As trees grow, they store carbon from the atmosphere in their biomass, through photosynthesis. When this biomass is burned in the absence of oxygen (a process called pyrolysis), one of the byproducts is a stable, carbon-rich residue called biochar.

When biomass decomposes naturally, carbon and methane are emitted into the atmosphere. Since biochar is very stable, the production of biochar using waste biomass – such as  waste timber from commercial forests – is a more permanent method of removing carbon dioxide from the atmosphere, and storing the carbon on long-term timescales, than allowing the biomass to decompose naturally. Biochar is also great because it avoids fossil fuel emissions if energy is produced after burning the biomass and it can trigger changes in GHG emissions after being added to the soil from increased plant growth, lower non-CO₂ GHG emissions from soil and reduce mineralization of soil organic matter.

Mixing the produced biochar into soil can therefore act to permanently lock away its stored carbon, and studies have also found that it can support the fertility and productivity of the soil.