Observational Constraints on the Global Methane Budget

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1 Observational Constraints on the Global Methane Budget Ed Dlugokencky NOAA Earth System Research Laboratory Global Monitoring Division Boulder, Colorado USA

2 Outline Data (NOAA CH 4 observations) Long-term trends Anomalies in CH 4 growth rate (IAV) Eruption of Mt. Pinatubo Economic collapse of former Soviet Union Recent changes in atmospheric CH 4 Causes of increased CH 4 since 2007 Potential for climate feedbacks in Arctic Summary

3 GMD Cooperative Global Air Sampling Network *Weekly samples *Portable sampler *Analyzed by GC/FID * Cooperative *Broad participation *

4 Barrow, AK:

6 Lifetime 9.4 yr [CH 4 ](t) = [CH 4 ] ss -([CH 4 ] ss -[CH 4 ] 0 )e -t/τ

7 Emissions = d[ch 4 ]/dt + [CH 4 ]/τ Average Emissions = 549 ± 11 Tg CH 4 Trend = 0.7 ± 0.4 Tg CH 4 yr -1 (95% c.i.) Trend = 0.0 ± 0.6 Tg CH 4 yr -1 (95% c.i.)

8 f 4 ( t) = a + a t + a t2 [ a sin( 2 it) a cos( 2 it)] π + π i = 1 2i+ 2 2i+ 3

9 Growth rate (ppb/yr)

10 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

11 fsu collapse Interpolar Difference

12 Globally averaged CH4

14 Potential Causes Increased anthropogenic emissions Expect gradual change Possibly. relative contribution unclear Decrease in OH increased CH 4 lifetime Not consistent with CO and other species Increased biomass burning Not consistent with CO nor δ 13 CH 4 Increased tropical wetland emissions Increased Arctic emissions

15 ENSO and tropical precipitation anomalies La Niña ~ El Niño Source: GPCP

16 Potential causes: Tropical wetlands Precipitation anomalies in tropics. (Source: GPCP) Increased Amazon CH 4 fluxes in wet years. Increased tropical emissions consistent with 0.4 decrease in δ 13 C since 2007

17 Potential causes: Arctic wetlands GISS: 2007 T anomalies 2007 also very wet CH 4 and δ 13 C suggest source with δ 13 C = -66

18 NSIDC: Sea Ice Loss (%) AIRS CH 4 : ppb

19 Potential causes: Arctic wetlands and clathrates? Only 2007 Difference between northern and southern polar annual means No recent changes in Arctic emissions based on polar zonal means. Economic collapse in fsu

20 Conclusions Observations constrain global CH 4 budget Provide budget terms with smallest uncertainties IAV tests understanding of processes Wetland emissions drive most IAV Other processes important too Increasing CH 4 since 2007 Tropical wetland and anthropogenic emissions No measureable change in Arctic emissions

21 Extra Slides

22 Global CH 4 Budget by Source Source Bousquet (Tg/yr) IPCC Range (Tg/yr) Anthropogenic Energy 110± Enteric fermentation 90± Rice agriculture 31± Biomass burning 50± Waste 55± Natural Wetlands 147± Termites 23± Oceans 19± Total 525± Sinks Bousquet (Tg/yr) IPCC (Tg/yr) Troposphere 448± Stratosphere 37± Soil 21± Total Bousquet et al., 2006, Nature, 443, , doi: /nature05132.

23 Quality Control

24 2007: Tropical WL NOAA VPs Arctic WLs -δ 13 CH 4 at ALT 2008: Inversions are inconsistent. Data suggest anomalous emissions in tropics and midlatitudes. High N latitudes recovered. *NOAA CT-CH is consistent. Bousquet et al., ACP, Dlugokencky et al., GRL, 2009.

25 1991: Pinatubo and the CH 4 Lifetime Eruption: 15 June MT SO 2 oxidized to SO 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), , doi: /96gl02638.

26 Potential causes: Arctic processes Rate of T increase is 3X global average Wetland emissions sensitive to soil T E T = E T0 Q 10 (T-T0/10) where Q 10 = E T+10 /E T ~1000 Pg C in top 3 m permafrost soils Melting PF expands wetland area and releases carbon 30 to 170 Pg CH 4 in Arctic Ocean hydrates

27 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

28 Source: BP Statistical Review of World Energy, June 2012

29 Potential causes: Sink Loss rate ( [OH]) CH 3 CCl 3 analysis suggests not (-2 to +1%) PCE suggests not (I. Simpson, UCI) CO suggests not

30 Potential causes: Anthropogenic emissions Anthropogenic emissions Expect gradual changes Source: BP Statistical Review of World Energy 2012

31 Potential causes: Biomass burning

32 IPY puts focus on the Arctic Methane Bubbles in the Arctic Ocean Give Climate Scientists the Willies (Discover, Sept., 2008) Study says methane from ocean floor is 'time bomb (CTV.ca, 27 Sept. 2008) Arctic 'methane chimneys' raise fears of runaway climate change (The Guardian 23 Sept. 2008) Methane 'Fart' from the Earth Poses Enormous Global Warming Risk (Independent, 24 Sept. 2008)

33 Data from Fisher (RHUL) Westbrook et al., GRL, 2009 Intercept ~ -65 Consistent with wetland source (Hydrates = -53 )