"Biochar" goes industrial with giant microwaves to lock carbon in charcoal

Giant microwave ovens that can "cook" wood into charcoal could become our best tool in the fight against global warming, according to a leading British climate scientist.

Chris Turney, a professor of geography at the University of Exeter, said that by burying the charcoal produced from microwaved wood, the carbon dioxide absorbed by a tree as it grows can remain safely locked away for thousands of years. The technique could take out billions of tonnes of CO2 from the atmosphere every year.

Fast-growing trees such as pine could be "farmed" to act specifically as carbon traps — microwaved, buried and replaced with a fresh crop to do the same thing again.

Turney has built a 5m-long prototype of his microwave, which produces a tonne of CO2 for $65. He plans to launch his company, Carbonscape, in the UK this month to build the next generation of the machine, which he hopes will process more wood and cut costs further.

He is not alone in touting the benefits of this type of charcoal, known as biochar or biocharcoal. The Gaia theorist, James Lovelock, and Nasa's James Hansen have both been outspoken about the potential benefits of biochar, arguing that it is one of the most powerful potential solutions to climate change. In a recent paper, Hansen calculated that producing biocharcoal by current methods of burning waste organic materials could reduce global carbon dioxide levels in the atmosphere by 8ppm [parts per million] over the next 50 years. That is the equivalent of three years of emissions at current levels.

Turney said biochar was the closest thing scientists had to a silver-bullet solution to climate change. Processing facilities could be built right next to forests grown specifically to soak up CO2. "You can cut trees down, carbonise them, then plant more trees. The forest could act on an industrial scale to suck carbon out of the atmosphere."

The biochar could be placed in disused coal mines or tilled into the ground to make soil more fertile. Its porous structure is ideal for trapping nutrients and beneficial micro-organisms that help plants grow. It also improves drainage and can prevent up to 80 per cent of greenhouse gases such as nitrous oxides and methane from escaping from the soil.

In a recent analysis of geo-engineering techniques published in the journal Atmospheric Chemistry, Tim Lenton, a climate scientist at the University of East Anglia, rated producing charcoal as the best technological solution to reducing CO2 levels. He compared it to other geo-engineering techniques such as dumping iron in oceans or seeding clouds to reflect the sun's radiation and calculated that by 2100 a quarter of the effect of human-induced emissions of CO2 could be sequestered with biochar production from waste organic matter, giving a net reduction of 40ppm in CO2 concentration.

Johannes Lehmann of Cornell university has calculated that it is realistically possible to fix 9.5bn tonnes of carbon per year using biochar. The global production of carbon from fossil fuels stands at 8.5bn tonnes.

Charcoal is usually produced by burning wood in high-temperature ovens but this process is dirty and only locks around 20-30 per cent of the mass of the wood into charcoal. Turney's idea to use a microwave, which he found could lock away up to 50 per cent of the wood's mass, came from a cooking accident when he was a teenager, in which he mistakenly microwaved a potato for 40 minutes and found that the vegetable had turned into charcoal. "Years later when we were talking about carbon sequestration I thought maybe charcoal was the way to go," he said.

A number of governments are investing their hopes for sequestering CO2 from the atmosphere in large-scale carbon capture and storage projects. But Turney said this would not provide a full solution. "It's only for large single sources of emissions like large power stations and that accounts for about 60% of emissions. It doesn't deal with anything up in the atmosphere already which is driving the changes we see today."

Chris Goodall, writer of the Carbon Commentary blog, proposed biochar as a solution to climate change in his recent book, Ten Technologies to Save the Planet. "The only big problem is organising it on a large enough scale, " he said. "Organising it so that farmers get paid and put the charcoal in the ground rather than burning it for their own food is a big problem to organise on a global scale."

This could be done if biochar were incorporated into the carbon markets making it more profitable to bury rather than burn. There is an emerging campaign, he said, to get governments to recognise biochar in the post-Kyoto agreement on climate change that will be negotiated in Copenhagen later this year.

This article first appeared on The Guardian

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