Carbon removal projects are used to remove carbon dioxide from the atmosphere with the goal to create negative emissions. They are an effective way to support global mitigation efforts and tackle historical greenhouse gas emissions. Carbon removal practises can be broadly divided into technology-based and nature-based solutions, but there are projects that also combine both elements.
Different carbon removal projects come with different costs and benefits, such as the permanence of removal, the sequestration period and wider social impacts. As a relatively new field, not all the carbon removal methods are fully developed and new techniques and projects are frequently introduced.
What is the cheapest way to remove carbon? What are the most efficient carbon removal projects? What are the upcoming carbon removal technologies? We looked into thirteen different projects across the world and this is what we found out!
Direct air capture and storage
Climeworks with Carbfix
Climeworks and Carbfix are working together in Iceland to remove CO2 directly from the air and store it in stone underground. In this technology-based solution, carbon dioxide is filtered from air and heated up to create high-purity and high-concentration carbon dioxide. This carbon is then injected into basalt rock where it is mineralized and eventually turned into stone. The current key project of Climeworks is Orca, the world’s largest direct air capture machine that has the capacity to store 4000 tons CO₂ per year. However, Climeworks is preparing to significantly scale up its operations in the future.
Climeworks offers a permanent and relatively fast solution to carbon removal as the sequestration only takes 4 months to 2 years. It also causes minimal damage to the environment. However, the cost of direct air capture and its energy use are sources of concern. Direct air capture and storage are currently very expensive: the cost of offsetting a ton of CO₂ is around US$ 1076. This is due to the technical development state of direct air capture and storage. Once the technologies develop further, it is expected to become more cost-effective. Another issue is the energy intensiveness of direct air harvesting. The high energy demand of this technology will require significant increases in renewable energy supply as well as increase the global demand for raw materials used in these technologies.
Cost/ton: US$ 1076
Duration: 4 months – 2 years
greenSand is a nature-based carbon removal project that sequesters carbon dioxide into a mineral called olivine through enhanced weathering. Enhanced weathering is a carbon removal method that amplifies the natural chemical weathering of minerals. In the case of olivine, the mineral reacts with the CO₂ in the atmosphere and turns into magnesium, silica and bicarbonate. These are nourishing elements for the soil and therefore offer further benefits from this carbon removal project.
Olivine is a cheap way to remove carbon and it has the capacity to sequester up to one time its own weight in carbon but the downside of this carbon removal method is the long sequestration period: 1 ton of olivine takes up to 1000 years to sequester 1 ton of CO₂. However, the sequestration rate is fastest at the start of this period and olivine will sequester 32.82% of its carbon capacity within the first 50 years.
Cost/ton: US$ 47
Duration: up to 1000 years
Future Forest seeks to use enhanced weathering to remove carbon from the atmosphere. By increasing the surface area of basic rocks, Future Forest is attempting to accelerate the naturally occurring mineralisation process of rocks from hundreds of thousands of years to less than a year. The solution is permanent as the mineralised CO₂ will remain stable for millions of years.
The project is still under research but the expectations are promising both in terms of efficiency and pricing. Future Forest seeks to process 100 tonnes of basalt rock per day which would allow the enhanced weathering to sequester 8400 tonnes of CO₂ per year. While processing basalt rock is more expensive than using olivine for enhanced weathering, processing rock would provide a fast solution for carbon capture: the processed basalt rock is expected to sequester 70% of the carbon dioxide within the first year, and the remaining 30% within the next couple of years.
Cost/ton: US$ 100 (anticipated)
Duration: Several years
Charm Industrial uses bio-oil storage as a method to capture carbon underground. This carbon removal project uses pyrolysis to convert biowaste such as corn stover into bio-oil. This bio-oil is then injected underground into the same rock formations that are used to store crude oil. Storing bio-oil underground removes CO₂ permanently from the atmosphere. By using biowaste, the project also helps to tackle global waste management issues.
1 ton of biomass leads to around 0.85 tons of carbon dioxide removal from the atmosphere. Because of the very fast sequestration period and the vast amount of biowaste that could be converted into bio-oil, bio-oil storage has huge potential for carbon removal if the project is scaled up. On the downside, the technologies are still under development and the cost of bio-oil storage is therefore high. There are also potential risks and environmental impacts that need to be taken into consideration, including particulate and nitrogen oxide emissions and road traffic if the biomass needs to be imported long distances. Seismic activity and its impacts on bio-oil storage are also considered to be risk factors and they need to be studied further.
Cost/ton: US$ 600
Duration: 48 hours after injection
Eden Reforestation Projects
Planting trees is undoubtedly the best-known nature-based solution to tackle climate change. Trees are constantly absorbing carbon dioxide from the atmosphere and have the capacity to absorb 10-40kg of CO₂ per year depending on various factors. It is also one of the cheapest ways to remove carbon. Eden Reforestation Projects has planted over 700 million trees with over 200 local communities across the world. By working together with local people, the restoration projects have created jobs and alleviated poverty in local communities alongside ecological restoration and climate mitigation.
The downsides of using forestation for carbon capture are the relatively short lifespan of trees and external risk factors such as wildfires. When trees burn down or rot at the end of their life cycle, the CO₂ stored in the trees gets released back into the atmosphere. By planting enough native trees a natural forest can return, requiring minimal human intervention and maintenance. Should trees die, new ones spring up in their place from the undergrowth. This restoration of the natural carbon cycle will help sequester CO₂ indefinitely. Planting trees is also relatively inefficient in terms of land use compared to other nature-based solutions like enhanced weathering.
