When is the Permafrost Carbon Tipping Point?
National Snow and Ice Data Center, University of Colorado
Tingjun Zhang
Kevin Schaefer
Tim Schaefer
Lin LiuMe
Alessio Gusmereli
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.
Permafrost Classification
Permafrost Classification by AreaPermafrost Classification by AreaContinuous (>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
Permafrost Distribution by Country
Permafrost ProfilePermafrost Profile
Active Layer
Vegetation
Permafrost
Permafrost Profile
Exposed permafrost by river, Siberia [Davis, 2000]
Thermokarst, Alaska
CryoturbationCryoturbation• Movement of soil or rock due to Movement of soil or rock due to
repeated freezing and thawingrepeated freezing and thawing
Vegetation
Active Layer
Permafrost
Pleistocene Cryoturbation, France
Permafrost FeaturesPermafrost Features
Frost Heave, Yamal Stone Circles, Svalbard
Stone Circles, NW Territories Stripes, Glacier NP
Ice Wedges and PolygonsIce Wedges and Polygons
Polygons, Yena Polygons, Prudhoe Bay [Zhang, 2009]
Active Layer
Permafrost
Frozen
100th Winter
Frozen
1st Winter
Soil contracts & cracks
Thawed
1st Spring
Crack fills with water & freezes
Thawed
100th Spring
Ice Wedge
Ice Lenses and LayersIce Lenses and Layers
Active Layer
Permafrost
Year 1
Capillary suction of water to permafrost
Water freezes & expands
Year 1,000
Ice LayerIce Lens
Active Layer
Permafrost
Ice Lenses
Permafrost is Like ConcretePermafrost is Like Concrete
WicklandSchaefer
ThermokarstThermokarst
Slope Mountain, Alaska [Schaefer, 2012]
• Thermokarst: subsidence or collapse of ground surface due to melting of ground ice
Impacts of DegradationImpacts of DegradationFoundation Settling in Chersky
Qinghai-Xizang Highway Bridge
Alaska Road Heaves
Thermokarst in Yakutsk [Skiklomanov, 2005]
Impacts of DegradationImpacts of Degradation
Drying lake, Tibet [Zhang, 2007]
Rockfall, Matterhorn [Gruber, 2003] Ice-wedge thaw, Alaska [Davis, 2000]
Coastal Erosion, Alaska
Global Carbon CycleGlobal Carbon Cycle
1.71.9 90 88
Ocean38,000 Gt
6
Fossil Fuel4000 Gt
Permafrost 1466 Gt
Atmosphere750 Gt + 3 Gt yr-1
119120
Soils 1400 GtVegetation 600 Gt
Permafrost Carbon Burial
Permafrost Horizon
Deposition (loess, peat, erosion, volcanic)
Soil Depth
Active Layer
Permafrost
~1466 Gt C in permafrost [Tarnocai et al., 2009]
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]
Permafrost Carbon Feedback
Amplification of warming due to release of CO2 and CH4 from thawing permafrost
Methane Release from Thawing Permafrost
K. Walter [email protected]
Thaw bulb
Permafrost
Peat
Methane production
Methane emissionemission Thermokarst
Erosion
Dead plant & animal remains
Burning methane over a thermokarst lake in Siberia (K. Walter)
IPCC A1B Scenario
200
300
400
500
600
700
800
1960 2000 2040 2080 2120 2160 2200
Date (year)
Atm
osph
eric
CO
2 (pp
m)
Current Permafrost
Active Layer Thickness ALT (cm)Active Layer Thickness ALT (cm)
Projected Permafrost DegradationHadCM3 (med)HadCM3 (med)
Active Layer Thickness ALT (cm)Active Layer Thickness ALT (cm)
Projected Permafrost Loss
CCSM3 (low)CCSM3 (low)29% loss29% loss
HadCM3 (med)HadCM3 (med)50% loss50% loss
MIROC3.2 (high)MIROC3.2 (high)59% loss59% loss
Increase in ALT by 2200 (cm)Increase in ALT by 2200 (cm)
Permafrost Carbon Tipping Point
PCF Tipping Point 2023±4
Date (year)
Cum
ulat
ive
NE
E (
Gt C
)
Arctic switches from a sink to a source
Cumulative Permafrost Carbon Flux
Date (year)
Per
maf
rost
Car
bon
Flu
x (G
t C)
190±64 Gt
104±37 Gt
65±23% of cumulative global land sink (~160 Gt C)Equivalent to 87±29 ppm
