Fundamental Dynamics of the Permafrost Carbon FeedbackSchaefer, Kevin1, Tingjun Zhang1, Lori Bruhwiler2, and Andrew Barrett1

1 National Snow and Ice Data Center, University of Colorado2NOAA Earth System Research Laboratory, Boulder, Colorado

Contact: Kevin Schaefer: 303-492-8869; kevin.schaefer@nsidc.org

Funded under NACP NASA grant NNX06AE65G and NOAA grant NA09OAR4310063

National Snow and Ice Data Center

Permafrost Carbon

Permafrost Horizon

Loess Deposition

Soil Depth

Active Layer

Permafrost

Siberia [Davis, 2000]

Active Layer

Deepens

CO2 Increases

Permafrost carbon decays

Atmospheric Warms

Net

Car

bon

Flux

2000 21002050

0.0

Figure 1: 950-1670 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 CO2 thaws permafrost carbon, which then decays, releasing additional CO2 and CH4 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.

Dmax = 1948-2007 maximum active layer depth

Slow

Metabolic

Structural

Dmax

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.

CO2Temperature

Humidity

NEE Latent Heat

Sensible Heat

Snow

R

Moi

stur

e

Tem

pera

ture

Canopy Air Space

Soil

GPP Canopy

NDVI (fPAR, 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 carbonWith permafrost carbon

PermafrostSeasonally FrozenIntermittently FrozenSnow Climatology

Black: no tipping point by 2200. Black: talik in 1973Grey: new talik by 2200.

(b) Active Layer Increase (cm)(a) Tipping Point (year)

NEE with permafrost carbonNEE 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 carbonNEE 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.