title: A simplified, data-constrained approach to estimate the permafrost carbon-climate feedback.
abstract: 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 Pg C °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.
authors.affiliation: Earth Sciences Division, Lawrence Berkeley National Lab, Berkeley, CA, USA cdkoven@lbl.gov.
authors.forename: C D
authors.initials: CD
authors.lastname: Koven
authors.affiliation: Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: E A G
authors.initials: EA
authors.lastname: Schuur
authors.affiliation: Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: C
authors.initials: C
authors.lastname: Schädel
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, USA School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Bohn
authors.affiliation: Met Office Hadley Centre, Exeter, UK.
authors.forename: E J
authors.initials: EJ
authors.lastname: Burke
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
authors.forename: G
authors.initials: G
authors.lastname: Chen
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, USA.
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE CEA-CNRS-UVSQ), Gif-sur-Yvette, France.
authors.forename: P
authors.initials: P
authors.lastname: Ciais
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Grosse
authors.affiliation: United States Geological Survey, Menlo Park, CA, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Harden
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Hayes
authors.affiliation: Department of Physical Geography, Bolin Centre of Climate Research, Stockholm University, Stockholm, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Hugelius
authors.affiliation: National Snow and Ice Data Center, University of Colorado, Boulder, CO, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Jafarov
authors.affiliation: Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS and Université Grenoble Alpes, Grenoble 38041, France.
authors.forename: G
authors.initials: G
authors.lastname: Krinner
authors.affiliation: Department of Physical Geography, Bolin Centre of Climate Research, Stockholm University, Stockholm, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Kuhry
authors.affiliation: Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Lawrence
authors.affiliation: School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada.
authors.forename: A H
authors.initials: AH
authors.lastname: MacDougall
authors.affiliation: Geophysical Institute Permafrost Laboratory, University of Alaska, Fairbanks, AK, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Marchenko
authors.affiliation: US Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks, AK, USA.
authors.forename: A D
authors.initials: AD
authors.lastname: McGuire
authors.affiliation: Woods Hole Research Center, Falmouth, MA, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Natali
authors.affiliation: Geophysical Institute Permafrost Laboratory, University of Alaska, Fairbanks, AK, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Nicolsky
authors.affiliation: Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Olefeldt
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE CEA-CNRS-UVSQ), Gif-sur-Yvette, France Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS and Université Grenoble Alpes, Grenoble 38041, France.
authors.forename: S
authors.initials: S
authors.lastname: Peng
authors.affiliation: Geophysical Institute Permafrost Laboratory, University of Alaska, Fairbanks, AK, USA.
authors.forename: V E
authors.initials: VE
authors.lastname: Romanovsky
authors.affiliation: National Snow and Ice Data Center, University of Colorado, Boulder, CO, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Schaefer
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Strauss
authors.affiliation: United States Geological Survey, Menlo Park, CA, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Treat
authors.affiliation: Department of Integrative Biology, University of Ontario, Guelph, Ontario, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Turetsky
mesh_terms: D002244:Carbon / Q000032:analysis / Q000737:chemistry*; D057231:Climate Change / Q000706:statistics & numerical data*; D003198:Computer Simulation; D016208:Databases, Factual; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D005246:Feedback; D005615:Freezing; D008956:Models, Chemical; D015233:Models, Statistical; D065946:Permafrost / Q000737:chemistry*
chemical_list: D002244:Carbon
keywords: carbon–climate feedbacks; climate change; methane; permafrost