What exactly is biochar and how does it work? While it seems a very twenty-first-century topic, biochar has actually been around in some form for centuries: the pre-Colombian Amazonians developed a dark, rich, and fertile soil, terra preta, or “black earth,” using a similar method. In brief, biochar is a kind of charcoal made from organic materials that have undergone a firing process known as pyrolysis, which takes place in the absence of oxygen. Added to soil, biochar can improve fertility and, by “sequestering” carbon—that is to say, by not allowing it to be broken down easily or rapidly—can reduce emissions from the biomass that would otherwise naturally degrade into greenhouse gases. The carbon in biochar resists degradation—in fact, biochar can hold carbon in soil for hundreds, even thousands, of years—thus preventing it from re-entering the carbon cycle.
Biochar, to put it simply, is a method of replenishing soil with carbon, making it rich and fertile. It is also a potential tool in the battle against climate change. One of the chief causes of global warming is the overload of carbon dioxide as a “greenhouse gas” in the air: humans produce CO2 (chiefly by burning fossil fuels, such as coal, natural gas, and oil, for energy and transportation), and also have depleted natural systems—like forests—that remove CO2 from the atmosphere. Biochar has the potential to mitigate that process; in fact, well-designed biochar systems can actually be carbon negative, because they result in the net transfer of carbon (which began as carbon dioxide in the atmosphere) to the soil, where it can be stable for a very long time. In other words, biochar may present a way for us to start taking back some of the carbon that humans have poured into the atmosphere.