The climate protection potential of biochar lies in its ability to store carbon in the long term. It is one of several biological CO2 storage options, also referred to as sinks, carbon dioxide removal (CDR) or negative emissions technologies (see FAQs: What are negative emissions?). While natural decay or combustion of biomass leads to the re-release of CO₂, when carbon is stored as biochar it remains trapped for hundreds to thousands of years – as long as the charcoal remains embedded in the soil. This means that one tonne of biochar can remove around two-and-a-half to three tonnes of CO₂ equivalents from the atmosphere.
Biochar is produced by pyrolysis: biomass such as waste wood, green prunings or straw is heated in the absence of oxygen at temperatures between 350 and 900 °C. Approximately half of the carbon contained in the biomass is converted into a stable form. The end product is porous, carbon-rich biochar, which can survive in the soil for centuries.
In addition to climate protection, biochar offers agro-ecological benefits. Mixed with compost or manure, it reduces nutrient losses and emissions of greenhouse gases such as nitrous oxide, improves soil structure and increases water retention. Soil microbiology is also promoted, which, in turn, can support plant growth. “Terra preta” – the black soil made by indigenous cultures in the Amazon region – evidences the long-term fertility of such soils enriched with biochar.
Despite its benefits, biochar is no miracle cure. How beneficial it is depends on the quality of the biomass used, the production process and the type of application. For example, if biochar is produced from wood that could otherwise have been used as a material (e.g. as construction timber), the carbon footprint is less positive. Energy recovery of the gases and oils produced during pyrolysis is also crucial for overall efficiency.
Another point: biochar is currently only available in small quantities and production is often still expensive. To better exploit the potential of biochar, a stable political context, support measures and clear quality standards are required. Switzerland could remove up to four million tonnes of CO2 annually by using biochar from sustainably produced biomass, according to Charnet, the Swiss biochar association. This means that biochar will be able to trap, in a sensible way, around a third of the fossil fuel emissions that are still being produced when we are at net zero (in 2050). Its use in agriculture will avoid the release of a further one to two million tonnes of CO2e.
In Europe, there are now standards for quality assurance, such as the European Biochar Certificate (EBC) from Carbon Standards International (CSI), which was co-developed with the Ithaka Institute, an international network for carbon strategies and climate-smart farming. The CSI Global Biochar C-Sink standard guidelines guarantee that the biochar originates from sustainable biomass, is produced by low-pollution methods and is used safely. The carbon sink capacity certified in this way constitutes an important contribution to climate protection and will enable us as a society to take a decisive step closer to the goal of net zero greenhouse gases.
Biochar is a fascinating tool for carbon sequestration and improving agricultural systems. Used correctly, it offers a robust, scalable and, at the same time, nature-based tool to combat climate change. But as with all solutions, it is not a substitute for drastically reducing emissions – whether in your own company or as a private individual. Rather, it is a useful addition. Realising its full potential requires close collaboration between the forestry, agriculture and energy sectors, awareness of the value of CO₂ and support for a wide range of climate protection projects involving biochar.
Sources:
IPCC 2018. Global Warming of 1.5°C. An IPCC Special Report
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