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.
What sets biochar apart from other removal methods are the really strong co-benefits that come from its application to soils. Food production has an enormous environmental impact. Amongst many other needed solutions, biochar could help reducing food system impacts, as well as lock carbon out of short carbon cycle for centuries.
Farmers are often reluctant to change their practices, and their awareness of the benefits of biochar is currently low. Very few farmers are willing or able to pay the full cost of biochar production. Therefore income through carbon credits is considered necessary to jump start the uptake of this technology. We hope that one day, the cost of biochar will come down and its value to farmers will go up so that the income from biochar credits will no longer be needed - at which point they will no longer be considered additional.
The one weakness of biochar is that it sometimes competes with other - real or potential future - uses for the biomass feedstock, such as bioenergy. Furthermore some scientists argue that we should be leaving trees standing rather than using them for anything at all. If this view prevails, it could lead to a reduced supply of waste woody biomass, which is currently one of the main feedstocks for biochar production.
Bojana Bajzelj
Head of Climate
Our suppliers
Our biochar projects include a family-owned and operated lumber producer in the US that sources its feedstock from sustainable sources, including forestry residues, agricultural waste, and waste wood.
Our partnership allows us to support a company that's committed to responsible forestry practices and environmental stewardship.
We also work with another American company that partners with paper mills to maximise the use of their waste streams. By sourcing FSC-certified pine bark waste as a feedstock for their biochar, the company demonstrates a strong commitment to sustainability and environmental responsibility.
Project locations 2
India
Bolivia
Verifications
Our climate team ensures only high-quality carbon removal makes it onto the Supercritical marketplace.
Each Project has completed our rigorous 8-point vetting process, with fewer than 6% passing.
The Supercritical marketplace only features projects that:
Remove carbon
We do not deal with carbon avoidance or carbon reduction offsets
Are net negative
A project’s removal must be net of lifecycle emissions
Are Measured, Reported and Verified
Projects must have MRV and unique retirement on an established registry
Are additional
The removal must not have occurred in the absence of a market for offset credits
Do no significant harm
Projects must cause no ecological, economic or social harm
Have clear permanence
Permanence must be well established, and be conservative
Have co-benefits
Environmental, social, economical co-benefits
Have potential
Projects must have significant future scaling potential
