Biochar
Description
Biochar as a negative emission technology uses plant growth to remove CO2 from the atmosphere. As plants grow, they absorb CO2 from the air through photosynthesis. Plant material is then turned into charcoal – known as biochar – through pyrolysis. During pyrolysis the plant material is heated to 400-500°C in the absence of oxygen in specialized facilities. Often crops or trees are grown specifically to produce biomass but some biochar projects use ‘leftover’ plant material, such as rice husks or plant material harvested during forest thinning. Biochar can be added to soil where under the natural conditions, it does not degrade for decades to centuries and so stores the carbon in the soil.
Reversal
Carbon storage reversal can occur if the soils, in which the biochar is buried, is disturbed so that the biochar decomposes and releases carbon back into the atmosphere. Reversal can also occur if issues occur during pyrolysis and the plant material is able to burn instead of being turned into charcoal.
Readiness and scale
Biochar as a NET is a relatively ready technology but there are only a small number of biochar projects around the world today. The upscaling of this technology is limited by the cost and availability of building, running and maintaining pyrolysis facilities. The potential scale of biochar depends heavily on the material used.
Co-benefits / limits
+ Incorporating biochar into soil can improve soil quality, water retention and can improve agricultural productivity.
+ The pyrolysis of plant material can also be used to produce electricity.
+ Use of biochar as soil amendment can reduce non-CO2 greenhouse gas emissions from soils.
– New biochar projects may be limited by the cost and availability of pyrolysis facilities needed to produce biochar.
– Verification and monitoring of the permanence of storage may be difficult.
– If crops are grown specifically to produce biochar, this can create competition with food crops for land and water and can cause deforestation.
Extra info
Biochar is often classified as a nature-based method, not a hybrid method. However, because of the necessary processing of the plant material to create biochar that is involved in this method, it can also be classified under hybrid methods.
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Support projects that use biochar and other methods and contribute to the removal of CO2 from the atmosphere.
