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Climate Change and Carbon Sequestration

How Can Biochar Be Carbon-Negative?

Fossil fuels are carbon-positive -- they add more carbon to the air. Ordinary biomass fuels are carbon neutral -- the carbon captured in the biomass by photosynthesis would have eventually returned to the atmosphere through natural processes -- burning plants for energy just speeds it up. Sustainable biochar systems can be carbon negative because they hold a substantial portion of the carbon in soil. The result is a net reduction of carbon dioxide in the atmosphere, as illustrated below.

Biochar and carbon sequestration

Biochar can hold carbon in the soil for hundreds and even thousands of years. Biochar also improves soil fertility, stimulating plant growth, which then consumes more CO2 in a feedback effect. And the energy generated as part of biochar production can displace carbonpositive energy from fossil fuels. Additional effects from adding biochar to soil can further reduce greenhouse gas emissions and enhance carbon storage in soil. These include:

  • Biochar reduces the need for fertilizer, resulting in reduced emissions from fertilizer production.
  • Biochar increases soil microbial life, resulting in more carbon storage in soil.
  • Because biochar retains nitrogen, emissions of nitrous oxide (a potent greenhouse gas) may be reduced.
  • Turning agricultural waste into biochar reduces methane (another potent greenhouse gas) generated by the natural decomposition of the waste.

Diagram courtesy of Nature Publishing Group

For more information on measuring the stability of carbon in soils, please see more about IBI's work with the Carbon Stability Test Methodology.

How Much Carbon Can Biochar Remove from the Atmosphere?

Carbon ScenariosIBI has developed a simple model to predict the carbon removing power of sustainable biochar systems. The figures here show the results of this preliminary model. We expect these answers will change as more is learned about the impacts of biochar, but the model gives a sense of what is possible.

The top figure on the right shows several scenarios that assume biochar production from waste biomass only, which is a small fraction of Earth's annual net primary production (NPP). Counting only the impacts of biochar burial in soil, and without considering the displacement of energy from fossil fuels, we can conservatively offset one quarter of a gigaton of carbon annually by 2030.

Optimistically, we could achieve one gigaton of offsets annually before 2050.

Annual carbon OffsetsIn the "Optimistic Plus" scenario, we account for reductions in nitrous oxide emissions and for the feedback effect of increased biochar production that may arise from increased plant growth in soils enhanced with biochar.

The second figure highlights additional carbon offsets possible if energy from biochar production displaces fossil fuel energy, and if CCS (carbon capture and storage) is used.

For a fuller explanation of the scenarios and references, please see How Much Carbon Can Biochar Systems Offset - and When?