Interactions between wetlands CH4 emissions and climate at global scale

Transcription

1 Interactions between wetlands CH4 and climate at global scale Bruno Ringeval - Laboratoire de Sciences du Climat et de l'environnement (LSCE), Gif-sur-Yvette - University of Bristol, UK and University of Utrecht, The Netherlands UMR TCEM, Bordeaux-Aquitaine Journée eau du CNRS Paris, le 8 Novembre 2013

2 CH4: role in the tropospheric chemistry (OH, O3) and on the climate (RFCH4 = 1/3 * RFCO2) CH4 atmospheric concentration : strong variability at different time scales CH4 atmospheric concentration (ppb) 105 yrs 103 yrs 102 yrs 1 yr IPCC, Dlugokencky et al., 2009 O Connor et al.,

3 CH4: role in the tropospheric chemistry (OH, O3) and on the climate (RFCH4 = 1/3 * RFCO2) CH4 atmospheric concentration : strong variability at different time scales CH4 atmospheric concentration (ppb) 105 yrs 103 yrs 102 yrs 1 yr Dlugokencky et al., 2009 O Connor et al., 2011 IPCC, 2001 => Evolution of the between sources and sinks 3

4 Current sources and sinks of atmospheric CH4: US Department of Energy WE T OCEAN CHLORINE LA ND S OH STRATOPH. LOSS SOILS Sources ~ 580 Tg/yr Sinks ~ 580 Tg/yr - Large uncertainties on the contribution of each source/sink - Wetlands (anaerobic decomposition of organic matter): Tg/yr (bottom-up); Tg/yr (top-down) 1-15 gc/m² of wetland/yr (Limpens et al., 2008) Large diversity of ecosystems + variability in time & space Wetland CH4 : major contribution, but very large uncertainty on the exact magnitude 4

5 Wetland CH4 are sensitive to the climate: Christensen et al., symbol = 1 site 5

6 Wetland CH4 are sensitive to the climate: Christensen et al., symbol = 1 site Weight in the total budget + sensitivity to climate => potential role of wetland in the variability of the CH4 atmospheric concentration in the past/present/future 6

7 Dlugokencky et al., 2009 Observations Present-day interannual variability, 7

8 1 Dlugokencky et al., 2009 Observations Present-day interannual variability, 1 wetlands.vs. anthropogenic.vs. OH? (Bousquet et al., 2006; Dlugokencky et al., 2003; EDGAR4) 2 2? wetlands.vs. biomass burning.vs. OH (Rigby et al., 2008; Bousquet et al., 2006, etc.)? 8

9 1 Dlugokencky et al., 2009 Observations Present-day interannual variability, 1 wetlands.vs. anthropogenic.vs. OH? (Bousquet et al., 2006; Dlugokencky et al., 2003; EDGAR4) 2 2? wetlands.vs. biomass burning.vs. OH (Rigby et al., 2008; Bousquet et al., 2006, etc.)? What is the wetland contribution to the atmospheric CH4 concentration variability? What are the controlling factors of the year-to-year variability in wetlands CH4? 9

10 Under future climate change, CO2 anthropogenic [CO2]atmo Climate ( T) e.g.: wetlands CH4 Shindell et al. (2004) => +78% under climate change generated by 2xCO 2

11 Under future climate change, CO2 anthropogenic [CO2]atmo Climate ( T) e.g.:? wetlands CH4 Shindell et al. (2004) => +78% under climate change generated by 2xCO 2 But very simple approach (statistical) How will the wetland CH4 evolve under future climate change?

12 Under future climate change, CO2 anthropogenic [CH4]atmo [CO2]atmo Climate ( T)? e.g.: wetlands CH4 Gedney et al. (2004) What is the sign and the amplitude of the climate-ch4 feedback?

13 Wetland CH4 sensitivity to climate at global scale: Vertical hydrologic processes (water table position, etc.) Horizontal hydrologic processes (wetland extent) Climate (temperature, precipitations, ) Methanogenesis substrate (quality and quantity) Wetland CH4 CH4 production/oxydation sensitivity to temperature Vegetation composition Nutrients Uncertainty on the contribution of each «process» and its evolution under a different climate => A process-based approach is required 13

14 What are the interactions between climate and wetlands CH 4 at global scale and at different time scales? Climate (temperature, precipitations, ) Atmospheric CH4 concentration Wetland CH4 14

15 What are the interactions between climate and wetlands CH 4 at global scale? Outlook: I Methods : development of a process-based approach to compute the global wetland CH4 II Involved processes in the wetland CH 4 sensitivity to climate over different temporal scales III Wetland contribution to temporal variability of all-sources and effect on the atmospheric concentration IV Potential feedback in the future 15

16 [CH4]atmo Two modelling approaches to simulate the wetland CH 4 : Top-down approach Seek the optimal that minimize the differences between transport model and observations Wetlands CH4 Bottom-up approach Representation with equations of the mechanisms that lead to CH4 + Close to atmospheric observations + Provide integral CH4 budget - Error amplification - Difficult to separate the different sources Complementarity (and could be independent) + Close to the processes + Could be extrapolated in the future - Extrapolation in spite of heterogeneities - Only wetlands 16

