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Tuesday, 19 June 2007

Save the world by burning trees

With everybody going nuts about greenhouse gas "offsets" through the planting of trees which will suck CO2 out of the atmosphere, this might sound a little weird. There's a growing interest in how much good we might be able to do by setting trees (and other plant material) on fire.

In the Global Warming context, the problem with using trees to soak up CO2 is that when the trees die they decompose and most of their captured carbon goes back into the atmosphere again, sometimes as methane (CH4) which is a far worse greenhouse gas than is CO2.

Researchers in South America studying the composition of some unnaturally fertile soils have discovered what appears to be large amounts of charcoal deliberately added by indigenous farmers over hundreds or perhaps thousands of years. While initially most excited by the prospect of being able to improve soil productivity by adopting similar approaches elsewhere, people began to realise that this was also a surprisingly simple and effective form of carbon sequestration.

Instead of burning trees and other vegetation in big bonfires which leave just ash, if you reduce the amount of oxygen available to the fire you will convert much of the carbon into solid charcoal - as much as 50% of it. Then you can bury this charcoal in the soil where it appears to remain quite happily for many hundreds of years. Do that in the right kind of soil conditions and you can improve crop yields by up to 800%, or so it's said.

As an added bonus, burning things gives of energy which can be harnessed for other purposes, and even the gases from the fire contain useful compounds which can be captured and processed.

That's about as much detail as I want to go into here but I'll post some links from time to time with new info. If you want to Google, the South American soils are known as "Terra Preta" and the modern process of producing charcoal, energy and chemical compounds all in one hit is being called "BioChar". A local bloke I met on the weekend is doing research on that front and is setting up a website at (At the time of writing, that page only displays correctly in Internet Explorer - Safari and FireFox users will need to try again later.)

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