Aug. 10, 2010

Biochar could reduce CO2 emissions by 12 percent, research shows

If every bit of biomass that could be collected sustainably were converted to biochar and the gas produced in the conversion process used for energy, human-caused (anthropogenic) greenhouse gas emissions could be reduced by 12 percent annually, according to new research.

That reduction could help slow the increase in total anthropogenic greenhouse gas emissions and boost the chances of stabilizing global temperatures.

The findings appear in the Aug. 10 issue of Nature Communications.

Johannes Lehmann, Cornell associate professor of soil science and a leading authority on biochar, was a consultant on the paper, which outlines three scenarios using biochar to sequester carbon and reduce global greenhouse gas emissions.

The paper's lead authors are Dominic Woolf of Swansea (UK) University and James E. Amonette of the Pacific Northwest National Laboratory in Richland, Washington.

Biochar is produced when grasses, crop residues, timber and forestry residues, manures and other organic waste are burned at low temperatures without using oxygen -- a process known as pyrolysis.

The process doubles carbon concentration in the residue (biochar), which can then be returned to the soil as a stable, long-term carbon repository -- slowing the rate at which carbon that has been absorbed by plants for photosynthesis is returned to the atmosphere.

Biochar improves the structure and fertility of soils, while exhaust gasses from the process can be converted into energy. Research has shown that in almost every case, use of biochar has the potential to mitigate climate change on a much larger scale than combustion of the same sustainably procured biomass for energy.

In the paper, the researchers demonstrate three models of varying intensity in which biochar use is incorporated into the global energy picture.

In the most optimistic scenario, called the maximum sustainable technical potential, the researchers assess the upper limit of biochar's potential -- the amount of anthropogenic greenhouse gas emissions that can be eliminated globally by biochar without harming the food supply or causing other environmental damage. That model, which assumes that all sustainably obtained biomass is converted to biochar, shows a maximum emissions reduction of 12 percent.

"The number is much better founded as a technical potential than what we had before, and it is vetted against what is sustainable," said Lehmann. "The maximum values are well in the area that justifies further efforts to explore the doability of biochar systems."

But before biochar systems can be deployed on a larger scale, some critical knowledge gaps have to be addressed in research as well as application, he added.

"This paper should answer the question: If you were implementing biochar systems to mitigate climate change, would it be worth discussing it as a global strategy? Would it potentially scale to an important approach? The answer is yes."