Dependence of near-surface permafrost inertia on direction, intensity, and temporal scale of global surface temperature change A.V. Eliseev, P.F. Demchenko, M.M. Arzhanov, and I.I. Mokhov A.M. Obukhov Institute of Atmospheric Physics RAS ENVIROMIS-2012
Motivation (1) - Global warming, observed in the late 20th century and expected to continue in the 21st century, may lead to degradation of near-surface and deep permafrost. Due to climate inertia, this degradation is able continue during next several centuries provided that anthropogenic GHG emissions are continued and sufficiently strong. - However, after cessation of these emissions and subsequent decay of anthropogenic forcing agents, climate is expected to return to initial state with respective return to permafrost Basic question Is relation between the climate state and permafrost extent depends on direction of climate change? If yes, does this relationship also depend on time scale and intensity of imposed external forcing?
Motivation (2): Dependence of potential continious permafrost extent sensitivity on global warming rate [Demchenko et al., 2006] k cont = S cont,0 -1 dS cont / dT gl S cont - extent of potential continious permafrost (calculated based on monthly mean SAT) S cont,0 - reference value of S cont T gl - globally averaged SAT EXP, LIN - series of the simulations with the IAP RAS CM forced by the idealised scenarios for q CO2 A2-GHG, A2-CO2, B2-GHG, B2-CO2, IS92a-GHG, IS92a-CO2 - simulations with the IAP RAS CM forced by the anthropogenic scenarios for the 21st century adapted either from the IPCC FAR or from the IPCC TAR Paleo is derived from the empirically estimated differences between the Holocene Optimum and the Eemian Interglacial [Velichko and Nechaev, 1992]
General structure of the IAP RAS CM insolation ATMOSPHERE strato- and mesosphere s l concentrations free troposphere o h n o N 2 O, freons, g r t w clouds w large-scale tropospheric and a a (single effective layer) v circulation, v stratospheric e e r aerosols r a a d synoptic-scale d i i a precipitation a processes are t anthropogenic t i convection i o o parametrised n emissions n СО 2 and CH 4 boundary layer heat, moisture, momentum, CO 2 heat, moisture, CO 2 , CH 4 SEA ICE OCEAN ICE SHEETS VEGETATION mixed layer (prescribed) (prescribed ecozones, in the whole ocean the following processes interactive carbon cycle) are considered: SNOW litterfall heat transport, SOIL PERMAFROST large-scale circulation, run synoptic-scale processes are parametrised, DSS: Deep Soil Simulator off prescribed salinity (thermal and hydrological processes, deep ocean CH 4 emissions from wetlands) bottom friction layer Horizontal resolution : 4.5 o * 6.0 o heat, CH 4 Turnaround time : ~ 17 sec per model SEDIMENTS year (Intel Core2 Quad 9400) (thermal processes, CH 4 in clathrates)
General structure of the DSS [Arzhanov et al., 2009] Governing R LW,d R SW,tot Pr E F sens R LW,u T air input equations: output - heat transport (diffusion); - moisture d snow snow T snow (z) transport (Richard equation); organics unfrozen d AL (2 m in (active layer) peatlands, Parameters 0.1 m depend on frozen elsewhere) (near-surface - soil type, T ground (z), permafrost) - soil state 60 m W ground (z) (frozen/unfrozen, d PT - soil moisture mineral unfrozen content W. soil (talik) frozen Δz: adaptive grid: (relic = 5 cm in the permafrost) upper 10 m of soil r u n column; at the lower boundary: o f f decreased to 1 cm F heat =const (typically, =0) near frost front F water =0
Simulations: AR5 EMIC Protocol: AR5 EMIC (http://climate.uvic.ca/EMICAR5) Duration : 850-4000 External forcings : - atmospheric concentrations of CO 2 , CH 4, and N 2 O; - tropospheric burdens of sulphate aerosols; - total solar irradiance; - stratospheric aerosol optical depth; - change in surface albedo due to land use.
