1. What have we learned from three decades of atmospheric CH 4 measurements? E. Dlugokencky 1, M. Crotwell 1,2, A. Crotwell 1,2, P.M. Lang 1, K.A. Masarie 1, L. Bruhwiler 1 1 NOAA ESRL GMD, 2 CIRES,

2. Outline NOAA CH 4 data –Quality control Long term trends –Approach to steady state –Estimates of emissions Interannual Variability –Eruption of Mt. Pinatubo Renewed increase since 2007 –Possible causes Summary and Conclusions

3. *Weekly samples*Portable sampler*Analyzed by GC/FID * Cooperative*Broad participation* www.esrl.noaa.gov/gmd/ccgg/iadv/ GMD Global Cooperative Air Sampling Network

4. Quality Control

5. Barrow, Alaska

7. [CH 4 ](t) = [CH 4 ] ss -([CH 4 ] ss -[CH 4 ] 0 )e -t/τ Lifetime ≈ 9.3 yr

8. Average Emissions = 551 ± 15 Tg CH 4 Trend = 0 ± 0.6 Tg CH 4 yr -1 Emissions = d[CH 4 ]/dt + [CH 4 ]/  Lifetime (  ) = 9.1 yr

9. From BP Statistical Review of World Energy, 2015

10. 1991: Pinatubo and the CH 4 Lifetime Eruption: 15 June 1991 20 MT SO 2 oxidized to SO 4 -2 3 to 5 km 3 ash Affects [OH] by affecting photochemistry: Direct absorption of UV by SO 2 Scattering of UV by ash and aerosols Dlugokencky, E. J., E. G. Dutton, P. C. Novelli, P. P. Tans, K. A. Masarie, K. O. Lantz, and S. Madronich (1996), Geophys. Res. Lett., 23(20), 2761–2764, doi:10.1029/96GL02638.

11. Chemistry (Largest term in CH 4 budget) OH + CH 4 → CH 3 + H 2 O O 3 + hν (330 ≥ λ ≥ 290 nm) → O( 1 D) + O 2 O( 1 D) + H 2 O → 2 OH Rate of formation O( 1 D) = j [O 3 ] j = ∫F(λ) σ(λ) φ(λ) dλ Also affected CO

12. O 3 + hν (330 ≥ λ ≥ 290 nm) → O( 1 D) + O 2 O( 1 D) + H 2 O → 2 OH Rate of formation O( 1 D) = j [O 3 ]

13. Louisa Emmons NCAR

14. Trend - SS

15. Louisa Emmons NCAR

16. Globally averaged CH 4 and δ 13 C(CH 4 ) Sylvia Michel, INSTAAR

18. SOI: Australian BoM Precipitation anomalies in tropical wetlands. (Source: GPCP) Increased Amazon CH 4 fluxes in wet years. Consistent with decrease in δ 13 C of CH 4

19. Late-1990s - mid-1980s Interpolar difference (53-90°) No measureable change in Arctic CH 4 emissions. Dlugokencky, E. J., et al.,Geophys. Res. Lett., 30(19), 1992, doi:10.1029/ 2003GL018126, 2003.

20. Summary and Conclusions No trend in global emissions: 1984-2006 –Emissions from some sectors changing –Changes in WL emissions may have masked increased anthropogenic emissions Much to learn from IAV Increased GR and emissions since 2007 –Changes in tropical precipitation (ENSO) –δ 13 C (CH 4 ) indicates microbial source 2014: CH 4 GR surged (~12 ppb) –Globally warm, Amazon wet, but reasons unclear

23. Base: 1961-1990

27. Possible changes to CH 4 emissions Rice: changing water management ↓ FF sector: decreased venting and flaring ↓ Emissions mitigation: M2M ↓ FF emissions: hydraulic fracturing ↑ Arctic permafrost and hydrates ↑

28. SourceBousquet (Tg/yr)IPCC Range (Tg/yr) Anthropogenic Energy110±1374-106 Enteric fermentation90±1476-92 Rice agriculture31±531-112 Biomass burning50±814-88 Waste55±1135-69 Natural Wetlands147±15100-231 Termites23±420-29 Oceans19±64-15 Total525±8503-610 SinksBousquet (Tg/yr)IPCC (Tg/yr) Troposphere448±1428-511 Stratosphere37±130-45 Soil21±326-34 Total506492-581 Global CH 4 Budget by Source Bousquet et al., 2006, Nature, 443, 439-443, doi:10.1038/nature05132.