy was chosen because it offered a largely self-contained test system.

As of day 24, nutrients, including nitrogen, phosphorus and silicic acid that diatoms use to construct their shells, declined. Dissolved inorganic carbon concentrations were reduced below equilibrium with atmospheric CO
₂. In surface water, particulate organic matter (algal remains) including silica and chlorophyll increased.

After day 24, however, the particulate matter fell to between 100 metres (330 ft) to the ocean floor. Each iron atom converted at least 13,000 carbon atoms into algae. At least half of the organic matter sank below, 1,000 metres (3,300 ft).

Haida Gwaii project

In July 2012, the Haida Salmon Restoration Corporation dispersed 100 short tons (91 t) of iron sulphate dust into the Pacific Ocean several hundred miles west of the islands of Haida Gwaii. The Old Massett Village Council financed the action as a salmon enhancement project with $2.5 million in village funds. The concept was that the formerly iron-deficient waters would produce more phytoplankton that would in turn serve as a « pasture » to feed salmon. Then-CEO Russ George hoped to sell carbon offsets to recover the costs. The project was accompanied by charges of unscientific procedures and recklessness. George contended that 100 tons was negligible compared to what naturally enters the ocean.

Some environmentalists called the dumping a « blatant violation » of two international moratoria. George said that the Old Massett Village Council and its lawyers approved the effort and at least seven Canadian agencies were aware of it.

According to George, the 2013 salmon runs increased from 50 million to 226 million fish. However, many experts contend that changes in fishery stocks since 2012 cannot necessarily be attributed to the 2012 iron fertilization; many factors contribute to predictive models, and most data from the experiment are considered to be of questionable scientific value.

On 15 July 2014, the data gathered during the project were made publicly available under the ODbL license.

International reaction

In 2007 Working Group III of the United Nations Intergovernmental Panel on Climate Change examined ocean fertilization methods in its fourth assessment report and noted that the field-study estimates of the amount of carbon removed per ton of iron was probably over-estimated and that potential adverse effects had not been fully studied.

In June 2007 the London Dumping Convention issued a statement of concern noting ‘the potential for large scale ocean iron fertilization to have negative impacts on the marine environment and human health’,. but did not define ‘large scale’. It is believed that the definition would include operations.^{[citation needed]}

In 2008, the London Convention/London Protocol noted in resolution LC-LP.1 that knowledge on the effectiveness and potential environmental impacts of ocean fertilization was insufficient to justify activities other than research. This non-binding resolution stated that fertilization, other than research, « should be considered as contrary to the aims of the Convention and Protocol and do not currently qualify for any exemption from the definition of dumping ».

In May 2008, at the Convention on Biological Diversity, 191 nations called for a ban on ocean fertilization until scientists better understand the implications.

In August 2018, Germany banned the sale of ocean seeding as carbon sequestration system while the matter was under discussion at EU and EASAC levels.

Rationale

The marine food chain is based on photosynthesis by marine phytoplankton that combine carbon with inorganic nutrients to produce organic matter. Production is limited by the availability of nutrients, most commonly nitrogen or iron. Numerous experiments have demonstrated how iron fertilization can increase phytoplankton productivity. Nitrogen is a limiting nutrient over much of the ocean and can be supplied from various sources, including fixation by cyanobacteria. Carbon-to-iron ratios in phytoplankton are much larger than carbon-to-nitrogen or carbon-to-phosphorus ratios, so iron has the highest potential for sequestration per unit mass added.

Oceanic carbon naturally cycles between the surface and the deep via two « pumps » of similar scale. The « solubility » pump is driven by ocean circulation and the solubility of CO₂ in seawater. The « biological » pump is driven by phytoplankton and subsequent settling of detrital particles or dispersion of dissolved organic carbon. The former has increased as a result of increasing atmospheric CO₂ concentration. This CO₂ sink is estimated to be approximately 2 GtC yr−1.

The global phytoplankton population fell about 40 percent between 1950 and 2008 or about 1 percent per year. The most notable declines took place in polar waters and in the tropics. The decline is attributed to sea surface temperature increases. A separate study found that diatoms, the largest type of phytoplankton, declined more than 1 percent per year from 1998 to 2012, particularly in the North Pacific, North Indian and Equatorial Indian oceans. The decline appears to reduce pytoplankton’s ability to sequester carbon in the deep ocean.

Fertilization offers the prospect of both reducing the concentration of atmospheric greenhouse gases with the aim of slowing climate change and at the same time increasing fish stocks via increasing primary production. The reduction reduces the ocean’s rate of carbon sequestration in the deep ocean.

Each area of the ocean has a base sequestration rate on some timescale, e.g., annual. Fertilization must increase that rate, but must do so on a scale beyond the natural scale. Otherwise, fertilization changes the timing, but not the total amount sequestered. However, accelerated timing may have beneficial effects for primary production separate from those from sequestration.

Biomass production inherently depletes all resources (save for sun and water). Either they must all be subject to fertilization or sequestration will eventually be limited by the one mostly slowly replenished (after some number of cycles) unless the ultimate limiting resource is sunlight and/or surface area. Generally, phosphate is the ultimate limiting nutrient. As oceanic phosphorus is depleted (via sequestration) it would have to be included in the fertilization cocktail supplied from terrestrial sources.

Approaches

« Ocean fertilisation options are only worthwhile if sustained on a millennial timescale and phosphorus addition may have greater long-term potential than iron or nitrogen fertilisation. » Phytoplankton require a variety of nutrients. These include macronutrients such as nitrate and phosphate (in relatively high concentrations) and micronutrients such as iron and zinc (in much smaller quantities). Nutrient requirements vary across phylogenetic groups (e.g., diatoms require silicon) but may not individually limit total biomass production. Co-limitation (among multiple nutrients) may also mean that one nutrient can partially compensate for a shortage of another. Silicon does not affect total production, but can change the timing and community structure with follow-on effects on remineralization times and subsequent mesopelagic.nutrient vertical distribution.

Low-nutrient low-chlorophyll (LNLC) waters occupy the oceans’ subtropical gyre systems, approximately 40 per cent of the surface, where wind-driven downwelling and a strong thermocline impede nutrient resupply from deeper water. Nitrogen fixation by cyanobacteria provides a major source of N. In effect, it ultimately prevents the ocean from losing the N required for photosynthesis. Phosphorus has no substantial supply route, making it the ultimate limiting macronutrient. The sources that fuel primary production are deep water stocks and runoff or dust-based.

Iron

Main article: Iron fertilization

Approximately 25 per cent of the ocean surface has ample macronutrients, with little plant biomass (as defined by chlorophyll). The production in these high-nutrient low-chlorophyll (HNLC) waters is primarily limited by micronutrients especially iron. The cost of distributing iron over large ocean areas is large compared with the expected value of carbon credits.

Phosphorus

In the very long term, phosphorus « is often considered to be the ultimate limiting macronutrient in marine ecosystems » and has a slow natural cycle. Where phosphate is the limiting nutrient in the photic zone, addition of phosphate is expected to increase primary phytoplankton production. This technique can give 0.83W/m² of globally averaged negative forcing, which is sufficient to reverse the warming effect of about half the current levels of anthropogenic CO₂ emissions. One water-soluble fertilizer is diammonium phosphate (DAP), (NH₄)₂HPO₄, that as of 2008 had a market price of 1700/tonne−1 of phosphorus. Using that price and the C : P Redfield ratio of 106 : 1 produces a sequestration cost (excluding preparation and injection costs) of some $45 /tonne of carbon (2008), substantially less than the trading price for carbon emissions.

Nitrogen

This technique (proposed by Ian Jones) proposes to fertilize the ocean with urea, a nitrogen rich substance, to encourage phytoplankton growth. This has also been considered by Karl. Concentrations of macronutrients per area of ocean surface would be similar to large natural upwellings. Once exported from the surface, the carbon remains sequestered for a long time.

An Australian company, Ocean Nourishment Corporation (ONC), planned to inject hundreds of tonnes of urea into the ocean, in order to boost the growth of CO₂-absorbing phytoplankton, as a way to combat climate change. In 2007, Sydney-based ONC completed an experiment involving one tonne of nitrogen in the Sulu Sea off the Philippines.

Macronutrient nourishment can give 0.38W/m² of globally averaged negative forcing, which is sufficient to reverse the warming effect of current levels of around a quarter of anthropogenic CO₂ emissions.

The Ocean Nourishment Corporation claimed, « One Ocean Nourishment plant will remove approximately 5–8 million tonnes of CO₂ from the atmosphere for each year of operation, equivalent to offsetting annual emissions from a typical 1200 MW coal-fired power station or the short-term sequestration from one million hectares of new growth forest ».

The two dominant costs are manufacturing the nitrogen and nutrient delivery.

Pelagic pumping

Local wave power could be used to pump nutrient-rich water from hundred- metre-plus depths to the euphotic zone. However, deep water concentrations of dissolved CO₂ could be returned to the atmosphere.

The supply of DIC in upwelled water is generally sufficient for photosynthesis permitted by upwelled nutrients, without requiring atmospheric CO₂. Second-order effects include how the composition of upwelled water differs from that of settling particles. More nitrogen than carbon is remineralized from sinking organic material. Upwelling of this water allows more carbon to sink than that in the upwelled water, which would make room for at least some atmospheric CO₂ to be absorbed. the magnitude of this difference is unclear. No comprehensive studies have yet resolved this question. Preliminary calculations using upper limit assumptions indicate a low value. 1,000 square kilometres (390 sq mi) could sequester 1 gigatonne/year.

Sequestration thus depends on the upward flux and the rate of lateral surface mixing of the surface water with denser pumped water.

Volcanic ash

Volcanic ash adds nutrients to the surface ocean. This is most apparent in nutrient-limited areas. Research on the effects of anthropogenic and aeolian iron addition to the ocean surface suggests that nutrient-limited areas benefit most from a combination of nutrients provided by anthropogenic, eolian and volcanic deposition. Some oceanic areas are comparably limited in more than one nutrient, so fertilization regimes that includes all limited nutrients is more likely to succeed. Volcanic ash supplies multiple nutrients to the system, but excess metal ions can be harmful. The positive impacts of volcanic ash deposition are potentially outweighed by their potential to do harm.^{[citation needed]}

Clear evidence documents that ash can be as much as 45 percent by weight in some deep marine sediments. In the Pacific Ocean estimates claim that (on a millennial-scale) the atmospheric deposition of air-fall volcanic ash was as high as the deposition of desert dust. This indicates the potential of volcanic ash as a significant iron source.

