Can an Ancient Charcoal Put the Brakes on Global Warming?

By Jeremy Jacquot, Popular Mechanics, December 30, 2008

Biochar was first created and used thousands of years ago to help plants grow. Researchers have found that this charcoal-like substance traps carbon and is a renewable source of fuel. Nine countries are pouring research dollars into the charcoal-like substance to see if it can sequester carbon, improve the soil and produce biofuels all at once—on an economically competitive scale. Could this ancient fertilizer really put a dent on global warming?

(Photograph by Brand New Images/Getty Images)

When pre-Columbian natives in the Amazon Basin first began to use biochar—a fine-grained, carbon-rich type of charcoal made from burning bone fragments and other food remains—some 7,000 years ago, they knew that it helped their crops grow. But they didn't realize that this charred biomass was extraordinarily good at absorbing and storing carbon dioxide, and that the process that made it released chemicals that could be used as fuel. (At the time, chemistry was still a few thousand years away.) Today, private companies, universities and government organizations in nine countries—Vietnam, Belize, Cameroon, Chile, Costa Rica, Egypt, India, Kenya and Mongolia—are setting up demonstration trials to evaluate biochar's ability to improve various types of soils while trapping carbon and making fuel to find out if this ancient substance is an economically viable solution to global warming.

Biochar is different from the dry charcoal that you'd burn in your grill: It is produced by heating plant waste to 400 to 500 degrees C in the absence of oxygen—a process known as low-temperature pyrolysis—which makes a substance that has a greater number of smaller pores than charcoal (the better to trap carbon dioxide with). The process to make biochar can be a closed, sustainable one: Biomass is fed into the oxygen-free burners and turned into the char. The gases that are released during the reaction is then captured and converted into electricity (from combustible gases) or biofuel, while the remaining char is safe to throw directly into the soil. Biochar does the rest of the work underground. The substance improves the ground's composition and fertility by locking in water and nutrients, thereby reducing the need for fertilizers while boosting crop yields. It also stores the carbon from the plant materials that made it— around 50 percent of the carbon produced from converting biomass into biochar can be trapped—and traps even more carbon from decomposing plants in the soil.

What makes biochar so appealing to researchers like Cornell University's Johannes Lehmann, who experimented with it firsthand when he conducted field trials in the central Amazon, is its dual purpose, long-term carbon-trapping. Biofuels are said to be carbon neutral because the carbon dioxide they release when they are burned is balanced by that which is absorbed by the growing biomass. Biochar goes beyond this, directly removing carbon dioxide from the atmosphere by stimulating plant growth as well as storing the carbon from decomposing plants in the soil as well as those that were burned to make it for as long as 5,000 years.

The main barrier that companies and researchers foresee is creating biochar on a scale that makes it a viable source of energy and carbon sink. So far, biochar has been used in small, localized efforts in South American and African communities, where they primarily use it to improve the soil. To effectively and economically make use of biochar as a carbon sink and a fertilizer, large biorefineries need to combine sequestration from agricultural land with bioenergy production (created from the byproduct of the process). Syngas (a mixture of carbon dioxide, carbon monoxide and hydrogen) and bio-oil (a liquid fuel) are both produced during pyrolysis, and, on a large enough scale can be converted into electricity or sold on the market. As an energy source, syngas may yield 2 to 7 megajoules (MJ) of electricity per MJ invested. By comparison, corn ethanol currently yields 0.7 to 2.2 MJ per MJ invested; cellulosic ethanol technologiesare projected to yield 4 Ð 6 MJ.

Perhaps the biggest plus for biochar is that it may be localized to fit the biomass and energy profile of a given area. In Belize, for example, Carbon Gold, a company founded by environmental entrepreneurs, Craig Sams and Dan Morrell, will carry out field trials in Belize with biochar produced from rice husks, oranges and cacao beans. Sams believes carbon dioxide could be returned to its pre-industrial levels by 2050 if 2.5 percent of the world's agricultural land were used to make biochar. (If all available land were used, he says, it could be done in just one year.) Jim Amonette, a senior research scientist with the DOE's Environmental Molecular Sciences Laboratory, says that while there are no obvious downsides to biochar, more work needs to be done to investigate its sequestration potential and longevity in the soil. An ideal study would consist of adding biochar to four types of soil (to get a good representation of the different types of soil found in agricultural land around the world) at eight locations worldwide, says Amonette. Using radiocarbon isotope measurements, scientists would be able to track new plant growth—to verify biochar's effect on crop yields—as well as the longevity of the stored carbon. This would allow researchers to obtain some much-needed data and to determine whether biochar sequestration will be effective as a tool against climate change on a global scale.

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