Thea Whitman digs into questions of soil, carbon, and biochar that could determine the ultimate trajectory of climate change BY ERIK NESS
In a small utility room in UW–Madison’s Animal Science Building, the world’s smallest and most precise forest fire is burning. The fuel today: 100 grams of white pine. The chips sit inside a steel tube enclosed in an oven-sized electrical furnace. In a few short hours, this woody mix of organic molecules will be pyrolyzed, reduced almost entirely to an essential grid of carbon. You’d call it charcoal, but assistant professor of soil science Thea Whitman calls it pyrogenic organic matter, or biochar. Burning wood is sometimes pleasantly chaotic and sometimes a terrifying force of nature, but for this fire, Whitman and first-year Ph.D. student Nayela Zeba seek absolute control. Biochar may have a big role to play in understanding — and even combatting — climate change. But not without control. The furnace, dubbed the Charcoalator, was custom-built by Whitman’s colleague and former labmate, Akio Enders, who drove through a February snowstorm to deliver it from Cornell University. Argon flows steadily through the chamber, the neutral gas crowding out any oxygen that would tip combustion out of control. A digital thermal controller raises the temperature by 5 degrees Celsius per minute until it reaches the desired temperature — usually between 300 and 600 degrees (572 and 1,112 degrees Fahrenheit) — then holds it for three hours. Water cooling halts the charring process and prevents spontaneous combustion when opening the chamber. 28
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Every soil scientist knows the challenge of keeping things clean. In her primary lab, Whitman has a “very clean room” and a “pretty clean room.” The Charcoalator, however, is inescapably dirty; by design, it’s housed in a different building altogether. The grinding and sifting of char has only been happening for a few weeks, but already a fine black dust lingers. Zeba has resigned herself to an all-black wardrobe — only the face mask and lab coat are white — for the days she bakes the biochar. While fire has a homogenizing impact on biological materials, not paying enough attention to the differences has led to some inconsistency in the way that we study and talk about biochar. The Charcoalator — and the techniques being refined by Zeba — are designed to bring some rigor to Whitman’s work in the field. “If you look at these chars under a scanning electron microscope, it looks like plant cell structure; you can still see the microstructure inside of a plant,” says Whitman. “Which means that different biomass will give it different properties. By being really consistent about the way we produce it, we can be more scientific.” Escalating fire seasons and a growing interest in producing energy from agricultural biomass have spurred soil scientists and climate change advocates to look more closely at the role of carbon in soil. It’s the very basis of life on Earth. It’s a