In August 2008 the Kasatochi volcanic eruption in the Aleutian Islands, Alaska, deposited ash in the nutrient-limited northeast Pacific. This ash (including iron) resulted in one of the largest phytoplankton blooms observed in the subarctic. Fisheries scientists in Canada linked increased oceanic productivity from the volcanic iron to subsequent record returns of salmon in the Fraser River two years later

Complications

While manipulation of the land ecosystem in support of agriculture for the benefit of humans has long been accepted (despite its side effects), directly enhancing ocean productivity has not. Among the reasons are:

Outright opposition

According to Lisa Speer of the Natural Resources Defense Council, « There is a limited amount of money, of time, that we have to deal with this problem….The worst possible thing we could do for climate change technologies would be to invest in something that doesn’t work and that has big impacts that we don’t anticipate. »

In 2009  Aaron Strong, Sallie Chisholm, Charles Miller and John Cullen opined in Nature « …fertilizing the oceans with iron to stimulate phytoplankton blooms, absorb carbon dioxide from the atmosphere and export carbon to the deep sea — should be abandoned. »

Efficiency

Algal cell chemical composition is often assumed to respect a ratio where atoms are 106 carbon: 16 nitrogen: 1 phosphorus (Redfield ratio): 0.0001 iron. In other words, each atom of iron helps capture 1,060,000 atoms of carbon, while one nitrogen atom only 6.

In large areas of the ocean, such organic growth (and hence nitrogen fixation) is thought to be limited by the lack of iron rather than nitrogen, although direct measures are hard.

On the other hand, experimental iron fertilisation in HNLC regions has been supplied with excess iron which cannot be utilized before it is scavenged. Thus the organic material produced was much less than if the ratio of nutrients above were achieved. Only a fraction of the available nitrogen (because of iron scavenging) is drawn down. In culture bottle studies of oligotrophic water, adding nitrogen and phosphorus can draw down considerably more nitrogen per dosing. The export production is only a small percentage of the new primary production and in the case of iron fertilization, iron scavenging means that regenerative production is small. With macronutrient fertilisation, regenerative production is expected to be large and supportive of larger total export. Other losses can also reduce efficiency.

Side effects

According to Gnadesikan and Marinou, 2008, Beyond biological impacts, evidences suggests that plankton blooms can affect the physical properties of surface waters simply by absorbing light and heat from the sun. Watson added that if fertilization is done in shallow coastal waters, a dense layer of phytoplankton clouding the top 30 metres or so of the ocean could hinder corals, kelps or other deeper sea life from carrying out photosynthesis (Watson et al. 2008).

Algal blooms

Toxic algal blooms are common in coastal areas. Fertilization could trigger such blooms. Chronic fertilization could risk the creation of dead zones, such as the one in the Gulf of Mexico.

Impact on fisheries

Adding urea to the ocean can cause phytoplankton blooms that serve as a food source for zooplankton and in turn feed for fish. This may increase fish catches. However, if cyanobacteria and dinoflagellates dominate phytoplankton assemblages that are considered poor quality food for fish then the increase in fish quantity may not be large. Some evidence links iron fertilization from volcanic eruptions to increased fisheries production.Other nutrients would be metabolized along with the added nutrient(s), reducing their presence in fertilized waters.

Krill populations have declined dramatically since whaling began. Sperm whales transport iron from the deep ocean to the surface during prey consumption and defecation. Sperm whales have been shown to increase the levels of primary production and carbon export to the deep ocean by depositing iron-rich faeces into surface waters of the Southern Ocean. The faeces causes phytoplankton to grow and take up carbon. The phytoplankton nourish krill. Reducing the abundance of sperm whales in the Southern Ocean, whaling resulted in an extra 2 million tonnes of carbon remaining in the atmosphere each year.

Ecosystem disruption

Many locations, such as the Tubbataha Reef in the Sulu Sea, support high marine biodiversity. Nitrogen or other nutrient loading in coral reef areas can lead to community shifts towards algal overgrowth of corals and ecosystem disruption, implying that fertilization must be restricted to areas in which vulnerable populations are not put at risk.

As the phytoplankton descend the water column, they decay, consuming oxygen and producing greenhouse gases methane and nitrous oxide. Plankton-rich surface waters could warm the surface layer, affecting circulation patterns.

Cloud formation

Many phytoplankton species release dimethyl sulfide (DMS), which escapes into the atmosphere where it forms sulfate aerosols and encourages cloud formation, which could reduce warming. However, substantial increases in DMS could reduce global rainfall, according to global climate model simulations, while halving temperature increases as of 2100.

International Law

International law presents some dilemmas for ocean fertilization. The United Nations Framework Convention on Climate Change (UNFCCC 1992) has accepted mitigation actions.^{[citation needed]} However, the UNFCCC and its revisions recognise only forestation and reforestation projects as carbon sinks.^{[citation needed]}

Law of the sea

According to United Nations Convention on the Law of the Sea (LOSC 1982), all states are obliged to take all measures necessary to prevent, reduce and control pollution of the marine environment, to prohibit the transfer of damage or hazards from one area to another and to prohibit the transformation of one type pollution to another. How this relates to fertilization is undetermined.

Solar radiation management

Main article: Solar radiation management

Fertilization may create sulfate aerosols that reflect sunlight, modifying the Earth’s albedo, creating a cooling effect that reduces some of the effects of climate change. Enhancing the natural sulfur cycle in the Southern Ocean by fertilizing with iron in order to enhance dimethyl sulfide production and cloud reflectivity may achieve this.

Enhanced weathering

Enhanced weathering refers to geoengineering approaches that use the dissolution of natural or artificially created minerals to remove carbon dioxide from the atmosphere. Since the carbon dioxide is usually first removed from ocean water, these approaches would attack the problem by first reducing ocean acidification.

Weathering and ocean alkalinity

Weathering is the natural process in which rocks are broken down and dissolved on the land surface. When silicate or carbonate minerals dissolve in rainwater, carbon dioxide is drawn into the solution from the atmosphere through the reactions below (Eq.1&2) to form bicarbonate ions:

Eq.1 Forsterite: Mg₂SiO₄ + 4CO₂ + 4H₂O → 2Mg²⁺ + 4HCO₃⁻ + H₄SiO₄

Eq.2 Calcite : CaCO₃ + CO₂ + H₂O → Ca²⁺ + 2HCO₃⁻

Rainwater and bicarbonate ions eventually end up in the ocean, where they are formed into carbonate minerals by calcifying organisms (Eq.3), which then sinks out of the surface ocean. Most of the carbonate is redissolved in the deep ocean as it sinks.

Eq.3 Ca²⁺ + 2HCO₃⁻ → CaCO₃ + CO₂ + H₂O

Over geological time periods these processes are thought to stabilise the Earth’s climate. For silicate weathering the theoretical net effect of dissolution and precipitation is 1 mol of CO₂ sequestered for every mol of Ca²⁺ or Mg²⁺ weathered out of the mineral. Given that some of the dissolved cations react with existing alkalinity in the solution to form CO₃²⁻ ions, the ratio is not exactly 1:1 in natural systems but is a function of temperature and CO₂ partial pressure. The net CO₂ sequestration of carbonate weathering (Eq.2) and carbonate precipitation (Eq.3) is zero.

Weathering and biological carbonate precipitation are thought to be only loosely coupled on short time periods (<1000 years). Therefore, an increase in both carbonate and silicate weathering with respect to carbonate precipitation will result in a buildup of alkalinity in the ocean.

Enhanced weathering research considers how these natural processes may be enhanced to sequester CO₂ from the atmosphere to be stored in solid carbonate minerals or ocean alkalinity.

Terrestrial enhanced weathering

‘Enhanced Weathering’ was initially used to refer specifically to the spreading of crushed silicate minerals on the land surface. Biological activity in soils has been shown to promote the dissolution of silicate minerals (see discussion in, but there is still uncertainty surrounding how quickly this may happen. As weathering rate is a function of saturation of the dissolving mineral in solution (decreasing to zero in fully saturated solutions), some have suggested that the quantity of rainfall may limit terrestrial enhanced weathering, although others suggest that secondary mineral formation or biological uptake may suppress saturation and promote weathering.

The amount of energy that is required for comminution depends on rate at which the minerals dissolve (less comminution is required for rapid mineral dissolution). Recent work has suggested a large range in potential cost of enhanced weathering largely down to the uncertainty surrounding mineral dissolution rates.

Enhanced rock weathering

In July 2020 one group of scientists assessed that the geoengineering technique of enhanced rock weathering – spreading finely crushed basalt on fields – has potential use for carbon dioxide removal by nations, identifying costs, opportunities and engineering challenges.

Oceanic enhanced weathering

To overcome the limitations of solution saturation and to use natural comminution of sand particles from wave energy, silicate minerals may be applied to coastal environments, although the higher pH of seawater may substantially decrease the rate of dissolution, and it is unclear how much comminution is possible from wave action.

Alternatively, the direct application of carbonate minerals to the up-welling regions of the ocean has been investigated. Carbonate minerals are supersaturated in the surface ocean but are undersaturated in the deep ocean. In areas of up welling this undersaturated water is brought to the surface. While this technology will likely be cheap, the maximum annual CO₂ sequestration potential is limited.

Transforming the carbonate minerals into oxides and spreading this material in the open ocean (‘Ocean Liming’) has been proposed as an alternative technology. Here the carbonate mineral (CaCO₃) is transformed into lime (CaO) through calcination. The energy requirements for this technology are substantial.

Mineral carbonation

The enhanced dissolution and carbonation of silicates (‘mineral carbonation’) was first proposed by Seifritz, and developed initially by Lackner et al. and further by the Albany Research Center. This early research investigated the carbonation of extracted and crushed silicates at elevated temperatures (~180 °C) and partial pressures of CO₂ (~15 MPa) inside controlled reactors (‘Ex-situ mineral carbonation’). Some research explores the potential of ‘In-situ mineral carbonation’ in which the CO₂ is injected into silicate rock formations to promote carbonate formation underground (see: CarbFix)

Mineral carbonation research has largely focused on the sequestration of CO₂ from flue gas. It could be used for geoengineering if the source of CO₂ was derived from the atmosphere, e.g. through direct air capture or biomass-CCS.

Direct air capture

Direct air capture (DAC) is a process of capturing carbon dioxide (CO2) 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 CO2 for sequestration or utilization. Carbon dioxide removal is achieved when ambient air makes contact with chemical media, typically an aqueous alkaline solvent or functionalized sorbents. These chemical media are subsequently stripped of CO₂ through the application of energy (namely heat), resulting in a CO₂ stream that can undergo dehydration and compression, while simultaneously regenerating the chemical media for reuse.

DAC is still in early stages of development, though several commercial plants are in operation or planning across Europe and the US. Large-scale DAC deployment may be accelerated through pairing to utilization (e.g., enhanced oil recovery, production of carbon-neutral synthetic fuel and plastics, as well as beverage carbonation) or policy incentives such as 45Q or the California Low Carbon Fuel Standard. When combined with long-term storage of CO2, DAC can act as a carbon dioxide removal tool whereby net negative emissions may be achieved, subject to a full cradle-to-grave lifecycle assessment.

DAC is not an alternative to traditional, point-source carbon capture and storage (CCS), but can be used to manage emissions from distributed sources, like exhaust fumes from cars.

The idea of using many small dispersed DAC scrubbers—analogous to live plants—to create environmentally significant reduction in CO2 levels, has earned the technology a name of artificial trees in popular media.