Vostok Ice Core Records
• CO2 lags behind temperature by 600±400 yr
80 ppm
Paleo-Permafrost Carbon FeedbackPalaeocene-Eocene Thermal Maximum (PETM)
Orbit perturbations trigger Antarctic permafrost thaw [DeConto et al. 2011, in review]
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
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]
Backup SlidesBackup Slides
The SiBCASA ModelThe SiBCASA Model
CO2 Temp
Humidity
NEE Latent Heat
Sensible Heat
Snow
R
Moi
stur
e
Tem
pera
tur
e
Car
bon
Canopy
Soil
GPP
Input Weather
Boundary Layer
Permafrost Carbon in SiBCASA
Dmin = max ALT during spinup
Active Layer Thickness (ALT)
Soil Carbon Pools
Dmax = 3 m
Active Layer
Permafrost
Thawed CarbonPermafrost
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]
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)
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
IPCC A1B Arctic Temperatures
Air
Tem
pera
ture
(°C
)CCSM3 (low warming)HadCM3 (medium warming)MIRC3.2 (high warming)
Average air temperature for permafrost regions
Permafrost Area Loss
Date (year)
Per
maf
rost
Are
a (%
)
169±54 Gt C203±63 Gt C
213±65 Gt C
Frozen Ground ExtentFrozen Ground ExtentPermafrostSeasonally Frozen GroundIntermittently Frozen Ground
Zhang et al., 2003. EICOP
Snow Limit
Permafrost covers 24% of land surface in Northern Hemisphere
Atmosphere
Vegetation
Snow cover
Geothermal
Organic layer
Permafrost
Buffer Layer
What Drives Permafrost Formation?What Drives Permafrost Formation?
Barrow, Barrow, AlaskaAlaska
Observed Soil Temperature (C) 1996-7
Month
Soi
l Dep
th (
m)
Sno
w D
epth
(cm
)A
ir T
emp
(C)
Soil Temperature (C)
Observed Snow Depth (cm) 2002-3
Observed Air Temperature (C) 2003-4
Repeated Soil Freeze/Thaw Cycles Shape Permafrost Landscape
• Water expands ~9% when it freezes into iceWater expands ~9% when it freezes into ice
• Frost Heave: rising of ground surface when : rising of ground surface when ground water Freezesground water Freezes
• Thaw Settlement: settling of ground surface : settling of ground surface when ground ice meltswhen ground ice melts
• Moisture Movement: soil moisture moves from : soil moisture moves from unfrozen zone to frozen frontunfrozen zone to frozen front
Permafrost FeaturesPermafrost Features
Frost Heave, Yamal Stone Circles, Svalbard
Stone Circles, NW Territories Stripes, Glacier NP
Permafrost Degradation [IPCC, 2007]Permafrost Degradation [IPCC, 2007]
>3 °C increase mid-1950s to 1990
1 to 3 °C increase in past several
decades0 to 1 °C increase since 1970s
4 to 6 C increase in 20th Century2 to 3 C in last 30 years
-4
-3
-2
-1
0
1
2
3
4
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000Year
Tem
pera
ture
Ano
mal
y (°
C)
0.2 m; Trend = +0.78°C/decade0.4 m; Trend = +0.79°C/decade0.8 m; Trend = +0.65°C/decade1.6 m; Trend = +0.55°C/decade3.2 m; Trend = +0.66°C/decade
Russian Permafrost Temperature TrendsRussian Permafrost Temperature Trends
Frauenfeld et al. [2004] Zhang et al. [2005]
Russian Active Layer TrendsRussian Active Layer Trends
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Year
Act
ive
Lay
er D
epth
Ano
mal
y (m
) 1960–1998 Change: +25 cm
Frauenfeld et al. [2004] Zhang et al. [2005]
Talik DevelopmentTalik 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
-1.0
-0.5
0.0
0.5
1.0
1950 1960 1970 1980 1990 2000Year
Soi
l Tem
pera
ture
(°C
)
Soil Temperature at 3.2 m in Central Siberia (°C)
Talik Forms
Permafrost CarbonPermafrost Carbon
• 1672 Gt C in permafrost 1672 Gt C in permafrost [[Tarnocai et al.Tarnocai et al., 2009], 2009]
• 750 Gt C in atmosphere 750 Gt C in atmosphere
