Burn the trees to save the world?

Could reviving the ancient technique of charcoal making really solve the global food crisis, halt deforestation and lock up carbon dioxide for good? Chris Goodall sifts fact from myth on biochar.

Hans-Peter Schmidt runs a small organic vineyard in the Swiss Alps. Careful to use no pesticides or artificial fertilisers, he relies on simple techniques to protect against pests and diseases, such as encouraging a wide variety of plants. But Schmidt also does something quite unique among Swiss winemakers to maintain soil fertility. He adds a rich substance known as ‘biochar’.

A ground-up form of almost pure charcoal, Schmidt’s biochar is made from the leftover pips and pulp from his grapes, which he has heated intensely in a kiln. The technique itself is not new: pre-Columbian populations were burning waste to create terra preta (black soil) hundreds of years ago, and many people still rely on charcoal-making as a source of cooking fuel. What is new is the sudden interest in biochar as an extraordinarily potent weapon in the fight against climate change. Scientists found that terra preta not only created pockets of land in the Amazon which are still extremely fertile 500 years later – but that it kept at least half the carbon in the charcoal ‘locked up’ for all that time [see box 'The lock up' below].

Today, many climatologists are as excited as agronomists about biochar. Professor Tim Lenton, from the UK’s Tyndall Centre for Climate Change Research, believes that, of all the large-scale solutions under discussion, biochar and reforestation stand out as the most viable options. Professor Johannes Lehmann, an eminent soil specialist from Cornell University, goes so far as to suggest that it is theoretically possible, by the end of this century, that we could capture 9.5 billion tonnes of carbon each year through biochar production in tropical agricultural systems. If we achieved that level of reduction, atmospheric concentrations of carbon dioxide would actually be falling. It’s no wonder that, in January, Gaia hypothesist James Lovelock told New Scientist that “There is one way we could save ourselves, and that is through the massive burial of charcoal”.

“Biochar is sure to crop up at Copenhagen”

That prospect came one step closer at last year’s Poznań climate change conference, where politicians raised the idea of carbon funding for the technique – and there’s no doubt the issue will crop up again at Copenhagen this December. If biochar became part of the carbon market, by joining the list of technologies qualifying for the UN’s Clean Development Mechanism, we could one day see the rich world offsetting some of its emissions by paying poor farmers to sequester carbon in their soils.

An example of how this might work is found in Cameroon, where the NGO Biochar Fund is giving subsistence farmers, many of them using destructive ‘slash and burn’ methods of agriculture, the skills to make their own biochar. Run by a young Belgian pioneer, the organisation is working with 75 grassroots groups to produce biochar from materials like palm fronds, cassava stems, weeds and wood, and to test the effects in different soil types. It is developing highly efficient, village-scale kilns which use pyrolysis to produce both biochar, and heat and electricity (‘combined heat, power and char’, or CHPC). They could potentially generate money as well by selling carbon credits through the voluntary offset market.

In effect, the Fund is helping farmers shift from ‘slash and burn’ to ‘slash and char’ agriculture, by encouraging them not to burn the trees that have been felled but rather to use the wood to make biochar. The char is then added to the soil. It helps improve fertility, enabling the soil to be used for many years, providing more food than can be provided by conventional ‘slash and burn’, and so reducing the frequency with which new areas of forest need to be cut. For the farmers, this means the chance to develop a more sustainable and prosperous agriculture. For the forests, it means the chance to recover from an increasingly destructive practice. About 400 million people in the Tropics rely on ‘slash and burn’ agriculture. The benefits for the planet could be huge if they adopted this ‘slash and char’ method instead.

Biochar Fund’s simple ceramic biochar stoves can even be used for cooking while the char is being made, so killing two birds with one stone, as it were. The idea’s being taken up in Central Asia, too, where the Mongolian Biochar Initiative is supplying simple biochar/cooking stoves to herders, vegetable gardeners and forestry workers. Compared to traditional cookstoves, these use far less fuel for the same amount of cooking. This both reduces the need to cut down more wood and also improves air quality. A large fraction of the world’s people do their cooking over open stoves that pollute indoor air, causing respiratory problems and reducing life expectancy.

“If farmers switch from 'slash and burn' to 'slash and char', the benefits could be huge”

If they prove viable, such stoves could be sold to poor farmers on a large scale using microcredit to make them affordable – in much the same way that Grameen Shakti, for example, is rolling out improved cooking stoves and solar home systems to villagers in Bangladesh.

This raises the prospect of a mass biochar movement across the developing world. It sounds ambitious, but it would be simple enough to tap into local charcoal-making expertise. The equipment is available locally and soil carbon levels could be measured reasonably accurately with simple devices.A carbon credit system could reward village-level enterprises for producing something to plough back into the soil, rather than something to sell as a fuel.

Stephen Joseph, from Australia’s University of New South Wales, has done a cost-benefit analysis of a typical village-scale biochar set-up, and found that it could be worth more than $50,000 over five years. This calculation factors in increased yields, savings from planting fewer trees for fuel, reduced medical expenses thanks to less indoor air pollution from smoky stoves – and, of course, carbon credits.