Cost/ton: around UD$ 10
Permanence: The lifespan of the tree
Duration: The lifespan of the tree
Storing carbon in concrete
The construction sector is one of the most carbon-heavy industries in the world and innovations in carbon capture in this field is crucial for climate mitigation. Neustark removes carbon dioxide from the atmosphere and permanently stores it in recycled concrete. A cubic meter of concrete has the capacity to store 10kg of carbon dioxide and by recycling materials, Neustark avoids new CO₂ emissions from fresh concrete. The recycled and carbon enriched granulate improves the climate balance of fresh concrete by around 10%.
Storing carbon in concrete is extremely effective time-wise. It’s a natural process that usually takes up to centuries, but with technology, this can be reduced to hours. The CO₂ is permanently stored and will not be released back into the atmosphere even if the concrete is later demolished. As the technologies are still under development, the capacity of concrete to sequester carbon is also expected to increase in the future.
Duration: 24 hours
CarbonCure manufactures carbon removal technologies for companies that are producing concrete. Their technologies remove carbon dioxide from the atmosphere by recycling CO₂ into fresh concrete. This happens by injecting CO₂ into concrete where it mineralizes through a chemical process and becomes permanently embedded. Besides climate mitigation, it also reduces economic costs and improves the compressive strength of concrete, making it an attractive option for businesses seeking to reduce their carbon footprint. Similarly to Neustark, CarbonCure offers a way to permanently store carbon in a short-time period. Compared to other technology-based methods, CarbonCure offers a fairly affordable carbon capture solution with the cost per ton being around $100.
Cost/ton: US$ 100
Puro.earth and VTT Technical Research centre of Finland are currently researching bio-concrete that would have a negative carbon footprint. The bio-concrete combines industrially available by-products such as bio-based ashes and silicon sources with carbon curing technology. The result performs like concrete but it does not contain cement which is a huge contributor to global CO₂ emissions. Puro.earth estimates that the bio-concrete has the possibility to reduce carbon emissions to gross negative -388kg per m³.
This technology-based carbon removal project is still to be validated at an industrial scale and there are potential risks, such as the compatibility of bio-concrete in the manufacturing processes and the performance of produced materials. However, if these risks aren’t met, bio-concrete has the possibility to massively reduce CO₂ emissions in the construction sector and change the way we build. The cost of bio-concrete is currently high as it is still being researched, but the cost per ton is expected to drop once the technologies are developed.
Cost/ton: US$ 230-960 (currently)
Duration: Immediately during manufacturing process
Carbofex is the leading biochar producer in Europe and it has captured 9800 tonnes of CO₂ since the carbon removal project started in 2017. Carbofex uses pyrolysis to convert waste biomass into energy by mineralizing the short-cycle carbon that is stored in biowaste into long-cycle carbon in the form of biochar. A kilogram of biochar binds around 3.5kg of CO₂ into the soil and this sequestration is permanent. In addition to carbon removal, converting biowaste into biochar creates energy. Carbofex alone has the capacity to distill seawater and generates 250 000 litres of clean water daily.
Producing biochar creates minimal emissions and with the additional benefits of energy production and waste reduction, it appears to be a good candidate for technology-based carbon removal. However, at its current state of development, biochar production is very expensive. Even though some costs can be reduced by, for example, selling the excess energy, biochar is by far the most expensive carbon removal method in this list.
Cost/ton: US$ 2000
Blue carbon projects
Seachange develops mineralization reactors to remove carbon dioxide from the sea. In these reactors, carbon is removed from water by forcing rapid precipitation of carbonates by combining CO₂ with other elements. Hydrogen is being produced as a co-product. As seawater contains nearly 150 times more carbon dioxide than air in a given space, removing carbon from the sea is an effective way to get rid of excess CO₂. At the prototype stage, Seachange is expecting to remove 1 tonne of carbon per day.
One of the key benefits of Seachange is that the technology does not require complex logistical facilities and it can therefore be easily applied in different locations by carbon emitters, water treatment entities or companies. However, the technology is still being researched and there are potential risks that might limit its success, such as the acidification of seawater. At the current state of research, the cost is also extremely high.
Cost/ton: US$ 1370 (currently)
Duration: 1-10 years
While still at the research phase, C Sink plans to remove CO₂ by collecting biomass and storing it in the deep sea. This nature-based carbon removal project relies on the natural carbon-absorbing properties of seaweed, plants, crop residue and tree cuttings. By placing them at the bottom of the ocean where the oxygen is limited, this biomass will decompose extremely slowly.
As the project is still under research, there are risks that the biological decomposition rate of the sunk biomass will be faster than expected. By placing the biomass in the anoxic waters of the Black Sea, the project will avoid the risk of the biomass being eaten by living organisms. Even if this method does not sequester CO₂ for thousands of years, it is still expected to capture it for at least a century, providing a temporary solution to tackling climate change at its best. It will also be one of the cheapest carbon removal methods in the market with the cost per ton being only $50.
Cost/ton: US$ 50 (anticipated)
Permanence: 100-1000 years
Duration: Unknown (likely less than a month)
Running Tide uses kelp to capture carbon and remove it from the atmosphere by sinking the kelp to the bottom of the ocean. As kelp is one of the fastest growing plants, it absorbs CO₂ faster than any other species in the world. The carbon removal method of Running Tide is essentially an accelerated version of the natural carbon removal process where CO₂ is stored in the deep sea through plants.
Some of the key benefits of this carbon sequestration project include minimal land use and energy inputs. It also doesn’t require manufactured storage like many other carbon removal methods. As oceans cover most of the Earth, there are also huge possibilities to scale up this carbon removal technique. While the cost of Running Tide isn’t currently comparable to nature-based solutions like planting trees or enhanced weathering, it still provides a cheaper alternative to many technological solutions.
Cost/ton: US$ 150
Permanence: Centuries to Millenia
Duration: 6-9 months