Fire as a Negative Climate Feedback?

Authors Mitra et al. (2009) write that "black carbon (BC) is a highly condensed, refractory and polymerized residue of combustion (Hammes et al., 2007) ranging from char to smaller-sized soot aerosols ~1 µm in diameter (Palmer and Cullis, 1965)," and that "because of its slow microbial oxidation rates (Hamer et al., 2004), BC represents a pool of carbon that may be sequestered into the geosphere over geological timescales."

Based on data obtained from a Chesapeake Bay sediment core collected just east of the Potomac River confluence, Mitra et al. compared down-core BC, non-BC organic carbon (OC) and polycyclic aromatic hydrocarbon (PAH) concentrations to identify large-scale combustion events that they compared to historical climate proxies "in order to examine the influence of climate on carbon sequestration in the coastal zone." The results revealed what the five researchers call "the first evidence of climate-controlled centennial- and millennial-scale oscillations in the sequestration of both BC and OC in the coastal zone."

Mitra et al. concluded that "while the increased incidence of wildfires that may occur with climate change could release additional CO₂ to the atmosphere (Wiednmyer and Neff, 2007), this could be countered over the long term by increased soil or sediment sequestration of BC," and they say that "this sink for atmospheric CO₂ into an estuarine environment would represent a negative climate feedback and may play a regulatory role in centennial and millennial-scale climate variability."

Additional References
Hamer, U., Marschner, B., Brodowski, S. and Amelung, W. 2004. Interactive priming of black carbon and glucose mineralization. Organic Geochemistry 35: 823-830.

Hammes, K., Schmidt, M.W.I., Smernik, R.J., Currie, L.A., Ball, W.P., Nguyen, T.H., Louchouarn, P., Houel, S., Gustafsson, O., Elmquist, M., Cornelissen, G., Skjemstad, J.O., Masiello, C.A., Song, J., Peng, P., Mitra, S., Dunn, J.C., Hatcher, P.G., Hockaday, W.C., Smith, D.M., Hartkopf-Fröder, C., Böhmer, A., Lüer, B., Huebert, B.J., Amelung, W., Brodowski, S., Huang, L., Zhang, W., Gschwend, P.M., Flores-Cervantes, D.X., Largeau, C., Rouzaud, J., Rumpel, C., Guggenberger, G., Kaiser, K., Rodionov, A., Gonzalez-Vila, F.J., Gonzalez-Perez, J.A., de la Rosa, J.M., Manning, D.A.C., López-Capél, E. and Ding, L. 2007. Comparison of quantification methods to measure fire-derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment and the atmosphere. Global Biogeochemical Cycles 21: 10.1029/2006GB002914.

Palmer, H.B. and Cullis, C.F. 1965. The formation of carbon from gases. In: Walker Jr., P.L. et al. (Eds.) Chemistry and Physics of Carbon - A Series of Advances, Marcel Dekker, New York, NY, USA, pp. 266-319.

Wiedinmyer, C. and Neff, J.C. 2007. Estimates of CO₂ from fires in the United States: Implications for carbon management. Carbon Balance Management 2: 10.1186/1750-0680-2-10.