Biochar: powdered gold or useless soot?

Today I will be assessing the case for biochar: a CDR scheme that involves burning biomass (plant material) under anaerobic conditions into charcoal and burying it. This process ‘locks’ CO₂ deep underground for centuries – similar to coal - that would otherwise be released during natural decomposition (Das et al, 2014). It is understood to be ‘carbon-negative’ as it results in a net outflux of atmospheric CO₂. Recent carbon sequestration potential has been estimated at 1.3 GtC yr^-1 (approx. 12% of GHG emissions) (Smith, 2016).

Influential scientists such as James Lovelock have supported the use of biochar in mitigating climate change:

It is proposed as a holistic solution to many anthropogenic issues: climate change, inefficient fertiliser use and poor agricultural yields (Figure 1). This is because biochar is understood to enrich highly weathered, infertile soils, thus maximising crop yield potential. Furthermore, it can increase soil pH which is beneficial for the availability of nutrients such as phosphorus. Inefficient use of phosphorus rock, a non-renewable mineral, is of major concern due to food security and water security in a heavily populated world (Carpenter and Bennett, 2011). Therefore, the use of biochar could safely regulate the P planetary boundary outlined by Steffen et al (2015) by reducing reliance on fertilisers.

Figure 1: The potential benefits of biochar

The video below explains biochar technology in greater depth:

Are James Lovelock’s claims of charcoal’s ‘infinite lifespan’ credible? Some experiments suggest biochar can be easily eroded after rainfall events (Fister et al, 2013) which would compromise its carbon sequestration potential. Furthermore, biochar functional quality depends on the biomass: e.g. woody biomass produces higher quality biochar than grass (Qian et al, 2015). Another key quality concern is the formation of toxic organic compounds during the burning stage (Dutta et al, 2016). The long term environmental fate of such contaminants is highly uncertain.

The scalability of biochar application is unknown: in the UK, the extent of land providing the most carbon-efficient use of biochar is small. Other key concerns include how global-scale biochar application would influence biodiversity and land-use decisions (Brownsort et al, 2010). Lastly, a robust regulatory framework for the biochar industry would be needed to prevent biochar-plantations at the expense of food crops  (Levitan, 2010).

On the whole – I think biochar technology is appealing due to its simple formation and efficient carbon sequestration potential. However, a significant amount of research is needed into the long-term fate of biochar application, as well as strong regulation to avoid it becoming gimmicky.

I will be wrapping up my blog soon and would be interested to hear your thoughts on geoengineering schemes – so please vote in the poll on my blog!