17 [CH4]atmo ORCHIDEE: Dynamic Global Vegetation Model (DGVM), component of the IPSL earth system model Climate forcing, maximum vegetation cover ORCHIDEE STOMATE Soil carbon, LAI SECHIBA Soil temperature, soil moisture Carbon processes Hydrologic/energy processes Krinner et al.,

18 [CH4]atmo ORCHIDEE: DGVM, component of the IPSL earth system model Climate forcing, maximum vegetation cover ORCHIDEE STOMATE Soil carbon, LAI SECHIBA Soil temperature, soil moisture Carbon processes Hydrologic/energy processes => DGVM: appropriate framework to study the interactions between climate and wetlands CH4 18

19 For each grid-cell and each time step, [CH4]atmo Climate forcing, maximum vegetation cover ORCHIDEE-WET STOMATE Soil carbon, LAI WTDi SECHIBA Soil temperature, soil moisture HYDRO1K Walter et al., 2001 CH4 flux density for a wetland with a Water Table Depth WTDi Di Evaluation against measures on sites TOPMODEL Fraction of wetland with WTDi Si Evaluation against remote sensing data (e.g. Prigent et al., 2007 ; Papa et al., 2011) or using riverflow For each grid-cell and wetland CH4 emissisions = i ( each time step, Si x Di ) 19

20 What are the interactions between climate and wetlands CH 4 at global scale? Outlook: I Methods : development of a process-based approach to compute the global wetland CH4 II Involved processes in the wetland CH 4 sensitivity to climate over different temporal scales III Wetland contribution to temporal variability of all sources-emission and effect on the atmospheric concentration IV Potential feedback in the future 20

21 [CH4]atmo Annual wetlands anomalies without variability in the wetland extent (TgCH4/yr) 1) Year-to-year variability of wetland CH 4 : role played by the variability in wetland extent 30 S-30 N Annual wetlands anomalies (TgCH4/yr) 21

22 [CH4]atmo Annual wetlands anomalies without variability in the wetland extent (TgCH4/yr) 1) Year-to-year variability of wetland CH 4 : role played by the variability in wetland extent 30 S-30 N x = Emission x flux density = wetland extent x = Annual wetlands anomalies (TgCH4/yr) Ringeval et al., 2010, GBC x = 1994 or or x 1996 Wetland extent : key-role in the year-to-year variability of wetland CH4 Relative complexity between the anomalies of climate/extent/ =

23 [CH4]atmo 2) Evolution of wetland CH4 under future global change Pre-industrial (1860 s) 10-3 Tg/yr SRES A2 scenario Additional in 2100 s due to CO2 + Climate 10-3 Tg/yr +70% 23

24 [CH4]atmo 2) Evolution of wetland CH4 under future global change Pre-industrial (1860 s) SRES A2 scenario Additional in 2100 s due to CO2 + Climate 10-3 Tg/yr 10-3 Tg/yr +70% Effect of CO2 alone: Effect of climate alone: % - 64% 24

25 [CH4]atmo 2) Evolution of wetland CH4 under future global change Effect of CO2 alone: Effect of climate alone: + 134% - 64% 25 Variable Variable Methanogenesis substrate (fertilizing effect) ~ +85% G S Wetland extent ~ +35% G S G/G: non-accounted/accounted for by Gedney et al. (2004) S/S: non-accounted/accounted for by Shindell et al. (2004) Methanogenesis rate (sensitivity to temperature) ~ +135% Methanogenesis substrate ~ -70% G S Wetland extent ~ -110% G S As in Shindell et al. (2004) and Gedney et al. (2004), we simulate an increase in wetland CH4 in 2100 BUT for very different involved reasons. Here, the effect of climate alone is to decrease the wetland CH 4 G S 25

26 What are the interactions between climate and wetlands CH 4 at global scale? Outlook: I Methods : development of a process-based approach to compute the global wetland CH4 II Involved processes in the wetland CH 4 sensitivity to climate over different temporal scales III Wetland contribution to temporal variability of all sources-emission and effect on the atmospheric concentration IV Potential feedback in the future 26

27 [CH4]atmo, All sources Top-down approach : ALL sources vs. wetlands => Wetlands dominate the time variability of CH 4 (~90%) : stagnation of CH 4 concentrations in the atmosphere Mismatch between bottom-up and top-down approaches Mismatch located in Tropics and in particular in Amazon basin Area of few constraints for top-down approach ; missing processes in bottom-up approach Pison et al., 2013, ACP Ringeval et al., 2013, BGD

28 What are the interactions between climate and wetlands CH 4 at global scale? Outlook: I Methods : development of a process-based approach to compute the global wetland CH4 II Involved processes in the wetland CH 4 sensitivity to climate over different temporal scales III Wetland contribution to temporal variability of all sources-emission and effect on the atmospheric concentration IV Potential feedback in the future 28

