1. When is the Permafrost Carbon Tipping Point? National Snow and Ice Data Center, University of Colorado Tingjun Zhang Kevin Schaefer Tim Schaefer Lin Liu Me Alessio Gusmereli

2. Permafrost Primer Skiklomanov [2007] Permafrost: Ground at or below 0°C for at least 2 consecutive years Active Layer: A layer over permafrost that freezes and thaws annually Permafrost Degradation: A decrease in permafrost extent; an increase in active layer thickness.

3. Permafrost Classification

4. Permafrost Classification by Area Continuous (>90% of area) Discontinuous (50-90% of area) Sporadic (10-50% of area) Isolated (<10% of area) Brown et al., 1998; Zhang et al., 1999

5. Permafrost Distribution by Country

6. Permafrost Profile Active Layer Vegetation Permafrost

7. Permafrost Profile Exposed permafrost by river, Siberia [Davis, 2000] Thermokarst, Alaska

8. Cryoturbation Movement of soil or rock due to repeated freezing and thawingMovement of soil or rock due to repeated freezing and thawing Vegetation Active Layer Permafrost Pleistocene Cryoturbation, France

9. Permafrost Features Frost Heave, YamalStone Circles, Svalbard Stone Circles, NW TerritoriesStripes, Glacier NP

10. Ice Wedges and Polygons Polygons, YenaPolygons, Prudhoe Bay [Zhang, 2009] Active Layer Permafrost Frozen 100 th Winter Frozen 1 st Winter Soil contracts & cracks Thawed 1 st Spring Crack fills with water & freezes Thawed 100th Spring Ice Wedge

11. Ice Lenses and Layers Active Layer Permafrost Year 1 Capillary suction of water to permafrost Water freezes & expands Year 1,000 Ice Layer Ice Lens Active Layer Permafrost Ice Lenses

12. Permafrost is Like Concrete Wickland Schaefer

13. Thermokarst Slope Mountain, Alaska [Schaefer, 2012] Thermokarst: subsidence or collapse of ground surface due to melting of ground ice

14. Impacts of Degradation Foundation Settling in Chersky Qinghai-Xizang Highway Bridge Alaska Road Heaves Thermokarst in Yakutsk [Skiklomanov, 2005]

15. Impacts of Degradation Drying lake, Tibet [Zhang, 2007] Rockfall, Matterhorn [Gruber, 2003]Ice-wedge thaw, Alaska [Davis, 2000] Coastal Erosion, Alaska

16. Global Carbon Cycle 1.71.99088 Ocean 38,000 Gt 6 Fossil Fuel 4000 Gt Permafrost 1466 Gt Atmosphere 750 Gt + 3 Gt yr -1 119120 Soils 1400 Gt Vegetation 600 Gt

17. Permafrost Carbon Burial Permafrost Horizon Deposition (loess, peat, erosion, volcanic) Soil Depth Active Layer Permafrost ~1466 Gt C in permafrost [Tarnocai et al., 2009]

18. Permafrost Carbon 30,000 year old roots, Siberia [Zimov et al., 2006] Mammoth, Siberia 32,000 year old grass, Alaska 15,000 year old moss, North Slope [Schaefer, 2012]

19. Permafrost Carbon Feedback Amplification of warming due to release of CO 2 and CH 4 from thawing permafrost

20. Methane Release from Thawing Permafrost K. Walter ftkmw1@uaf.edu Thaw bulb Permafrost Peat Methane production Methane emission Thermokarst Erosion Dead plant & animal remains Burning methane over a thermokarst lake in Siberia (K. Walter)

21. IPCC A1B Scenario Date (year) Atmospheric CO 2 (ppm)

22. Current Permafrost Active Layer Thickness ALT (cm)

23. Projected Permafrost Degradation HadCM3 (med) Active Layer Thickness ALT (cm)

24. Projected Permafrost Loss CCSM3 (low) 29% loss HadCM3 (med) 50% loss MIROC3.2 (high) 59% loss Increase in ALT by 2200 (cm)

25. Permafrost Carbon Tipping Point PCF Tipping Point 2023±4 Date (year) Cumulative NEE (Gt C) Arctic switches from a sink to a source

26. Cumulative Permafrost Carbon Flux Date (year) Permafrost Carbon Flux (Gt C) 190±64 Gt 104±37 Gt 65±23% of cumulative global land sink (~160 Gt C) Equivalent to 87±29 ppm

27. Vostok Ice Core Records CO 2 lags behind temperature by 600±400 yr 80 ppm

28. Paleo-Permafrost Carbon Feedback Palaeocene-Eocene Thermal Maximum (PETM) Orbit perturbations trigger Antarctic permafrost thaw [DeConto et al. 2011, in review]

29. PCF and Fossil Fuel Emissions Both inject old carbon into atmosphere Both irreversible A1B scenario: 700 ppm by 2100 1345 Gt C total emissions 190 Gt C permafrost carbon flux 1157 Gt C fossil fuel emissions Must reduce fossil fuel emissions by additional 15% or overshoot target climate

