How strong are the global biogeochemical feedbacks between permafrost and climate?

NEESPI - Focus Research Center Biogeochemical Cycle Studies MPI - BGC, Jena, Germany How strong are the global biogeochemical feedbacks between permafrost and climate? Martin Heimann Max-Planck-Institute for Biogeochemistry, Jena, Germany martin.heimann@bgc-jena.mpg.de

Carbon cycle - climate system feedbacks Climate CO2 Atmosphere Emissions from burning of fossil fuels and cement production Changes in landuse and land management Landbiosphere Ocean Climate response!t,!p,...!co2,!ch4 + Antropogenic emissions Climate driven feedback sources Y coupled = f Y uncoupled

Global CO2 budget over the next 100 years: Based on C 4 MIP results 20 A2-SRES Emissions PgC yr 1 15 10 C 4 MIP Simulations: Global climate-carbon cycle feedback factor: 1.18±0.11 Climate feedbacks 5 0 1950 2000 2050 Total uptake by land and ocean Decadal averages, smoothed C 4 MIP Simulations, Friedlingstein et al., 2006

C 4 MIP: Cumulative climate feedback effect on carbon stocks (Ncou-Nunc)t=2080 - (Ncou-Nunc)t=1910 Global 60N-90N 10 10 8 8 Model No. 6 Model No. 6 4 4 2 2 300 250 200 150 100 50 0 PgC yr 1 20 10 0 10 20 30 PgC yr 1 C 4 MIP Simulations, Friedlingstein et al., 2006

Missing processes: Permafrost soil carbon - climate feedbacks

Missing processes: Permafrost soil carbon - climate feedbacks Air Temperature + CO 2, CH 4 concentration + Soil Temperature + Soil carbon release (CO 2, CH 4 ) + + Soil thawing depth + + Microbial metabolic activty Heat production

Permafrost extent in northern hemisphere National Snow and Ice Data Center

Land carbon stocks in boreal and arctic zone (PgC) low high soils 1000 1000 peatlands 200 450 frozen soils 200 500 vegetation 60 70 McGuire et al., 2009, Ecological Monographs

How much permafrost carbon is vulnerable on a time scale of 100 years (based on typical global warming scenario)? Source Cumulative release (PgC) Annual emissions (PgC yr -1 ) Zhuang et al. 2006 ~20 0.2 Gruber et al. 2004 100 1.0 Khvorostyanov et al., 2008 (Yedoma only) 260 (CO2) 30 (CH4) 2.6 (CO2) 0.3 (CH4)

Idealized 1-d Model of CH4, CO2 and O2 in permafrost soil F Khvorostyanov et al., Tellus, 2008

7 8 9 10 11 12 13 14 15 16 e 17 of 19 17 Tellus B (a) Soil temperature ( C): talik formation when decomposi18 With metabolic heat generation metabolic heat generation VULNERABILITY OF PERMAFROST CARBON TO GLOBAL WARMING.Without PART 1. MODEL DESCRIPTION AND ROLE OF HEAT GEN tion heat is On. Contour interval is 4 C 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 (a) Soil temperature ( C): talik formation when decomposi(b) restoring when decom37 (c) Soil Soil temperature temperature (( C): C): permafrost no talik formation when decompo tion heat is On. Contour interval is 4 C position heatis is Off. On.Contour Contourinterval intervalisis4 4CC sition heat 38 39 Talik formation 40 41 Khvorostyanov et al., Tellus, 2008 Atmospheric step change warming experiment (+5 C at model year 1000) r Fo Pe R er Fo r

Global Carbon Cycle - Additional Feedback from Permafrost Degradation 20 PgC yr 1 15 10 5 A2-SRES Emissions Climate feedbacks on vegetation and soils (C4MIP) Additional Feedback from permafrost degradation 0.2-3 PgC yr -1? 0 1950 2000 2050 Total uptake by land and ocean Decadal averages, smoothed C 4 MIP Simulations, Friedlingstein et al., 2006

Feedback Analysis, Carbon Cycle Net feedback factor: f = 1 (1 g) 1.38 Feedback Factor 1.36 1.34 1.32 1.30 1.28 1.26 IPSL MPI 0 50 100 150 200 250 300 Cumulative Permafrost Release PgC Friedlingstein et al., 2006

Global Feedback from Methane Release Upper Range: 0.3 PgC yr-1 = 400 TgCH4 yr -1 At steady state ~ 1500 ppb Radiative forcing: 0.48 (current) ~1.0 Wm-2

Observing strategy - Top-down method: Possible surface source uncertainty reduction from atmospheric concentration measurement network

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CH4 Inversions: No evidence of positive trend in northern latitudes Bousquet et al., 2006, ICOS CarboScope (www.carboscope.eu)

CO2 Inversions: No evidence of positive trend in northern latitudes ICOS CarboScope (www.carboscope.eu), CARBONTRACKER-EU, LSCE-Inversion, MPI-BGC Jena Inversion

Conclusions

Conclusions Northern hemisphere land permafrost contains a huge, potentially vulnerable carbon pool.

Conclusions Northern hemisphere land permafrost contains a huge, potentially vulnerable carbon pool. Traditional permafrost melting yields small carbon releases on a 100 yr time scale (~ 0.2 PgC/yr).

Conclusions Northern hemisphere land permafrost contains a huge, potentially vulnerable carbon pool. Traditional permafrost melting yields small carbon releases on a 100 yr time scale (~ 0.2 PgC/yr). Worst case scenario: Triggering of postulated organic carbon decomposition heat strong permafrost degradation over next 100 years. Upper bounds: ~ 3 PgC/yr as CO2, ~ 400 TgCH4/yr.

Conclusions Northern hemisphere land permafrost contains a huge, potentially vulnerable carbon pool. Traditional permafrost melting yields small carbon releases on a 100 yr time scale (~ 0.2 PgC/yr). Worst case scenario: Triggering of postulated organic carbon decomposition heat strong permafrost degradation over next 100 years. Upper bounds: ~ 3 PgC/yr as CO2, ~ 400 TgCH4/yr. Worst case scenario increases global net carbon cycle feedback factor from 1.2 to 1.3, and doubles CH4 radiative forcing.

Conclusions Northern hemisphere land permafrost contains a huge, potentially vulnerable carbon pool. Traditional permafrost melting yields small carbon releases on a 100 yr time scale (~ 0.2 PgC/yr). Worst case scenario: Triggering of postulated organic carbon decomposition heat strong permafrost degradation over next 100 years. Upper bounds: ~ 3 PgC/yr as CO2, ~ 400 TgCH4/yr. Worst case scenario increases global net carbon cycle feedback factor from 1.2 to 1.3, and doubles CH4 radiative forcing. Top-down atmospheric inversions do not show any convincing trends of enhanced CO2 or CH4 releases in the northern latitudes.

Conclusions Northern hemisphere land permafrost contains a huge, potentially vulnerable carbon pool. Traditional permafrost melting yields small carbon releases on a 100 yr time scale (~ 0.2 PgC/yr). Worst case scenario: Triggering of postulated organic carbon decomposition heat strong permafrost degradation over next 100 years. Upper bounds: ~ 3 PgC/yr as CO2, ~ 400 TgCH4/yr. Worst case scenario increases global net carbon cycle feedback factor from 1.2 to 1.3, and doubles CH4 radiative forcing. Top-down atmospheric inversions do not show any convincing trends of enhanced CO2 or CH4 releases in the northern latitudes. Zero th order assessment. Ignores a host of possible secondary biogeochemical and biophysical feedbacks. These need to be studied in more detail to quantify better the global net feedback factor. But will very unlikely change the overall magnitude of the effect.