1. The global cycle of methane CMI methane project
François M. M. Morel

2. Publications per year CO2 in atmosphere CH4 in atmosphere
Publications per year
CO2 in atmosphere
CH4 in atmosphere
(Web of Science)

3. ~ 410 ppm
~ 1870 ppb
today
CO2 & CH4
through ice ages
&
modern times

4. The global cycle of methane
1. Earth radiation & methane
2. Sources & sinks of atmospheric methane
3. Current trends in atmospheric methane
4. CMI - methane project

5. Infrared absorption by CO2 & CH4
Wavelength (µm)
IR Spectrum of Earth
CO2
IRRADIANCE (mW m-2 sr-1 cm)
CH4
Wavenumber (cm-1)

6. Indirect effects of methane on GHG
Methane yields stratospheric water
CH OH CH3 + H2O
& tropospheric ozone (via NOx)
O2 + hν + NO NO + O3
CH4 & O2

7. H2O CO2 CH4 O3 H2O Infrared absorption by O3 & H2O
Wavelength (µm)
IR Spectrum of Earth
H2O
CO2
IRRADIANCE (mW m-2 sr-1 cm)
CH4 O3
H2O
Wavenumber (cm-1)

8. CH4: 2nd most important anthropogenic greenhouse gas
Strat H2O, Trop. O3, CH4
0.97 Wm-2
Adapted from IPCC (2013) for Fiore et al. (2015)

9. The global cycle of methane
1. Earth radiation & methane
2. Sources & sinks of atmospheric methane
3. Current trends in atmospheric methane & causes
4. CMI - methane project

10. Global Methane Budget 2003-2012
Top-down budget
~ atmospheric inversion
Current
Increase
~6 ppb/y

11. Global Methane Budget 2003-2012
Current
Increase
~6 ppb/y
Sinks

12. Atmospheric methane sinks

13. Global Methane Budget 2003-2012
Current
Increase
~6 ppb/y
Several sources with similar magnitudes
& large error bars…

14. The global cycle of methane
1. Earth radiation & methane
2. Sources & sinks of atmospheric methane
3. Current trends in atmospheric methane & causes
4. CMI - methane project

16. Why?
Why?
(many papers…)

17. Why?
Why?
New information based on 13CH4
~ δ13C (‰)
- 60 microbial
- 40 fossil fuels
- 20 biomass burning

18. Schaefer et al. Science. April 2016
fossil fuel emissions down
Biogenic up:
rice & ruminants?
-47.2
-47.4
δ13C (‰)

19. Yes but FF emissions 20-60% larger than thought
Schaefer et al. Science. April 2016
fossil fuel emissions down
Biogenic up:
rice & ruminants?
Schwietzke et al. Nature. October 2016
Yes but FF emissions 20-60% larger than thought
due to 5‰ lower FF δ13C

20. Fugitive Emission Rate CH4 emission/production
2.2%
Large decrease over 30 years
Fugitive Emission Rate
CH4 emission/production
Inventory of CH4 emissions based on δ13C
fossil fuel emissions decreasing
but > previous estimates
Schwietzke et al. 2016

21. Yes but FF emissions 20-60% larger than thought
Schwietzke et al. Nature. October 2016
Yes but FF emissions 20-60% larger than thought
due to 5‰ lower FF δ13C
Mostly from tropical wetlands
due to increased rainfall and temperature
Nisbet et al. GBC. September 2016
Schaefer et al. Science. April 2016
fossil fuel emissions down
Biogenic up:
rice & ruminants?

22. Nisbet et al. 2016: data from more latitudes
Alert, Canada (82°N)
CH4 (ppb)
δ13C (‰)
Ascencion Island (8°S)

23. Conclusions from Nisbet et al. (2016)
Increase in methane since 2007 due to biogenic sources
Not variations in OH
Not fossil fuel emissions

24. Conclusions from Nisbet et al. (2016)
Increase in methane since 2007 due to biogenic sources
Not variations in OH
Not fossil fuel emissions
With a dominant contribution from tropical wetlands
responding to increased rainfall and temperature

25. N.B. The interpretation of 12CH4 and 13CH4 data is still uncertain
For example
Turner, Frankenberg, Wennberg & Vaulot, (PNAS, 2017) conclude:
“…the problem, as currently formulated, is underdetermined…”
“…the mathematically most likely explanation… counterintuitively involves a 20-Tg/year decrease in methane emissions… offset by a 7% decrease in global mean OH concentrations…”

26. Conclusions from Nisbet et al. (2016)
Increase in methane since 2007 due to biogenic sources
Not variations in OH
Not fossil fuel emissions
With a dominant contribution from tropical wetlands
responding to increased rainfall and temperature
Why?

