Biochar: An answer to global warming or a menace?

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By Renfrey Clarke

May 21, 2009 -- Sometimes you have to hand it to capitalism. It’s sheer magic the way the system takes promising concepts, steeps them in the transformative power of the market – and turns them into howling social and environmental disasters.

Take biofuels, for example. With fossil fuels warming the planet, why not, indeed, take advantage of the fact that plants use carbon dioxide from the atmosphere to produce sugars and oils that can be turned into substitutes for petrol and diesel?

We all know where that finished up. A big chunk of the US corn crop was distilled into grain ethanol. Corn prices soared on the extra demand, increasing costs for a broad range of food production. Anyone unable to pay went hungry. When US drivers filled up with bio-ethanol, they were in effect burning the tortillas of the Mexican poor.

But is the technology the problem? Or the system?

Whatever the case, when activists of the international group Biofuel Watch noted the attention being paid to another attractive concept – sequestering carbon by turning plant matter into biochar (finely divided charcoal), and incorporating it in agricultural soils – their suspicions were raised immediately. A research paper was prepared, critically examining biochar and the promises made for it. An international appeal was circulated -- entitled “‘Biochar’, a new big threat to people, land and ecosystems” -- and opposing calls to include biochar in the international carbon trading scheme, the Clean Development Mechanism (CDM). 

So far, the appeal has been signed by more than 120 environmental organisations around the world. Among their number is Friends of the Earth Australia.


The biochar sceptics have cause to be suspicious. Enthusiasts for biochar now include Malcom Turnbull, leader of the conservative Australian federal parliamentary opposition. Considering Turnbull’s other enthusiasms – “clean coal”, for one – his championing of biochar set alarm bells ringing immediately.

Added to which, some of the proposals made for biochar sequestration are downright barmy. British writer George Monbiot records New Zealand environmentalist Peter Read as calling for new worldwide biomass plantations of trees and sugarcane covering 1.4 billion hectares, with the plant matter to be turned into biochar and ploughed into soils. Trouble is, the world’s total cropland only comes to 1.36 billion hectares.

Furthermore, and as Biofuel Watch’s appeal rightly points out, the effects in the developing world of including biochar in the CDM trading scheme would be disastrous. An assured world market for biochar would turn the substance into an internationally traded commodity. Biochar is non-perishable and easily transported; give it a further boost by allotting it carbon credits, and producing it for export would in all likelihood yield better profits in developing-world settings than growing food crops.


In ideal circumstances, the growing of tree crops for biochar could be incorporated into village agricultural systems as a superior use for degraded or marginal land used previously for sparse (and highly destructive) grazing. The biochar produced in small local kilns would be dug into soils, and its dramatic benefits for soil productivity (this is well demonstrated) would aid local nutrition and increase the food surpluses which farmers could supply to towns.

But add in carbon credits, and the world capitalist market would destroy this harmonious picture. The biochar would not be used locally, but would be exported. Large-scale commercial agriculture, often internationally based, would respond to the price signals and move in. The tree plantations, offering superior profits, would spread from the former goat pastures to occupy prime agricultural land, where they would enjoy first call on resources of water and fertiliser.

Food production would shrink. An array of economic pressures would drive small farmers off their land, and wealth in rural districts would become tightly concentrated in the hands of the richest entrepreneurs able to take advantage of the new conditions. Local communities would be ravaged.

The problem, however, would not be biochar, but capitalism.

Dodgy science

So should environmental organisations sign up to Biofuel Watch’s appeal? As things stand, no. Action is needed, but the ammunition needs to be of much higher quality. The science in the document is dodgy, and many of the arguments irrelevant or overblown. That may seem a harsh judgment, but it is borne out if we look in detail at some of the appeal’s assertions:

  • “It is not yet known whether charcoal in soil represents a carbon sink at all...”

In what is a relatively new field of research, many unanswered questions remain. This, however, is not one of them. In a set of notes posted in March, one of Australia’s most respected authorities on biochar, CSIRO land and water scientist Evelyn Krull, points out that biochar “has a chemical structure that makes it very difficult to break down by physical, biological and chemical processes”. “We know”, Krull continues, “that biochar is stable over the timescales of any [carbon] abatement scheme (100 years).”