30. Conclusions PCF can explain past climate variability PCF tipping point in mid 2020s PCF is strong: 190±64 Gt C by 2200 Emission reductions must account for PCF Tellus B paper: Schaefer et al. [2011]

31. Backup Slides

32. The SiBCASA Model CO 2 Temp Humidity NEE Latent Heat Sensible Heat Snow R Moisture Temperature Carbon Canopy Soil GPP Input Weather Boundary Layer

33. Permafrost Carbon in SiBCASA D min = max ALT during spinup Active Layer Thickness (ALT) Soil Carbon Pools D max = 3 m Active Layer Permafrost Thawed Carbon Permafrost Carbon Pool Active Layer Permafrost Carbon Pool Permafrost 313 Gt C in permafrost carbon pool 91 Gt C in active layer 414 Gt C in top 3 m (575 Gt C estimated*) *Tarnocai et al. [2009]

34. Experiment Setup SiBCASA + ERA40 + A1B scenario Continuous/discontinuous permafrost 1973-2001: “spin up“ 2002-2200: random ERA40 + linear trend MIROC3.2 (high) HadCM3 (med) CCSM3 (low)

35. Estimating Uncertainty 18 ensemble members 3 warming rates 3 permafrost carbon densities 2 sub-grid permafrost extents Best estimate: ensemble mean Uncertainty: ensemble standard deviation

36. IPCC A1B Arctic Temperatures Air Temperature (°C) CCSM3 (low warming) HadCM3 (medium warming) MIRC3.2 (high warming) Average air temperature for permafrost regions

37. Permafrost Area Loss Date (year) Permafrost Area (%) 169±54 Gt C 203±63 Gt C 213±65 Gt C

38. Frozen Ground Extent Permafrost Seasonally Frozen Ground Intermittently Frozen Ground Zhang et al., 2003. EICOP Snow Limit Permafrost covers 24% of land surface in Northern Hemisphere

39. Atmosphere Vegetation Snow cover Geothermal Organic layer Permafrost Buffer Layer What Drives Permafrost Formation?

40. Barrow, Alaska Observed Soil Temperature (C) 1996-7 Month Soil Depth (m) Snow Depth (cm) Air Temp (C) Soil Temperature (C) Observed Snow Depth (cm) 2002-3 Observed Air Temperature (C) 2003-4

41. Repeated Soil Freeze/Thaw Cycles Shape Permafrost Landscape Water expands ~9% when it freezes into iceWater expands ~9% when it freezes into ice : rising of ground surface when ground water FreezesFrost Heave: rising of ground surface when ground water Freezes : settling of ground surface when ground ice meltsThaw Settlement: settling of ground surface when ground ice melts : soil moisture moves from unfrozen zone to frozen frontMoisture Movement: soil moisture moves from unfrozen zone to frozen front

42. Permafrost Features Frost Heave, YamalStone Circles, Svalbard Stone Circles, NW TerritoriesStripes, Glacier NP

43. Permafrost Degradation [IPCC, 2007] >3 °C increase mid-1950s to 1990 1 to 3 °C increase in past several decades 0 to 1 °C increase since 1970s 4 to 6 C increase in 20 th Century 2 to 3 C in last 30 years

44. -4 -3 -2 0 1 2 3 4 19501955196019651970197519801985199019952000 Year Temperature Anomaly (°C) 0.2 m; Trend = +0.78°C/decade 0.4 m; Trend = +0.79°C/decade 0.8 m; Trend = +0.65°C/decade 1.6 m; Trend = +0.55°C/decade 3.2 m; Trend = +0.66°C/decade Russian Permafrost Temperature Trends Frauenfeld et al. [2004] Zhang et al. [2005]

45. Russian Active Layer Trends -0.3 -0.2 -0.1 0 0.1 0.2 0.3 1955196019651970197519801985199019952000 Year Active Layer Depth Anomaly (m) 1960–1998 Change: +25 cm Frauenfeld et al. [2004] Zhang et al. [2005]

46. Talik Development Seasonally frozen ground Talik Permafrost Talik: Unfrozen soil layer above permafrost, but below seasonally frozen surface layer -3.0 -2.5 -2.0 -1.5 -0.5 0.0 0.5 1.0 195019601970198019902000 Year Soil Temperature (°C) Soil Temperature at 3.2 m in Central Siberia (°C) Talik Forms

47. Permafrost Carbon 1672 Gt C in permafrost [Tarnocai et al., 2009]1672 Gt C in permafrost [Tarnocai et al., 2009] 750 Gt C in atmosphere750 Gt C in atmosphere Roots, Siberia [Zimov et al., 2006] Humus, Siberia [Davis, 2000] Mammoth, Siberia

48. Projections of Permafrost Degradation General Pattern: lose area from the south, increase active layer thickness everywhereGeneral Pattern: lose area from the south, increase active layer thickness everywhere

