Biochar remains promising

By Bryan Walker 18/08/2011


A recent commenter on Hot Topic made critical reference to biochar, providing links to publications from Biofuelwatch. Since I have written posts in the past highlighting the favourable possibilities which biochar may offer I thought it was perhaps time to revisit the matter. Biofuelwatch is an organisation which works ’to raise awareness of the negative impacts of industrial biofuels and bioenergy on biodiversity, human rights, food sovereignty and climate change’.  It has recently published a report Biochar: A Critical Review of Science and Policy which sets out its disagreement with the claims of biochar advocates.

First, on the claim that biochar can act as a means of sequestering carbon over a long period, the review agrees that it is clear that charcoal can in some cases be stable over long periods, but adds that it is also clear that this is not always the case, and that the reasons for this variability are not well understood or controllable.

To the claim that biochar increases soil fertility the review responds that studies of soil fertility effects to date are all short term and therefore do not represent the impacts over time. It therefore objects to the promotion of biochar as a technology for improving the livelihoods of subsistence farmers in the developing world.

Overall the review accuses the biochar advocates of hype unsupported by scientific research or experience on the ground.

Biofuelwatch is clearly concerned that looming behind the advocacy of biochar on a large scale may be the spectre of forest monocultures and corresponding threats to biodiversity. That’s a proper concern, and it has already become apparent in the area of biofuels and bioenergy that some practices and proposals are unsustainable.

I certainly felt dismay when I read in the review that the only multinational so far lending support to biochar is ConocoPhillips and their main interest appears to be in a new source of carbon offsets for their tar sands investments in Canada. That’s not my interest. The attraction of carbon capture through biochar is that it might be a technology which enables us to pull down the current level of atmospheric CO2, not one that seemingly allows exploitation of fossil fuels to continue unabated.

However, it was difficult to understand why Biofuelwatch was so insistently negative about biochar’s possibilities, and there was a notable lack of specific reference to back up their objections. Even a company like World Stove, which makes pyrolysis stoves for the developing world, producing gas and leaving a residue of biochar, is criticised.

I had a look at World Stove’s response to the Biofuelwatch review and, seeking somewhere to start in a single post on a complex and contentious issue, thought I’d report some of what they have to say in their very reasonable eight-page statement.  They are somewhat bemused at the criticisms handed out by Biofuelwatch since they consider their stoves are intended ’to empower small farmers, increase food sovereignty, and decrease forestation, thereby preserving ecosystems and mitigating climate change’, aims very much in sympathy with what Biofuelwatch stands for.

Some 20 percent of the small waste biomass used to power the pyrolytic stoves is converted to biochar, and in this respect World Stove claims their process is actually carbon negative in leaving a residue which can be sequestered in the soil.

One of the criticisms levelled at them is that the amount of biochar produced is inadequate for the purpose of increasing crop yields, which needs to be at the rate of 20 tonnes per hectare to be effective. World Stove’s reply is that the common agricultural practice of side dressing allows even small amounts of char to achieve the high concentrations that are acknowledged as being beneficial to plants and soil.

The question of whether there is sufficient waste matter to supply biochar manufacture on a large scale is frequently raised, and it appears in Biofuelwatch’s criticism. World Stove has an impressive array of figures in response, of which I’ll mention only a few here. They quote one study which estimates that just 30 percent of crop waste from five major crops would provide 600 million tons of residue safely available for charring without reducing soil fertility or increasing danger of erosion.  Another study reports that in Egypt alone 20 million tons of rice straw are burned annually for disposal. Food waste is of enormous proportions; in the US alone it has been calculated to be the energetic equivalent of annual extraction from oil and gas reserves off the nation’s coastlines. All this is part of the biomass resource which can be accessed immediately, and World Stove repeats that biomass processing with a balance of energy and char products is the only method of producing energy that is potentially carbon negative.

Finally, World Stove offers some explanations to those presuming that small stoves in developing countries can hardly make much difference to the climate challenge the world is facing. The figures surprised me. People in developing nations have been calculated to use between 0.36 and 1.4 metric tons of wood, per capita, per year, for cooking and heating. The lower of these equates to emissions of 1,650,150,000 metric tons of CO2 per year from all traditional cooking stoves and open cook fires. Changing open burning to pyrolysis stoves would save that carbon already sequestered in trees. Using waste biomass for pyrolysis stove fuel would sequester another 265,530,000 metric tons of CO2 per year. A combination of the two values gives a total of 1,917,680,000 metric tons of CO2 saved per year by not harvesting trees and by creating biochar from waste biomass. That’s the equivalent of nearly two Pacala/Socolow wedges. For comparison, this would be similar to adding four times the current nuclear capacity to replace coal-burning power plants worldwide.  Of course, changing open burning to pyrolizing stoves throughout the developing world would be difficult, but on these figures it’s well worth attempting.

No doubt biochar can be over-hyped.  But I wouldn’t have thought that was the case with World Stove. Nor is it the case with the painstaking research being conducted in many centres in many countries. One of those is the New Zealand Biochar Research Centre at Massey University. An excellent Our Changing World programme on radio NZ gives a good idea of the range of the detailed research being undertaken there, and along the way outlines the issues associated with both the carbon sequestration and the soil enrichment aspects of biochar.  Well worth half an hour of listening time. It still looks a promising technology to me.