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Could Photosynthesis Be Our Best Defense Against Climate Change?

Some scientists think that biochar is the key to extracting carbon dioxide from the atmosphere.

| Fri Jul. 19, 2013 2:24 PM EDT

As biochar attracts more scientific and commercial attention, it has also acquired proponents and detractors. George Monbiot, a columnist for the Guardian, blasted the entire idea by seizing on one advocate's proposal to obtain biochar from vast tree plantations. Monbiot was correct that relying on plantations to produce biochar could cause poor farmers to be kicked off their land and food prices to rise as land was diverted to biochar. But Monbiot unfairly tarred all biochar supporters with the same brush, as he later admitted. In fact, Lehmann has always clearly stated that he did not favor the plantation approach. Joining Lehmann in this position is James Hansen, the NASA scientist who put climate change on the public agenda with his 1988 testimony to the US Senate that human activities were raising global temperatures. Hansen has endorsed biochar, along with expanded growing of trees, as vital tools for drawing down atmospheric CO2 levels to 350 ppm, the amount he believes is needed to stabilize Earth's climate.

Others remain skeptical that soil carbon sequestration could remove enough CO2 from the atmosphere to make a difference, and they point to a paucity of peer-reviewed studies validating the linkage. Lehmann, however, has tested biochar's carbon storage potential and other characteristics in field research in Kenya, Colombia, and the Amazon, as well as at the agricultural research station Cornell operates in New York state. At Cornell, he is producing biochar in a kiln whose shiny metal pipes and funnels make it look more like part of an electric power station than a cutting-edge agricultural device.

Notwithstanding my brave personal foray into compost testing at Cornell, Lehmann told me he does not plan to rely on the university's compost supplies to produce biochar. There are more ecologically efficient uses for that compost heap, he explains. Rather, Lehmann will use post-harvest cornstalks from other Cornell agricultural research plots. He adds that the kiln will also "generate liquid fuel from the gases that are produced while making biochar."

Such simultaneous fuel production is but one of the co-benefits of producing biochar. Studies by Lehmann and others have documented that adding biochar to soil also increases soil's fertility and ability to retain water, which in turn encourages greater crop yields. Adding biochar to soil therefore is also a form of climate change adaptation: Increasing a given piece of land's ability to absorb and retain water will make the land more resilient in the face of flooding as well as drought, both of which are projected to become more frequent and severe as climate change accelerates in the years ahead.

There is no one-size-fits-all technology for extracting carbon and sequestering it in soil, mainly because local circumstances, both social and physical, differ around the world. And despite his enthusiasm for biochar, Lehmann is the first to emphasize that it is neither a silver bullet nor the only feasible way of extracting carbon dioxide from the atmosphere. "There are and have to be several if not many approaches to sequestering [i.e., storing] carbon," he told me.

Other proven methods, he said, include growing trees—both in forests and mixed among field crops—and changing to less invasive tillage systems. Instead of industrial agriculture's practice of removing crop residues and plowing soil before planting, which releases large amounts of carbon into the atmosphere, "no-till" cropping leaves residues in place and inserts seeds into the ground with a small drill, leaving the earth basically undisturbed. A calculation by the Rodale Institute, a nonprofit agricultural operation in Pennsylvania, found that if no-till were used on all 3.5 billion acres of the Earth's tillable land, it would sequester more than half of humanity's annual greenhouse gas emissions. "If ideas such as biochar emerged recently," Lehmann asks, "what other ideas might still be out there?"

Climate change policy traditionally has focused on the energy sector, but under the new paradigm advocated here, the agriculture sector would gain prominence as well. Earlier in this monthlong Slate series on climate change and agriculture, Michael Pollan and I discussed how taking advantage of photosynthesis could turn eating meat from a climate sin into a blessing by relying on the same ecological principles that make biochar possible. The key is not meat versus no meat. The key is to reform agricultural systems away from the current industrial approach that uses vast amounts of petroleum to produce food in favor of systems that rely on natural processes such as photosynthesis. Pollan calls it the "oil food" versus "sun food" choice.

Critics are right that much practical work remains to be done to demonstrate whether a "sun food" system can actually succeed in both feeding humanity and fighting climate change. But there is good reason to think that humans can indeed harness photosynthesis to draw down the rising level of CO2 in the atmosphere. If we can then safely store that extracted carbon in places where it will not contribute to global warming, we could significantly reduce the 400 ppm of CO2 that are currently overheating our planet (assuming that we limit the 2 ppm of annual emissions as well). In short, we might begin to turn back the clock on global warming. And not a moment too soon.

This article arises from Future Tense, a collaboration among Arizona State University, the New America Foundation, and Slate. On July 25, Future Tense will be hosting an event on agriculture’s role in climate change at the New America Foundation in Washington, D.C. For more information and to RSVP, visit the New America Foundation website.

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