What Is Charcoal And How Can Bio Char Help Mitigate Climate Change?

Brian Crawley
Tuesday, 18th October 2011

Charcoal has a long history of different uses, but could it be an answer to solving escalating climate change.

Carbon appears to us in three different forms: diamonds, graphite and charcoal. The sparkly things that have romantic connotations are probably considered the most valuable, but is it possible that charcoal could reclaim this description? Chemically they are identical but this is difficult to grasp when they are so different in appearance and physical properties. Let's look at the less exciting of these in more detail.

Human beings would not have moved from the Stone Age to the Iron Age without the discovery of the high temperature burning properties of charcoal that made iron smelting possible. This characteristic of charcoal was then exploited through the start of the Industrial Revolution to the early 20th century. Although the discovery of coke's similar properties by Abraham Darby in 1709 led to a huge increase in iron production using the new heat source, charcoal was still used up until 1926 in one foundry at Backbarrow in the Lake District and still is in a number of other countries.

An early advance into civilisation found another more fundamental use for the black material. Wood fires provided the simplest source of heat for cooking, but using charcoal was much cleaner and hotter. This of course necessitated human organisation in order for some to specialise in the making of the cooking fuel.

 These specialists were the 'wood colliers'. The second part of this name was subsequently adopted by coal miners and is still a regular English family name. A public house sign in Bewdley, near the Wyre Forest, carries the 'Woodcolliers' name and a picture of the collier tending his 'charcoal burn' from which the more normal 'charcoal burner' title is derived.

So charcoal making and using was, and still is in some developing countries, a major industry. Charcoal is produced by 'destructive distillation' usually of wood, although all organic materials yield charcoal. This is brought about by slowly heating the wood up to a temperature just below that at which the charcoal itself burns and then allowing it to cool. This 'distils' off the other constituents in the wood, many of which burn to provide the heat to maintain the process until the end result of charcoal.

Traditionally this was accomplished by slowly burning a large stack of wood under a covering of earth until the smoke almost disappeared; then the resulting charcoal is cooled and extracted. Evidence of this process can still be found in many of the old woodlands in England in the form of round flat areas, 3-5m (10-16.5ft) in diameter, often dug into hillsides at the rear and 'revetted' (built up) at the front to provide a level working platform. 

These 'pitsteads' can be found 50-100m (164-328ft) apart, usually on slopes where the trees to be charcoaled would have been 


felled in a quadrant area above the pitstead. This minimised the effort of moving the felled raw material. The subsequent charcoal product weighed only 20 per cent of the original weight of wood and was therefore more easily transported to its final destination. Associated with these pitsteads can sometimes be found the stone foundation circles of the huts in which the charcoal burners lived whilst tending their burns which would each take several days and required continuous attention. A rarer find is a hut circle fireplace that still has its lintel. One of these pitsteads and hut circles in the Rusland Valley in the Lake District was made famous when the children visited it in the 1970s film of Arthur Ransome's story, 'Swallows and Amazons'.

Much of the wood for charcoal making, like in Ransome's adventure, was grown as coppice, where a tree is cut to a stump which is then allowed to grow further multistems which can be harvested again and again on a regular cycle (5-25 years). This is a sustainable and environmentally beneficial practice providing biodiverse habitat for a variety of butterfly and bird species, as well as the raw materials for a number of other woodland products other than charcoal.

Chinese Innovation

Charcoal made by the industrious colliers was not used only for iron smelting and cooking. Its high temperature burning property was discovered many centuries ago by the Chinese, perhaps in the Ming Dynasty, and used in fireworks. This was possibly the first use of gunpowder in which charcoal is an essential ingredient. Again, extensive archaeological remains of gunpowder factories, especially in South Cumbria, derive from an industry of major importance to British dominance for many centuries.

Other significant uses of the material survive to the present day. The absorption properties of activated charcoal, resulting from its porous structure, are used extensively for air and water purification. Household uses are in cooker hoods and garden pond water filters. Gas masks using charcoal saved many lives in the second world war. We recently paid a substantial price for a stomach treatment for one of our dogs who was being sick. Yes – medicinal activated charcoal. Have you no

ticed the black colour of some of the Shapes dog biscuits? Charcoal biscuits are also available for human consumption. It also has steel hardening, hand warming and horticultural uses. And let's not forget of course the wonderful, versatile artist's drawing charcoal.