It all sounds too good to be true – and perhaps it is. As biochar has risen up the agenda, it’s also attracted its share of sceptics.

Some argue that, if biochar does indeed become profitable, it could drive deforestation. Writing in the Guardian, George Monbiot envisages a ‘rush’ for biochar as we have seen with biofuels. He argues that financial incentives would encourage people to cultivate vast plantations of fast-growing trees in place of ancient forests, or on valuable land needed for food.

“We don't yet have a system that makes economic sense of biochar”

Biochar enthusiasts respond that the flow of carbon credits would encourage farmers to continuously harvest and replant trees, using the charcoal to enrich the land as they do so. Chris Turney, Professor of Geography at the University of Exeter, adds that this type of cyclical scheme would be much more effective at removing emissions from the atmosphere than one-off reforestation schemes, “because mature trees reach a saturation point in their absorption capacity”. Meanwhile crop waste – such as straw, husks and leaves – is also a ready source of raw material for biochar. Almost half the nine billion tonnes of agricultural material produced each year is effectively waste material – which contributes to global warming as it rots or is burned off.

More fundamentally, there’s the question: does biochar actually work as a carbon sink? Certainly, Amazonian earth would suggest so. One study shows that a hectare of terra preta typically holds two and half times the carbon of adjacent soils. Scientists believe biochar can sequester carbon in the soil for hundreds to thousands of years, but they haven’t yet calculated its half-life. “We don’t have a predictive theory for its behaviour,” says Mike Mason, founder of carbon offsetting company Climate Care and bio-energy company Biojoule. “We still need to find out what plant materials should be used, the right temperature for the kiln, what else should be added to the ground...”

There are question marks, too, over whether biochar is universally effective as a soil fertiliser. There are even cases where adding char has been shown to deplete fertility. Current evidence suggests that fertility enhancements seem to be greatest in the Tropics, where soils are often low in other sources of carbon.

Exploratory projects such as those under way in Cameroon and Mongolia should start to provide answers to some of these questions. Along with seven others, they’re being closely followed by the International Biochar Initiative – a network of academics, NGOs, investment bankers and politicians looking to promote commercial biochar production.

Biochar does not, of course, need to be added to the soil to capture carbon. It can even be buried in underground chambers. This has some superficial similarities with the grand-scale carbon capture and storage (CCS) schemes mooted for coal-fired power stations. But, unlike most CCS schemes, the technology is cheap and simple to install. And, while CCS can only prevent emissions entering the air (at a power station, for example), biochar can ‘claw back’ carbon that is already out there and seal it in the ground – thanks to its unique way of ‘interrupting’ a plant’s carbon cycle.

“It's the most potent engine of atmospheric cleansing we possess”

Developing viable biochar businesses will mean coming up with a business model that rewards everyone involved. And here, says Mason, “the devil is in the detail”. He reminds us that we don’t yet have a system that makes economic sense of the complex relationships in biochar production. Who gets the credit? – he asks. “Is it the farmer, because he isn’t using so many pesticides? ... If electricity is produced as well, how is this credited?” While there is still this lack of clarity, it may hold back investors from getting involved on a large scale, he says.

Despite remaining uncertainties, governments are starting to show an interest. The New Zealand Government has included biochar in a $10 million energy research fund; in Australia, the opposition Liberal Party is claiming the technique could cut the country’s emissions by a fifth; and the California Energy Commission is hopeful that biochar could be a recognised technology under a proposed new federal cap-and-trade programme. Britain, in comparison, seems a little slow on the uptake. The UK Biochar Research Centre opened late last year at the University of Edinburgh, but the government, for the most part, remains agnostic.

Overall, though, as scientific attention has focused on the benefits of biochar, excitement has grown rather than diminished. As well as its numerous other benefits, biochar stands a good prospect of being one of the simplest, cheapest and most effective ways of capturing carbon dioxide from the atmosphere and storing it safely. One of the world’s best-respected earth scientists, Tim Flannery, has described biochar as “the most potent engine of atmospheric cleansing we possess”. In a world where the climate news is usually bad, that is one of the few glimmers of real hope.

The lock up

Producing biochar ‘locks up’ carbon dioxide from organic matter, because it interrupts a plant’s natural carbon cycle. Schmidt’s vines, for example, abstract CO2 from the air as they grow, temporarily reducing the net stock of gases in the atmosphere – but the leftover pips and skins would eventually release greenhouse gases as they rotted, if Schmidt didn’t step in with his biochar kiln to transform them into a substance that holds onto the carbon for hundreds, maybe thousands, of years. There’s also evidence that applying biochar to soil curbs the release of methane and nitrous oxide – even more powerful global warming agents than CO2.

The soil booster
Biochar has been shown to double or triple yields in the right conditions. Scientists believe this is because:
• it holds water, so can work well in dry land
• it’s fungi-friendly, because a vast network of tiny pores provides a safe home for beneficial soil micro-organisms
• it reduces acidity, creating a soil more favourable to plant growth
• it makes nutrients more accessible, such as potassium and phosphorus.

Biochar is one of the ‘Ten Technologies to Save the Planet’, written by Chris Goodall and published by Profile Books. Additional material by Hannah Bullock.