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Credit: Jim Richardson/National Geographic Creative

Food

Biochar

Researchers and archeologists from Embrapa, a network of Brazil’s agricultural research stations, hover around an excavation showing how deep biochar (terra preta) is buried in Amazonian soils. In Manaus, the Embrapa staff has planted annual crops in terra preta–laden soils for forty years and has been unable to exhaust or ruin their fertility or productivity. Some scientists call the potential of terra preta nova the equivalent of a “black revolution” in agriculture.

In ancient Amazonia, the waste disposal method of choice was to bury and burn. Wastes were baked beneath a layer of soil. This process, known as pyrolysis, produced a charcoal soil amendment rich in carbon. The result was terra preta, literally “black earth” in Portuguese. Today, terra preta soils cover up to 10 percent of the Amazon basin, retaining extraordinary amounts of carbon.

These ancient roots of what is now called biochar have modern promise for agriculture and the atmosphere. Biochar is commonly made from waste material ranging from peanut shells to rice straw to wood scraps. During the slow baking of biomass in the near or total absence of oxygen, gas and oil separate from carbon-rich solids. The output is twofold: fuels that can be used for energy and biochar that can be used to enrich soil.

When biomass decomposes on the earth’s surface, carbon and methane escape into the atmosphere. Biochar retains most of the carbon present in biomass feedstock and buries it. Rendered stable, that carbon can be held for centuries in the soil—a much-delayed return to the atmosphere. Theoretically, experts argue, biochar could sequester billions of tons of carbon dioxide every year.

References

terra preta soils…10 percent of the Amazon: Mann, C. C. “The Real Dirt on Rainforest Fertility.” Science 297, no. 5583 (August 2002): 920–923.

Wim Sombroek uncovered…black earth: Sombroek, Wim. Amazon Soils: A Reconnaissance of the Soils of the Brazilian Amazon Region. Pudoc, Centre for Agricultural Publications and Documentation, 1966.; Woods, William I., Wenceslau G. Teixeira, Johannes Lehmann, Christoph Steiner, Antoinette WinklerPrins, and Lilian Rebellato, eds. Amazonian Dark Earths: Wim Sombroek’s Vision. Berlin: Springer, 2009.

one gram of biochar…surface area: Chia, Chee H., Adriana Downie, and Paul Munroe. “Characteristics of Biochar: Physical and Structural Properties.” In Biochar for Environmental Management: Science and Technology, 89-109. London: Earthscan, 2015.

crop yield increase of 15 percent: Jeffery, Simon, Diego Abalos, Kurt A. Spokas, and Frank G.A. Verheijen. “Biochar Effects on Crop Yield.” In Biochar for Environmental Management: Science, Technology and Implementation, 301-326. London: Earthscan, 2015; Jeffery, Simon, Frank G.A. Verheijen, Martijn van der Velde, and Ana Catarina Bastos. “A Quantitative Review of the Effects of Biochar Application to Soils on Crop Productivity Using Meta-Analysis.” Agriculture, Ecosystems and Environment 144, no. 1 (2011): 175-187.

[potential to] sequester…carbon dioxide: Kleiner, Kurt. “The Bright Prospect of Biochar.” Nature Reports Climate Change (2009): 72-74; Hertsgaard, Mark. “As Uses of Biochar Expand, Climate Benefits Still Uncertain.” Yale Environment 360. January 21, 2014.

[growth in] companies: IBI. State of the Biochar Industry 2015, International Biochar Initiative, 2015.

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Errata

p. 64

Revision: It was the hallmark of an agricultural system that differs dramatically from pervasive practices today: the wholesale conversion of Amazonian forest to annual crops, such as soybeans for livestock feed. When forest is cleared and vegetation burned, a residual layer of carbon remains, but only for a short period of time.

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Technical Summary

Biochar

Project Drawdown defines biochar as: a biosequestration process for converting biomass to long-lived charcoal (and energy) which can be used as a soil amendment. This solution provides an alternative to disposing of unused biomass through burning or decomposition.

Biochar is a carbon-rich, highly stable charcoal soil amendment produced as a byproduct of pyrolysis, a bioenergy generation process. The production of biochar effectively stabilizes photosynthetic carbon by abating emissions that would otherwise occur if biomass feedstocks were allowed to follow their typical decomposition and disposal pathways, particularly for the great quantity of crop residues that are burned today.

Applying biochar to soils further stabilizes its carbon by protecting it from alternate loss pathways and can reduce other soil greenhouse gas emissions (though this emissions reduction impact is not modeled in this study). In infertile soils, such as sandy soils with low cation exchange capacity, biochar can reduce loss of nutrients through leaching.

Biochar is something of a new category and is not precisely replacing a current practice, but can be seen as an alternative to other uses of biomass such as burning.

Methodology

Total Addressable Market [1]

Total demand for biochar in 2050 is estimated at 108.5 million metric tons. Current biochar production is estimated at 0.007 million metric tons. The limit for production is biomass feedstock availability, which was calculated using Food and Agriculture Organization data on tons of crop residue biomass burned per year from 1961-2014 (FAO, 2017).