What about where we almost started – cooking? Indians use it in their tandoori ovens, the Western equivalent being of course the barbecue. I am aware that sadly the charcoal is being pushed aside by bottled gas; I say sadly because I feel that the essence of the enjoyment of a barbecue is the fire, but mainly because of another fundamental feature of charcoal.

 Whilst the trees from which charcoal is made were growing, they absorbed carbon dioxide from the air. Although this is released again when the charcoal is burned the r

eplacement tree crop that is growing – as coppice – is re-absorbing that carbon dioxide. This overall process, like burning log fires and biomass, is referred to as 'carbon neutral', unlike burning bottled gas derived from fossil fuel sources.

A small resurgence of charcoal making in this country has occurred in the latter years of the 20th century to supply the demand of the barbecuers. The largest portion of this market is met by imports, but a small band of dedicated workers continue the tradition of charcoal making in British and other woodlands. Most of this is now produced in easily transportable round metal kilns that take the place of the earth covering to exclude the majority of the air from the burn. Smaller quantities are made in 'retorts' or even old oil drums.


Whilst much of this supply is low key, one project that gained international environmental attention was the UK Case Study presented by WWF International at the Rio de Janeiro Earth Summit meeting in 1997. The case studies generally reflected the implementation of Local Agenda 21. This UK project, initiated and managed by the Bioregional Charcoal Company1 based in Croydon, supplies all B&Q stores across the UK locally and directly from small individual makers charcoal. At the time it was hailed as the only contract in the world with these credentials.

Apart from its excellent environmental attributes this locally made barbecue charcoal is generally acknowledged for its easiest lighting properties – without the use of foodtainting lighting fluid!


Mentioned previously were the horticultural benefits of charcoal for which the small particles, produced as a by-product of the barbecue material, have been used. The International Biochar Initiative,2 stimulated by the amazing fertility of the Terra Preta soils in the Amazon rainforests, is promoting the use of 'biochar'. 

This is charcoal particles made from any previously living matter, e.g. biomass, forestry waste, food waste, etc, which is produced by pyrolysis – another name for charcoal burning but in this case even more controlled. Many of the products released during pyrolysis can be collected and are suitable for use as fuels, i.e. biofuels. Biochar has enormous benefits as a soil conditioner to aid plant growth, minimising the use of unnatural fertilizers. 

Digging biochar into the ground and leaving it locked up – firmly for many, many years – together with its benefits to crop growth must surely be the very best form of carbon sequestration – being not just 'carbon neutral', but 'carbon negative'. The International Biochar Initiative is involved in many projects around the world to stimulate this development. Is this not better for the world than digging up diamonds?

Brian Crawley is a 'retired' coppice worker and charcoal maker. Coming from an engineering background he and his wife got into the coppice business only in 1995. He is the treasurer of Coppice Association North West and has been a committee member of the Bill Hogarth MBE Memorial Apprenticeship Trust since its start.

See PM70 page 21 for how to make charcoal at home using a Kadia Charcoal Maker.



