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

Publications per year CO2 in atmosphere CH4 in atmosphere 1985 1995 2005 2015 Publications per year CO2 in atmosphere CH4 in atmosphere (Web of Science)

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

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

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

Indirect effects of methane on GHG Methane yields stratospheric water CH4 + OH CH3 + H2O & tropospheric ozone (via NOx) O2 + hν + NO2 NO + O3 CH4 & O2

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)

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)

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

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

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

Atmospheric methane sinks

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

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

Why? Why? (many papers…)

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

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

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

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

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?

Nisbet et al. 2016: data from more latitudes Alert, Canada (82°N) CH4 (ppb) δ13C (‰) 2000 2004 2008 2012 Ascencion Island (8°S) 2000 2004 2008 2012

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

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

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…”

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?

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

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

What controls methane inputs from wetlands? CMI – Xinning Zhang

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

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

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)

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

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

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

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.

Mauna Loa Mace Head Cape Grim Palmer Station

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

Questions? Xinning Zhang Elena Shevliakova Vaishali Naik