Biochar: a cause for concern?
Biochar: a cause for concern?
By Almuth Ernsting /

Back in 2009, I discussed the claims that incorporating biochar in soils could help mitigate climate change in an Ecologist article.  At the time, biochar was included in a draft UN climate agreement: biochar carbon offsets were proposed and proponents were speaking about the potential for sequestering billions of tonnes of carbon from the atmosphere every year through biochar. 

The term biochar is generally used for charcoal added to soils. It can be made from any type of biomass. A widely promoted idea is for biochar to be produced in modern pyrolysis plants which also generate heat and electricity.However, such systems are not technically proven at a commercial scale. Virtually all biochar sold at present – commonly with promises of soil improvement as well as climate benefits - and most of the biochar used in scientific studies, has been produced through traditional charcoal making methods. Different types of biochar have very different chemical structures and properties, depending on how they were produced, at which temperatures, from which type of biomass, and how they were cooled and handled. 

In my previous article, I highlighted the lack of scientific field studies to show whether or not the basic claims made by biochar proponents were valid, i.e. the claims that biochar will sequester carbon over long periods while benefitting crop yields at the same time. I cited a declaration signed by 150 organisations worldwide which described biochar as “a new big threat to people, land, and ecosystems” and warned that carbon credits for biochar could trigger a new wave of land-grabbing for monoculture plantations. 

Four years on – have those concerns been realised? In August 2010, science magazine Nature Communications published an article which suggested that 12% of the world’s annual greenhouse gas emissions could be offset with ‘sustainable biochar’. As one of the authors later confirmed, this figure was based on the assumption that 556 million hectares of land would be converted to biochar production. That is an area 1.7 times the size of India. This confirmed my fears that an ambitious global biochar programme would require land-conversion to plantations on a vast scale.  

Yet the prospect of ambitious biochar programmes being implemented – and thus the threat of large-scale biochar land grabs - has receded. References to biochar were dropped from the UN negotiating text soon after civil society groups and government delegates objected. Biochar remains ineligible for carbon offsets under any carbon trading mechanism. Even if that was to change, it would make little difference: The UK Biochar Research Centre estimates that, if UK biochar was produced at a cost of £148 to £389, it would require a carbon price between £39 and £57 per tonne of carbon to make most types of biochar financially viable. Right now, the only two commercial suppliers in the UK, Oxford Biochar and Carbon Gold, are selling biochar at £4,333 and £5,950 per tonne respectively. Global carbon markets meantime have effectively collapsed. This collapse is due largely to governments failing to set or enforce emissions caps and over-allocating carbon emissions permits to polluters, thus destroying the demand for carbon offsets – although the very principle of carbon trading as a way of reducing emissions has come under increasing criticism, too. Under the EU Emissions Trading Scheme, which accounts for 90% of carbon trading worldwide, the price of a tonne of carbon is now “below junk status”, according to the Economist

Corporate support, albeit limited in scale, has mainly come from the Canadian tar sands industry, led by ConocoPhillips, who have been promoting it amongst a wider range of ‘carbon sequestration’ geoengineering approaches and undoubtedly as one way of ‘greening’ the image of one of the world’s most destructive industries. For example, ConocoPhillips has sponsored the ‘Biochar Protocol’ which aims to get biochar included into two carbon trading schemes – one of them being the Alberta Offset System, a carbon offset scheme primarily for the tar sands industry.  

Despite these concerns, the number of biochar projects worldwide has continued to grow. A World Bank funded survey in 2011 identified 150 biochar projects in 38 developing countries. Only a small minority of those projects has resulted in peer-reviewed studies. Project developers commonly announce spectacularly successful results without scientific scrutiny or statistical analysis.