Roots, Siberia [Zimov et al., 2006]
Humus, Siberia [Davis, 2000]Mammoth, Siberia
Projections of Permafrost DegradationProjections of Permafrost Degradation
• General Pattern: lose area from the south, General Pattern: lose area from the south, increase active layer thickness everywhereincrease active layer thickness everywhere
SourceReduction in
Permafrost Area by 2100 (%)
Increase in Active Layer
Thickness (cm)
Schaefer et al . [2010] 4 19-28Zhang et al . [2008] 16-19 30-80Saito et al . [2007] 60 100-300Lawrence and Slater [2005] 90 500Lawrence et al . [2008] 90 500
Feedbacks to AtmosphereFeedbacks to Atmosphere
• Energy balanceEnergy balance• Snow Albedo FeedbackSnow Albedo Feedback• Vegetation Albedo FeedbackVegetation Albedo Feedback• Sea Ice Loss and Arctic AmplificationSea Ice Loss and Arctic Amplification• Bowen ratio seasonalityBowen ratio seasonality
• Trace Gas FeedbacksTrace Gas Feedbacks• COCO22 Fertilization Fertilization• Permafrost Carbon FeedbackPermafrost Carbon Feedback
Net Ecosystem Exchange (NEE)Net Ecosystem Exchange (NEE)
• NEE < 0 means net carbon uptake
NEE = Respiration - Photosynthesis
Enhanced by Permafrost
Carbon Feedback
Enhanced by CO2
Fertilization
58±19 Gt C by 2200 is a lot of carbon58±19 Gt C by 2200 is a lot of carbon
• 3.5% of permafrost carbon3.5% of permafrost carbon
• 26±9 ppm26±9 ppm increase comparable increase comparable Vostok Ice Core (80 ppm)Vostok Ice Core (80 ppm)
• 13-27% of global land sink13-27% of global land sink
• 4±1% of fossil fuel emissions 4±1% of fossil fuel emissions for 700 ppm targetfor 700 ppm target
Walking Points on PermafrostWalking 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 Permafrost Carbon Feedback will impact climate and fossil fuel reduction strategiesclimate and fossil fuel reduction strategies
When is the Permafrost Carbon Tipping Point?
Kevin Schaefer1, Tingjun Zhang1, Lori Bruhwiler2, Andrew P. Barrett1
1National Snow and Ice Data Center, University of Colorado2NOAA Earth System Research Laboratory
Observed Permafrost
Rock Circle Formation
Expand out in winter when frozen
Drop down in spring when thawed
Permafrost Area by Country
Permafrost Class by Country
Variations of area extent of seasonally frozen ground and snow in the Northern Hemisphere during the winter of 1998/99.
Seasonally Frozen Ground
Monthly maximum area extent of seasonally frozen ground
Seasonally frozen ground is ~65 x 106 km2 or 68% of the land area in the Northern Hemisphere.
Seasonally Frozen Ground
Climate/Weather
Geothermal heat flux
Ground temperature regime
Thermal diffusion equation
Soil thermal properties
Q* QH QLEQG = 0Soil moisture
conditions
Site-specific factors (albedo, roughness, slope, aspect, snow,
soil texture, etc.)
A Permafrost Model
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 = ks()
hs(t) = (x,t)
C= CFr(x,T)
k = kFr (x, T)
C= CFr (x,T)
T(Zfr ) = Tf
k = kTh (x, T)
C = CTh(x,T)
T(Zth ) = 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
Permafrost classificationPermafrost 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 • RelicRelic
• 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)
Frozen Ground Data ProductsFrozen 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)
Permafrost MonitoringPermafrost Monitoring
Permafrost Carbon in SiBCASA
permafrost carbon density is 2% by massDthreshold = 1973-2001 maximum active layer depthDactive = active layer depth
Slow (80%)
Metabolic (5%)
Structural (15%)
Soil Carbon PoolsDthreshold
Permafrost Carbon Pool
Dactive
Dthreshold
Dactive
Thawed Carbon
Permafrost Carbon Pool