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

• Published in: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
• Main Authors: Koven, CD, Schuur, EAG, Schädel, C, Bohn, TJ, Burke, EJ, Chen, G, Chen, X, Ciais, P, Grosse, G, Harden, JW, Hayes, DJ, Hugelius, G, Jafarov, EE, Krinner, G, Kuhry, P, Lawrence, DM, MacDougall, AH, Marchenko, SS, McGuire, AD, Natali, SM, Nicolsky, DJ, Olefeldt, D, Peng, S, Romanovsky, VE, Schaefer, KM, Strauss, J, Treat, CC, Turetsky, M
• Format: Article in Journal/Newspaper
• Language: English
• Published: eScholarship, University of California 2015
• Subjects: permafrost
• Online Access: http://www.escholarship.org/uc/item/7t14r7vv

© 2015 The Authors. 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 two warming 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-1on a 100 year time scale. For CH4emissions, our approach assumes a fixed saturated area and that increases in CH4emissions are related to increased heterotrophic respiration in anoxic soil, yielding CH4emission 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.