The effect of Interannul climate variability on the methane emissions of tropical wetlands Changhui Peng Centre ESCER/CEF, University of Quebec at Montreal, Canada QiuAn Zhu Northwest A & F University, China Laboratoire de modélisation écologique et de science du carbone (Eco-MSC) Ecological Modelling and Carbon Science Laboratory (Eco-MCS)
TOPICS FOR TODAY 1. Why do we care about methane? 2. Connecting CH4 with climate variability and tropical wetlands 3. Modelling methane emissions from natural wetlands in tropics 4. Ongoing challenges and future direction
WHY DO WE CARE ABOUT METHANE (CH4)? 1) Methane (CH4) is the second most important wellmixed greenhouse gas contributing to humaninduced climate change. 2) In a time horizon of 100 years, CH4 has a Global Warming Potential 28 times larger than CO2. 3) CH4 is responsible for 20% of the global warming produced by all well-mixed greenhouse gases IPCC [2013]
? The Methane Mystery Methane ups and downs. Globally averaged atmospheric methane concentrations rose quickly before 1992. The rise then slowed and almost stopped between 1999 and 2006, but resumed in 2007. Data from ftp://ftp.cmdl.noaa.gov/ ccg/ch4/fl ask/event/.
Connecting CH4 with wetlands and climate variability Observed methane trends in recent decades: Emission trends or climate variability? 1. Aydin et al., Nature, 2011 (fossil fuel) Study period: 20 th century; ethane:methane in firn air 2. Kai et al., Nature, 2011 (NH microbial sources) study period: 1984 2005; isotopic source signature 3. Kirschke et al., Nature Geo. 2013 ( wetlands and ENSO) study period: 1980 2010; Top down (atmospheric inversion), Bottom up (process modeling), and Inventories (atmospheric observation)
Wetlands are the single largest source of atmospheric CH4. Natural Methane Sources (2000s) Global Carbon Project 2013; Figure based on Kirschke et al. 2013
BERGAMASCHI ET AL.: CH4 INVERSE MODELING 2000 2010 Wetlands are concentrated in tropical/subtropical regions (30 S and 30 N ) CH4 emissions from tropical regions contributed 78% of global CH4 emissions
2013 - The hypothesis that tropical wetland CH4 emissions respond strongly to rainfall anomalies and trends (e.g. ENSO) - The Amazon drought in 2010 should have resulted in a drop in wetland CH4 emissions.
The El Niño Southern Oscillation (ENSO) cycle of alternating warm El Niño and cold La Niña events is the most dominant year-to-year climate variation on Earth. ENSO originates in the tropical Pacific through interactions between the ocean and the atmosphere,
Three Main Approaches to Investigating Effect of Climate Change on Ecosystems Long-term observation Experimental manipulation Model simulation (J.M. Melillo, 1999, Science, 283: 183)
Methods (TRIPLEX GHG) CH4 module (Zhu et al. 2014, GMD) ECO-FGC Northwest A&F University
Data Climate: CRU TS 3.1 Climate Database Wetland map: GLWD Level 3 data set of Lehner and Doll (2004) (0.5º x 0.5º resolution) Soil property: Digital Soil Map of the World (DSMW), (soil clay, sand, silt fraction; soil ph) Initial soil carbon: IGBP DIS 2000 A spin up run of about 300 years ECO-FGC Northwest A&F University
Data for Model Validation ECO-FGC Northwest A&F University
Results Comparison of modeled and observed CH 4 emissions for the sites in Canada ECO-FGC Northwest A&F University
Results Comparison of modeled and observed CH 4 emissions for the sites in America ECO-FGC Northwest A&F University
Results Coparison of modeled and observed CH 4 emissions for the sites in Europe ECO-FGC Northwest A&F University
Model Validation Results (Zhu et al. 2014, GMD) Comparison of modeled and observed CH 4 emissions for the two selected sites in China ECO-FGC Northwest A&F University
