Does biochar hold promise at helping to remove CO2 from the atmosphere, or is it fiction?
In the natural carbon cycle, plants absorb CO2 as they grow. When they die and decompose, the CO2 returns to the atmosphere. If, however, the plants are subjected instead to pyrolysis (a process of controlled burning in a low-oxygen atmosphere) the result is charcoal, a substance that is mostly elemental carbon. Although life is, in essence, a complicated form of carbon chemistry, living creatures cannot process carbon in its elemental form. Charcoal, therefore, does not decay very fast. If buried in the soil, and it will stay there unchanged for a substantial period of time. Some of the so-called terra preta (black earth) found in the Brazilian Amazon is thousands of years old. Such soil also shows some significant benefits in that plants grow more intensely, thus removing more CO2 from the atmosphere; further, erosion appears to be diminished in sites with terra preta.
Moreover, studies seem to support the allegation that soil containing biochar releases less methane and less nitrous oxide than its untreated counterparts, probably because the charcoal acts as a catalyst for the destruction of these gases. Since both of these chemicals are more potent greenhouse gases than carbon dioxide, this effect, too, can help combat global warming.