Ploughing millions of tonnes of charcoal into the soil should be recognised as a way of cutting carbon emissions under the Kyoto Protocol’s clean development mechanism (CDM).1 So says the secretariat of the UN Convention to Combat Desertification in a proposal to the UN climate summit in Poznan (ENDS Report 407, pp 6-8 ) in regard to the Bali Action Plan.
Biochar is produced during pyrolysis of plant material, where the feedstock is heated in the absence of oxygen. A mixture of oil, carbon monoxide and hydrogen also result, which can be used for electricity generation or to fuel the pyrolysis equipment. Potential feedstocks include wood, crop residues, dedicated bioenergy crops or other organic wastes.
Both climate and agricultural benefits are claimed for biochar. It is carbon-rich and much more stable than other organic forms of carbon, so it can be used to sequester carbon in soils. Some uncertainty remains over its longevity, but it probably persists for at least hundreds of years depending on local soil type and climate.
Biochar has a porous structure with a high surface area that promotes soil colonisation by bacteria and fungi and is said to improve soil structure, nutrient and water retention especially in sandy soils. Reductions in the amount of water or fertiliser required might be expected, as well as fertility gains and reduced nutrient run-off to ground and surface waters.
Further investigation will be required to confirm the magnitude of these benefits, while problems may crop up. For instance, recent evidence from a long-term study in Sweden suggests biochar’s microbe-friendly environment can speed up the decomposition of other soil organic matter, releasing carbon dioxide or methane.2
More emissions savings through reduced fertiliser use, suppressing nitrous oxide formation, preventing methane from rotting biomass and displacing fossil-fuel derived energy are potentially available. But these are harder to quantify and are surrounded by increased uncertainties, making it harder to claim carbon credits.
A UK Biochar Research Centre has been set up at Edinburgh University to examine the issues surrounding biochar. It is receiving £1.8 million over five years from the Engineering and Physical Sciences Research Council.
Simon Shackley of the Centre’s research team is looking at socio-economic and regulatory aspects, including potential CDM accreditation. He points out the CDM’s executive board is inherently conservative, as they must protect the already-shaky credibility of Kyoto-tradeable carbon offsets. They will expect to see an evidence-based method for biochar, which is likely to need more research.
NGO Biofuels Watch points to the well-known unintended consequences of biofuels production, such as carbon debt from land-use change and increased food prices. Growth of dedicated biomass crops to produce biochar could face similar criticisms.
Emissions of particulates and persistent organic pollutants such as dioxins or polycyclic aromatic hydrocarbons from pyrolysis equipment will also face scrutiny, as will any potential health hazards of biochar application to farmland.
If is deemed to be a by-product of pyrolysis, biochar might be classified as waste in the EU. It would then be subject to the stringent requirements of the waste framework Directive, with permits required before application to farmland would be allowed.
Carbon Gold, a firm set up to run biochar projects funded through carbon offsets, believes these problems can be overcome. It was started by confectionery firm Green and Black’s founder Craig Sams and Dan Morrell, who founded Future Forests (now the Carbon Neutral Company). Mr Sams summarised their philosophy as "beyond biofuels… a lot of lessons have been learned."
Carbon Gold has advanced plans to trial biochar in the Toledo region of Belize, starting in mid-2009. It hopes to recruit up to 1,200 organic cacao farmers who already supply chocolatier Green and Black’s, now owned by Cadbury. They would collect 10-20 tonnes per hectare a year of shade-tree trimmings and other crop waste, which would be burned or left to rot. From a total area of up to 6,000 hectares this could yield about 12-24,000 tonnes of biochar a year.
Assuming 80% carbon content in the biochar, the firm hopes the Toledo project will generate carbon offsets equivalent to 35-70,000 tonnes of CO2 a year. Proponents say that if implemented for crop wastes worldwide, biochar could offset 3-4 billion tCO2 per year.
Carbon Gold’s offsets will initially be sold under the Voluntary Carbon Standard (VCS), which will provide "ample" funds until 2012. Mr Sams hopes their VCS methodology will be a stepping stone for eventual inclusion in the CDM.
But advocates "have to avoid creating the impression there’s some sort of magic bullet here," warns Edinburgh University’s Dr Shackley. He makes clear that biochar will only ever form one part within a broader climate mitigation strategy and meanwhile "there is a danger of overselling before it’s been properly investigated".