Fundamental Dynamics of the Permafrost Carbon Feedback Schaefer, Kevin 1, Tingjun Zhang 1, Lori Bruhwiler 2, and Andrew Barrett 1 1 National Snow and Ice Data Center, University of Colorado 2 NOAA Earth System Research Laboratory, Boulder, Colorado Contact: Kevin Schaefer: ; Funded under NACP NASA grant NNX06AE65G and NOAA grant NA09OAR National Snow and Ice Data Center Permafrost Carbon Permafrost Horizon Loess Deposition Soil Depth Active Layer Permafrost Siberia [Davis, 2000] Active Layer Deepens CO 2 Increases Permafrost carbon decays Atmospheric Warms Net Carbon Flux Figure 1: Gt of carbon is frozen in permafrost [Zimov et al., 2006, Tarnocai et al., 2009]. Loess deposition 20,000-30,000 years ago increased soil depth, freezing organic matter at the bottom of the active layer into permafrost. The Tipping Point Figure 3: The permafrost carbon tipping point occurs when increased respiration from the thaw of permafrost carbon overpowers enhanced plant uptake due to longer growing seasons, marking the start of the Permafrost Carbon Feedback. Figure 2: The positive Permafrost Carbon Feedback occurs when warming due to increased atmospheric CO 2 thaws permafrost carbon, which then decays, releasing additional CO 2 and CH 4 and amplifying the warming rate. None of the IPCC models currently include the permafrost carbon feedback. Permafrost Carbon Feedback SiBCASA Model Setup Figure 4: The Simple Biosphere /Carnegie-Ames-Stanford Approach (SiBCASA) model [Schaefer et al., 2008]. We ran SiBCASA to 2200 driven by randomly selected years from the NCEP reanalysis with a 4 °C century -1 linear increase in air temperature, the mean rate of temperature increase predicted by IPCC models for Arctic regions. D max = maximum active layer depth Slow Metabolic Structural D max Active Layer Permafrost D Thawed Carbon 80% 5% 15% Soil Carbon Pools D = active layer depth Figure 5: Currently, permafrost carbon is below the maximum active layer depth. As the active layer deepens, thawed carbon is transferred to soil carbon pools. Permafrost carbon density (2% by mass) and pool allocations are based on observations in Siberia and Alaska. CO 2 Temperature Humidity NEE Latent Heat Sensible Heat Snow R Moisture Temperature Canopy Air Space Soil GPP Canopy NDVI (f PAR, LAI) NCEP Reanalysis (Weather) Boundary Layer Carbon Pools Estimated Tipping Points Figure 6: Our domain is continuous and discontinuous permafrost north of 45° latitude. 1) A permafrost carbon tipping point could occur this century. 2) The Permafrost carbon feedback is strong relative to global land sink and fossil fuel emissions. 3) More simulations driven by IPCC scenarios will quantify uncertainty. Conclusions Siberia [Zimov et al., 2006] Tipping Point No permafrost carbon With permafrost carbon Permafrost Seasonally Frozen Intermittently Frozen Snow Climatology Black: no tipping point by 2200.Black: talik in 1973 Grey: new talik by (b) Active Layer Increase (cm)(a) Tipping Point (year) NEE with permafrost carbon NEE no permafrost carbon Tipping Point 2047±7 114±13 Gt C (52±6 ppm) 30±1.5 Gt C Tipping Point 2115 NEE with permafrost carbon NEE no permafrost carbon Figure 7: A sample tipping point of 2115 for a point in central Siberia (63°N, 150°E). Figure 8: Tipping points (a) and active layer increases (b). Talik formed along southern margins. Tipping points only occur where active layers increase by more than 40 cm. Figure 9: We estimate a pan-Arctic permafrost carbon tipping point of 2047±7. The Permafrost Carbon Feedback strength is 114±13 Gt C in 2200, equivalent to a change in atmospheric CO2 of 52±6 ppm.