1. 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

2. Introduction > 10 ppb /year ±5 ppb/year ±0 ppb/year Possible reasons: Slow down in sources? Increase of sinks? courtesy: E.J. Dlugokencky

3. Model set up 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) Biomass Burning: derived from CO emissions of : Duncan et al.(2003) for 1987-1996 Generoso et al.(2003) for 1996-2005. Termites: Fung et al. (1991) Sink Stratospheric conditions: CH 4 decay prescribed from a 2-D Stratospheric model. Tropospheric OH from a full-chemistry simulation, scaled by 0.8 (scaled OH – 9.92.10 5 molec/cm 3 )

4. Wetland scheme « Tropical » emissions « Temperate » emissions E temp E trop 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…) Tr : factor of “tropicness” HR : Heterotrophic Respiration Wf: Wetland fraction Mf: Moisture factor Ef: Emission factor

5. Extra tropics NHTropics NHTropics SHExtra 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 )

6. Evaluation: Ground Measurements South PoleMahe Island (Seychelles) 1800 1850 1650 1700 1750 1650 1700 1750 1800 [CH 4 ] ppb Mace Head (Irland) 1900 1850 1800 1750 [CH 4 ] ppb 92 94 96 98 00 02 04 1900 1750 92 94 96 98 00 02 04 Alert (Canada) CMDL GEOS-Chem 1950 1800

7. Global trends 19901992 1994 1996 1998 2000 2002 2004 1700 1750 1800 1850 1992 1994 1996 1998 2000 2002 5 0 10 Global mean CH 4 concentrations Global mean CH 4 growth rate [CH4] ppb ppb/year CMDL GEOS-Chem

8. Evaluation: CH 4 total column Sciamachy retrievals GEOS-Chem X 0.975 1650 1700 1750 1800 GEOS-Chem Sciamachy retrievals ppb 1650 1700 1750 1800 R 2 =0.75 1640 1820 1730 ppb Data from Frankenberg et al., 2005

9. Sensitivity of the CH 4 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

10. CH 4 Budget - 1994 Tg/years Our work Fiore et al. 2006 BASE simulation Wang et al. 2003 Low OH Wang et al. 2003 high OH Wang et al. 2003 best guess Anthropogenic emissions 271.7 243 - 299 261232.3261.4244.3 Wetlands 151.5 142 - 165 204106.4258.1176.2 Biomass burning 48.9 37 - 73 7220.428.427.7 Termites 20 20 - 20 19.521.120.3 Hydrates 4.43.84.1 Total emissions 492.1537383542.8472.6 Trop Sink 439456336.7531428.3 Strat Sink 31.75532.527.730.4 Total Sink 470.7511392.2558.7458.7 Trop mean OH 9.928.28.513.610.7 CH 4 lifetime (years) 9.610.514.49.111.3

11. 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 CH 4 variations. Biomass burning emissions control peaks in growth rate. 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, NO x and CO emissions are constant after 1998 in the present simulation But, in reality, Chinese NO x 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!

12. 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 1.71.81.71.81.71.81.71.8 ppm 1000 800 600 400 200 1000 800 600 400 200 1000 800 600 400 200 800 600 400 200 1000 hPa

13. Global trends Global mean CH 4 concentrations Global mean CH 4 growth rate ppb ppb/year 19901992 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

14. Budget 90 92 94 96 98 00 02 04 Tropospheric burdenTrop-Strat fluxes Tropospheric decayEmissions Tg Tg/year