Methods of capture

Commercial techniques require large fans to push ambient air through a filter. There, a liquid solvent—usually amine-based or caustic—absorbs CO2 from a gas. For example, a common caustic solvent: sodium hydroxide reacts with CO2 and precipitates a stable sodium carbonate. This carbonate is heated to produce a highly pure gaseous CO2 stream. sodium hydroxide can be recycled from sodium carbonate in a process of causticizing. ^{[failed verification]} Alternatively, the CO2 binds to solid sorbent in the process of chemisorption. Through heat and vacuum, the CO2 is then desorbed from the solid.

Among the specific chemical processes that are being explored, three stand out: causticization with alkali and alkali-earth hydroxides, carbonation, and organic−inorganic hybrid sorbents consisting of amines supported in porous adsorbents.

Other explored methods

This section needs expansion. You can help by adding to it. (September 2019)

Moisture swing sorbent

In cyclical a process designed in 2012 by professor Klaus Lackner, the director of the Center for Negative Carbon Emissions (CNCE), dilute CO2 can be efficiently separated using an anionic exchange polymer resin called Marathon MSA, which absorbs air CO2 when dry, and releases it when exposed to moisture. The technology requires further research to determine its cost-effectiveness.

Metal-organic frameworks

Main article: Carbon dioxide scrubber § Metal-organic frameworks (MOFs)

Other substances which can be used are Metal-organic frameworks (or MOF’s).

Membranes

Membrane separation of CO2 rely on semi-permeable membranes. This method requires little water and has a smaller footprint.

Environmental impact

Proponents of DAC argue that it is an essential component of climate change mitigation. Researchers posit that DAC could help contribute to the goals of the Paris Climate Agreement (namely limiting the increase in global average temperature to well below 2 °C above pre-industrial levels). However, others claim that relying on this technology is risky and might postpone emission reduction under the notion that it will be possible to fix the problem later, and suggest, that reducing emissions may be a better solution.

DAC relying on amine-based absorption demands significant water input. It was estimated, that to capture 3.3 Gigatonnes of CO2 a year would require 300 km³ of water, or 4% of the water used for irrigation. On the other hand, using sodium hydroxide needs far less water, but the substance itself is highly caustic and dangerous.

DAC also requires much greater energy input in comparison to traditional capture from point sources, like flue gas, due to the low concentration of CO2. The theoretical minimum energy required to extract CO2 from ambient air is about 250 kWh per tonne of CO2, while capture from natural gas and coal power plants requires respectively about 100 and 65 kWh per tonne of CO2. Because of this implied demand for energy, some geoengineering promoters have proposed to use « small nuclear power plants » connected to DAC installations, potentially introducing a whole new set of environmental impacts.

When DAC is combined with a carbon capture and storage (CCS) system, it can produce a negative emissions plant, but it would require a carbon-free electricity source. The use of any fossil-fuel-generated electricity would end up releasing more CO2 to the atmosphere than it would capture. Moreover, using DAC for enhanced oil recovery would cancel any supposed climate mitigation benefits.

Economic viability

Practical applications of DAC include:

• enhanced oil recovery,
• production of carbon-neutral synthetic fuel and plastics,
• beverage carbonation,
• carbon sequestration,
• improving concrete strength,
• creating carbon-neutral concrete alternative,
• enhancing productivity of algae farms,
• air purification of greenhouses.

These applications require differing concentrations of CO2 product formed from the captured gas. Forms of carbon sequestration such as geological storage require pure CO2 products (concentration > 99%), while other applications such as agriculture can function with more dilute products (~ 5%). Since the air being processed through DAC originally contains 0.04% CO2 (or 400 ppm), creation of a pure product through DAC requires a large amount of thermal energy to facilitate CO2 bonding and thus is more expensive than a dilute product.

DAC is not an alternative to traditional, point-source carbon capture and storage (CCS), rather it is a complementary technology that could be utilized to manage carbon emissions from distributed sources, fugitive emissions from the CCS network, and leakage from geological formations.Because DAC can be deployed far from the source of pollution, synthetic fuel produced with this method can use already existing fuel transport infrastructure.

One of the largest hurdles to implementing DAC is a cost required to separate CO2 and air. A study from 2011 estimated that a plant designed to capture 1 megatonne of CO2 a year would cost $2.2 billion. Other studies from the same period put the cost of DAC at $200–1000 per tonne of CO2 and $600 per tonne.

An economic study of a pilot plant in British Columbia, Canada, conducted from 2015 to 2018, estimated the cost at $94–232 per tonne of atmospheric CO2 removed. It is worth noting that the study was done by Carbon Engineering, which has financial interest in commercializing DAC technology.

As of 2011, CO2 capture costs for hydroxide based solvents generally cost $150 per tonne CO2. Current liquid amine-based separation is $10–35 per tonne CO2. Adsorption based CO2 capture costs are between $30–200 per tonne CO2. It is difficult to find a specific cost for DAC because each method has wide variation in sorbent regeneration and capital costs. ^{[verification needed]}

Development

Carbon Engineering

Main article: Carbon Engineering

It is a commercial DAC company founded in 2009 and backed, among others, by Bill Gates and Murray Edwards. As of 2018, they run a pilot plant in British Columbia, Canada that has been in use since 2015 and is able to extract about a tonne of CO2 a day. An economic study of their pilot plant conducted from 2015 to 2018 estimated the cost at $94–232 per tonne of atmospheric CO2 removed.

While partnering with California energy company Greyrock, they convert a portion of its concentrated CO2 into synthetic fuel, including gasoline, diesel, and jet fuel.

The company uses a potassium hydroxide solution. It reacts with CO2 to form potassium carbonate, which removes a certain amount of CO2 from the air.

Climeworks

Main article: Climeworks

Their first industrial scale DAC plant, which started operation in May, 2017 in Hinwil, in the canton of Zurich, Switzerland, is capable of capturing 900 tonnes of CO2 per year. To lower its energy requirements, the plant uses heat from a local waste incineration plant. The CO2 is used to increase vegetable yields in a nearby greenhouse.

The company stated that it costs around $600 to capture one tonne of CO2 from the air.

Climeworks partnered with Reykjavik Energy in CarbFix project launched in 2007. In 2017, CarbFix2 project was started and received funding from European Union’s Horizon 2020 research program. The CarbFix2 pilot plant project runs alongside a geothermal power plant in Hellisheidi, Iceland. In this approach, CO2 is injected 700 meters under the ground and mineralizes into basaltic bedrock forming carbonate minerals. DAC plant uses low-grade waste heat from the plant, effectively eliminating more CO2 than they both produce.

Global Thermostat

It is private company founded in 2010, located in Manhattan, New York, with a plant in Huntsville, Alabama. Global Thermostat uses amine-based sorbents bound to carbon sponges to remove CO2 from the atmosphere. The company has projects ranging from 40 to 50,000 tonne/year. ^{[verification needed][third-party source needed]}

The company claims to remove CO2 for a $120 per tonne at its facility in Huntsville.

Global Thermostat has closed deals with Coca-Cola (which aims to use DAC to source CO2 for its carbonated beverages) and ExxonMobil which intends to pioneer a DAC‑to‑fuel business using Global Thermostat’s technology.

Prometheus Fuels

Main article: Prometheus Fuels

Is a start-up company based in Santa Cruz which launched out of Y Combinator in 2019 to remove CO₂ from the air and turn it into zero-net-carbon gasoline and jet fuel. The company uses a DAC technology, adsorbing CO₂ from the air directly into process electrolytes, where it is converted into alcohols by electrocatalysis. The alcohols are then separated from the electrolytes using carbon nanotube membranes, and upgraded to gasoline and jet fuels. Since the process uses only electricity from renewable sources, the fuels are carbon neutral when used, emitting no net CO₂ to the atmosphere.

Other companies

• Infinitree – earlier known as Kilimanjaro Energy and Global Research Technology. Part of US-based Carbon Sink. Demonstrated a pre-prototype of economically viable DAC technology in 2007.

• Skytree – a company from Netherlands,
• UK Carbon Capture and Storage Research Centre,
• Antecy – a Dutch company founded in 2010, ^{[verification needed][third-party source needed]}
• Center for Negative Carbon Emission of Arizona State University

Carbon capture and storage

Carbon capture and storage (CCS), or carbon capture and sequestration and carbon control and sequestration, is the process of capturing waste carbon dioxide (CO2) usually from large point sources, such as a cement factory or biomass power plant, transporting it to a storage site, and depositing it where it will not enter the atmosphere, normally an underground geological formation. The aim is to prevent the release of large quantities of CO2 into the atmosphere from heavy industry. It is a potential means of mitigating the contribution to global warming and ocean acidification of carbon dioxide emissions from industry and heating. Although CO2 has been injected into geological formations for several decades for various purposes, including enhanced oil recovery, the long-term storage of CO2 is a relatively new concept. Direct air capture is a type of CCS which scrubs CO2 from ambient air rather than a point source.

Carbon dioxide can be captured directly from the air or from an industrial source (such as power plant flue gas) using a variety of technologies, including absorption, adsorption, chemical looping, membrane gas separation or gas hydrate technologies. Amines are used as solvents in the leading carbon scrubbing technology. CCS applied to a modern conventional power plant could reduce CO2 emissions to the atmosphere by approximately 80–90% compared to a plant without CCS. If used on a power plant capturing and compressing CO2, other system costs are estimated to increase the cost per watt-hour of energy produced by 21–91% for fossil fuel power plants; and applying the technology to existing plants would be even more expensive, especially if they are far from a sequestration site. As of 2019 there are 17 operating CCS projects in the world, capturing 31.5Mt of CO2 per year, of which 3.7 is stored geologically. Most are industrial not power plants.

It is possible for CCS, when combined with biomass, to result in net negative emissions. A trial of bio-energy with carbon capture and storage (BECCS) at a wood-fired unit in Drax power station in the UK started in 2019: if successful this could remove one tonne per day of CO2 from the atmosphere.

Storage of the CO2 is envisaged either in deep geological formations, or in the form of mineral carbonates. Pyrogenic carbon capture and storage (PyCCS) is also being researched. Deep ocean storage is not used, because it could acidify the ocean. Geological formations are currently considered the most promising sequestration sites. The US National Energy Technology Laboratory (NETL) reported that North America has enough storage capacity for more than 900 years worth of carbon dioxide at current production rates. A general problem is that long term predictions about submarine or underground storage security are very difficult and uncertain, and there is still the risk that some CO2 might leak into the atmosphere.

Capture

Capturing CO2 is most effective at point sources, such as large fossil fuel or biomass energy facilities, industries with major CO2 emissions, natural gas processing, synthetic fuel plants and fossil fuel-based hydrogen production plants. Extracting CO2 from air is also possible, although the far lower concentration of CO2 in air compared to combustion sources presents significant engineering challenges.

Organisms that produce ethanol by fermentation generate cool, essentially pure CO2 that can be pumped underground. Fermentation produces slightly less CO2 than ethanol by weight.

Impurities in CO2 streams, like sulfurs and water, could have a significant effect on their phase behavior and could pose a significant threat of increased corrosion of pipeline and well materials. In instances where CO2 impurities exist, especially with air capture, a scrubbing separation process would be needed to initially clean the flue gas. According to the Wallula Energy Resource Center in Washington state, by gasifying coal, it is possible to capture approximately 65% of carbon dioxide embedded in it and sequester it in a solid form.

