Biochar is a form of charcoal that is made by burning organic matter in a combustion chamber with limited oxygen, a technique known as ‘pyrolysis’.
Pyrolysis makes the wood, manure, or crop waste used in the process more structurally stable, making biochar difficult to break down. This means that biochar can remain in the same form for hundreds of thousands of years.
Because of its stability, biochar can store carbon. And because plants are part of the natural carbon cycle, taking carbon from the air and releasing oxygen, by locking plants’ carbon in biochar, carbon is removed from the atmosphere. This means that biochar could be a long-term carbon sink, helping to sequester carbon from the atmosphere are store it safely for millennia.
Pyrolysis also releases a great deal of heat and gas, which can be used to produce energy. About half of the initial biomass can be used as energy, and the other half turns into biochar, which can then be sequestered.
This remnant organic matter is useful as a soil conditioner. Biochar improves soil quality by decreasing acidity, increasing water-holding capacity, improving nutrient retention, and reducing the release of other greenhouse gases such as methane. This means that by mixing biochar with agricultural soil, the quality of the land can improve, helping to increase food production.
While biochar sounds miraculous – it is carbon negative, boosts crop yields and provides sustainable energy – it is not without its flaws.
Because biochar relies primarily on plantations, it could take land away from forests and agriculture. This might mean deforestation and reduced food production.
Indeed, in order to grow the quantity of biomass required to sequester and offset all of our current carbon emissions, every piece of agricultural land would need to grow biochar plantations.
That would mean turning productive farmland into ash, and native forests into water-sapping monocultures, causing water shortages and global famine.
Considering that the 2007-2008 world food crisis was caused by changing agricultural lands into biofuel plantations, some caution is warranted before embracing biochar as a primary solution to climate change.
CSIRO Land and Water, ‘Biochar’, CSIRO, 21 January 2009, p. 1,http://www.csiro.au/files/files/pnzp.pdf
Suzannah Lyons, ‘What is Biochar?’, ABC Science, 4 March 2009, http://www.abc.net.au/science/articles/2009/03/04/2507270.htm
CSIRO Land and Water, ‘Biochar’, CSIRO, 21 January 2009, p. 2, http://www.csiro.au/files/files/pnzp.pdf
Geotimes, ‘Black Gold Agriculture’, American Geological Institute, 5 June 2008, http://www.youtube.com/watch?v=2Ae9a8EaQds&feature=player_embedded
George Monbiot, ‘Woodchipthins with Everything’, The Guardian, 24 March 2009, http://www.guardian.co.uk/environment/2009/mar/24/george-monbiot-climate-change-biochar
Oxfam International, ‘Another Inconvenient Truth’, June 2008, http://www.oxfam.org/en/policy/another-inconvenient-truth