2

Stefan Schwietzke1,2, Owen Sherwood2, Pieter P. Tans1,

Sylvia Englund Michel2, Giuseppe Etiope3, Artur Ionescu4,

John B. Miller1,2, Edward J. Dlugokencky1, Lori M. P. Bruhwiler1,

Victoria A. Arling2

1NOAA/GMD Boulder, 2Univ. of Colorado Boulder, 3INGV Italy, 4Babes-Bolyai Univ. Romania

Funding: National Research Council RAP, CIRES IRP

Global methane budget and natural gas leakage

based on long-term δ13CH4 measurements and

updated isotopic source signatures

2

2

0% 20% 40% 60% 80% 100%

Uncertainties in attribution of global CH4 sources

Photo sources: Wikimedia

• Based on atmospheric measurements of CH4, δ13CH4, and/or C2H6

Mikaloff et al. 2004

(illustrative)

Bousquet et al. 2006

(illustrative)

2

3

-48

-47.5

-47

-46.5

-46

19851989199319972001200520092013

Globalannualm

ean

δ13C(‰

)

Year

Confidence in observational and δ13C signature constraints

0

100

200

300

400

500

600

1550

1600

1650

1700

1750

1800

1850

19851989

1993

1997

2001

2005

2009

2013

GlobalCH4fluxes(Tg/year)

Globalannualm

ean

CH4(ppb)

Year

Global mean CH4 mixing ratio and flux

Global δ13CH4 observations δ13CH4 source signatures

CH4 lifetime

9.4 ± 0.3 years

(9.1 ± 0.9

years)

Uncertainties ± 0.1‰

incl. site-selection bias

NOAA Global GHG Reference Network

• Only few published

global estimates

• Uncertainties not well

characterized

• New analysis in this work

2

4

Mass balance of 3 CH4 source categories

-53‰ -47‰

(Obs.)

“Other”

Wetlands,

ruminants,

rice, landfills,

termites

Isotopic fractionation

Biomass

burning

Oil/gas,

coal

• Global δ13CH4 signature database for the different CH4 sources

• Monte Carlo simulation

- Propagation of all uncertainties in source allocation

Total CH4

isotopically more depleted isotopically more enriched

2

5

Global δ13CH4 source signature literature database developm. (1)

Sample

size

Sample percentage of

global production

Oil/Ga

s 3,085 40%

Coal 660 58%

Oil/Gas Coal Oil/Gas,

Coal Quay et al.

1999 Miller

2005

Fossil fuels, this work

GLOREG

(Global Reservoir Gas

data-set)

2

6

Sample size Sample regions

Biomass

burning 11 Boreal, temperate, tropical

Other* 70 5 continents, 13 countries * Wetlands, ruminants,

rice, landfills, termites

Quay et al.

1999 Miller

2005

Biomass

burning

This

work

Quay et al.

1999 Miller

2005

This

work

Other

Global δ13CH4 source signature literature database developm. (2)

2

7

0

50

100

150

200

250

300

350

400

450

1985

1989

1993

1997

2001

2005

2009

2013

GlobalCH4emissions(Tg/yr)

Year

Other(Wetlands,Ruminants,Rice,Landfills,Termites)

Oil/Gas,Coal

Results: fossil fuel CH4 higher than most previous estimates

Literature range of Oil/Gas, Coal

(incl. geolog. seeps)

2

8

0

50

100

150

200

250

300

350

400

450

1985

1989

1993

1997

2001

2005

2009

2013

GlobalCH4emissions(Tg/yr)

Year

Literature range of Oil/Gas, Coal

–45‰ (this study)

Other

Oil/Gas, Coal

–40‰ (Quay et al. 1999, Miller 2005)

Strong influence of oil/gas, coal δ13CH4 signature on emissions

2

9

0 50 100 150 200 250

δOther

τ

ε

BBemissions

δBB

δFossilfuels

Soilsink

GlobalFFemissionsin2011(TgCH4/yr)

FF CH4 emissions sensitivity analysis

C.I. (10, 90th

Percentiles)

-59, -63 ‰

10.0, 8.2 yr

-7.1, -5.5 ‰

55, 32 Tg/yr

-20, -32 ‰

-44.7, -46.5 ‰

34, 30 Tg/yr

δ Other

τ

ε

BB emissions

δ BB

δ Fossil fuels

Soil sink

Parameters

Median

*

*

2

10

ALT

Inter-hemispheric gradient test: preliminary TM5 results

Measurement sites

BR

W

CB

A

UU

M

AZ

R

TA

P

WIS

KE

Y

MLO

RP

B

CH

R

SE

Y

AS

C

EIC

CR

Z

SP

O

(annual mean 2001)

2

11

Paleo test – same parameter distributions as 1984-2013

• Geological seeps: 15–100 Tg/yr

• Pre-industrial δ13CH4 (ice core) measurements and biomass burning emissions

from Ferretti et al. 2005

0

50

100

150

200

250

300

350

50 200350

500

650

800

950

110

0125

0140

0155

0170

0185

0200

0

GlobalCH4emissions(Tg/yr)

Year

Other(Wetlands,Ruminants,Rice,Landfills,Termites)

Geologicseeps

Includes

fossil

fuel

industries

2

12

-2

0

2

4

6

8

10

12

14

1985

1989

1993

1997

2001

2005

2009

2013

GlobalaverageFER

(%)

Year

Natural gas fugitive emissions rate (% of production) decreasing

• Median natural gas fugitive emissions rate 2.5% (based on δ13CH4)

during most recent 5 years (geological seepage accounted for)

• Bottom-up coal and oil CH4 emissions, and natural gas composition

from Schwietzke et al. 2014

2

13

Conclusions

• Global fossil fuel CH4 emissions – comparison with previous studies

- Higher than CH4 inversion studies (~150 Tg/yr prelim.)

- Largely due to lighter fossil fuel δ13CH4 source signature and

updates in atmospheric transport (TM5)

- Consistent with ice core data, which confirms bottom-up estimates

of global geological seep (≥15 Tg/yr)

• Natural gas fugitive emissions rate declining since the mid-1980s,

with current best estimate of 2.5%