27. The global cycle of methane
1. Earth radiation & methane
2. Sources & sinks of atmospheric methane
3. Current trends in atmospheric methane & causes
4. CMI - methane project

28. What controls methane inputs from wetlands?
CMI Methane Project
What controls methane inputs from wetlands?
Xinning Zhang (Princeton, Geosciences)
Modeling: Quantifying individual sources and sinks of atmospheric CH4 (atmosphere & land models) Elena Shevliakova & Vaishali Naik (GFDL; NOAA)
Princeton and NOAA logo

29. What controls methane inputs from wetlands?
CMI – Xinning Zhang

30. Deep wetland peat – poor methane source
organic carbon
methanogens
CH4
CO2
+ O2
Methanotrophs
Shoemaker and Schrag 2010 & 2012
~ 10% of total flux
few cm

31. Surface wetland peat – strong methane source?
organic carbon
methanogens
CH4
CO2
+ O2
Methanotrophs
Shoemaker and Schrag 2010 & 2012
Surface wetland peat – strong methane source?
few cm

32. An Earth System Model for methane
Modeling: Quantifying individual sources and sinks to atmospheric CH4 (atmosphere & land models)
An Earth System Model for methane
Elena Shevliakova & Vaishali Naik
Geophysical Fluid Dynamics Laboratory (NOAA)

33. Limitations of current approaches
Global inversions, inventories and data-driven methods require observations – cannot project future
Interactions between climate and CH4 cycle are ignored –e.g. chemical transport models do not account for many atmospheric physical processes
Wetland process models require prescribed inputs of wetland extent -- ranging from 7 to 27 Mkm2
Large uncertainties about processes underlying anaerobic sources and oxidative sinks

34. Atmospheric Chemistry
Forcing
Solar Radiation
Volcanic Aerosols
WMGGs (CO2, CH4, N2O)
ODSs (CFC-11, CFC-12, CFC-113, HCFC-22)
Concentrations of
N2O, CFCs, Halons, HCFCs at model lower boundary
CH4 and isotopes (13CH4 and CH3D), Short-lived Pollutant Emissions
(anthropogenic, fire, natural, ships and aircraft)
MOM6 (Ocean/Ice)
Atmospheric Dynamics and Physics
Radiation, Convection (includes wet deposition of tropospheric species), Clouds, Vertical diffusion, and Gravity waves
Atmospheric Chemistry
Chemistry of O3, HOy, NOy, Cly, Bry, and Polar Stratospheric Clouds
Chemistry of gaseous species (O3, CO, CH4 and isotopes, NOx, hydrocarbons) and aerosols (sulfate, carbonaceous, mineral dust, nitrate, seasalt, secondary organics)
Aerosol-Cloud Interactions
Dry Deposition
86 km
0 km
Land Model
(soil physics, canopy physics, vegetation dynamics, disturbance, land use, and wetland emissions)
GFDL Earth System
Model (ESM4)
Comprehensive Bottom-Up Earth System Model facilitates investigation of methane interactions and feedbacks
Number of transported chemical species = 103
Vertical levels = 49 upto 86 km
Horizontal Resolution = 1x1.25

35. GFDL-AM3 with prescribed methane emissions is able to capture the observed latitudinal gradient
Old inventory
Distribution only for year 2000
Would like to simulate variation in time
Measurements from NOAA ESRL/GMD Carbon Cycle Cooperative Global Air Sampling Network

36. Preliminary tests of initial model
Global Surface Monthly Mean Methane Abundance
Global Methane Growth Rate
NOAA data
Optimized Total Emissions
Prescribed Concentrations
Simulation with optimized global total emissions captures observed methane trend and variability
Here we are running the model with observed meteorology to evaluate against measurements.

37. Mauna Loa
Mace Head
Cape Grim
Palmer Station

38. Preliminary tests of initial model
NOAA GMD
Optimized Total Emissions
Prescribed Concentrations 2
Mauna Loa
Cape Grim
Mace Head
Palmer Station
Uncertainties in methane sources and chemistry affect at individual sites model simulation

39. Questions?
Xinning Zhang
Elena Shevliakova
Vaishali Naik