Not all biochars are the same – their individual properties depend on the feedstock and on the temperature and duration of the pyrolysis process through which they are made. But charcoal can remain intact in nature for more than 10,000 years – it provides, after all, the basis for carbon dating. Highly fertile, carbon-rich terra preta (dark earth) soils in the Amazon region of South America indicate very strongly that when incorporated into agricultural land, biochar can persist for thousands of years. The terra preta soils are believed to have been created deliberately by ancient peoples who produced charcoal and dug it into the ground along with food scraps and other organic matter.

  • “There is no consistent evidence that charcoal can be relied upon to make soil more fertile….”

If this were the case, the Amazonian peoples would hardly have bothered. True, the evidence is not 100 per cent consistent. But will, say, 90 per cent do?

Trials of biochar in relatively carbon-rich soils in Sweden found that soil fertility actually declined, apparently because the boost to soil microbial activity provided by the biochar speeded the decomposition of existing soil organic matter. But in leached tropical soils, and also in the ancient, low-fertility soils characteristic of Australia, the experience has been diametrically different. Evelyn Krull again: “We know that biochar application can have positive results, particularly in sandy and infertile soils. Due to its chemical and physical nature (e.g. high degree of porosity and absorptive capacity), biochar has been shown to enhance soil fertility, resulting in increased productivity and in turn a build-up of organic matter in soil.”

  • “Combinations of charcoal with fossil fuel-based fertilisers made from scrubbing coal power plant flue gases… will help to perpetuate fossil fuel burning as well as emissions of nitrous oxide, a powerful greenhouse gas.”

One suspects energy companies have weightier reasons for continuing to burn coal than supplying biochar firms with extracts of flue gases. Meanwhile, there is good evidence that biochar, by improving soil structure and retention of plant nutrients, can allow crops to flourish with markedly lower applications of artificial fertilisers.

Nitrous oxide, which volume-for-volume has hundreds of times the warming effect of carbon dioxide, enters the atmosphere largely through the breakdown of nitrogen fertilisers. Not only does biochar allow the use of these fertilisers to be cut, but as NSW Department of Primary Industries scientist Annette Cowie observes, the reduction in nitrogen dioxide exceeds what would be expected from lower fertiliser use. “It seems that when you apply the biochar, that nitrogen transformation process is inhibited”, the G-Online site reported Cowie as saying in March. Studies have found that in some soils, nitrous oxide emissions decline by as much as 80 per cent.

  • “The process for making charcoal and energy (pyrolysis) can result in dangerous soil and air pollution.”

In principle, the slow pyrolysis process used to create biochar is exceptionally clean. Plant matter is heated in an enclosed, oxygen-poor environment at about 500º Celsius. Volatile carbon compounds are driven off, some of them to be condensed into a useful bio-oil. The remaining gases are burnt to provide heat to sustain the process and (in many cases) to generate carbon-neutral electricity. The exhaust gases that result from this combustion consist almost entirely of water vapour and carbon dioxide; small quantities of oxides of nitrogen that are created can be scrubbed from the exhaust stream using the biochar itself. The solid residues from the pyrolysis process are inoffensive – apart from the biochar, silica ash, plus nutrient elements including potassium and phosphorus.

Biochar, however, is a “garbage in – garbage out” proposition. If you make it out of toxic industrial wastes, you’re likely to have problems. Such practices need to be prohibited. But that is an argument for appropriate regulation, not for rejecting the technology out of hand.

No to market scams

In its handling of the science, Biofuel Watch’s appeal ignores salient facts while stretching others to make them seem to validate particular, preconceived conclusions. Thoughtful readers will spot this, and will not be encouraged to support the document’s correct and necessary criticisms of the CDM and of other market-based emissions abatement schemes.

The truth is that capitalist markets are a completely inappropriate mechanism for regulating environmental matters. Markets operate to secure profits for private entrepreneurs, not to allow optimum outcomes in dealing with complex natural systems.

Points such as these can be argued convincingly without giving strained and selective accounts of scientific findings, or creating needless prejudices against potentially valuable innovations.

[A shorter version of this article appeared in Green Left Weekly.]