Results Comparison o modeled and observed CH 4 emissions for the sites in Australia ECO-FGC Northwest A&F University
CH4 emission anomalies spatial distribution of tropical wetlands (to mean 2000-2012; 30 S and 30 N)
CH4 Growth Rate & Temperate Change (Anomaly) Methane growth rate by latitude. Contours of methane growth rate with sine of latitude. Data from www.esrl.noaa.gov/gmd/ccgg/mbl (Nisbet et al. Science, 2014) Temperature anomaly by latitude. NCEP DOE Reanalysis 2 temperature data was acquired from http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis2.surface.html
Contribution of tropical wetlands to the seesaw of global CH4 concentration Interannual Variation CH4 Emissions Triggered by El Nino and La Nina Events Mount Pinatubo (1991) 1999/2000 1982/1983 1997/1998 ECO-FGC Northwest A&F University
Southern Oscillation Index (SOI) & CH4 Emissions ECO-FGC Northwest A&F University
Possible Mechanisms: Carbon supply hypothesis Moisture supply hypothesis Net biogenic emission ECO-FGC Northwest A&F University
Effect of ENSO on CH4 Emissions of Wetlands in Amazon La Nina (Cold) ECO-FGC El Nino (Drought) El Nino (Drought) Northwest A&F University
Methane ups and downs. Globally averaged atmospheric methane concentrations rose quickly before 1992. The rise then slowed and almost stopped between 1999 and 2006, but resumed in 2007. Data from ftp://ftp.cmdl.noaa.gov/ ccg/ch4/fl ask/event/.
La Nina
What did we learn from this modeling study? CH4 emissions from tropical wetlands responded strongly to repeated ENSO cycles, with greater negative anomalies occurring during El Niño and greater positive anomalies occurring during La Niña. Interannual variability is dominated by natural wetlands. Repeated ENSO events throughout 1950s- 2000s, which has probably contributed to stabilized observed atmospheric CH4 concentrations during the stagnation period of 1999-2006. This study also support a recent hypothesis: ENSOinduced droughts in the Amazon basin have resulted in a drop in wetland CH4 emissions (Kirschke et al., 2013)
Research Needs and Ongoing Challenges: An improved network of observations CH4, both ground based and remotely sensed, is needed to quantify global CH4 budget Very few wetland CH4 flux measurements and data sets limit our ability to test and validate large scale modelled CH4 emissions. The further extension of the CO2 FLUXNET measurements and database Flux Towers with Li Co 7700 (CH4) Wetlands in Tibet Plateau ECO-FGC Tropical Rain Forests Northwest A&F University
Future Direction: Agriculture PFT Nitrogen cycling Phosphorus cycling DOC transference Land surface module Vegetation Dynamic module Plant phenology module Soil biogeochemical module Based on IBIS (Foley et al (1996)) Plant function trait Land use change Fire disturbance Vegetation phenology GHG emission (CO2, CH4, N2O) Major Framework of TRIPLEX GHG ECO-FGC Northwest A&F University
Future of the assessment : CH 4 and N 2 O climate feedbacks CH 4 Temperature Feedbacks that were not included in CMIP5 models: Climate sensitivity of wetland CH 4 emissions Stability of ocean CH 4 hydrate pools Response of soil N 2 O emission processes to climate and elevated CO 2 Response of ocean N 2 O emissions to changes in O 2 & circulation
Thank you and Merci Beaucoup! Acknowledgments: Funding for this study was provided by the NSERC Discovery Grant (Canada) and National Natural Science Foundation of China
Results The global multi year mean for the period 1990 to 2009 of CH 4 emission rates from wetlands ECO-FGC Northwest A&F University