Broadly, three different configurations of technologies for capture exist: post-combustion, pre-combustion, and oxyfuel combustion:

• In post combustion capture, the CO2 is removed after combustion of the fossil fuel—this is the scheme that would be applied to fossil-fuel burning power plants. Here, carbon dioxide is captured from flue gases at power stations or other large point sources. The technology is well understood and is currently used in other industrial applications, although not at the same scale as might be required in a commercial scale power station. Post combustion capture is most popular in research because existing fossil fuel power plants can be retrofitted to include CCS technology in this configuration.
• The technology for pre-combustion is widely applied in fertilizer, chemical, gaseous fuel (H₂, CH₄), and power production. In these cases, the fossil fuel is partially oxidized, for instance in a gasifier. The CO from the resulting syngas (CO and H₂) reacts with added steam (H₂O) and is shifted into CO2 and H₂. The resulting CO2 can be captured from a relatively pure exhaust stream. The H₂ can now be used as fuel; the carbon dioxide is removed before combustion takes place. There are several advantages and disadvantages when compared to conventional post combustion carbon dioxide capture. The CO2 is removed after combustion of fossil fuels, but before the flue gas is expanded to atmospheric pressure. This scheme is applied to new fossil fuel burning power plants, or to existing plants where re-powering is an option.^{[citation needed]} The capture before expansion, i.e. from pressurized gas, is standard in almost all industrial CO2 capture processes, at the same scale as required for power plants.
• In oxy-fuel combustion the fuel is burned in oxygen instead of air. To limit the resulting flame temperatures to levels common during conventional combustion, cooled flue gas is recirculated and injected into the combustion chamber. The flue gas consists of mainly carbon dioxide and water vapour, the latter of which is condensed through cooling. The result is an almost pure carbon dioxide stream that can be transported to the sequestration site and stored. Power plant processes based on oxyfuel combustion are sometimes referred to as « zero emission » cycles, because the CO2 stored is not a fraction removed from the flue gas stream (as in the cases of pre- and post-combustion capture) but the flue gas stream itself. A certain fraction of the CO2 generated during combustion will inevitably end up in the condensed water. To warrant the label « zero emission » the water would thus have to be treated or disposed of appropriately.

CO2 separation technologies

Carbon dioxide can be separated out of air or flue gas with absorption, adsorption, membrane gas separation, or gas hydrates technologies. Absorption, or carbon scrubbing, with amines is the dominant capture technology.

Carbon dioxide adsorbs to a MOF (Metal–organic framework) through physisorption or chemisorption based on the porosity and selectivity of the MOF leaving behind a Greenhouse gas poor gas stream that is more environmentally friendly. The carbon dioxide is then stripped off the MOF using temperature swing adsorption (TSA) or pressure swing adsorption (PSA) so the MOF can be reused. Adsorbents and absorbents require regeneration steps where the CO2 is removed from the sorbent or solution that collected it out of the flue gas in order for the sorbent or solution to be reused. Monoethanolamine (MEA) solutions, the leading amine for capturing CO2, have a heat capacity between 3–4 J/g K since they are mostly water. Higher heat capacities add to the energy penalty in the solvent regeneration step. Thus, to optimize a MOF for carbon capture, low heat capacities and heats of adsorption are desired. Additionally, high working capacity and high selectivity are desirable in order to capture as much CO2 as possible from the flue gas. However, there is an energy trade off with selectivity and energy expenditure. As the amount of CO2 captured increases, the energy, and therefore cost, required to regenerate increases. A large drawback of using MOFs for CCS is the limitations imposed by their chemical and thermal stability. Current^[when?] research is looking to optimize MOF properties for CCS, but it has proven difficult to find these optimizations that also result in a stable MOF. Metal reservoirs are also a limiting factor to the potential success of MOFs.

About two thirds of the total cost of CCS is attributed to capture, making it limit the wide-scale deployment of CCS technologies. To optimize a CO2 capture process would significantly increase the feasibility of CCS since the transport and storage steps of CCS are rather mature technologies.

An alternate method under development is chemical looping combustion (CLC). Chemical looping uses a metal oxide as a solid oxygen carrier. Metal oxide particles react with a solid, liquid or gaseous fuel in a fluidized bed combustor, producing solid metal particles and a mixture of carbon dioxide and water vapor. The water vapor is condensed, leaving pure carbon dioxide, which can then be sequestered. The solid metal particles are circulated to another fluidized bed where they react with air, producing heat and regenerating metal oxide particles that are recirculated to the fluidized bed combustor. A variant of chemical looping is calcium looping, which uses the alternating carbonation and then calcination of a calcium oxide based carrier as a means of capturing CO2.

Direct air capture

Main article: Direct air capture

Direct air capture is the process of removing CO2 directly from the ambient air (as opposed to from point sources). Combining DAC with carbon storage could act as a carbon dioxide removal technology and as such would constitute a form of climate engineering if deployed at large scale.

A few engineering proposals have been made for DAC, but work in this area is still in its infancy. A private company Global Research Technologies demonstrated a pre-prototype of air capture technology in 2007. A pilot plant owned by Carbon Engineering has operated in British Columbia, Canada since 2015. An economic study of this plant in 2018 estimated the cost at US$94–$232 per tonne of atmospheric CO
2 removed. Several companies are now working on this approach.

CO₂ transportation

After capture, the CO2 would have to be transported to suitable storage sites. This would most likely be done by pipeline, which is generally the cheapest form of transport for large volumes of CO2.

Ships can also be utilized for transport where pipelines are not feasible, methods which are currently used for transporting CO2 for other applications.

For example, there were approximately 5,800 km of CO2 pipelines in the United States in 2008, and a 160 km pipeline in Norway, used to transport CO2 to oil production sites where it is then injected into older fields to extract oil. This injection of CO2 to produce oil is called enhanced oil recovery. There are also several pilot programs in various stages of development to test the long-term storage of CO2 in non-oil producing geologic formations. As the technology develops, costs, benefits and detractions are changing. According to the United States Congressional Research Service, « There are important unanswered questions about pipeline network requirements, economic regulation, utility cost recovery, regulatory classification of CO2 itself, and pipeline safety. Furthermore, because CO2 pipelines for enhanced oil recovery are already in use today, policy decisions affecting CO2 pipelines take on an urgency that is unrecognized by many. Federal classification of CO2 as both a commodity (by the Bureau of Land Management) and as a pollutant (by the Environmental Protection Agency) could potentially create an immediate conflict which may need to be addressed not only for the sake of future CCS implementation, but also to ensure consistency of future CCS with CO2 pipeline operations today. » In the United Kingdom, the Parliamentary Office of Science and Technology revealed that they would also envisage pipelines as the main transport throughout the UK.

Sequestration

Main article: Carbon sequestration

Various forms have been conceived for permanent storage of CO2. These forms include gaseous storage in various deep geological formations (including saline formations and exhausted gas fields), and solid storage by reaction of CO2 with metal oxides to produce stable carbonates. In the past it was suggested that CO2 could be stored in the oceans, but this would exacerbate ocean acidification and has been made illegal under the London and OSPAR conventions. Ocean storage is no longer considered feasible.

Geological storage

Also known as geo-sequestration, this method involves injecting carbon dioxide, generally in supercritical form, directly into underground geological formations. Oil fields, gas fields, saline formations, unmineable coal seams, and saline-filled basalt formations have been suggested as storage sites. Various physical (e.g., highly impermeable caprock) and geochemical trapping mechanisms would prevent the CO2 from escaping to the surface.

Unmineable coal seams can be used to store CO2 because the CO2 molecules attach to the surface of coal. The technical feasibility, however, depends on the permeability of the coal bed. In the process of absorption the coal releases previously absorbed methane, and the methane can be recovered (enhanced coal bed methane recovery). The sale of the methane can be used to offset a portion of the cost of the CO2 storage. Burning the resultant methane, however, would negate some of the benefit of sequestering the original CO2.

Saline formations contain highly mineralized brines, and have so far been considered of no benefit to humans. Saline aquifers have been used for storage of chemical waste in a few cases. The main advantage of saline aquifers is their large potential storage volume and their common occurrence. The major disadvantage of saline aquifers is that relatively little is known about them, especially compared to oil fields. To keep the cost of storage acceptable, the geophysical exploration may be limited, resulting in larger uncertainty about the aquifer structure. Unlike storage in oil fields or coal beds, no side product will offset the storage cost. Trapping mechanisms such as structural trapping, residual trapping, solubility trapping and mineral trapping may immobilize the CO2 underground and reduce the risk of leakage.

Enhanced oil recovery

Carbon dioxide is often injected into an oil field as an enhanced oil recovery technique, but because carbon dioxide is released when the oil is burned, it is not a carbon neutral process.

Carbon dioxide degrading algae or bacteria

An alternative to geochemical injection would instead be to physically store carbon dioxide in containers with algae or bacteria that could degrade the carbon dioxide. It would ultimately be ideal to exploit the carbon dioxide metabolizing bacterium Clostridium thermocellum in such theoretical CO2 storage containers. Using this bacteria would prevent overpressurization of such theoretical carbon dioxide storage containers.

Mineral storage

This section needs to be updated. Please update this article to reflect recent events or newly available information. (June 2019)

In this process, CO2 exothermically reacts with available metal oxides, which in turn produces stable carbonates (e.g. calcite, magnesite). This process occurs naturally over many years and is responsible for a great amount of surface limestone. The idea of using olivine has been promoted by the geochemist Olaf Schuiling. The reaction rate can be made faster, for example, with a catalyst or by reacting at higher temperatures and/or pressures, or by pre-treatment of the minerals, although this method can require additional energy. The IPCC estimates that a power plant equipped with CCS using mineral storage will need 60–180% more energy than a power plant without CCS.

The economics of mineral carbonation at scale are now being tested in a world-first pilot plant project based in Newcastle, Australia. New techniques for mineral activation and reaction have been developed the GreenMag Group and the University of Newcastle and funded by the New South Wales and Australian Governments to be operational by 2013.

In 2009 it was reported that scientists had mapped 6,000 square miles (16,000 km²) of rock formations in the United States that could be used to store 500 years’ worth of U.S. carbon dioxide emissions. A study on mineral sequestration in the US states:

Carbon sequestration by reacting naturally occurring Mg and Ca containing minerals with CO2 to form carbonates has many unique advantages. Most notabl[e] is the fact that carbonates have a lower energy state than CO2, which is why mineral carbonation is thermodynamically favorable and occurs naturally (e.g., the weathering of rock over geologic time periods). Secondly, the raw materials such as magnesium based minerals are abundant. Finally, the produced carbonates are unarguably stable and thus re-release of CO2 into the atmosphere is not an issue. However, conventional carbonation pathways are slow under ambient temperatures and pressures. The significant challenge being addressed by this effort is to identify an industrially and environmentally viable carbonation route that will allow mineral sequestration to be implemented with acceptable economics.

The following table lists principal metal oxides of Earth’s crust. Theoretically, up to 22% of this mineral mass is able to form carbonates.