Globally averaged annual mean TOA radiative forcing 2300-4000 850-2300 (RCP 8.5 as an example) W/m 2 W/m 2 year year q CO2 returns to PI value in 3000-3100 historic q CO2 returns to PI value in 3000-4000 RCP 2.6 q CO2 is calculated by the model in 3000- RCP 4.5 RCP 6.0 4000 assuming E CO2,ant =0 RCP 8.5 other agents are fixed at the values for year 2300
Globally averaged annual mean SAT and extent of near-surface permafrost: 850-2300 ΔT g , K S p , mln km 2 year year historic RCP 2.6 RCP 4.5 RCP 6.0 RCP 8.5 obs. (ΔT g : HadCRUT3; S p : [Zhang et al., 1999; Tarnocai et al., 1999]
Globally averaged annual mean SAT and extent of near-surface permafrost: RCP 6.0, 2300-4000 ΔT g , K S p , mln km 2 year year q CO2 returns to PI value in 3000-3100 q CO2 returns to PI value in 3000-4000 q CO2 is calculated by the model in 3000- 4000 assuming E CO2,ant =0
Globally averaged annual mean SAT and extent of near-surface permafrost: RCP 8.5, 2300-4000 ΔT g , K S p , mln km 2 year year q CO2 returns to PI value in 3000-3100 q CO2 returns to PI value in 3000-4000 q CO2 is calculated by the model in 3000- 4000 assuming E CO2,ant =0
Modelled near-surface permafrost-covered area vs . globally averaged annual mean SAT q CO2 returns to PI S p , mln km 2 S p , mln km 2 value in 3000- 3100 RCP 2.6 RCP 4.5 q CO2 returns to PI value in 3000- 4000 q CO2 is calculated by the model in 3000-4000 assuming T g , K E CO2,ant =0 RCP 6.0 RCP 8.5 T g , K
κ = d S p / d T g [mln km 2 K -1 ] (only when q CO2 returns to PI value in 3000-3100) RCP 2.6 RCP 4.5 all dT g / dt > 0 dT g / dt < 0 mean ± 2 * STD RCP 6.0 RCP 8.5
Near-surface permafrost mask (RCP 8.5; q CO2 returns to PI value in 3000-3100) dT g /dt > 0 difference 0.75 0.5 0.25 dT g /dt < 0 For every individual year in every grid cell: M=1 if permafrost is diagnosed, M=0 otherwise. Then composites of M are constructed by averaging in 288.4 K < T g < 290.0 K (this range depends on the RCP scenario) when hysteresis branches in coordinates (T g , S p ) are separated.
Area covered by continious potential permafrost (as calculated based on monthly mean local SAT) vs . globally averaged annual mean SAT q CO2 returns to PI S p , mln km 2 S p , mln km 2 value in 3000- 3100 RCP 2.6 RCP 4.5 q CO2 returns to PI value in 3000- 4000 q CO2 is calculated by the model in 3000-4000 assuming T g , K E CO2,ant =0 RCP 6.0 RCP 8.5 T g , K
Tentative mechanism for permafrost hysteresis 1. dT g /dt > 0 seasonal thaw talik develops frozen unfrozen 2. dT g /dt < 0 Talik generally delays soil response talik exists talik disappears to atmospheric forcing Longer impact of talik on soil state in the case of global cooling in comparison to the case of global warming Permafrost hysteresis
Amplification through hydrological cycle: Composite differences for July (RCP 8.5; q CO2 returns to PI value in 3000-3100) soil moisture content in radiation budget at the the upper 7 cm of soil cloud amount [] surface [W/m 2 ] column [m/m] ΔM = 0.25
Therefore: - The relationship between globally averaged surface air temperature T g and the near-surface permafrost extent S p is multivalued. - This transient permafrost hysteresis is visible more clearly for more aggressive anthropogenic scenarios. In contrast, it does not depend on the way how q CO2 returns to the PI value, at least among studied here scenarios. - It is likely to related to the impact of phase transitions of soil moisture on apparent heat capacity of soil. This mechanism is amplified via atmospheric hydrological feedbacks and radiative budget at the surface. It is tempting to study this mechanism in a systematic way
Simulations: Idealised Duration : ( 45 simulations ) * ( model years 1-3000 ) = 135,000 years External forcings : periodically varying q CO2 : q CO2 = q CO2,0 exp [ A sin ( 2 π t / P) ], q CO2 , ppmv q CO2,0 = 500 ppmv A = 0.1, P = 100 yr A = 0.1, P = 1000 yr A = 0.5, P = 100 yr A = 0.5, P = 1000 yr year Model versions : - standard, specific latent heat of freezing L = L 0 = 3.34*10 5 J / kg; - L = L 0 / 10 in soil; - L = L 0 / 100 in soil;
P = 100 yr, A = 0.1 T g , K S p , mln km 2 standard version L = L 0 / 10 L = L 0 / 100 P = 1000 yr, A = 0.5 model year T g , K S p , mln km 2 model year
Hysteresis of near-surface permafrost: dependence on type of external forcing (standard model version) idealised: P = 1000 yr, A = 0.5 RCP 8.5 S p , mln km 2 S p , mln km 2 T g , K T g , K q CO2 returns to PI value in 3000-3100 q CO2 returns to PI value in 3000-4000 q CO2 is calculated by the model in 3000-4000 assuming E CO2,ant =0
Between-branches difference of near-surface permafrost mask ( standard version) idealised simulation RCP 8.5 P = 1000 yr, A=0.3 q CO2 returns to PI value in 3000-3100 0.25 0.5 0.75
Amplification mechanism via hydrological cycle: dependence on type of external forcing. Moisture content in the upper 7 cm of soil column [m/m] (standard model version) RCP 8.5 idealised simulation q CO2 returns to PI value in 3000-3100 P = 1000 yr, A=0.3 This mechanism is likely not important for -0.2 -0.1 -0.05 permafrost hysteresis. However, it does amplify the separation between the hysteresis branches. ΔM = 0.25
Hysteresis of near-surface permafrost: dependence on model version ( P = 1000 yr, A = 0.5 ) standard ( L = L 0 ) L = L 0 / 10 L = L 0 / 100 S p , mln km 2 S p , mln km 2 S p , mln km 2 T g , K T g , K T g , K Consistent with the tentative mechanism proposed above
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