As companies look to increase their climate impact ambitions and set net zero emission goals, they are realizing that they will need new approaches to offset their hard-to-abate emissions. The best options are a set of approaches, technological or nature-based - chemical, mineralogical, and biological processes—designed to remove carbon from the atmosphere.
Leading organizations, such as the Science Based Targets Initiative, recommend that climate mitigation efforts use methods that actively remove carbon from the atmosphere and store it in a durable form, using processes that can be verified. (They also emphasize that companies should first focus on optimizing their operations to reduce emissions, using carbon removal credits only for the remainder.)
Currently, most of these carbon removal credits involve planting or replanting forests. Trees do capture and store carbon, but they are vulnerable to fires and logging. More recently, a significant amount of effort in innovation and investment is being directed towards other technologies that will remove carbon dioxide from the atmosphere and securely store it for thousands of years. Few of these technologies are already in full deployment, some are beginning to be deployed and others are still years away.
Here is a quick rundown of four recognized approaches that offer long term carbon sequestration, show high scalability potential, and are currently under development - therefore, represent the most promising approaches to date.
Number One: Biochar/PyCCs
Biochar
How it works:
Wood or other organic matter is brought to high temperatures in a low-oxygen environment, producing a charcoal-like, carbon-rich substance known as biochar.
The process is best incorporated in locations where large amounts of carbon-rich residual biomass is available and can be easily adopted by facilities that utilize biomass for energy or facilities that require heat for their processes.
Biochar is often used as a soil amendment or animal feed, or can be added to construction materials such as concrete or asphalt.
Current status:
Over the past 10 years, hundreds of biochar projects have been introduced worldwide.
There is significant and increasing investment in biochar facilities.
Carbon removal credits based on biochar are being issued according to third-party standards and made available to companies looking to neutralize their residual emissions.
Currently, there is more demand for biochar credits than there is supply.
The agricultural market for biochar is still small.
Cost:
Biochar-based credits have been available recently for $75 to $200 per tonne of CO2.
The underlying economics will improve with higher-volume production and the further development of agricultural markets.
Number two: Direct Air Capture/DACCS
Direct Air Capture and Storage (DACCS)
How it works:
Carbon dioxide is directly removed from the atmosphere through chemical processes.
The CO2 is bound to a sorbent and then needs to be stored for the long term, either by injecting it deep into the earth or bound into durable construction materials like concrete.
Current status:
Investment has been robust, and there are more than a dozen direct air capture plants in operation.
In 2021, Climeworks opened a facility in Iceland that removes up to 4,000 tonnes of carbon a year, then mixes the carbon dioxide with water and pumps it underground where it is expected to turn into stone.
Carbon Engineering is working with Occidental to build a direct-air-capture facility in Texas meant to remove 500,000 tonnes of carbon annually, starting in 2024.(Note that EOR is in use here, which does not fall under the category of carbon removal)
Most direct air capture techniques are energy-intensive and very expensive, although costs are expected to fall with increasing carbon removal volumes.
Unlike some carbon removal technologies that rely on local natural resources, many direct air capture techniques use commonly available chemicals. This could allow for a larger spread of facilities.
Direct air capture doesn’t have the co-benefits that some other approaches do, such as producing soil amendments that improve soil health and crop yields.
Most DAC applications developed to date require high temperature processes, which in turn need heat sources. The type of thermal energy used for the process has a large impact on the electricity requirements of a given process. So far, DAC companies have been using a variety of sources such as geothermal energy, natural gas, or photovoltaic electricity to cover their energy needs.
Cost:
The estimated cost of the process is $75–$500 per tonne of CO2 (cdr.fyi).
Number three: Enhanced weathering
Enhanced Weathering
How it works:
Artificial acceleration of the natural weathering process in which the chemical breakdown of rocks with rainwater converts CO2 to bicarbonate solids, which eventually drain away through rivers to the oceans.
Typically, the weathering process is accelerated by finely grinding silicate rock, increasing its surface area and reactivity.
The resulting ground rocks are spread to land where the weathering reaction takes place when it rains. The minerals also serve as a soil amendment replacing lime in agriculture.
Enhanced Rock Weathering directly in coastal areas is also being proposed. Project Vesta for instance uses an enhanced weathering technique that deposits ground olivine, a volcanic rock, in beaches where it binds with CO2 and the resulting carbonate precipitates enter the ocean carbon cycle where they end up in the ocean beds for millenia.
Future issues:
The process of rock weathering and precipitation into dissolved organic carbon is well characterized and studied but challenges remain to measure this carbon removal process in the field.
The quantification and mechanisms of the weathering process and the fate of the resulting carbonates are currently the subject of extensive research efforts. Consensus has not yet been reached on a method for reliably measuring and verifying the amount of carbon captured through enhanced weathering.
A potential sustainability challenge for enhanced weathering projects is their reliance on mining activities, which can have significant environmental impacts themselves. Certain projects source their mineral feedstocks from mining tailings (waste materials), effectively minimizing this sustainability challenge.
The proximity of mines to the enhanced weathering sites is also critical due to high transportation costs of heavy and bulky rock materials. A local source of input materials is required to make projects economically viable.
Cost:
The estimated cost of the process is $75–$500 per tonne of CO2 (cdr.fyi).
Number four: Ocean Capture
Ocean Capture
How it works:
Several approaches are being proposed to utilize the carbon sink potential of the ocean, which has been the second largest carbon sink for human-made CO2 emissions since the industrialisation. An increasing number of carbon removal initiatives are looking to increase the CO2 removal potential or make use of the carbon sink capacities of the ocean.
Some techniques increase the alkalinity of the ocean, counteracting the harm of acidification and increasing the natural CO2 removal capacity of seawater through the creation of carbonate precipitates.
Other approaches propose to sink carbon-rich materials to the deep seabeds where carbon decomposition is minimal.
Current status:
Multiple technologies are in development.
Heimdal injects sodium hydroxide into the ocean, increasing the alkalinity of seawater and hence increasing its natural capacity to sequester CO2 is ultimately sequestered in the form of precipitated carbonates.
Several companies, including Phykos and Running Tide use fast-growing kelp to absorb carbon, before sinking it to the bottom of the oceans where carbon decomposition is minimal.
Future issues:
All these technologies are early-stage, and their long-term economics are not known.
Since carbon is dispersed in the ocean, it will be very difficult to monitor the amount removed and the duration of its sequestering.
Ecosystem effects are not well understood and characterized yet.
Cost:
Unclear, but it is expected to be lower than direct air capture because much of the capture occurs in the ocean rather than in an energy-driven machine.
Though only one of these technologies is currently at the point at which it can sequester carbon at scale (biochar), forward-thinking businesses are beginning to get involved with promising early stage carbon removal initiatives. Some companies, such as Stripe, Meta, Google, Shopify (who together formed the Frontier Climate fund) or Microsoft, have agreed to purchase carbon credits in the future in deals that provide funding for the development of carbon removal technology.
Carbonfuture is a end-to-end platform and marketplace that connects corporations wishing to balance their residual emissions with high-quality carbon-removal programs. We help companies develop portfolios of highest-tier carbon removal credits that often include advanced purchase agreements for emerging technologies. We also carbon removal producers incorporate best practices, including rigorous certification and tracking. In fact, at present, our Catalyst program is incubating several startups with innovative carbon capture technologies.
At Carbonfuture, we build trust throughout the carbon removal journey with our rigorous, data-driven approach, ensuring unmatched quality and reliability of carbon removal.