Earthen oxide	Percent of crust	Carbonate	Enthalpy change (kJ/mol)
SiO2	59.71
Al2O3	15.41
CaO	4.90	CaCO3	−179
MgO	4.36	MgCO3	−118
Na2O	3.55	Na2CO3	−322
FeO	3.52	FeCO3	−85
K2O	2.80	K2CO3	−393.5
Fe2O3	2.63	FeCO3	112
	21.76	All carbonates

Ultramafic mine tailings are a readily available source of fine-grained metal oxides that can act as artificial carbon sinks to reduce net greenhouse gas emissions in the mining industry. Accelerating passive CO2 sequestration via mineral carbonation may be achieved through microbial processes that enhance mineral dissolution and carbonate precipitation.

Energy requirements

Carbon sequestration adds about $0.18/kWh to the cost of energy, placing it far out of reach of profitability and competitive advantages over renewable power.

In one paper, sequestration consumed 25% of the plant’s rated 600-megawatt output capacity^[clarify]. After adding CO2 capture and compression, the capacity of the coal-fired power plant is reduced to 457 MW.

Leakage

Long term retainment of stored CO2

For well-selected, designed and managed geological storage sites, IPCC estimates that leakage risks are comparable to those associated with current hydrocarbon activity. However, this finding is contested due to a lack of experience in such long-term storage. CO2 could be trapped for millions of years, and although some leakage occurs upwards through the soil, well selected storage sites are likely to retain over 99% of the injected CO2 over 1000 years. Leakage through the injection pipe is a greater risk.

Mineral storage is not regarded as having any risks of leakage. The IPCC recommends that limits be set to the amount of leakage that can take place.

To further investigate the safety of CO2 sequestration, Norway’s Sleipner gas field can be studied, as it is the oldest plant that stores CO2 on an industrial scale. According to an environmental assessment of the gas field which was conducted after ten years of operation, the author affirmed that geosequestration of CO2 was the most definite form of permanent geological storage of CO2:

Available geological information shows absence of major tectonic events after the deposition of the Utsira formation [saline reservoir]. This implies that the geological environment is tectonically stable and a site suitable for carbon dioxide storage. The solubility trapping [is] the most permanent and secure form of geological storage.

In March 2009 StatoilHydro issued a study showing the slow spread of CO2 in the formation after more than 10 years operation.

Phase I of the Weyburn-Midale Carbon Dioxide Project in Weyburn, Saskatchewan, Canada has determined that the likelihood of stored CO2 release is less than one percent in 5,000 years. A January 2011 report, however, claimed evidence of leakage in land above that project. This report was strongly refuted by the IEAGHG Weyburn-Midale CO2 Monitoring and Storage Project, which issued an eight-page analysis of the study, claiming that it showed no evidence of leakage from the reservoir.

To assess and reduce liability for potential leaks, the leakage of stored gasses, particularly carbon dioxide, into the atmosphere may be detected via atmospheric gas monitoring, and can be quantified directly via the eddy covariance flux measurements.

Hazards from sudden accidental leakage of CO2

CCS schemes will involve handling and transportation of CO2 on a hitherto unprecedented scale. A CCS project for a single standard 1,000 MW coal-fired power plant will require capture and transportation of 30,000 tonnes CO2 per day to the storage site. Transmission pipelines may leak or rupture. Pipelines can be fitted with remotely controlled block valves that upon closure will limit the release quantity to the inventory of an isolatable section. For example, a severed 19″ pipeline section 8 km long may release 1,300 tonnes of carbon dioxide in about 3–4 min. At the storage site, the injection pipe can be fitted with non-return valves to prevent an uncontrolled release from the reservoir in case of upstream pipeline damage.

Large-scale releases of CO2 presents asphyxiation risk. In 1953, a release of several thousand tonnes of CO2 – a quantity comparable to an accidental release from a CCS CO2 transmission pipeline – from the Menzengraben salt mine killed a person at distance of 300 meters due to asphyxiation. Malfunction of a carbon dioxide industrial fire suppression system in a large warehouse released 50 t CO2 after which 14 citizens collapsed on the nearby public road. The Berkel en Rodenrijs incident in December 2008 was another example, where a modest release of CO2 from a pipeline under a bridge resulted in the deaths of some ducks sheltering there. In order to measure accidental carbon releases more accurately and decrease the risk of fatalities through this type of leakage, the implementation of CO2 alert meters around the project perimeter has been proposed^{[by whom?]}. The most extreme sudden CO2 release on record took place in 1986 at Lake Nyos.

Monitoring geological sequestration sites

In order to detect carbon dioxide leaks and the effectiveness of geological sequestration sites, different monitoring techniques can be employed to verify that the sequestered carbon stays trapped below the surface in the intended reservoir. Leakage due to injection at improper locations or conditions could result in carbon dioxide being released back into the atmosphere. It is important to be able to detect leaks with enough warning to put a stop to it, and to be able to quantify the amount of carbon that has leaked for purposes such as cap and trade policies, evaluation of environmental impact of leaked carbon, as well as accounting for the total loss and cost of the process. To quantify the amount of carbon dioxide released, should a leak occur, or to closely watch stored CO2, there are several monitoring methods that can be done at both the surface and subsurface levels.

Subsurface monitoring

In subsurface monitoring, there are direct and indirect methods to determine the amount of CO2 in the reservoir. A direct method would be drilling deep enough to collect a fluid sample. This drilling can be difficult and expensive due to the physical properties of the rock. It also only provides data at a specific location. Indirect methods would be to send sound or electromagnetic waves down to the reservoir where it is then reflected back up to be interpreted. This approach is also expensive but it provides data over a much larger region; it does however lack precision. Both direct and indirect monitoring can be done intermittently or continuously.

Seismic monitoring

Seismic monitoring is a type of indirect subsurface monitoring. It is done by creating vibrational waves either at the surface using a vibroseis truck, or inside a well using spinning eccentric mass. These vibrational waves then propagate through the geological layers and reflect back creating patterns that are read and interpreted by seismometers. It can identify migration pathways of the CO2 plume. Two examples of monitoring geological sequestration sites using seismic monitoring are the Sleipner sequestration project and the Frio CO2 Injection test. Although this method can confirm the presence of CO2 in a given region, it cannot determine the specifics of the environment or concentration of CO2.

Surface monitoring

Eddy covariance is a surface monitoring technique that measures the flux of CO2 from the ground’s surface. It involves measuring CO2 concentrations as well as vertical wind velocities using an anemometer. This provides a measure of the total vertical flux of CO2. Eddy covariance towers could potentially detect leaks, however, the natural carbon cycle, such as photosynthesis and the respiration of plants, would have to be accounted for and a baseline CO2 cycle would have to be developed for the location of monitoring. An example of Eddy covariance techniques used to monitor carbon sequestration sites is the Shallow Release test. Another similar approach is utilizing accumulation chambers. These chambers are sealed to the ground with an inlet and outlet flow stream connected to a gas analyzer. This also measures the vertical flux of CO2. The disadvantage of accumulation chambers is its inability to monitor a large region which is necessary in detecting CO2 leaks over the entire sequestration site.

InSAR monitoring

InSAR monitoring is another type of surface monitoring. It involves a satellite sending signals down to the Earth’s surface where it is reflected back to the satellite’s receiver. From this, the satellite is able to measure the distance to that point. In CCS, the injection of CO2 in deep sublayers of geological sites creates high pressures. These high pressured, fluid filled layers affect those above and below it resulting in a change of the surface landscape. In areas of stored CO2, the ground’s surface often rises due to the high pressures originating in the deep subsurface layers. These changes in elevation of the Earth’s surface corresponds to a change in the distance from the inSAR satellite which is then detectable and measurable.

Carbon capture and utilization (CCU)

Main article: Carbon capture and utilization

Carbon Capture and Utilization (CCU) differs from CCS as CCU does not result in geological storage of carbon dioxide. Carbon capture and utilization may offer a response to the global challenge of significantly reducing greenhouse gas emissions from major stationary (industrial) emitters. CCU aims to use the carbon dioxide produced to make other substances (e.g. plastics, concrete, biofuel) such that the whole process is carbon neutral.

Technologies under development, such as Bio CCS Algal Synthesis, utilises pre-smokestack CO2 (such as from a power station) as a useful feedstock input to the production of oil-rich algae in solar membranes to produce oil for plastics and transport fuel (including aviation fuel), and nutritious stock-feed for farm animal production. The CO2 and other captured greenhouse gases are injected into the membranes containing waste water and select strains of algae causing, together with sunlight or UV light, an oil rich biomass that doubles in mass every 24 hours^{[citation needed]}. The Bio CCS Algal Synthesis process is based on earth science photosynthesis: the technology is entirely retrofittable and collocated with the emitter, and the capital outlays may offer a return upon investment due to the high value commodities produced (oil for plastics, fuel and feed). Bio CCS Algal Synthesis test facilities were being trialed^{[further explanation needed]} at Australia’s three largest coal-fired power stations (Tarong, Queensland; Eraring, NSW; Loy Yang, Victoria) using piped pre-emission smokestack CO2 (and other greenhouse gases) as feedstock to grow oil-rich algal biomass in enclosed membranes for the production of plastics, transport fuel and nutritious animal feed.

Another potentially useful way of dealing with industrial sources of CO2 is to convert it into hydrocarbons where it can be stored or reused as fuel or to make plastics. There are a number of projects investigating this possibility. For instance, several Carbon dioxide scrubbing variants based on potassium carbonate allow capture of carbon dioxide which can later be used to create liquid fuels, even though this process requires a substantial energy input. The creation of fuel from atmospheric CO2 does not result in carbon dioxide removal as carbon dioxide is re-released when the fuel is burned. For this reason, synfuels do not represent a climate engineering technique, but still represent a potentially useful source of net-zero-carbon fuel.

Other uses are the production of stable carbonates from silicates (e.g. olivine produces magnesium carbonate). These processes are still under research and development.

Considering the different potential options for capture and utilization, research suggests that those involving chemicals, fuels and microalgae have limited potential for CO2 removal, while those that involve construction materials and agricultural use can be more effective.

Single step methods: methanol

A proven process to produce a hydrocarbon is to make methanol. Methanol is easily synthesized from CO2 and H₂. Based on this fact the idea of a methanol economy was born.

Single step methods: hydrocarbons

At the department of Industrial Chemistry and Engineering of Materials at the University of Messina, Italy, there is a project to develop a system which works like a fuel-cell in reverse, whereby a catalyst is used that enables sunlight to split water into hydrogen ions and oxygen gas. The ions cross a membrane where they react with the CO2 to create hydrocarbons. ^{[further explanation needed]}

Two step methods

If CO2 is heated to 2400 °C, it splits into carbon monoxide (CO) and oxygen. The Fischer-Tropsch process can then be used to convert the CO into hydrocarbons. The required temperature can be achieved by using a chamber containing a mirror to focus sunlight on the gas. Rival teams are developing such chambers, at Solarec and at Sandia National Laboratories, both based in New Mexico. ^{[further explanation needed]} According to Sandia these chambers could provide enough fuel to power 100% of domestic vehicles using 5800 km²; unlike biofuels this would not take fertile land away from crops but would be land that is not being used for anything else. James May, the British TV presenter, visited a demonstration plant in a programme in his Big Ideas series.

