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Evolution of methane concentrations for the period 1990-2004 :�Interannual variability in sinks and sources

J. Drevet, I. Bey, J.O. Kaplan, S. Koumoutsaris,

S. Generoso

​

GEOS-Chem Meeting, 04-11-07

jerome.drevet@epfl.ch

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Introduction

> 10 ppb /year

±5 ppb/year

±0 ppb/year

Possible reasons:

  • Slow down in sources?
  • Increase of sinks?

courtesy: E.J. Dlugokencky

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Model set up

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  • Model version: v.07.02.04
  • Meteorological fields: GEOS-4
  • Resolution: 4x5° - 30 vertical levels (up to 0.01hPa)

​

​

Emissions

  • Anthropogenic: IIASA (Dentener et al. 2005), constant after 2000

Industry, Agriculture, Waste and waste water

​

  • Wetland: scheme from Kaplan et al. (2002)

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  • Biomass Burning: derived from CO emissions of :

Duncan et al.(2003) for 1987-1996

Generoso et al.(2003) for 1996-2005.

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  • Termites: Fung et al. (1991)

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Sink

  • Stratospheric conditions: CH4 decay prescribed from a 2-D Stratospheric model.

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  • Tropospheric OH from a full-chemistry simulation, scaled by 0.8 (scaled OH – 9.92.105 molec/cm3)

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Wetland scheme

« Tropical »

emissions

« Temperate »

emissions

Etemp

Etrop

Kaplan et al. (2002)

Input data

​

Soil humidity

(GEOS)

​

Soil temperature

(GEOS)

​

Soil carbon content

(Lund-Potsdam-Jena Dynamic Global Vegetation model)

​

Wetland fraction

(derived from different data sources: Canadian Peatlands Database, US National Land Cover, etc…)

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Tr : factor of “tropicness”

HR : Heterotrophic Respiration

Wf: Wetland fraction

Mf: Moisture factor

Ef: Emission factor

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Extra tropics NH

Tropics NH

Tropics SH

Extra tropics SH

Column

(surface-

250 hPa)

Surface-

750 hPa

750-

500 hPa

500-

250 hPa

Interannual variability in OH in different regions

(1e4 molec. cm-3)

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Evaluation: Ground Measurements

South Pole

Mahe Island (Seychelles)

1800

1850

1650

1700

1750

1650

1700

1750

1800

[CH4] ppb

[CH4] ppb

[CH4] ppb

Mace Head (Irland)

1900

1850

1800

1750

[CH4] ppb

92 94 96 98 00 02 04

92 94 96 98 00 02 04

1900

1750

92 94 96 98 00 02 04

92 94 96 98 00 02 04

Alert (Canada)

CMDL

GEOS-Chem

1950

1800

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Global trends

1990 1992 1994 1996 1998 2000 2002 2004

1700

1750

1800

1850

1992 1994 1996 1998 2000 2002

5

0

10

Global mean CH4 concentrations

Global mean CH4 growth rate

[CH4] ppb

ppb/year

CMDL

GEOS-Chem

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Evaluation: CH4 total column

Sciamachy retrievals

GEOS-Chem X 0.975

1650 1700 1750 1800

GEOS-Chem

Sciamachy retrievals

ppb

1650

1700

1750

1800

R2=0.75

1640

1640

1820

1820

1730

1730

ppb

ppb

Data from Frankenberg et al., 2005

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Sensitivity of the CH4 growth rate

ppb/year

Standard simulation – simulation with constant OH

Standard simulation – simulation with constant anthropogenic emissions

Standard simulation – simulation with constant wetland emissions

Standard simulation – simulation with constant biomass burning emissions

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CH4 Budget - 1994

9.1

13.6

558.7

27.7

531

542.8

3.8

21.1

28.4

258.1

261.4

Wang et al. 2003 high OH

10.7

8.5

8.2

9.92

Trop mean OH

11.3

14.4

10.5

9.6

CH4 lifetime (years)

458.7

392.2

511

470.7

Total Sink

30.4

32.5

55

31.7

Strat Sink

428.3

336.7

456

439

Trop Sink

472.6

383

537

492.1

Total emissions

4.1

4.4

Hydrates

20.3

19.5

20

20 - 20

Termites

27.7

20.4

72

48.9

37 - 73

Biomass burning

176.2

106.4

204

151.5

142 - 165

Wetlands

244.3

232.3

261

271.7

243 - 299

Anthropogenic emissions

Wang et al. 2003 best guess

Wang et al. 2003 Low OH

Fiore et al. 2006

BASE simulation

Our work

Tg/years

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Conclusion

  • Fairly good model-to-observations agreement for the first period of the study but significant deviation after 2000.
  • Long-term trend driven by OH and anthropogenic emissions.
  • Wetland emissions are important but not primary contribution to interannual CH4 variations.
  • Biomass burning emissions control peaks in growth rate.

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  • Limitations of the present study:
    • Large uncertainties in methane emissions after 2000.
    • Trend in OH after 2000.
      • Variability in OH is largely driven by change in anthropogenic emissions.
      • However, NOx and CO emissions are constant after 1998 in the present simulation
      • But, in reality, Chinese NOx emissions increased by 71% between 1996 and 2005 and CO by 20% (D. Streets, pers. comm. 2007)
      • Would that change our trends in methane after 2000? Simulations are underway!

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Evaluation: tropospheric profiles

Central Canada

ABLE3A

July 1988

Eastern Brazil

TRACE-A

September 1992

China Sea

PEM-WEST B

February 1994

Hawaï

TRACE-P

April 2001

1.7

1.8

1.7

1.8

1.7

1.8

1.7

1.8

ppm

ppm

ppm

ppm

1000

800

600

400

200

1000

800

600

400

200

1000

800

600

400

200

800

600

400

200

1000

hPa

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Global trends

Global mean CH4 concentrations

Global mean CH4 growth rate

ppb

ppb/year

1990 1992 1994 1996 1998 2000 2002 2004

1700

1750

1800

1850

1992 1994 1996 1998 2000 2002

5

0

10

CMDL

GEOS-Chem

CMDL

GEOS-Chem

R=0.8

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Budget

90 92 94 96 98 00 02 04

90 92 94 96 98 00 02 04

90 92 94 96 98 00 02 04

90 92 94 96 98 00 02 04

Tropospheric burden

Trop-Strat fluxes

Tropospheric decay

Emissions

Tg

Tg/year

Tg/year

Tg/year