Charcoal burning

Is biochar our only chance? Charcoal goes carbon negative

In Business and Environment, Environment, Ethical and Eco Agriculture, Sustainable Building, Development and Energy by Martin Oliver2 Comments

Scientists investigating climate change are pointing to a difficult future ahead. As the world warms, positive feedback mechanisms are causing emissions to accelerate.


In Siberia, the melting permafrost is starting to release methane hydrates, and as the Arctic shrinks and white ice becomes dark ocean, increasing amounts of heat are being absorbed there.

Influential NASA scientist James Hansen has endorsed the view that the world needs to keep CO2 levels below 350 parts per million (ppm) to avoid the risk of reaching a ‘tipping point’. This challenge is made far harder by the fact that we are already at 385 ppm and carbon concentrations are rising annually by about 2.5 ppm. If Hansen is right, we will need to find a way to pull carbon out of the atmosphere in huge quantities.

Charcoal soils

In the 1950’s, a Dutch soil scientist known as Wim Sombroek discovered numerous pockets of highly fertile soil in the Amazon Basin. Added together, these were found to extend over a vast area roughly equivalent in size to France.

Containing numerous pottery shards, these soils are believed to have been deliberately created by a vanished civilisation hundreds of years ago. Black in colour, they are very rich in carbon, and were given the name terra preta (Portuguese for ‘dark earth’.) They were formed by the addition of charcoal to the soil, a practice that also has a long history in Japan.

Johannes Lehmann, a soil management professor at Cornell University, has spent the last few years thoroughly researching terra preta, and investigating a remarkable fine-grained charcoal known as biochar, or agrichar. This is arousing much interest among environmentalists, and is subject to energetic debate and research.

A carbon-negative breakthrough: pyrolysis

Traditionally, waste material from trees was often destroyed through burning. This still continues today, despite having been acknowledged as a significant source of carbon and soot entering the atmosphere. However, when sustainably sourced biomass is used for energy production, it is considered to be carbon neutral; carbon dioxide emitted via the combustion process is later absorbed by growing trees.

Biochar goes a step further and is actually carbon negative, removing carbon from the atmosphere to store it in the soil. To avoid the release of carbon during production, biochar is created in a special low-temperature kiln or oven designed for the chemical decomposition (pyrolysis) of organic matter in the absence of oxygen. It is charred rather than being burned.

Using biochar, the ‘slash and burn’ agriculture of tropical regions could be transformed into an environmentally beneficial ‘slash and char’ process. While today’s primitive shifting cultivation practices (slash/burn/move to the next area) lock people into a cycle of deforestation and generate huge carbon emissions, a biochar alternative could solve numerous problems in one stroke. The low-fertility soils of tropical regions could be improved, poverty would be alleviated, rural economies boosted and food security enhanced.

According to Mike Mason of the UK biomass energy company Biojoule, the world creates around four billion tonnes of agricultural waste products annually. From a waste minimisation perspective, unwanted organic materials are an obvious candidate for biochar production, and in some cases would otherwise be pollutants. Australian examples include :

  • Industrial waste such as paper manufacturing byproducts.
  • Timbermill waste such as sawdust.
  • Forestry waste from timber harvesting.
  • Sewage sludge
  • Municipal waste
  • Wheat straw
  • Sugarcane waste (bagasse.)

Soil benefits

When organic matter is left to decompose on the soil in a traditional manner, only a small percentage will eventually turn into soil carbon. Unlike this practice, biochar added in the form of pellets sequesters carbon in the soil for hundreds or thousands of years, depending on the material used and the temperature at which it was created.

The numerous benefits for soils include improved water quality, less leaching of nutrients, reduced soil acidity, and less need for irrigation. Biochar is extremely porous, giving it a large surface area that serves as a suitable habitat for soil micro-organisms and fungi to thrive. Plant experiments have shown dramatic increases in growth, with yields doubling, and in some cases trebling. Soil emissions of the greenhouse gases methane (21 times more powerful than CO2) and nitrous oxide (296 times more powerful) are greatly reduced.

Addition of biochar to the soil also reduces the need for chemical fertilisers that contribute to climate change through the large quantities of fossil fuels used in their manufacture, and their associated nitrous oxide emissions.

Inevitably, biochar is set to become an important part of the solution to world hunger. It refutes those interests warning us that we can only hope to feed the world with broadscale mechanised agriculture, monocultures, corporate control, and genetic engineering.

