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

  • Author(s): 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
  • et al.
Abstract

© 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.

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