49. Feedbacks to Atmosphere Energy balanceEnergy balance Snow Albedo Feedback Snow Albedo Feedback Vegetation Albedo Feedback Vegetation Albedo Feedback Sea Ice Loss and Arctic Amplification Sea Ice Loss and Arctic Amplification Bowen ratio seasonality Bowen ratio seasonality Trace Gas FeedbacksTrace Gas Feedbacks CO 2 Fertilization CO 2 Fertilization Permafrost Carbon Feedback Permafrost Carbon Feedback

50. Net Ecosystem Exchange (NEE) NEE < 0 means net carbon uptake NEE = Respiration - Photosynthesis Enhanced by Permafrost Carbon Feedback Enhanced by CO 2 Fertilization

51. 58±19 Gt C by 2200 is a lot of carbon 3.5% of permafrost carbon3.5% of permafrost carbon 26±9 ppm increase comparable Vostok Ice Core (80 ppm)26±9 ppm increase comparable Vostok Ice Core (80 ppm) 13-27% of global land sink13-27% of global land sink 4±1% of fossil fuel emissions for 700 ppm target4±1% of fossil fuel emissions for 700 ppm target

52. Walking Points on Permafrost Freeze/thaw cycles shape the landscapeFreeze/thaw cycles shape the landscape Permafrost degradation has already startedPermafrost degradation has already started Permafrost Carbon Feedback will impact climate and fossil fuel reduction strategiesPermafrost Carbon Feedback will impact climate and fossil fuel reduction strategies

53. When is the Permafrost Carbon Tipping Point? Kevin Schaefer 1, Tingjun Zhang 1, Lori Bruhwiler 2, Andrew P. Barrett 1 1 National Snow and Ice Data Center, University of Colorado 2 NOAA Earth System Research Laboratory

54. Observed Permafrost

55. Rock Circle Formation Expand out in winter when frozen Drop down in spring when thawed

56. Permafrost Area by Country

57. Permafrost Class by Country

58. Variations of area extent of seasonally frozen ground and snow in the Northern Hemisphere during the winter of 1998/99. Seasonally Frozen Ground

59. Monthly maximum area extent of seasonally frozen ground Seasonally frozen ground is ~65 x 10 6 km 2 or 68% of the land area in the Northern Hemisphere. Seasonally Frozen Ground

60. Climate/Weather Geothermal heat flux Ground temperature regime Thermal diffusion equation Soil thermal properties Q*  Q H  Q LE  Q G = 0 Soil moisture conditions Site-specific factors (albedo, roughness, slope, aspect, snow, soil texture, etc.) A Permafrost Model

61. Snow Atmosphere Lower Boundary Frozen ground Permafrost or unfrozen ground Thawed ground Moving phase plane: heat conduction with or without phase change Moving phase plane Heat conduction Snow-soil interface: heat conduction with or without phase change k = k s (  ) h s (t)  =  (x,t)  C=  C Fr (x,T) k = k Fr (x, T)  C=  C Fr (x,T) T(Z fr ) = T f k = k Th (x, T)  C =  C Th (x,T) T(Z th ) = T f Moving boundary: heat conduction in deforming medium Boundary condition: Prescribed temperature, or heat flux, or surface energy balance Boundary condition: prescribed temperature or heat flux Modeling Permafrost

62. Permafrost classification By area coverageBy area coverage Continuous (>90% of area) Continuous (>90% of area) Discontinuous (50-90% of area) Discontinuous (50-90% of area) Sporadic (10-50% of area) Sporadic (10-50% of area) Isolated (<10% of area) Isolated (<10% of area) By Location:By Location: Terrestrial Terrestrial Sub-ice Sub-ice Sub-sea Sub-sea Relic Relic By Coupling with climate:By Coupling with climate: Exposed (terrestrial) Exposed (terrestrial) Submerged (sub-ice, sub-sea, and relic) Submerged (sub-ice, sub-sea, and relic)

63. Frozen Ground Data Products http://nsidc.org/fgdc Arctic EASE-Grid Freeze and Thaw Depths, 1901 - 2002 Arctic Soil Freeze/Thaw Status from SMMR and SSM/I, Version 2 Circumpolar Active-Layer Permafrost System (CAPS) Global Annual Freezing and Thawing Indices Modeled Daily Thaw Depth and Frozen Ground Depth Northern Hemisphere EASE-Grid Annual Freezing and Thawing Indices, 1901 - 2002 Northern Hemisphere Seasonal and Intermittently Frozen Ground Areas 1901-2001 Russian Historical Soil Temperature Data Time Series of Active Layer Thickness in the Russian Arctic, 1915-1990 Circumpolar Active-Layer Permafrost System (CAPS)

64. Permafrost Monitoring

65. Permafrost Carbon in SiBCASA permafrost carbon density is 2% by mass D threshold = 1973-2001 maximum active layer depth D active = active layer depth Slow (80%) Metabolic (5%) Structural (15%) Soil Carbon Pools D threshold Permafrost Carbon Pool D active D threshold D active Thawed Carbon Permafrost Carbon Pool