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Biochar

From £130/tonne

Overview

Biochar is charcoal-like material rich in stable carbon. It is produced by heating biomass in an oxygen-limited environment in a process called pyrolysis. It is most commonly used as soil amendment in agriculture and horticulture.

The feedstock to produce biochar is typically waste biomass. This biomass contains temporarily stored carbon that was removed from the atmosphere by plants through photosynthesis. Without undergoing the pyrolysis process, this carbon would be re-released through the burning or decomposition of waste biomass. While biochar itself could also be burned in the presence of oxygen (as charcoal can be), the application and mixing with soils prevents this from ever happening.

Furthermore spreading of biochar on farmland soil brings significant additional co-benefits, such as yield improvements and reduced need for fertilizers.

The science

Biochar is a heterogenous material that consists of two distinct carbon pools with different degrees of permanence: labile and recalcitrant (stable, aromatic) fraction; larger recalcitrant fraction means better permanence, as the stable polycyclic aromatic carbon has been shown to persist over 1000 years in soils.

The ratio between labile and recalcitrant fraction mostly depends on pyrolysis conditions such as pressure and temperature and somewhat on the chemical composition of the feedstock. Molar ratio between hydrogen and carbon (H:C) is used as a proxy for the degree of aromatization, as it can be easily and precisely measured. A ratio below 0.4 indicates a high portion (~75%) of the stable, aromatic carbon. All our current suppliers produce biochar with H:C below 0.4, as this has been introduced as a vetting requirement in autumn 2022.

Permanence of biochar carbon also depends on soil type and temperature. Colder soils means slower degradation.

We currently classify biochar credits as medium permanence (100-1000 years). At 100 years the amount of carbon stored by 1 credit will be 1 tonne of CO₂; this may mean a slightly higher amount (buffering) needs to be sequestered in the first place. From there, the two respective carbon pools show distinct degradation dynamics, each following a degradation curve. Labile pool degrades over decades to centuries, but aromatic pool may persist over 1000 years. The science of biochar permanence is still evolving, and we will update permanence estimates when firmer scientific consensus forms.

Biochar has a large, sponge-like surface area and slight electrical charge, which means it binds water and nutrients and holds them better in the soil.

The two main beneficial consequences of this property are improved water retention and therefore reducing crop exposure to droughts, and reduced need for nitrogen fertilizers (as less nitrogen is lost from field). The latter also means reduced nitrogen pollution and reduced emissions of nitrous oxide, another potent green-house gas. Furthermore it helps build-up soil organic carbon content, meaning there is additional carbon removal and fertility improvement. Particularly in tropical regions, biochar was shown to significantly improve crop yields. There is also evidence from traditional use of charcoal in soils, the most well-known example being the fertile Terra Pretasoils in Brazil.

While all of these co-benefits, including additional removal and emission avoidance, come with biochar application, none of them are used in the calculation of the carbon removal credit - meaning the co benefits come as ‘extra’ on top of the core biochar carbon removal.

Supercritical‘s view

Biochar stands out due to its potential to become the first permanent carbon removal method to achieve gigatonne scale, alongside significant co-benefits for soil application.

It has quickly emerged as the most accessible and scalable permanent CDR method available today, thanks to a high technology readiness level (TRL). This results from its strong permanence, lower cost per tonne compared to other permanent solutions, and high availability and delivery rates. However, demand is focused on high-quality credits, which are likely to face a supply shortage soon.

The co-benefits further enhance biochar's appeal. Food production significantly impacts the environment, and biochar can help mitigate these effects by reducing food system impacts and sequestering carbon for centuries. Despite these benefits, farmers are often hesitant to change their practices and have limited awareness of biochar's advantages. Few farmers are willing or able to cover the full cost of biochar production, making income from carbon credits essential to promote the adoption of this technology. Ideally, as the cost of biochar decreases and its value to farmers increases, reliance on carbon credits will diminish.

One drawback of biochar is its competition with other potential uses for biomass feedstock, such as bioenergy. Additionally, some scientists argue for preserving trees rather than utilizing them for any purpose, which could reduce the supply of waste woody biomass — a primary feedstock for biochar production — if this perspective gains traction.

Bojana Bajzelj

Head of Climate

Our suppliers

Our biochar suppliers are located all over the world. These projects often source feedstock from sustainable sources such as forestry residues, agricultural waste, and waste wood.

Our partnership with these projects allows us to support companies that are committed to responsible practices, environmental stewardship, and benefiting local communities.

Project locations 4

  • Map of Kenya
    Kenya
  • Map of Namibia
    Namibia
  • Map of India
    India
  • Map of Bolivia
    Bolivia

Verifications

Every project in the marketplace receives a score through our science-driven, commercially-focused vetting protocol.

Covering 118 criteria across four key dimensions, this rigorous evaluation yields top-line scores, allowing you to objectively compare projects and evaluate quality. Dive deeper with our vetting explainer.

Supercritical Vetted Project badge
  • Climate science

    Is the climate science that underpins the carbon credit rock solid?

    • Remove carbon

    • Have clear permanence

    • Accurately issue credits

    • Is additional

    • Does not suffer leakage

    • Strong MRV (Measured, Reported and Verified)

  • Environmental factors

    Beyond the removal of CO2, does the project have a positive or negative impact on the local environment?

    • Neutral or positive impact on biodiversity

    • Neutral or positive impact on air quality

    • Neutral or positive impact on soil health

    • No negative effects on groundwater

  • Delivery risk

    What is the risk of non-delivery of credits?

    • Site development

    • Site operational track record

    • Team experience and capability

    • Business plan and funding

    • Levels of geopolitical risk

  • Social impact

    Does the project have a positive or negative impact on local communities, per UN Sustainable Development Goals (SDGs)?

    • Economic empowerment of local communities

    • Integrates education and community engagement

    • Better health outcomes

Browse our removal methods

  • Biochar

    Biochar is charcoal-like material rich in stable carbon. It is produced by heating biomass in an oxygen-limited environment in a process called pyrolysis.

    Permanence: MEDIUM From: £130/t
  • Enhanced weathering

    Enhanced rock weathering (ERW) takes natural weathering of silicate rocks that removes & mineralizes atmospheric CO₂ and speeds it up dramatically.

    Permanence: HIGH From: £246/t
  • Woody biomass sinking

    This is a method that sequesters carbon by submerging leftover woody materials in the oxygen-depleted layer of the Black Sea, which is approximately 2 kilometers deep.

    Permanence: MEDIUM From: £296/t
  • Direct air capture

    Direct air capture (DAC) is a chemical process to capture ambient CO₂ from the atmosphere.

    Permanence: HIGH From: £488/t
  • Bio-oil

    Bio-oil and biochar production both convert waste biomass through pyrolysis. Bio-oil is a liquid stored in geological repositories, while biochar is applied to soils.

    Permanence: HIGH From: £592/t
  • DAC with ocean storage

    This employs seawater electrolysis to capture and convert atmospheric CO₂ into carbonate solids for construction and permanently stores dissolved bicarbonate ions in the ocean.

    Permanence: HIGH From: £641/t
  • Tree planting

    Afforestation and forest restoration, if done effectively, combat climate change by removing carbon dioxide and protecting biodiversity.

    Permanence: LOW From: £41/t