CO₂ electrolysis

CO₂ can be captured and converted to carbon-neutral fuels in an aqueous catalysis process. It is possible to convert CO₂ in this way directly to ethanol, which can then be upgraded to gasoline and jet fuel

Example CCS projects

Industrial-scale projects

As of September 2017, the Global CCS Institute identified 37 large-scale CCS facilities in its 2017 Global Status of CCS report which is a net decrease of one project since its 2016 Global Status of CCS report. 21 of these projects are in operation or in construction capturing more than 30 million tonnes of CO₂ per annum. For the most current information, see Large Scale CCS facilities on the Global CCS Institute’s website. For information on EU projects see Zero Emissions Platform website. Some of the most notable CCS large scale facilities include:

Terrell Natural Gas Processing Plant – US

Opening in 1972, the Terrell plant in Texas, United States is the oldest operating industrial CCS project as of 2017. CO₂ is captured during gas processing and transported primarily via the Val Verde pipeline where it is eventually injected at Sharon Ridge oil field and other secondary sinks for use in enhanced oil recovery. The facility captures an average of somewhere between 0.4 and 0.5 million tons of CO₂ per annum.

Enid Fertilizer – US

Beginning its operation in 1982, the facility owned by the Koch Nitrogen company is the second oldest large scale CCS facility still in operation. The CO₂ that is captured is a high purity byproduct of nitrogen fertilizer production. The process is made economical by transporting the CO₂ to oil fields for EOR.

Shute Creek Gas Processing Facility – US

Around 7 million tonnes per annum of carbon dioxide are recovered from ExxonMobil‘s Shute Creek gas processing plant in Wyoming, and transported by pipeline to various oil fields for enhanced oil recovery. This project has been operational since 1986 and has the second largest CO₂ capture capacity of any CCS facility in the world.

Sleipner CO₂ Injection – Norway

Sleipner is a fully operational offshore gas field with CO₂ injection initiated in 1996. CO₂ is separated from produced gas and reinjected in the Utsira saline aquifer (800–1000 m below ocean floor) above the hydrocarbon reservoir zones. This aquifer extends much further north from the Sleipner facility at its southern extreme. The large size of the reservoir accounts for why 600 billion tonnes of CO₂ are expected to be stored, long after the Sleipner natural gas project has ended. The Sleipner facility is the first project to inject its captured CO₂ into a geological feature for the purpose of storage rather than economically compromising EOR.

Century Plant – US

Occidental Petroleum, along with Sandridge Energy, is operating a West Texas hydrocarbon gas processing plant and related pipeline infrastructure that provides CO₂ for use in EOR. With a total CO₂ capture capacity of 8.4 Mt/a, the Century plant is the largest single industrial source CO₂ capture facility in the world.

Abu Dhabi – United Arab Emirates

After the success of their pilot plant operation in November 2011, the Abu Dhabi National Oil Company and Abu Dhabi Future Energy Company moved to create the first commercial CCS facility in the iron and steel industry. The CO₂, a byproduct of the iron making process, is transported via a 50 km pipeline to Abu Dhabi National Oil Company oil reserves for EOR. The total carbon capture capacity of the facility is 800,000 tonnes per year.

Petra Nova – US

The Petra Nova project is a billion dollar endeavor taken upon by NRG Energy and JX Nippon to partially retrofit their jointly owned W.A Parish coal-fired power plant with post-combustion carbon capture. The plant, which is located in Thompsons, Texas (just outside of Houston), entered commercial service in 1977, and carbon capture began operation on 10 January 2017. The WA Parish unit 8 generates 240 MW and 90% of the CO₂ (or 1.4 million tonnes) is captured per year. The carbon dioxide captured (99% purity) from the power plant is compressed and piped about 82 miles to West Ranch Oil Field, Texas, where it will be used for enhanced oil recovery. The field has a capacity of 60 million barrels of oil and has increased its production from 300 barrels per day to 4000 barrels daily. This project is expected to run for at least another 20 years.

Illinois Industrial – US

The Illinois Industrial Carbon Capture and Storage project is one of five currently operational facilities dedicated to geological CO₂ storage. The project received a 171 million dollar investment from the DOE and over 66 million dollars from the private sector. The CO₂ is a byproduct of the fermentation process of corn ethanol production and is stored 7000 feet underground in the Mt. Simon Sandstone saline aquifer. The facility began its sequestration in April 2017 and has a carbon capture capacity of 1 Mt/a.

In Salah CO₂ injection – Algeria

In Salah was a fully operational onshore gas field with CO₂ injection. CO₂ was separated from produced gas and reinjected into the Krechba geologic formation at a depth of 1,900m. Since 2004, about 3.8 Mt of CO₂ has been captured during natural gas extraction and stored. Injection was suspended in June 2011 due to concerns about the integrity of the seal, fractures and leakage into the caprock, and movement of CO₂ outside of the Krechba hydrocarbon lease. This project is notable for its pioneering in the use of Monitoring, Modeling, and Verification (MMV) approaches.

NET Power Facility. La Porte, Tx

NET Power Demonstration Facility – US

The NET Power Demonstration Facility is an oxy-combustion natural gas power plant that operates by the Allam power cycle. Due to its unique design, the plant is able to reduce its air emissions to zero by producing a near pure stream of CO₂ as waste that can be shipped off for storage or utilization. The plant first fired in May 2018.

Developing projects

ANICA – Advanced Indirectly Heated Carbonate Looping Process

The ANICA Project is focused on developing economically feasible carbon capture technology for lime and cement plants, which are responsible for 5% of the total anthropogenic carbon dioxide emissions. Since the year 2019, a consortium of 12 partners from Germany, United Kingdom and Greece has been working on the developing novel integration concepts of the state-of-the-art indirectly heated carbonate lopping (IHCaL) process in cement and lime production. The project aims at lowering the energy penalty and CO₂ avoidance costs for CO₂ capture from lime and cement plants. Within 36 months, the project will bring the IHCaL technology to a high level of technical maturity by carrying out long-term pilot tests in industry-relevant environments and deploying accurate 1D and 3D simulations.

Port of Rotterdam CCUS Backbone Initiative

Expected in 2021, the Port of Rotterdam CCUS Backbone Initiative aims to implement a « backbone » of shared CCS infrastructure for use by several businesses located around the Port of Rotterdam in Rotterdam, Netherlands. The project, overseen by the Port of Rotterdam, natural gas company Gasunie, and the EBN, looks to capture and sequester 2 million tons of carbon dioxide per year starting in 2020 and increase this number in future years. Although dependent on the participation of companies, the goal of this project is to greatly reduce the carbon footprint of the industrial sector of the Port of Rotterdam and establish a successful CCS infrastructure in the Netherlands following the recently canceled ROAD project. Carbon dioxide captured from local chemical plants and refineries will both be sequestered in the North Sea seabed. The possibility of a CCU initiative has also been considered, in which the captured carbon dioxide will be sold to horticultural firms, who will use it to speed up plant growth, as well as other industrial users.

Alternative carbon capture methods

Although the majority of industrial carbon capture is done using post-combustion capture, several notable projects exist that utilize a variety of alternative capture methods. Several smaller-scale pilot and demonstration plants have been constructed for research and testing using these methods, and a handful of proposed projects are in early development on an industrial scale. Some of the most notable alternative carbon capture projects include:

Climeworks Direct Air Capture Plant and CarbFix2 Project

Climeworks opened the first commercial direct air capture plant in Zürich, Switzerland. Their process involves capturing carbon dioxide directly from ambient air using a patented filter, isolating the captured carbon dioxide at high heat, and finally transporting it to a nearby greenhouse as a fertilizer. The plant is built near a waste recovery facility that uses its excess heat to power the Climeworks plant.

Climeworks is also working with Reykjavik Energy on the CarbFix2 project with funding from the European Union. This project, located in Hellisheidi, Iceland, uses direct air capture technology to geologically store carbon dioxide by operating in conjunction with a large geothermal power plant. Once carbon dioxide is captured using Climeworks’ filters, it is heated using heat from the geothermal plant and bound to water. The geothermal plant then pumps the carbonated water into rock formations underground where the carbon dioxide reacts with basaltic bedrock and forms carbonite minerals.

Duke Energy East Bend Station

Researchers at the Center for Applied Energy Research of the University of Kentucky are currently^[when?] developing the algae-mediated conversion of coal-fired power plant flue gas to drop-in hydrocarbon fuels. Through their work, these researchers have proven that the carbon dioxide within flue gas from coal-fired power plants can be captured using algae, which can be subsequently harvested and utilized, e.g. as a feedstock for the production of drop-in hydrocarbon fuels.

Canada

Canadian governments have committed $1.8 billion for the sake of funding different CCS projects over the span of the last decade.^[when?] The main governments and programs responsible for the funding are the federal government’s Clean Energy Fund, Alberta’s Carbon Capture and Storage fund, and the governments of Saskatchewan, British Columbia, and Nova Scotia. Canada also works closely with the United States through the U.S.–Canada Clean Energy Dialogue launched by the Obama administration in 2009.

Alberta

This section needs to be updated. Please update this article to reflect recent events or newly available information. (June 2019)

Alberta has committed $170 million in 2013/2014 – and a total of $1.3 billion over 15 years – to fund two large-scale CCS projects that will help reduce CO₂ emissions from oil sands refining.

Alberta Carbon Trunk Line Project

The Alberta Carbon Trunk Line Project (ACTL), pioneered by Enhance Energy, consists of a 240 km pipeline that will collect carbon dioxide from various sources in Alberta and transport it to Clive oil fields for use in EOR (enhanced oil recovery) and permanent storage. This CAN$1.2 billion project will be collecting carbon dioxide initially from the Redwater Fertilizer Facility and the Sturgeon Refinery. The projections for ACTL make it the largest carbon capture and sequestration project in the world, with an estimated full capture capacity of 14.6 Mtpa. Construction plans for the ACTL are in their final stages and capture and storage is expected to start sometime in 2019.

Quest Carbon Capture and Storage Project

The Quest Carbon Capture and Storage Project was developed by Shell for use in the Athabasca Oil Sands Project. It is cited as being the world’s first commercial-scale CCS project.^[120] Construction for the Quest Project began in 2012 and ended in 2015. The capture unit is located at the Scotford Upgrader in Alberta, Canada, where hydrogen is produced to upgrade bitumen from oil sands into synthetic crude oil. The steam methane units that produce the hydrogen also emit CO₂ as a byproduct. The capture unit captures the CO₂ from the steam methane unit using amine absorption technology, and the captured CO₂ is then transported to Fort Saskatchewan where it is injected into a porous rock formation called the Basal Cambrian Sands for permanent sequestration. Since beginning operation in 2015, the Quest Project has stored 3 Mt CO₂ and will continue to store 1 Mtpa for as long as it is operational.