The study assumes that a maximum of 50 percent of the crop biomass which is currently burned would be available for biochar production, with the remainder used in conservation agriculture, compost production, methane digestion, etc. The carbon content of the biomass was assumed to be 50 percent on a dry weight basis. The growth trend in biomass burning was extended to 2050 via our data interpolator. The implementation unit for this solution is biochar production facilities.

Future adoption of biochar was based on interpolation of data from biochar sales data from 2013-2015 (International Biochar Initiative, 2015).

Adoption Scenarios [2]

Impacts of increased adoption of biochar from 2020-2050 were generated based on three growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

  • Plausible Scenario: This scenario leads to the production of 983 biochar facilities.
  • Drawdown Scenario: As the carbon benefits of biochar are much higher than those of crop residues left lying on the fields, an aggressive production of 1,644 biochar facilities was considered under this scenario.
  • Optimum Scenario: An aggressive production of 1,827 biochar facilities was considered under this scenario.

Emissions, Sequestration, and Yield Model

Avoided emissions from biochar are estimated at 0.82 tons of carbon dioxide-equivalent per ton of feedstock. This reflects the amount of carbon dioxide-equivalent sequestered in the form of biochar, that would otherwise have been emitted from the biomass used as feedstock if it had been burned or decomposed. This figure is the result of meta-analysis of 49 data points from 10 sources.

An 18 percent yield gain was modeled for biochar-amended soils, based on figures used by the Intergovernmental Panel on Climate Change (IPCC).

Financial Model

The first cost per biochar facility is US$25.3 million. [3] This is based on meta-analysis of 17 data points from 2 review sources. Operating costs are US$58 per ton of biochar produced, based on meta-analysis of 15 data points from 2 review sources. These figures are not comparable with a conventional practice, as biochar represents a new industry.

Note: The first printing of Drawdown incorrectly states that financials are too variable to be determined. Costs were modeled, but the profits and savings to both producers and end users are too variable to determine as the modern biochar industry is still in its infancy. Drawdown is in the process of revising the model to incorporate costs and savings along the chain to the end user.

Integration [4]

A key constraint for this solution is the total availability of biomass feedstock. The model assumes that the maximum feedstock available is 50 percent of crop residues that are currently burned, with no dedicated feedstock production. This is because crop residues are utilized in solutions like conservation agriculture, and in the model all dedicated biomass feedstocks are used in biomass energy production, with none available for biochar.

Results

Total adoption in the Plausible Scenario is 983 biochar facilities producing 58.3 million metric tons of biochar by 2050. This represents 54 percent of the total addressable market. Climate impact is 0.8 gigatons of carbon dioxide-equivalent sequestered from 2020-2050. Net cost is US$31.3 billion. Financial data was too limited and variable to estimate net savings.

Total adoption in the Drawdown Scenario is 1,644 biochar facilities producing 97.5 million metric tons of biochar by 2050. This represents 89.8 percent of the total addressable market. Climate impact is 1.4 gigatons of carbon dioxide-equivalent sequestered from 2020-2050.

Total adoption in the Optimum Scenario is 1,827 biochar facilities producing 108.4 million metric tons of biochar by 2050. This represents 99.9 percent of the total addressable market. Climate impact is 1.6 gigatons of carbon dioxide-equivalent sequestered from 2020-2050.

Discussion

Benchmarks

Climate impacts produced by the Drawdown model (0.08-0.09 gigatons of carbon dioxide-equivalent per year in 2050) are much lower than a benchmark reported by the IPCC, which estimates 3.67 gigatons of carbon dioxide-equivalent per year (2014). This is in part based on their estimate of 1.01 gigatons of biomass carbon, ten times higher than out maximum feedstock estimate. This benchmark also includes impacts of soil sequestration from biochar application, which this study determined was lacking sufficient data to model effectively.

Limitations

The biochar solution has a number of limitations, most based in the nascent state of the industry. A key area is biomass feedstock availability, which would be useful to model across the many solutions that utilize it (e.g., clean cookstoves, biomass, conservation agriculture, etc.). Availability of more robust data on the soil sequestration impact of biochar application would also be useful. More financial data, particularly revenues and profit margins, will be key to economic projections. Future studies could also model the energy production impact of biochar production.

Conclusions

For a period of time, biochar was billed as a "silver bullet" to mitigate climate change. While our model certainly does not show this to be the case, biochar has an important role to play in biosequestration and soil fertility improvement.


[1] To learn more about the Total Addressable Market for the Food Sector, click the Sector Summary: Food link below.

[2] To learn more about Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Land Use Sector-specific scenarios, click the Sector Summary: Food link.

[3] All monetary values are presented in US2014$.

[4] For more on Project Drawdown’s Food Sector integration model, click the Sector Summary: Food link below.

Full models and technical reports coming in late 2017.

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