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Earth System Dynamics An interactive open-access journal of the European Geosciences Union

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Earth Syst. Dynam., 9, 663-677, 2018
https://doi.org/10.5194/esd-9-663-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
28 May 2018
The biomass burning contribution to climate–carbon-cycle feedback
Sandy P. Harrison1, Patrick J. Bartlein2, Victor Brovkin3, Sander Houweling4, Silvia Kloster3, and I. Colin Prentice5 1Department of Geography and Environmental Science, University of Reading, Whiteknights, Reading, RG6 6AB, UK
2Department of Geography, University of Oregon, Eugene, Oregon 97403–1251, USA
3Max Planck Institute for Meteorology, Bundesstraße 53, 20146 Hamburg, Germany
4Department of Earth Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
5AXA Chair of Biosphere and Climate Impacts, Department of Life Sciences, Imperial College London, Ascot, SL5 7PY, UK
Abstract. Temperature exerts strong controls on the incidence and severity of fire. All else equal, warming is expected to increase fire-related carbon emissions, and thereby atmospheric CO2. But the magnitude of this feedback is very poorly known. We use a single-box model of the land biosphere to quantify this positive feedback from satellite-based estimates of biomass burning emissions for 2000–2014 CE and from sedimentary charcoal records for the millennium before the industrial period. We derive an estimate of the centennial-scale feedback strength of 6.5 ± 3.4 ppm CO2 per degree of land temperature increase, based on the satellite data. However, this estimate is poorly constrained, and is largely driven by the well-documented dependence of tropical deforestation and peat fires (primarily anthropogenic) on climate variability patterns linked to the El Niño–Southern Oscillation. Palaeo-data from pre-industrial times provide the opportunity to assess the fire-related climate–carbon-cycle feedback over a longer period, with less pervasive human impacts. Past biomass burning can be quantified based on variations in either the concentration and isotopic composition of methane in ice cores (with assumptions about the isotopic signatures of different methane sources) or the abundances of charcoal preserved in sediments, which reflect landscape-scale changes in burnt biomass. These two data sources are shown here to be coherent with one another. The more numerous data from sedimentary charcoal, expressed as normalized anomalies (fractional deviations from the long-term mean), are then used – together with an estimate of mean biomass burning derived from methane isotope data – to infer a feedback strength of 5.6 ± 3.2 ppm CO2 per degree of land temperature and (for a climate sensitivity of 2.8 K) a gain of 0.09 ± 0.05. This finding indicates that the positive carbon cycle feedback from increased fire provides a substantial contribution to the overall climate–carbon-cycle feedback on centennial timescales. Although the feedback estimates from palaeo- and satellite-era data are in agreement, this is likely fortuitous because of the pervasive influence of human activities on fire regimes during recent decades.
Citation: Harrison, S. P., Bartlein, P. J., Brovkin, V., Houweling, S., Kloster, S., and Prentice, I. C.: The biomass burning contribution to climate–carbon-cycle feedback, Earth Syst. Dynam., 9, 663-677, https://doi.org/10.5194/esd-9-663-2018, 2018.
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Short summary
Temperature affects fire occurrence and severity. Warming will increase fire-related carbon emissions and thus atmospheric CO2. The size of this feedback is not known. We use charcoal records to estimate pre-industrial fire emissions and a simple land–biosphere model to quantify the feedback. We infer a feedback strength of 5.6  3.2 ppm CO2 per degree of warming and a gain of 0.09 ± 0.05 for a climate sensitivity of 2.8 K. Thus, fire feedback is a large part of the climate–carbon-cycle feedback.
Temperature affects fire occurrence and severity. Warming will increase fire-related carbon...
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