29 Climate-CH4 feedback from wetlands and its interaction with the climate-co 2 feedback CO2 anthropogenic [CO2]atmo αc αm [CH4]atmo Climate ( T) e.g.: γm 1) wetlands CH4 Using a more process-oriented approach than Gedney et al. (2004)

30 Climate-CH4 feedback from wetlands and its interaction with the climate-co 2 feedback CO2 anthropogenic [CO2]atmo Fertilizing effect αm αc Climate ( T) βc e.g.: terrestrial C sinks [CH4]atmo Effect on diffusive fluxes β C M γc γm CH4 anthropogenic βm e.g.: wetlands CH4 1) Using a more process-oriented approach than Gedney et al. (2004) 2) Accouting for interactions between the two feedbacks a) Climate interaction b) Fertilization interaction

31 Climate-CH4 feedback from wetlands and its interaction with the climate-co 2 feedback CO2 anthropogenic αm αc [CO2]atmo Climate ( T) Fertilizing effect βc e.g.: Effect on diffusive fluxes β C M γc terrestrial C sinks γm CH4 anthropogenic [CH4]atmo βm e.g.: wetlands CH4 Frieldingstein et al., 2003 CO2 = Atm. CO2 (2100) Atm. CO2 (1860) CO2 COU 1 UNC = CO2 1 gc CH COU 4 1 = CH 1 g UNC 4 M With gc,m=f(sensitivity terms) Each feedback considered alone

32 Climate-CH4 feedback from wetlands and its interaction with the climate-co 2 feedback CO2 anthropogenic [CO2]atmo αm αc Climate ( T) Fertilizing effect βc e.g.: Effect on diffusive fluxes βm β C M γc terrestrial C sinks γm CH4 anthropogenic [CH4]atmo e.g.: wetlands CH4 Frieldingstein et al., 2003 CO2 = Atm. CO2 (2100) Atm. CO2 (1860) CO2 COU 1 UNC = CO2 1 gc Then, when the two feedbacks are considered together: CH 4 COU CH COU 4 1 = CH 1 g UNC 4 M = 1 g g 1 g M + C M 1 gc CH 4 UNC + f (gc, gm). CO 2 UNC => Express the gain of each feedback and the interaction between the feedbacks as function to sensivity terms

33 Climate-CH4 feedback from wetlands and its interaction with the climate-co2 feedback 5000 (ppb) = Atm. CH (2100) Atm. CH (1860) CH CH4 computed using ORCHIDEE with sensitivity to climate is: 4500 estimated from ORCHIDEE estimated from Gedney et al. (2004) All feedbacks ; ppb in anthropogenic + climate-ch4 feedback +0.16; C in climate interaction + fertilization interaction Accouting for interactions with the climate-co2 feedback Ringeval et al., 2011, BG 33

34 Climate (temperature, precipitations, ) (1) (3) Atmospheric CH4 concentration (2) Wetland CH4 (1) Wetland CH4 sensitivity to climate: Role of wetland extent in the current year-to-year variability Role of methanogenesis substrate during LGM (2) Role of wetland in the year-to-year variability of the atmospheric CH 4 concentration (3) Climate/CO2/wetland CH4 : Future climate alone could decrease the CO2 fertilizing effect => C under SRES-A2 scenario But missing key-processes in the model: - Floodplains processes (Amazon basin) - Fertilizing effect could be limited (interaction with other nutrients, change in vegetation, etc.)

35 Climate (temperature, precipitations, ) Atmospheric CH4 concentration Wetland CH4 Multi-disciplinarité de la question de recherche : - «Thématique» : hydrologie, cycle du carbone, paléoclimat - «Techniques» : modélisation directe & inverse, mesures, satellites Verrous : - Intercomparaison de modèles de surfaces (WETCHIMP, Melton et al., Wania et al., 2013) => grande diversité des caractéristiques de base des émissions (émissions totales, distribution latitudinale, etc.) => grande diversité de la sensibilité des émissions à T, Precip, CO 2 - Processus manquants : e.g. floodplains, couplage N & émissions de CH 4 - Changement d'échelle difficile à cause de la diversité des types de wetlands - Difficulté de représenter les étendues de wetlands dans le modèle - Difficulté de contraindre le modèle : e.g. : évaluation sur certains sites de la densité de flux nette à une échelle cohérente avec celle du modèle (tour de flux >> chambre à flux) Amazonie

36 Wetland and Wetland CH4 Inter-comparison of Models Project (WETCHIMP) (Melton et al., 2013 ; Wania et al., 2013): Aim : to investigate our present ability to simulate large-scale wetland characteristics and corresponding CH4. A common experimental protocol to driving all models with the same climate and CO2 forcing datasets. Diversity in approach to compute the two components of the CH 4 (e.g. CH4 flux density) Ccl : Large range in simple metrics of wetland CH 4 : e.g. mean annual = 190 ± 40 Tg/yr Latitudinal distribution :

37 Thank you for your attention! 37