craigsams |
Thu, 20/10/2011 - 22:07
At Carbon Gold we believe that global warming is too serious an issue to allow for burning of any carbon that trees or plants have taken out of the atmosphere - that's what solar, wind and fossil fuels can do. So we have created a kiln that is much more efficient and has much lower emissions than traditional charcoal kilns. We are members of the International Biochar Initiative and have had great results with biochar with cacao farmers in Belize and with cabbages, lettuces and chard here in East Sussex on my smallholding. It is ideal for agroforestry and its effects seem to be cumulative, even though you only need to apply it once. We are buyers of good quality biochar from sustainable sources and always welcome and support producers beginning on this path. We also sell a range of composts and biochar products as well as kilns to biochar enthusiasts. www.carbongold.com
Duncan Law |
Fri, 17/02/2012 - 19:06
This was published in the latest Permaculture Magazine. I beg permaculturists to be suspicious of biochar as a silver bullet. Applied by sensitively by permaculturists it may help. The biochar industry is seeking local legitimacy to enable it to scale up to global operations that will have scary unintended consequences. ---- Dear Maddy, Please can I write a corrective of Brian Crawley's fascinating article on Charcoal which ended by advocating Biochar. Biochar is the opposite of a solution to escalating climate change. Field studies show that even at the field level, biochar cannot be relied upon to sequester carbon. In a 4-year long study in Colombia for example, high levels of biochar were added to some plots and not to others and two years later those without biochar held more carbon than those with biochar! And if scaled up worldwide, biochar could quickly become an escalator of climate change because large areas of land and lots of woods and crops would be needed to make it, potentially repeating the biofuel disaster. It is a classic false solution promoted by a mix of people who cannot do the systems thinking to see unintended consequences and cynical profiteering exploiters of carbon market via the disaster that is REDD and the Clean Development Mechanism. Biochar is not not a fertiliser and studies show that impacts on crops are mixed and unpredictable - ranging from positive, to no impacts to negative, which poses a significant risk to farmers who think they can rely on biochar.The act of digging it in at many tonnes a hectare can do huge amounts of damage to any surviving soil structure and release any remaining humic carbon by oxidisation. Terra Preta contains charcoal but also all the other waste products of that civilisation including fish bones and pottery that have survived to be found by archeologists. Nobody has ever been able to recreate it by using biochar. The International Biochar Initiative is a lobby organisation which has been pushing hard to get biochar included into carbon trading. Their closest corporate links are with ConocoPhillips, who are interested in biochar as a pretence for offsetting emissions from their destructive and disastrous tar sands enterprise. IBI members recently contributed to an article which claimed that 12% of all greenhouse gas emissions could be offset with 'sustainable biochar', forgetting to make it clear that by that they meant biochar from 556 million hectares of new dedicated plantations (as a co-author later confirmed). Biochar is of great interest to biofuel companies which are keen on pyrolysis products - syngas, bio-oil - including to the aviation industry which posits business as usual but greened by using biofuels. They can also use the pyrolysis process to do industrial processes needing heat and even generate electricity. The biochar is a by-product from which they seek to make money. Biochar plantations - which we'd soon see if there was enough demand for biochar - could, like biofuel ones, directly or indirectly replace virgin ecosystems, even rainforest, causing huge releases of carbon from the soil in the clearing. Monoculture tree plantations are still designated as 'forest' under the Clean Development Mechanism and REDD+ and so able to receive carbon credits - ie subsidies. The Amazon is literally teetering on the brink of extinction which will release billions of tonnes of carbon and remove a vital carbon sink and its destruction has been speeded up by the demand for biofuels, so the last thing forests need is to create yet another major demand for biomass. If it goes we go - we will definitely be over the edge of the climate change cliff. But we even before that we may disrupt the rainfall and weather patterns on which global agriculture depends - in which case goodbye civilisation in even shorter order. Please read http://www.biofuelwatch.org.uk/docs/biocharbriefing.pdf http://www.biofuelwatch.org.uk/2011/a-critical-review-of-biochar-science-and-policy/ The (permaculture) solution to carbon sequestration is to support nature to bury carbon. Farmers have achieved 5% increase in soil carbon in single figure years by reducing soil disturbance and mimicing natural systems which encourage root growth and die-off in cycles. They also see great on-farm benefits. Scaled up via sustainable farm practice this could sequester securely vast amounts of carbon. - see Carbon Fields by Graham Harvey and Holistic Management by Allan Savory; the Soil Carbon Coalition Otherwise great magazine as ever. Best regards Duncan
PipHoward |
Tue, 24/04/2012 - 12:28
The effect on mychorrizal fungi from Biochar is still very much in the early days of research, but so far seems to have a negative effect in general - not just on fungi but other soil organisms also. I have been involved in the assessment of soils (In France) suitable for fruit tree planting which contained plots where Biochar had been used - the soils in these plots were similar with urban technosols (despite being in an organic managed rural location) and visibly depleted of macro soil organisms. The truth is that the lack of good research stretching across the complex and diverse soils in Europe and other temperate areas means that playing about with Biochar is a gamble which is frankly far too dangerous to take at this critical moment in time.
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