Introduction ECO-FGC Northwest A&F University
Methods Water Table module 0 + _ φ Theta_u_s Theta_s,min saturated unsaturated Z theta,min Water Table, z Z acro Low Boundary Granberg et al. (1999) Vtot Zacro if WT 0 3.0*( Zacro Vtot ) Water _ Table if WT Z 2.0* Az 3.0*( Zacro Vtot ) if WT Z 2.0*( s,min) s,min s,min ECO-FGC Northwest A&F University
Methods Methane module CH 4 production R H :is the soil heterotrophic respiration rate f ST, f ph, and f Eh : CH 4 production factors of soil temperature, ph, and redox potential R: the release ratio of CH 4 to CO 2. ECO-FGC Northwest A&F University
Methods Methane module CH 4 oxidation f CH4 : CH 4 concentration factor f ST : Soil temperature effects on CH 4 oxidation C CH4 : CH 4 concentration f Eh :Redox potential effects on CH 4 oxidation ECO-FGC Northwest A&F University
Methods Methane module CH 4 emission processes Ebullition CH 4 concentrations in the soil profile exceeds a certain threshold (750 umol L 1 ) ECO-FGC Northwest A&F University
Methods Methane module CH 4 emission processes Diffusion 1 Da :CH 4 molecular diffusion coefficients in air (0.2 cm 2 s 1 ) Dw: CH 4 molecular diffusion coefficients in water(0.00002 cm 2 s 1 ) f coarse : relative volume of coarse pores f tort : tortuousity coefficient (0.66) WFPS: water filled pore space ECO-FGC Northwest A&F University
Methods Methane module CH 4 emission processes Plant mediated transport f rhi : rhizospheric oxidation factor f aer : plant aerenchyma factor CH 4gra : CH 4 concentration deficit between soil and atmosphere ECO-FGC Northwest A&F University
HISTORICAL TRENDS IN METHANE The last 20 years The last 1000 years Currently, atmospheric concentration of methane is 1774 ppm (unprecedented in last 650 kyr) IPCC [2007]
Atmospheric Observations Emission Inventories Biogeochemistry Models Inverse Models OH Sink The Tools and Data Ground based data from observation networks (AGAGE, CSIRO, NOAA, UCI). Airborne observations. Satellite data. Agriculture and waste related emissions, fossil fuel emissions (EDGAR, EPA, IIASA). Fire emissions (GFED, GICC, FINN, RETRO). Ensemble of different wetland models, (LPJ WHyMe, LPJ wsl, ORCHIDEE). Data and models to calculate annual flooded area. Suite of different atmospheric inversion models (TM5 4DVAR, LMDZ MIOP, CarbonTracker CH 4, GEOS Chem, LMDZt SACS, MATCH, TM2, GISS). Long term trends and decadal variability of the OH sink. ACCMIP CTMs intercomparison. TransCom intercomparison.
The El Niño Southern Oscillation (ENSO) affects climatic conditions in the tropical Pacific, where it originates, and also influences global climate. ENSO like fluctuations, known as the Pacific Decadal Oscillation, can influence climatic conditions for decades at a time. Heffernan, 2014, Nature CC
CH 4 Atmospheric Growth Rate, 1983-2009 1983-1989: 12 ± 6 ppb 1990-1999: 6 ± 8 ppb 2000-2009: 2 ± 2 ppb Slowdown of atmospheric growth rate before 2005 Resumed increase after 2006 Kirschke et al. 2013, Nature Geoscience; Data from NOAA, CSIRO, AGAGE, UCI atmospheric networks
(Peng, Zhu et al. unpublished)
The Methane Mystery: Leveling Off then Rebounding Heimann, Science, 2011, news and views
The Methane Mystery: Leveling Off then Rebounding http://www.esrl.noaa.gov/gmd/aggi/ The uptick: observational evidence suggests natural sources in 2007 and 2008: 2007 Arctic depleted in 13C (wetlands) Warm Arctic Temp 2008 tropics (zero growth rate in Arctic) La Nina, tropical precip Dlugokencky et al., GRL, 2009 Help characterizing sources from isotopes + co-emitted species Inverse constraints on sinks (confidence?) [Montzka et al., 2011]