British Columbia

British Columbia has been making strides with regards to reducing their carbon emissions. The province implemented North America’s first large-scale carbon tax in 2008. An updated carbon tax in 2018 set the price at $35 per tonne of carbon dioxide equivalent emissions. This tax will increase by $5 every year until it reaches $50 in 2021. Carbon taxes will make carbon capture and sequestration projects more financially feasible for the future.

Saskatchewan

Boundary Dam Power Station Unit 3 Project

Boundary Dam Power Station, owned by SaskPower, is a coal fired station that was originally commissioned back in 1959. In 2010, SaskPower committed to retrofitting the lignite-powered Unit 3 with a carbon capture unit in order to reduce CO₂ emissions. The project was completed in 2014. The retrofit utilized a post-combustion amine absorption technology in order to capture the CO₂. The captured CO₂ was planned to be sold to Cenovus to be used for EOR in Weyburn field. Any CO₂ not used for EOR was planned to be used by the Aquistore project and stored in deep saline aquifers. Many complications has kept Unit 3 and this project from being online as much as expected, but between August 2017 – August 2018, Unit 3 was online for 65% of every day on average. Since the start of operation, the Boundary Dam project has captured over 1 Mt CO₂ and has a nameplate capacity of capture of 1 Mtpa. SaskPower does not intend to retrofit the rest of its units as they are mandated to be phased out by the government by 2024. The future of the one retrofitted unit at Boundary Dam Power Station is unclear.

Great Plains Synfuel Plant and Weyburn-Midale Project

The Great Plains Synfuel Plant, owned by Dakota Gas, is a coal gasification operation that produces synthetic natural gas and various petrochemicals from coal. The plant has been in operation since 1984, but carbon capture and storage did not start until 2000. In 2000, Dakota Gas retrofitted the plant with a carbon capture unit in order to sell the CO₂ to Cenovus and Apache Energy, who intended to use the CO₂ for enhanced oil recovery (EOR) in the Weyburn and Midale fields in Canada. The Midale fields are injected with 0.4 Mtpa and the Weyburn fields are injected with 2.4 Mtpa for a total injection capacity of 2.8 Mtpa. The Weyburn-Midale Carbon Dioxide Project (or IEA GHG Weyburn-Midale CO₂ Monitoring and Storage Project), an international collaborative scientific study conducted between 2000–2011 also took place here, but injection has continued even after the study has concluded. Since 2000, over 30 Mt CO₂ has been injected and both the plant and EOR projects are still operational.

Pilot projects

This section needs to be updated. Please update this article to reflect recent events or newly available information. (February 2019)

The Alberta Saline Aquifer Project (ASAP), Husky Upgrader and Ethanol Plant pilot, Heartland Area Redwater Project (HARP), Wabamun Area Sequestration Project (WASP), and Aquistore.^{[failed verification]}

Another Canadian initiative is the Integrated CO₂ Network (ICO₂N), a group of industry participants providing a framework for carbon capture and storage development in Canada. Other Canadian organizations related to CCS include CCS 101, Carbon Management Canada, IPAC CO₂, and the Canadian Clean Power Coalition.

Netherlands

Developed in the Netherlands, an electrocatalysis by a copper complex helps reduce carbon dioxide to oxalic acid.

Norway

In Norway, the CO2 Technology Centre (TCM) at Mongstad began construction in 2009, and completed in 2012. It includes two capture technology plants (one advanced amine and one chilled ammonia), both capturing fluegas from two sources. This includes a gas-fired power plant and refinery cracker fluegas (similar to coal-fired power plant fluegas).

In addition to this, the Mongstad site was also planned to have a full-scale CCS demonstration plant. The project was delayed to 2014, 2018, and then indefinitely. The project cost rose to US$985 million. Then in October 2011, Aker Solutions’ wrote off its investment in Aker Clean Carbon, declaring the carbon sequestration market to be « dead ».

On 1 October 2013 Norway asked Gassnova not to sign any contracts for Carbon capture and storage outside Mongstad.

In 2015 Norway was reviewing feasibility studies and hoping to have a full-scale carbon capture demonstration project by 2020.

United States

This section needs to be updated. Please update this article to reflect recent events or newly available information. (May 2019)

In October 2009, the U.S. Department of Energy awarded grants to twelve Industrial Carbon Capture and Storage (ICCS) projects to conduct a Phase 1 feasibility study. The DOE plans to select 3 to 4 of those projects to proceed into Phase 2, design and construction, with operational startup to occur by 2015. Battelle Memorial Institute, Pacific Northwest Division, Boise, Inc., and Fluor Corporation are studying a CCS system for capture and storage of CO2 emissions associated with the pulp and paper production industry. The site of the study is the Boise White Paper L.L.C. paper mill located near the township of Wallula in Southeastern Washington State. The plant generates approximately 1.2 MMT of CO2 annually from a set of three recovery boilers that are mainly fired with black liquor, a recycled byproduct formed during the pulping of wood for paper-making. Fluor Corporation will design a customized version of their Econamine Plus carbon capture technology. The Fluor system also will be designed to remove residual quantities of remnant air pollutants from stack gases as part of the CO2 capture process. Battelle is leading preparation of an Environmental Information Volume (EIV) for the entire project, including geologic storage of the captured CO2 in deep flood basalt formations that exist in the greater region. The EIV will describe the necessary site characterization work, sequestration system infrastructure, and monitoring program to support permanent sequestration of the CO2 captured at the plant.^{[needs update]}

In addition to individual carbon capture and sequestration projects, there are a number of United States programs designed to research, develop, and deploy CCS technologies on a broad scale. These include the National Energy Technology Laboratory’s (NETL) Carbon Sequestration Program, regional carbon sequestration partnerships and the Carbon Sequestration Leadership Forum (CSLF).

SECARB

In October 2007, the Bureau of Economic Geology at the University of Texas at Austin received a 10-year, $38 million subcontract to conduct the first intensively monitored long-term project in the United States studying the feasibility of injecting a large volume of CO
2 for underground storage. The project is a research program of the Southeast Regional Carbon Sequestration Partnership (SECARB), funded by the National Energy Technology Laboratory of the U.S. Department of Energy (DOE).

The SECARB partnership will demonstrate CO2 injection rate and storage capacity in the Tuscaloosa-Woodbine geologic system that stretches from Texas to Florida. The region has the potential to store more than 200 billion tons^[vague] of CO2 from major point sources in the region, equal to about 33 years of overall United States emissions at present rates. Beginning in fall 2007, the project will inject CO2 at the rate of one million tons^[vague] per year, for up to 1.5 years, into brine up to 10,000 feet (3,000 m) below the land surface near the Cranfield oil field, which lays about 15 miles (24 km) east of Natchez, Mississippi. Experimental equipment will measure the ability of the subsurface to accept and retain CO2.

The $1.4 billion FutureGen power generation and carbon sequestration demonstration project, announced in 2003 by President George W. Bush, was cancelled in 2015, due to delays and inability to raise required private funding.

Kemper Project

The Kemper Project, is a natural gas-fired power plant under construction in Kemper County, Mississippi, which was originally planned as a coal-fired plant. Mississippi Power, a subsidiary of Southern Company, began construction of the plant in 2010. The project was considered central to President Obama’s Climate Plan. Had it become operational as a coal plant, the Kemper Project would have been a first-of-its-kind electricity plant to employ gasification and carbon capture technologies at this scale. The emission target was to reduce CO2 to the same level an equivalent natural gas plant would produce. However, in June 2017 the proponents – Southern Company and Mississippi Power – announced that they would only burn natural gas at the plant at this time.

The plant experienced project management problems. Construction was delayed and the scheduled opening was pushed back over two years, at a cost of $6.6 billion—three times original cost estimate. According to a Sierra Club analysis, Kemper is the most expensive power plant ever built for the watts of electricity it will generate.

United Kingdom

This section needs to be updated. Please update this article to reflect recent events or newly available information. (September 2019)

In the Northeast of England, The Northeast of England Process Industry Cluster (NEPIC) of commodity chemical manufacturers are amongst the largest single point producers of carbon dioxide in the United Kingdom and they have created within NEPIC the Process Industry Carbon Capture and Storage Initiative (PICCSI) to study the possibility of a carbon capture and storage (CCS) solution being provided for the chemical and steel manufacturing industry on Teesside, as well as for any carbon based energy production. This CCS technology option is being considered as a result of climate change regulations and the carbon taxation that could become a prohibitive cost for such energy intensive industries.

The Crown Estate is responsible for storage rights on the UK continental shelf and it has facilitated work on offshore carbon dioxide storage technical and commercial issues.

China

Due to its large abundance in northern China, coal accounts for around 60% of the country’s energy consumption. The majority of CO₂ emissions in China come from either coal-fired power plants or coal-to-chemical processes (e.g. the production of synthetic ammonia, methanol, fertilizer, natural gas, and CTLs). According to the IEA, around 385 out of China’s 900 gigawatts of coal-fired power capacity are near locations suitable for carbon dioxide storage. In order to take advantage of these suitable storage sites (many of which are conducive to enhanced oil recovery) and reduce its carbon dioxide emissions, China has started to develop several CCS projects. Three such facilities are already operational or in late stages of construction, but these projects draw CO₂ from natural gas processing or petrochemical production. At least eight more facilities are in early planning and development, most of which will capture emissions from power plants. Almost all of these CCS projects, regardless of CO₂ source, inject carbon dioxide for the purpose of EOR.

CNPC Jilin Oil Field

China’s very first carbon capture project is the Jilin oil field in Songyuan, Jilin Province. It started as a pilot EOR project in 2009, but has since developed into a commercial operation for the China National Petroleum Corporation (CNPC), with the final phase of development completed in 2018. The source of carbon dioxide is the nearby Changling gas field, from which natural gas with about 22.5% CO₂ is extracted. After separation at the natural gas processing plant, the carbon dioxide is transported to Jilin via pipeline and injected for a 37% enhancement in oil recovery at the low-permeability oil field. At commercial capacity, the facility currently injects 0.6 MtCO₂ per year, and it has injected a cumulative total of over 1.1 million tonnes over its lifetime.

Sinopec Qilu Petrochemical CCS Project

The Sinopec Qilu Petrochemical Corporation is a large energy and chemical company currently developing a carbon capture unit whose first phase will be operational in 2019. The facility is located in Zibo City, Shandong Province, where there is a fertilizer plant that produces large amounts of carbon dioxide from coal/coke gasification. The CO₂ is to be captured by cryogenic distillation and will be transported via pipeline to the nearby Shengli oil field for enhanced oil recovery. Construction of the first phase has already begun, and upon completion it will capture and inject 0.4 MtCO₂ per year. The Shengli oil field is also expected to be the destination for carbon dioxide captured from Sinopec’s Shengli power plant, although this facility is not expected to be operational until the 2020s.

Yanchang Integrated CCS Project

Yanchang Petroleum is developing carbon capture facilities at two coal-to-chemicals plants in Yulin City, Shaanxi Province. The first capture plant is capable of capturing 50,000 tonnes CO₂ per year and was finished in 2012. Construction on the second plant started in 2014 and is expected to be finished in 2020, with a capacity of 360,000 tonnes captured per year. This carbon dioxide will be transported to the Ordos Basin, one of the largest coal, oil, and gas-producing regions in China with a series of low- and ultra-low permeability oil reservoirs. Lack of water in this area has limited the use of water flooding for EOR, so the injected CO₂ will support the development of increased oil production from the basin.

