Removing Carbon from the Atmosphere

Ing. Vaclav Kurel
November 10, 2021
Climate and carbon credits

How are different ways of removing carbon from the atmosphere being applied? They are all developing because each has its advantages.

In addition to reducing greenhouse gas emissions, different ways of directly removing carbon from the atmosphere are beginning to get support. There are big differences between them. They have their advantages and disadvantages. There is not just one right option among them. We need all of them to prevent the planet from warming by more than 1.5 °C. They must be used on a large scale and as soon as possible. For the time being, however, they all have insufficient capacity. Their necessary development will be assisted, in particular, by companies that have ambitious climate targets.

In terms of emissions, we can divide companies into two types. The first are direct CO2 emitters, such as coal-fired power stations, heating plants, steel and cement producers. Their emissions are regulated by a system of emission allowances. They are financially incentivised to reduce emissions gradually. And these reductions are happening because the price of emission allowances is rising dramatically, accelerating the shift away from coal.

The second type are companies that do not emit CO2 directly from any of their chimneys, but indirectly contribute to CO2 emissions through their consumption of electricity, gas, petrol, etc. These companies are not obliged to reduce their carbon footprint today. However, they will be under increasing pressure from their shareholders, creditors and customers to reduce their carbon footprint significantly over time. Progressive companies are setting ambitious targets to achieve carbon neutrality by 2030. Komerční banka, for instance, wants to achieve carbon neutrality even as early as 2026. And it is precisely the position of these companies that will support the development of various ways of removing carbon from the atmosphere in the coming years, because they will need someone to remove their indirect emissions from the atmosphere on their behalf. And so they will buy carbon credits, so-called offsets, because without using them, they will not be able to achieve carbon neutrality throughout their entire supply and demand chain.

More than 95 % of the offsets offered up to 2020 were projects that sought to avoid further emissions by protecting rainforests, or by trying to reduce emissions by using more efficient technology to generate electricity or heat. Nowadays, offsets that directly remove carbon from the atmosphere, known as carbon dioxide removal (CDR), are becoming increasingly popular. This either makes use of natural principles of photosynthesis or mineralisation, or uses modern technology.

There are six main ways to remove carbon from the atmosphere:

1) Reforestation and afforestation

Trees are particularly good at storing carbon removed from the atmosphere by photosynthesis. Expanding, restoring and better managing forests to encourage greater carbon uptake can harness the power of photosynthesis and convert atmospheric carbon dioxide into carbon stored in wood and soil.

The main advantage of this solution is its high absorption capacity with prices around USD 10 per tonne of CO2. At the same time, they bring significant co-benefits such as cleaner water and air. Forests also support the small water cycle, cool the local climate and help maintain biodiversity in the landscape. This is also why it is the most used CDR project method.

One of the main challenges is to ensure that the expansion of forests in one area is not at the expense of forests elsewhere. Afforestation of agricultural land, for example, would reduce food supply. This could necessitate the conversion of other forests to farmland if improvements in farm productivity do not fill the gap. Similarly, failure to harvest timber in one forest may lead to over-harvesting in another forest. Afforestation thus has its limits in the insufficiency of suitable sites for afforestation. It is all the more important to ensure that rainforests do not get cleared, as they are a huge carbon sink. Tropical forest restoration typically captures 11 tonnes of CO2 per hectare per year, but the loss of one hectare of mature forest can release more than 30 times that amount of CO2 - over 400 tonnes all at once.

Examples of such projects include Pachama and NCX.

2) Carbon in the soil

Soil naturally stores carbon in organic matter. There is 3 times more carbon in the soil than in the atmosphere. Historically, industrial agriculture has released large amounts of carbon into the atmosphere, causing that agricultural soils are now degraded in many places, losing fertility as well as the ability to retain enough water and to resist wind and water erosion. Since agricultural land is so vast, even a small increase in the amount of carbon in the soil could have a big impact.

Regenerative farming has been proven to increase soil carbon and provide many side benefits. Planting cover crops at a time when fields are otherwise bare can extend photosynthesis throughout the year and, if mechanical and chemical disturbance to the soil is reduced, about 10 tonnes of CO2 per hectare per year can be stored, as projects in Austria and Germany have demonstrated. The biggest challenge is a radical change in farming practices, which must also be permanent, since a return to ploughing can wipe out previous carbon gains in the soil.

Examples of projects include Carbocert, Carboneg, Nori, Indigo, Grassroots Carbon.

A large natural carbon stock exists in peatlands. Although they make up only 3 % of the Earth's mainland, they contain 42 % of the total carbon stored in the soil. Hence, projects are being set up to restore peatlands to boost the carbon sequestration capacity of this ecosystem.

Moor Futures is an example of such project.

3) Use of biomass

Bioenergy production with carbon capture and storage (BECCS) is another way to use photosynthesis to combat climate change. However, it is much more complex than planting trees or managing land - and not always beneficial for the climate.

BECCS is the process of using biomass to generate energy in industry, power or transport, capturing its emissions before releasing them back into the atmosphere and then storing the captured carbon either underground or in long-life products such as concrete.

It is important that BECCS are carbon negative overall and primarily use agricultural residues or wood waste from nearby areas as fuel. These materials may be key to the future of BECCS as they would not require special land use. In such a case, BECCS can bring the anticipated climate benefits.

Another option for using biomass for carbon sequestration is the conversion of biomass by pyrolysis into biochar or carbon oils that can get almost permanently stored underground, which is their main advantage.

Project examples: Biouhel, Charm, Carbofex.

4) Direct carbon capture from the air

Direct Air Capture (DAC) is the process of chemically cleaning carbon dioxide directly from the ambient air and then storing it either underground or in long-life products. This new technology is similar to the carbon capture and storage technology used to capture emissions from sources such as power plants and industrial facilities. The difference is that direct atmospheric capture removes excess carbon directly from the atmosphere instead of capturing it at the source.

It is relatively easy to measure and account for DAC's climate benefits, and its potential range of deployment is enormous. However, the technology is still expensive and energy demanding. The current capacity of existing projects is therefore still relatively small, as they need sufficient emission-free energy to achieve net carbon removal. At the same time, suitable permanent storage must be available nearby.

Project examples: Climeworks, Carbon Engineering.

5) Carbon mineralisation

Some minerals, such as olivine, naturally react with CO2 to convert carbon from a gas to a solid. This process is commonly referred to as carbon mineralization or enhanced weathering and naturally occurs very slowly over hundreds or thousands of years.

The aim of this CDR project is to accelerate the natural chemical weathering of the mineral by spreading a large amount of grinded rock containing olivine over a large area. The main advantage is the virtually permanent storage of carbon. Limitations lie in finding a suitable and sufficient source of the particular mineral, a sufficient area for dispersal and low-emission extraction and transport of large quantities of rock.

Project examples: Vesta, Heirloom.

6) Ocean exploitation

The main method of carbon sequestration in the ocean is through photosynthesis in coastal plants, seaweeds or phytoplankton. Seaweed cultivation could remove carbon while boosting ecosystem restoration and also reducing ocean acidification. The advantage of this option is the vast expanse of oceans available and the great potential in carbon sequestration due to the rapid growth of algae. However, little is still known about the wider ecological impacts of these approaches and further research is needed to better understand the potential risks before such methods can be implemented on a large scale.

In the near future, cultivated seaweed could also be used to produce products such as food, fuel and fertiliser, which, while not carbon-removing, could reduce emissions compared to conventional production and provide an economic return that will support the growth of this field.

Project example: RunningTide.

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