Biochar is charcoal created by pyrolysis of biomass waste. The resulting material is added to a landfill or used as a soil improver to create terra preta. Addition of pyrogenic organic carbon (biochar) is a novel strategy to increase the soil-C stock for the long term and to mitigate global warming by offsetting the atmospheric C (up to 9.5 Gigatons C annually). In the soil, the biochar carbon is unavailable for oxidation to  and consequential atmospheric release. However concerns have been raised about biochar potentially accelerating release of the carbon already present in the soil.
Terra preta, an anthropogenic, high-carbon soil, is also being investigated as a sequestration mechanism. By pyrolysing biomass, about half of its carbon can be reduced to charcoal, which can persist in the soil for centuries, and makes a useful soil amendment, especially in tropical soils (biochar or agrichar).