Regulation of atmospheric carbon dioxide by vegetation fires

Vegetation fires release some fraction of the carbon in the biomass back to the atmosphere as CO2 and deposit some of the carbon onto the ground as charcoal or pyrogenic carbon. It is an open, but not unanswerable, question as to whether the formation of pyrogenic carbon can effectively sequester carbon from atmospheric CO2. The purpose of this article is to conceptualise the question in terms of the global Charcoal Challenges, which deal with the scientific and socio economic questions associated with increasing the refractory (or long-term) black carbon pool at the expense of the atmospheric carbon pool, and to investigate the formation and decay of charcoal within this paradigm. Three particular Charcoal Challenges are examined: (1) the feasibility of lowering atmospheric CO2 by biochar production, (2) the tension between nature's use of fire to distribute carbon between long-term black carbon and short-term atmospheric pools and humans' need to suppress fire and (3) the premise that black carbon is a sink for CO2 only if its rate of formation exceeds its rate of decay; otherwise, it is a source. I show how the thermal decomposition of cellulose, the major constituent of vegetation, during fires acts as a thermokinetic oscillator that regulates the global distribution of carbon between atmospheric and black carbon reservoirs. I conclude that we cannot yet assume with certainty that the global black carbon reservoir is a carbon sink.