the effect of interannul climate variability on the ...laboratoire de modélisation écologique et...

Laboratoire de modélisation écologique et de science du carbone (Eco-MSC)Ecological Modelling and Carbon Science Laboratory (Eco-MCS)

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 ZhuNorthwest A & F University, China

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)?

IPCC [2013]

1) Methane (CH4) is the second most important well-mixed greenhouse gas contributing to human-induced 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

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/.

? “The Methane Mystery”

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: 20th 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.

Global Carbon Project 2013; Figure based on Kirschke et al. 2013

Natural Methane Sources (2000s)

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

- 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.

2013

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)

ECO-FGC Northwest A&F University

Methods (TRIPLEX‐GHG)• CH4 module

(Zhu et al. 2014, GMD)


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


Data for Model Validation


Results

Comparison of modeled and observed CH4 emissions for the sites in Canada


Results

Comparison of modeled and observed CH4 emissions for the sites in America


Results

Coparison of modeled and observed CH4 emissions for the sites in Europe


Model Validation Results (Zhu et al. 2014, GMD)

Comparison of modeled and observed CH4 emissions for the two selected sites in China


Results

Comparison o modeled and observed CH4 emissions for the sites in Australia

CH4 emission anomalies spatial distribution of tropical wetlands (to mean 2000-2012; 30°S and 30°N)

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

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)

CH4 Growth Rate & Temperate Change (Anomaly)


Interannual Variation CH4 Emissions Triggered by El Nino and La Nina Events

Contribution of tropical wetlands to the “ seesaw” of global CH4 concentration

Mount Pinatubo (1991)

1997/1998

1999/2000

1982/1983


Southern Oscillation Index (SOI) & CH4 Emissions


Possible Mechanisms:‐ Carbon supply hypothesis‐ Moisture supply hypothesis‐ Net biogenic emission


Effect of ENSO on CH4 Emissions of Wetlands in Amazon

El Nino (Drought) El Nino (Drought)La Nina (Cold)

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: ENSO-induced 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

Tropical Rain ForestsWetlands in Tibet Plateau

Flux Towers with Li‐Co 7700 (CH4)


Future Direction:

Land surface module

Vegetation Dynamic module

Plant phenology module

Soil biogeochemical module

Based on IBIS (Foley et al (1996))

Agriculture PFT

Plant function trait

Nitrogen cycling

Phosphorus cycling

Land use change

Fire disturbance

GHG emission (CO2, CH4, N2O)DOC transference

Vegetation phenology

Major Framework of TRIPLEX‐GHG

Future of the assessment :CH4 and N2O climate feedbacks

CH4 Temperature

Feedbacks that were not included in CMIP5 models:Climate sensitivity of wetland CH4 emissionsStability of ocean CH4 hydrate pools Response of soil N2O emission processes to climate and elevated CO2Response of ocean N2O emissions to changes in O2 & 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


ResultsThe global multi‐year mean for the period 1990 to 2009 of CH4emission rates from wetlands


Introduction


Methods• Water Table module

_

+

Ztheta,min

Water Table, z

Zacro

Low Boundary

0

Theta_u_s

Theta_s,min

φ saturated

unsaturated

,min

,min,min

0

3.0*( )_2.0*

3.0*( )2.0*( )

tot acro

acro tots

z

acro tots

s

V Z if WT

Z VWater Table if WT ZA

Z V if WT Z

Granberg et al. (1999)


Methods

• Methane module– CH4 production

∗ ∗ ∗ ∗

RH :is the soil heterotrophic respiration ratefST, fpH, and fEh :CH4 production factors of soil temperature, pH, and redox potentialR: the release ratio of CH4 to CO2.


Methods

• Methane module– CH4 oxidation

∗ ∗ ∗

fCH4 : CH4 concentration factorfST : Soil temperature effects on CH4 oxidationCCH4 : CH4 concentrationfEh :Redox potential effects on CH4 oxidation


Methods

• Methane module– CH4 emission processes

• EbullitionCH4 concentrations in the soil profile exceeds a certain threshold (750 umol L‐1)


Methods


• Diffusion

∗ ∗ ∗ ∗ 1 ∗

Da :CH4 molecular diffusion coefficients in air (0.2 cm2s‐1) Dw: CH4 molecular diffusion coefficients in water(0.00002 cm2s‐1) fcoarse : relative volume of coarse poresftort : tortuousity coefficient (0.66)WFPS: water filled pore space


Methods


• Plant mediated transport

∗ ∗

frhi : rhizospheric oxidation factorfaer : plant aerenchyma factorCH4gra : CH4 concentration deficit between soil and atmosphere

HISTORICAL TRENDS IN METHANE

The last 1000 years

The last 20 years

IPCC [2007]

Currently, atmospheric concentration of methane is 1774 ppm (unprecedented in last 650 kyr)

Atmospheric Observations OH SinkBiogeochemistry

ModelsEmission Inventories Inverse Models

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‐CH4, GEOS‐Chem, LMDZt‐SACS, MATCH, TM2, GISS). TransCom intercomparison.

Long‐term trends and decadal variability of the OH sink.ACCMIP CTMs intercomparison.

The Tools and Data

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

CH4 Atmospheric Growth Rate, 1983-2009

Kirschke et al. 2013, Nature Geoscience; Data from NOAA, CSIRO, AGAGE, UCI atmospheric networks

1983-1989: 12 ± 6 ppb

• Slowdown of atmospheric growth rate before 2005

• Resumed increase after 2006

1990-1999: 6 ± 8 ppb

2000-2009: 2 ± 2 ppb

(Peng , Zhu et al. unpublished)

The Methane Mystery: Leveling Off then ReboundingHeimann, Science, 2011, “news and views”

The Methane Mystery: Leveling Off then Reboundinghttp://www.esrl.noaa.gov/gmd/aggi/

Help characterizing sources from isotopes + co-emitted species Inverse constraints on sinks (confidence?)[Montzka et al., 2011]

Dlugokencky et al., GRL, 2009

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

the effect of interannul climate variability on the ...laboratoire de modélisation écologique et...

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