A simplified, data-constrained approach to estimate the permafrost carbon–climate feedback

cdkoven [ at ] lbl.gov


We present an approach to estimate the feedback from large-scale thawing of permafrost soils using a simplified, data-constrained model that combines three elements: soil carbon (C) maps and profiles to identify the distribution and type of C in permafrost soils; incubation experiments to quantify the rates of C lost after thaw; and models of soil thermal dynamics in response to climate warming. We call the approach the Permafrost Carbon Network Incubation–Panarctic Thermal scaling approach (PInc-PanTher). The approach assumes that C stocks do not decompose at all when frozen, but once thawed follow set decomposition trajectories as a function of soil temperature. The trajectories are determined according to a three-pool decomposition model fitted to incubation data using parameters specific to soil horizon types. We calculate litterfall C inputs required to maintain steady-state C balance for the current climate, and hold those inputs constant. Soil temperatures are taken from the soil thermal modules of ecosystem model simulations forced by a common set of future climate change anomalies under twowarming scenarios over the period 2010 to 2100. Under a medium warming scenario (RCP4.5), the approach projects permafrost soil C losses of 12.2–33.4 Pg C; under a high warming scenario (RCP8.5), the approach projects C losses of 27.9–112.6 Pg C. Projected C losses are roughly linearly proportional to global temperature changes across the two scenarios. These results indicate a global sensitivity of frozen soil C to climate change (γ sensitivity) of −14 to −19 PgC°C−1 on a 100 year time scale. For CH4 emissions, our approach assumes a fixed saturated area and that increases in CH4 emissions are related to increased heterotrophic respiration in anoxic soil, yielding CH4 emission increases of 7% and 35% for the RCP4.5 and RCP8.5 scenarios, respectively, which add an additional greenhouse gas forcing of approximately 10–18%. The simplified approach presented here neglects many important processes that may amplify or mitigate C release from permafrost soils, but serves as a data-constrained estimate on the forced, large-scale permafrost C response to warming.

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DOI 10.1098/rsta.2014.0423

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Koven, C. D. , Schuur, E. A. G. , Schädel, C. , Bohn, T. , Burke, E. , Chen, G. , Chen, X. , Ciais, P. , Grosse, G. , Harden, J. W. , Hayes, D. J. , Hugelius, G. , Jafarov, E. E. , Krinner, G. , Kuhry, P. , Lawrence, D. M. , MacDougall, A. H. , Marchenko, S. S. , McGuire, A. D. , Natali, S. M. , Nicolsky, D. J. , Olefeldt, D. , Peng, S. , Romanovsky, V. E. , Schaefer, K. M. , Strauss, J. , Treat, C. C. and Turetsky, M. (2015): A simplified, data-constrained approach to estimate the permafrost carbon–climate feedback , Proceedings of the Royal Society A-Mathematical Physical and Engineering Sciences, 373 . doi: 10.1098/rsta.2014.0423

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