Biochar fuel sources

The production of biochar yields two other useful substances – bio-oil and syngas. Bio-oil is an organic alternative to petrochemical fuel oil, and can be further refined to produce petrol and diesel substitutes. The other fuel byproduct, syngas, is a mixture of carbon monoxide and hydrogen that can be used in place of natural gas and LPG. These carbon-negative fuels represent an important breakthrough, as other energy sources so far identified are carbon neutral at best.

When carrying out pyrolysis, the biochar, bio-oil and syngas yields are determined by temperature. Lower temperatures yield more biochar, while high temperature pyrolysis (also known as gasification) results in a higher proportion of syngas. Lehmann has concluded from his calculations that emissions reductions are far greater from biochar soil applications than via the production of biochar fuels. However, there is a risk that our insatiable demands may lead to fuel production becoming the major focus.

Carbon credits

By 2100, Lehmann speculates that biochar could be capable of sequestering all the CO2 generated on the planet. However, this is unlikely without some kind of economic incentive. In his opinion, the biochar-making process will become economically viable once the price of carbon reaches US $37 (AUD $59) a tonne.

Biochar has the major advantage of providing the most dependable form of carbon sequestration. We might discover that the underground burial of CO2 from coal-fired power stations is limited by available space, and there is no certainty that it will remain underground indefinitely.

Carbon offset trees have a finite life, are at risk from forest fires, vandalism, wind, and pest attack. Questions have been raised about carbon accounting practices that immediately offset an amount of carbon that a tree will not have sequestered until many years into the future. Most importantly, forests could switch from being carbon sinks to become net carbon sources, as has already occurred in Canada.

However, before biochar can be treated as a carbon credit, one hurdle is the boring question of standardisation. Biochar is not a standard product, and the range of variable factors includes the feedstock, the production temperature and its stability in the soil.

In Australia, under current proposals, agriculture will not be included in the government’s Carbon Pollution Reduction Scheme until 2015 at the earliest, with a decision to be made by 2013. It seems unlikely that biochar will be part of the scheme for several years, although in January, Coalition leader Malcolm Turnbull put forward an alternative climate action plan featuring biochar as one of the planks.

Research around the world

Knowledge of biochar is still at an early stage, and research is underway in many countries. Australia is at the forefront of these investigations, and for a good reason. Most of our soils contain less than 1% carbon, while 2% would be ideal for productive agricultural systems. In comparison, terra preta soils have a carbon content of up to 9%.

At Wollongbar in Northern New South Wales, Dr. Lukas van Zwieten of the Wollongbar Primary Industries Institute is carrying out trials with biochar made from timber mill and paper mill waste. So far, he has found that adding twenty tonnes per hectare to old dairy paddocks has resulted in a 150% increase in corn yields. Measurements of nitrous oxide emissions from the fields have also shown a sharp drop.

Biochar is currently being produced commercially in Australia on a relatively small scale. On the Central Coast, north of Sydney, a company known as Best Energies has designed its biochar plant with a feedback loop in which some of the syngas is fed back to power the production process. The NSW Department of Primary Industries is also developing the technology, and is investigating the feasibility of a further pyrolysis plant in the state located close to sources of suitable waste materials.

This May, the Gold Coast will host the Asia Pacific Biochar Conference. Van Zwieten emphasises that this will not just be a gathering of ‘boffins’, and that interested members of the general public are very welcome too.

Among the encouraging developments in overseas countries are these:

  • Last year, New Zealand’s Massey University created two new biochar professorships, and has plans to become a world centre for biochar research.
  • A Chilean research project by the University of Tarapaca is looking at how biochar can improve desert soils by tackling salinity and increasing water retention.
  • More than a thousand cacao farmers in a Belize cooperative that supplies Green and Black’s are involved in a biochar production trial.
  • A remarkable Irish biochar pioneer named Robert Flanagan has designed a cook stove-cum-biochar maker that can use agricultural waste as a feedstock. Half of world’s population currently uses charcoal for cooking

Is biochar our only hope?

James Lovelock, originator of the Gaia Hypothesis, is notorious for his trenchant criticism of environmental initiatives that he believes are too ineffectual. In a recent New Scientist interview, he goes so far as to say that biochar is our only chance for staving off the effects of climate change.

News about biochar has spread far more quickly than would have been possible in the pre-Internet era, and the world is quickly waking up to the central role it could take in tackling climate change. Biochar is an interesting solution too because it creates a focus of the debate some distance away from the contentious issue of industry emissions reductions, and transcends polarisations between environmentalists and the business community.

The question remains whether the world can fast-track the process and start creating industrial quantities of biochar soon enough.



Johannes Lehmann & Stephen Joseph – Biochar for Environmental Management (Earthscan, 2009)

International Biochar Initiative:

Biochar Fund:

BEST Energies Australia:

Australian Biochars:

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