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An Introduction to Biochar

The following is excerpted from The Biochar Debate: Charcoal’s Potential to Reverse Climate Change and Build Soil Fertility, available from Chelsea Green.

Charcoal and biochar

Charcoal is one of the oldest industrial technologies, perhaps the oldest. In the last decade there has been a growing wave of excitement engulfing it. Why?

Because some scientists are saying that we might be saved from the worst effects of global warming if we bury large quantities of it. Not only that: we can restore degraded land and get better harvests by mixing fine-grained charcoal — biochar — with soil. Others say that charcoal’s use could be just one of several technologies to mitigate climate change. Yet some maintain that it is an extremely dangerous technology. The jury is out on which is closest to reality. This Briefing aims to provide an overall view of the subject and describes the best way to encourage the appropriate use of biochar.

The theory is simple. Plants, through photosynthesis, capture carbon dioxide-the main greenhouse gas-from the air as they grow. The carbon of CO2 provides their structure and the oxygen is released for animals to breathe. If the plants are left to rot, the C and O combine again in a relatively short time to release carbon dioxide back into the air. However, if the plants are heated in the absence of oxygen — called pyrolysis — charcoal is formed. Charcoal is largely carbon. As anyone who has organized a barbecue knows, charcoal can be burned, in which case the carbon goes back up into the atmosphere. But if it is buried, the two elements take a long time to recombine as carbon dioxide. This means that some of the most abundant greenhouse gas can be taken out of the atmosphere and locked into the ground for a long time. Deep burial-rather like putting coal back where it belongs-is one way. But there is another option.

Additional excitement came with the discovery of deep dark areas of “terra preta do indio” — Indian black earth — in the Amazon rainforest where the soil generally is thin, red, acidic and infertile. The patches of terra preta are alkaline with a high carbon content, and contain pot­shards indicating that it was not natural: a pre-Columbian civilization had created it. It is extracted and widely used by garden contractors because it is so fertile. It has remained fertile and retained its carbon content through the centuries.

Terra preta is black because it contains large amounts of charcoal. Infertile land had been converted to fertile land that supported a thriving civilization through the wise use of the trees that had been felled. Could charcoal, therefore, not only be a vehicle for reducing global warming but also a means to increase the fertility of degraded land, and help feed the world?

Charcoal used for this purpose is referred to as biochar. Biochar is pulverised charcoal made from any organic material (not just wood) and, when mixed with soil, it enhances its fertility. It locks carbon into the soil and increases the yield of crops. To many, this appears the closest thing to a miracle.

The process of converting plant material to charcoal gives off heat together with gases and oils. Certain plants and certain processes produce a high proportion of charcoal, whereas others produce more gases and oils. This is where the problems start. These chemicals could become the main commercial attraction of biochar. As has been found with biofuel, growing crops to fuel cars can be more profitable than growing food to feed people. If left to the market, producers of biochar might buy up productive land, plant monocultures, and develop their equipment primarily to produce fuel and industrial chemicals.

Then there is the suggestion that the burial of charcoal should earn carbon credits. As above, the financial motive could lead to “growing carbon credits” in preference to growing food. And if widely adopted, as hoped, the carbon market would be flooded with credits; industry would buy them at fire-sale prices and carry on with business as usual to the detriment of the climate. A strong financial incentive to use bio­char is desirable, but carbon credits may not be the best approach.

There are two prime objectives. It is essential to find ways to sequester greenhouse gases if we are to avoid the worst effects of global warming. It is essential also to enable farmers throughout the world to use biochar if it can bring degraded land back to fertility and increase yields. The process cannot be left to “the market,” which has been described as an out-of-control demolition ball swinging from a high crane.

In the final chapter I outline twin policies for reducing greenhouse gases in the atmosphere. The first policy would ensure a reduction in the use of fossil fuels. The second concerns our use of land. The requirements for the two are so different that separate regulations are necessary. The first is called cap-and-dividend (in the US). The second is the Irish proposal for a Carbon Maintenance Fee (CMF), which would provide a powerful incentive for every country, rich and poor, to enable its farmers, businesses and individuals to maintain land-based carbon.

Read the full excerpt on Reality Sandwich.

Charcoal image by Gregory Moine, courtesy of Creative Commons license.

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