Germany

This section needs to be updated. Please update this article to reflect recent events or newly available information. (February 2019)

The German industrial area of Schwarze Pumpe, about 4 kilometres (2.5 mi) south of the city of Spremberg, is home to the world’s first demonstration CCS coal plant, the Schwarze Pumpe power station. The mini pilot plant is run by an Alstom-built oxy-fuel boiler and is also equipped with a flue gas cleaning facility to remove fly ash and sulfur dioxide. The Swedish company Vattenfall AB invested some €70 million in the two-year project, which began operation 9 September 2008. The power plant, which is rated at 30 megawatts, is a pilot project to serve as a prototype for future full-scale power plants. 240 tonnes a day of CO2 are being trucked 350 kilometers (220 mi) where it will be injected into an empty gas field. Germany’s BUND group called it a « fig leaf« . For each tonne of coal burned, 3.6 tonnes of carbon dioxide is produced. The CCS program at Schwarze Pumpe ended in 2014 due to nonviable costs and energy use.

German utility RWE operates a pilot-scale CO2 scrubber at the lignite-fired Niederaußem power station built in cooperation with BASF (supplier of detergent) and Linde engineering.

In Jänschwalde, Germany, a plan is in the works for an Oxyfuel boiler, rated at 650 thermal MW (around 250 electric MW), which is about 20 times more than Vattenfall’s 30 MW pilot plant under construction, and compares to today’s largest Oxyfuel test rigs of 0.5 MW. Post-combustion capture technology will also be demonstrated at Jänschwalde.

Australia

Main article: Carbon capture and storage in Australia

This section needs to be updated. Please update this article to reflect recent events or newly available information. (February 2019)

The Federal Resources and Energy Minister Martin Ferguson opened the first geosequestration project in the southern hemisphere in April 2008. The demonstration plant is near Nirranda South in South Western Victoria. (35.31°S 149.14°E) The plant is owned by CO2CRC Limited. CO2CRC is a non profit research collaboration supported by government and industry. The project has stored and monitored over 80,000 tonnes of carbon dioxide-rich gas which was extracted from a natural gas reservoir via a well, compressed and piped 2.25 km to a new well. There the gas has been injected into a depleted natural gas reservoir approximately two kilometers below the surface. The project has moved to a second stage and is investigating carbon dioxide trapping in a saline aquifer 1500 meters below the surface. The Otway Project is a research and demonstration project, focused on comprehensive monitoring and verification.

This plant does not propose to capture CO2 from coal-fired power generation, though two CO2CRC demonstration projects at a Victorian power station and research gasifier are demonstrating solvent, membrane, and adsorbent capture technologies from coal combustion. Currently, only small-scale projects are storing CO2 stripped from the products of combustion of coal burnt for electricity generation at coal-fired power stations. Work currently being carried out by the GreenMag Group and the University of Newcastle and funded by the New South Wales and Australian Governments and industry intends to have a working mineral carbonation pilot plant in operation by 2013.

Gorgon Carbon Dioxide Injection Project

The Gorgon Carbon Dioxide Injection Project is part of the Gorgon Project, the world’s largest natural gas project. The Gorgon Project, located on Barrow Island in Western Australia, includes a liquefied natural gas (LNG) plant, a domestic gas plant, and a Carbon Dioxide Injection Project.

The initial carbon dioxide injections were planned to take place by the end of 2017. Once launched, the Gorgon Carbon Dioxide Injection Project will be the world’s largest CO2 injection plant, with an ability to store up to 4 million tons of CO2 per year – approximately 120 million tons over the project’s lifetime, and 40 percent of total Gorgon Project emissions.^{[citation needed]}

The project started extracting gas in February 2017, but carbon capture and storage is now not expected to begin until the first half of 2019, requiring a further five million tonnes of CO2 to be released, because:

A Chevron report to the State Government released yesterday said start-up checks this year found leaking valves, valves that could corrode and excess water in the pipeline from the LNG plant to the injection wells that could cause the pipeline to corrode.

The Planet Venus

Terraforming of Venus by removing CO₂ from the atmosphere was first proposed in academic circles by the astronomer Carl Sagan in 1961, although fictional treatments, such as The Big Rain of The Psychotechnic League by novelist Poul Anderson, preceded it. Adjustments to the existing environment of Venus to support human life would require at least three major changes to the planet’s atmosphere: Reducing Venus’s surface temperature of 462 °C (864 °F), eliminating most of the planet’s dense 9.2 MPa (91 atm) carbon dioxide and sulfur dioxide atmosphere via removal or conversion to some other form, and the addition of breathable oxygen to the atmosphere. These three changes are closely interrelated, because Venus’s extreme temperature is due to the high pressure of its dense atmosphere, and the greenhouse effect.

Political debate

CCS has met some political opposition from critics who say large-scale CCS deployment is risky and expensive and that a better option is renewable energy. Some environmental groups have said there is a risk of leakage during the extremely long storage time required, so have compared CCS technology to storing dangerous radioactive waste from nuclear power stations.

The use of CCS could reduce CO2 emissions from the stacks of coal power plants by 85–90% or more, but it has no effect on CO2 emissions due to the mining and transport of coal. It will actually « increase such emissions and of air pollutants per unit of net delivered power and will increase all ecological, land-use, air-pollution, and water-pollution impacts from coal mining, transport, and processing, because the CCS system requires 25% more energy, thus 25% more coal combustion, than does a system without CCS ».

Additionally, when the net energy efficiencies of CCS fossil-fuel power plants and renewable electricity were compared, a 2019 study found CCS plants to be less effective. The electrical energy returned on energy invested ratios (EROEI) of both production methods were estimated, accounting for their operational and infrastructural energy costs. Renewable electricity production included solar and wind with sufficient energy storage. Thus, in climate crisis mitigation, rapid expansion of scalable renewable electricity and storage would be preferable over fossil-fuel CCS.

On one hand, Greenpeace claims that CCS could lead to a doubling of coal plant costs. It is also claimed by opponents to CCS that money spent on CCS will divert investments away from other solutions to climate change. On the other hand, BECCS is used in some IPCC scenarios to help meet mitigation targets such as 1.5 degrees C.

Use for heavy industry

In some countries, such as the UK, although CCS will be trialled for gas-fired power stations it will also be considered to help with decarbonization of industry and heating.

Cost

This section needs to be updated. Please update this article to reflect recent events or newly available information. (February 2019)

The reasons that CCS is expected to cause price increases if used on gas-fired power plants are several. Firstly, the increased energy requirements of capturing and compressing CO2 significantly raises the operating costs of CCS-equipped power plants. In addition, there are added investment and capital costs.

The increased energy required for the carbon capturing process is also called an energy penalty. It has been estimated that about 60% of the energy penalty originates from the capture process itself, 30% comes from compression of CO2, while the remaining 10% comes from electricity requirements for necessary pumps and fans. CCS technology is expected to use between 10 and 40 percent of the energy produced by a power station. CCS would increase the fuel requirement of a plant with CCS by about 15% for a gas-fired plant. The cost of this extra fuel, as well as storage and other system costs, are estimated to increase the costs of energy from a power plant with CCS by 30–60%, depending on the specific circumstances.

And as with most chemical plants, constructing CCS units is capital intensive. Pre-commercial CCS demonstration projects are likely to be more expensive than mature CCS technology; the total additional costs of an early large-scale CCS demonstration project are estimated to be €0.5–1.1 billion per project over the project lifetime. Other applications are possible. CCS was trialled for coal-fired plants in the early 21st century but was found to be economically unviable in most countries (as of 2019 trials are still ongoing in China but face transport and storage logistical challenges).

Cost of electricity generated by different sources including those incorporating CCS technologies can be found in cost of electricity by source.

As of 2018 a carbon price of at least 100 euros has been estimated to be needed for industrial CCS to be viable.

According to UK government estimates made in the late 2010s, carbon capture (without storage) is estimated to add 7 GBP per Mwh by 2025 to the cost of electricity from a modern gas-fired power plant: however most CO2 will need to be stored so in total the increase in cost for gas or biomass generated electricity is around 50%.

Possible business models for industrial carbon capture include:

Contract for Difference CfDC CO2 certificate strike price

Cost Plus open book

Regulated Asset Base (RAB)

Tradeable tax credits for CCS

Tradeable CCS certificates + obligation

Creation of low carbon market

Governments around the world have provided a range of different types of funding support to CCS demonstration projects, including tax credits, allocations and grants. The funding is associated with both a desire to accelerate innovation activities for CCS as a low-carbon technology and the need for economic stimulus activities.

Financing CCS via the Clean Development Mechanism

One way to finance future CCS projects could be through the Clean Development Mechanism of the Kyoto Protocol. At COP16 in 2010, The Subsidiary Body for Scientific and Technological Advice, at its thirty-third session, issued a draft document recommending the inclusion of Carbon dioxide capture and storage in geological formations in Clean Development Mechanism project activities. At COP17 in Durban, a final agreement was reached enabling CCS projects to receive support through the Clean Development Mechanism.

Environmental effects

Fossil fuel power plants

The theoretical merit of CCS systems is the reduction of CO2 emissions by up to 90%, depending on plant type. Generally, environmental effects from use of CCS arise during power production, CO2 capture, transport, and storage. Issues relating to storage are discussed in those sections.

Additional energy is required for CO2 capture, and this means that substantially more fuel has to be used to produce the same amount of power, depending on the plant type. For new super-critical pulverized coal (PC) plants using current technology, the extra energy requirements range from 24 to 40%, while for natural gas combined cycle (NGCC) plants the range is 11–22% and for coal-based gasification combined cycle (IGCC) systems it is 14–25% [IPCC, 2005]. Obviously, fuel use and environmental problems arising from mining and extraction of coal or gas increase accordingly. Plants equipped with flue-gas desulfurization (FGD) systems for sulfur dioxide control require proportionally greater amounts of limestone, and systems equipped with selective catalytic reduction systems for nitrogen oxides produced during combustion require proportionally greater amounts of ammonia.

In 2005 the IPCC provided estimates of air emissions from various CCS plant designs. While CO2 is drastically reduced though never completely captured, emissions of air pollutants increase significantly, generally due to the energy penalty of capture. Hence, the use of CCS entails a reduction in air quality. Type and amount of air pollutants still depends on technology. CO2 is captured with alkaline solvents catching the acidic CO2 at low temperatures in the absorber and releasing CO2 at higher temperatures in a desorber. Chilled Ammonia CCS Plants have inevitable ammonia emissions to air. « Functionalized Ammonia » emit less ammonia, but amines may form secondary amines and these will emit volatile nitrosamines by a side reaction with nitrogendioxide, which is present in any flue gas even after DeNOx. Nevertheless, there are advanced amines in testing with little to no vapor pressure to avoid these amine- and consecutive nitrosamine emissions. Nevertheless, all the capture plants amines have in common, that practically 100% of remaining sulfur dioxide from the plant is washed out of the flue gas, the same applies to dust/ash.