In 2011, Biofuelwatch commissioned an independent researcher in Cameroon to investigate a project by the Belgian Biochar Fund in that country, which had reported ‘exceptional results’ and benefits for poor farmers. The reality was different: small farmers had been persuaded through spurious promises of carbon credits to provide land and labour for pilot ‘trials’, without remuneration. By the time the researcher, Benoit Ndameu, visited, the project had been abandoned and farmers were left angry, speaking of high hopes and broken promises. While farmers clearly did not benefit, Biochar Fund’s Managing Director used claims about the project to leverage 315 million from the Congo Basin Forest Fund for a biochar project in DR Congo, for which no results were ever published. As this shows, the fact that a project is small-scale and does not involve land-grabs does not guarantee it is beneficial or even benign. 

Fortunately, there are some biochar field studies that have been published – albeit few in number and none longer than 4 years in term, but this has allowed us to research many of the biochar claims and broader soil science reviews have also looked at biochar. Answers to some of the questions we raised in 2009 have begun to emerge – and they do not back up optimistic forecasts.

In 2011, we found and analysed the results of five relevant field studies which, between them, tested biochar on 11 different combinations of soil and vegetation. In 5 out of those 11 samples, adding biochar (except in one case at an extremely high rate of over 100 tonnes per hectare) did not increase the amount of carbon in the soils – i.e. there was zero carbon sequestration. In another case, adding biochar led to a temporary overall loss of soil carbon.  The authors did not offer any explanation for the likely reasons of this carbon loss in the article, however other studies have demonstrated that adding biochar to soils can stimulate soil microbes to degrade existing soil carbon, causing it to be emitted as carbon dioxide. 

In 3 cases, biochar increased soil carbon compared to adding nothing to soils – but not when compared to other common soil amendments, such as saw dust, manure and geen manure.  In just 3 out of 11 cases did biochar result in additional carbon sequestration, at least short-term but its long-term stability is still in question. This rather contradicts claims such as those by the UK Biochar Foundation that “biochar has properties which make it suitable for the safe and long-term storage of carbon in the environment”.  

Most biochar research now focuses on identifying and producing different ‘designer’ biochars with different properties including with particularly ‘stable’ carbon. Yet soil science reviews show that such findings tell us very little. As two such reviews show, the fate of any type of soil carbon cannot be predicted from looking at molecular structures or at what happens under laboratory conditions.

Carbon in organic residues may not last long under laboratory conditions but may remain in living soils for millennia. And black carbon, the form of carbon in biochar, which appears extremely stable under sterile laboratory conditions, may disappear rapidly from soils. It appears that the stability of carbon depends primarily on highly variable soil and climatic conditions. Those insights fundamentally undermine the case for biochar as a reliable way of sequestering carbon, although this has not stopped the International Biochar Initiative and their members and supporters from continuing to claim that “The carbon in biochar resists degradation and can hold carbon in soils for hundreds to thousands of years.”  

Biochar is also promoted as a way of improving crop yields. Those claims, too, are contradicted by science. Field studies reveal highly variable impacts. A recent synthesis review found that in half of all published studies, biochar had either no effect on plants or more worryingly, even suppressed their growth. The author cautioned that due to possible ‘publication bias’, the reported success in 50% of cases should not be taken “as evidence of an overall biochar likelihood of producing positive impacts”. 

Even if the claims made for biochar as a way to sequester carbon do not stack up, can it do any wider harm if farmers or gardeners in the UK use it?  Unfortunately, yes. Since modern pyrolysis plants remain unproven, biochar relies on traditional charcoal making – which is so inefficient that 85-90% of biomass carbon gets lost as carbon dioxide emissions to the atmosphere in the process.  From 2007-2011, the UK imported on average 70,876 tonnes of charcoal every year, which is a rising trend. Imports – from Africa, Latin America and SE Asia - account for 95% of charcoal used in the UK, adding to the pressure on tropical forests and to carbon emissions from shipping. Various charcoal projects aim to replace imports with UK-produced charcoal, but those efforts are futile if the demand for charcoal keeps going up. Promoting a new use of charcoal in this context seems irresponsible – all the more so when that use does not even have any proven benefits. 

Almuth Ernsting is a member of the Biofuelwatch team. 

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Biochar: a cause for concern?