Jul 06 2009

Is Biochar the Solution?

Posted by: Jonathan Marshall

Vanished civilizations that cultivated the Amazon jungle long before the arrival of European explorers may hold a key to slowing or even reversing the onset of global warming.

Archeologists who once believed the Amazon basin, with its notoriously unproductive soil, was only thinly populated by Stone Age tribes now have abundant evidence that it was extensively inhabited and farmed many hundreds of years ago. Evidence of this pre-Columbian civilization was literally buried under jungle that encroached when European diseases wiped out the indigenous population.

The fertility secret that made these early urban cultures viable was a potent soil called terra preta, or dark earth. Recent scientific studies show the soil was man-made, not natural, formed by mixing earth with plant material that was allowed to smoulder without fully burning.

Today biochar is made by heating biomass in kilns without oxygen. Instead of burning, this process of pryolysis creates energy-rich syngas, liquid bio-oil and fine-grained, porous biochar.

Biochar doesn't directly provide nutrients, but it improves crop yields by reducing soil acidity, fostering the growth of favorable microorganisms and improving water quality, among other factors.

The relevance of terra preta today goes beyond its promise for helping farmers in the developing world. The very act of converting biomass into biochar and burying it in the earth may be one of the most effective ways to suck carbon dioxide out of the atmosphere and prevent it from contributing to runaway greenhouse warming.

Radio-carbon dating of Amazon soils shows that biochar can store carbon in the earth for hundreds or even thousands of years. Johannes Lehmann, a Cornell University biogeochemist and leading expert on biochar, said,

By sequestering huge amounts of carbon, this technique constitutes a much longer and significant sink for atmospheric carbon dioxide than most other sequestration options, making it a powerful tool for long-term mitigation of climate change. In fact we have calculated that up to 12 percent of the carbon emissions produced by human activity could be offset annually if slash-and-burn were replaced by slash-and-char.

Tim Lenton, a climate scientist at the University of East Anglia, compared all major geoengineering proposals for mitigating global warming and rated biochar production as one of the most promising. Other biochar enthusiasts include NASA earth scientist James Hansen,  whose prescient warnings in 1988 launched much of the research and subsequent activism on global warming, and James Lovelock, famed originator of the Gaia hypothesis of Earth as a self-regulating environment.

Lovelock, who turns 90 this month, told New Scientist earlier this year that biochar could be humanity's salvation:

There is one way we could save ourselves and that is through the massive burial of charcoal. It would mean farmers turning all their agricultural waste - which contains carbon that the plants have spent the summer sequestering - into non-biodegradable charcoal, and burying it in the soil. Then you can start shifting really hefty quantities of carbon out of the system and pull the CO2 down quite fast. . . . This scheme would need no subsidy: the farmer would make a profit. This is the one thing we can do that will make a difference, but I bet they won't do it.

Despite his pessimism, biochar enthusiasts have made headway with the United Nations and even with Congress: The 2008 Farm Bill established the first national policy in support of biochar production and utilization in the world. And several companies, including Carbonscape and Carbon Diversion, Inc. are attempting to bring the technology of biochar carbon sequestration to market.

Biochar may of course prove too good to be true. But if you like to garden and want to attempt a little geoengineering in your yard, check out this FAQ. The earth may thank you for it. 

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