Biochar can sequester carbon cheaply

Amazonian topsoil enriched with charcoalOrganic matter, such as agricultural waste, heated in the absence of oxygen splits into two types of material: a charcoal (biochar), and hydrocarbon gases and liquids. When added to soils, the charcoal can provide a powerful fertiliser. The hydrocarbons can be burnt, either to generate electricity or to power an internal combustion engine. Biochar is exciting growing attention around the world. Charcoal’s ability to improve soils can sometimes be spectacular. But more importantly from a climate change perspective, charcoal is almost pure carbon and is strangely stable in soils. It seems to persist for centuries. Charcoal can therefore offer substantial opportunities for long-term sequestration of carbon. The valuable fuels from the biogases and liquids are also carbon-neutral since they contain CO2 previously captured during photosynthesis. As a third major benefit, soils fertilised with charcoal seem to need less artificial fertiliser, thus saving fossil fuels. Fewer applications of fertiliser would reduce the level of emissions of nitrous oxide, a particularly dangerous greenhouse gas.

Biochar manufacture represents a way of productively storing large amounts of carbon. But the carbon in the charcoal could be burnt to generate electricity instead of being stored in soil. Current emissions trading schemes, such as the European ETS, do not allow sequestered carbon to be considered as equivalent to a reduction in greenhouse warming emissions. This is a mistake that will need to be rectified. It make more sense to use agricultural land to make biochar and biogases/bioliquids than to burn the biomass in power stations. Power stations burning wood benefit from buying fewer emissions certificates and from the renewable energy subsidy, but there is no comparable benefit from storing carbon in the soil. This is an anomaly that should be removed.

Read More