Every civilisation is dependent on the food it can grow itself and acquire or extort from neighbours. Evidence is now being found almost monthly that one flourished in the Amazon where the land is unsuitable for crops, being thin and acidic, and distances were too great to get supplies from neighbours. The civilisation appears to have lasted from the time of Plato until wiped out by a pandemic from Europe 500 years ago. Its secret was charcoal.

Black gold

Large areas of rich deep black soil in which potsherds are found at all levels, exist and remain extremely fertile. The soil is called terra preta and was obviously made by the incorporation of charcoal. The reason why charcoal increases fertility can be appreciated when it is seen under an electron microscope. Even charcoal dust consists of cavities surrounded by the skeletal carbon structure of the plants from which the charcoal was made. The cavities, of course, can accumulate and retain moisture. So mixing crushed charcoal with soil immediately increases the soil’s ability to retain moisture. This property immediately appealed to farmers I talked to in southern India where monsoon showers stream off the surface and leach out what little fertility exists in semi-desert conditions.

But the structure of charcoal has other properties as well. In the presence of dung, food waste, urine or other decaying matter, microbes will attach themselves to the endless carbon surfaces that surround the voids. Scientists have found that one gram of charcoal can have a surface area equivalent to two tennis courts. The skeletal structure of charcoal protects microbes from predators, and plant hyphae colonise the voids to feed on the nutrients that have been released by microbial activity. Once the charcoal has been crushed and charged, and mixed with soil, it will provide rich humus for plants. Fine-grained charcoal is now referred to as biochar because of its ability to increase biological activity.

Carbon capture

When land is converted to organic farming the soil carbon increases for at least twenty years. If charcoal is incorporated the amount of carbon in the soil increases even more. Industrial farming on the other hand reduces the land’s ability to retain carbon.

The soil in the tropics is particularly prone to losing carbon because of its temperature, so the most beneficial use of biochar would be for the practice to be adopted by small-scale farmers in the tropics, since these are the people that manage most of the land. Many trials and experiments are being carried out by individual enthusiasts. From those I have seen there is no single best approach. Once the idea is demonstrated or the theory explained, smallholders try to find ways to use it to suit their particular micro-climate, soil, crops and equipment. And their findings spread naturally to neighbouring farmers.

Biochar and climate

Globally, there are 800GtC (gigatonnes of carbon) in the atmosphere. Every year plants capture 58GtC and transfer most of it to the soil. In due course 58GtC is released back to the atmosphere. This is the carbon cycle: every 14 years the entire weight of atmospheric carbon passes through the soil. The longer this carbon remains in the soil the less of it will be present as carbon dioxide in the atmosphere at any given time.

Plants, even their leaves, can be charred before they release their carbon. If this charcoal is incorporated into the soil it will lock carbon away almost permanently in the way that forest fires have locked charcoal into the soil. No precise figures are available for the process but the potential is huge. Sustainable farming and the burial of charcoal therefore provide the best means available to reduce atmospheric carbon. Both are natural processes so have none of the dangers of some geo-engineering proposals. James Lovelock has even said, referring to global heating, 'there is one way we could save ourselves and that is through the massive burial of charcoal. It would mean farmers turning all their agricultural waste ... into non-biodegradable charcoal and burying it in the soil ... this scheme would need no subsidy: the farmer would make a profit.'

I find it scarcely believable that this fact is ignored in climate negotiations.

The risks

However there is a danger. If the burial of charcoal is incorporated into ‘economic mechanisms’ like CDMs or offsets, the monetary value of carbon credits could result in land being acquired by corporations for monoculture plantations to provide credits rather than food.

There are two sources of greenhouse gas emissions. Those from fossil fuels - coal, gas and oil - should be controlled at source where the fuels are dug out of the ground. Land-based emissions need a separate regulation. The best one I have found is called the Carbon Maintenance Fee.

Under the Carbon Maintenance Fee proposals, countries would be paid an annual fee for the carbon contained within their borders. This can be measured with the aid of satellites - both NASA and the FAO have most of the information in their tabulations of Net Primary Product (NPP), which record the amount of carbon in ‘above-ground biomass’ (trees and crops etc) together with the extent of different crops. Simple soil sampling can provide the soil carbon content for each crop. The technology and fee structure is already widely used in New Zealand and Australia.

Other proposals are based on regulations that would be difficult to enforce, e.g. 'you must reduce emissions by x percent!' The fee approach, however, would work by incentive. If a country’s carbon pool increases, its fee would also increase but, in addition, it would receive a substantial bonus. The reverse would apply to countries whose carbon pool reduces. Countries would therefore have an incentive to encourage organic farming, to bury charcoal and to retain their forests. The fee would need to be substantial so could be drawn from the proposed Tobin tax on currency trading.

James Bruges is the author of The Biochar Debate: Charcoal's Potential to Reverse Climate Change and Build Soil Fertility, published by Chelsea Green

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