HU2506 | Summer 2008 | Science & The Public Sphere: The Example of Biochar | Terra Preta Nova

Biochar mitigating climate change




In addition to the garden and small-farm applications we’ve been considering for biochar, one of the scientific appeals of biochar is its potential to help mitigate global warming by sequestering carbon that would otherwise be released into the atmosphere. A new book — Slash and Char as Alternative to Slash and Burn — discusses the science behind biochar in some detail:


Energy and agricultural systems based on biochar could help tackle four of the world’s most pressing issues all at once:

  • they could allow resource poor farmers in the tropics to improve agricultural yields considerably and thus fight poverty and food insecurity;
  • they can reduce global carbon emissions on a massive scale by creating a stable carbon sink: as plants take CO2 from the atmosphere, store it in their tissue and are then turned into biochar sequestered in soils, the carbon stays locked up for centuries, possibly millenia;
  • they allow for the production of renewable carbon-negative bioenergy, either in the form of electricity or liquid fuels, and can thus bring energy to millions of the world’s rural households who currently lack access to modern energy;
  • they could become one of the keys to slowing tropical deforestation – itself a major source of greenhouse gas emissions – by prompting millions of shifting cultivators to change their current practise of ‘slash and burn’ agriculture to ‘slash and char’ instead. Shifting cultivation is caused by the rapid depletion of soils, forcing farmers to clear forest for new land every few years; in contrast, biochar amended soils would boost soil fertility, bring the farmers higher yields, thus limiting their need to take new land into cultivation.

Other readings that specifically address the potential for mitigating climate change from biochar development and use:

Lehmann, Johannes. “Biochar for mitigating climate change: carbon sequestration in the black.” FORUM GEOÖKOL. 18 (2), 2007.

Lehmann, J., Gaunt, J. and Rondon, M. (2006); “Bio-char sequestration in terrestrial ecosystems – a review”, Mitigation and Adaptation Strategies for Global Change, 11, 403–427.

Lehmann, J., “Bio-energy in the black.” Front Ecol Environ 2007; 5(7): 381–387.

At best, common renewable energy strategies can only offset fossil fuel emissions of CO2 – they cannot reverse climate change. One promising approach to lowering CO2 in the atmosphere while producing energy is biochar bio-energy, based on low-temperature pyrolysis. This technology relies on capturing the off-gases from thermal decomposition of wood or grasses to produce heat, electricity, or biofuels. Biochar is a major by-product of this pyrolysis, and has remarkable environmental properties. In soil, biochar was shown to persist longer and to retain cations better than other forms of soil organic matter.

Periman, Richard D. “Visualizing the Anthropocene: Human Land Use History and Environmental Management.” USDA Forest Service Proceedings RMRS-P-42CD. 2006.

“Significant Climate Mitigation Is Available from Biochar.”
IGSD/INECE Climate Briefing Note: 10 July 2008.

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