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

Outline CH 4 Budget Data –Sampling and measurements –Quality control Long-term trends Anomalies in CH 4 growth rate –Eruption of Mt. Pinatubo –Economic collapse of former Soviet Union Recent changes in atmospheric CH 4 –Potential for climate feedbacks in Arctic

SourceBousquet (Tg/yr)IPCC Range (Tg/yr) Anthropogenic Energy110± Enteric fermentation90± Rice agriculture31± Biomass burning50± Waste55± Natural Wetlands147± Termites23± Oceans19±64-15 Total525± SinksBousquet (Tg/yr)IPCC (Tg/yr) Troposphere448± Stratosphere37± Soil21± Total Global CH 4 Budget by Source Bousquet et al., 2006, Nature, 443, , doi: /nature05132.

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

Quality Control

Barrow, AK:

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

Average Emissions = 559 ± 10 Tg CH 4 Trend = 0.5 ± 0.5 Tg CH 4 yr -1 (95% c.l.) Emissions = d[CH 4 ]/dt + [CH 4 ]/  Trend = 0.0 ± 0.6 Tg CH 4 yr -1 (95% c.l.)

Growth rate (ppb/yr)

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), 2761–2764, doi: /96GL02638.

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

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 ]

Source: BP Statistical Review of World Energy, June 2012

Interpolar Difference fSU collapse

Summary so far: High quality obs constrain CH 4 budget Decreasing CH 4 GR – approach to SS –Assuming constant τ, emissions constant –Significant IAV Pinatubo decreased [OH] → observed increased CH 4 and CO Economic collapse in fSU affected observed latitude gradient

Globally averaged CH 4

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

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

Potential causes: Biomass burning

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

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

Potential causes: Arctic processes Rate of T increase is 3X global average –Wetland emissions sensitive to soil T –E T = E T 0 Q 10 (T-T 0 /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

GISS: 2007 T anomalies 2007 also very wet ΔCH 4 and Δδ 13 C suggest source with δ 13 C = -66‰

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

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)

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

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

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

Conclusions Since 2007, CH 4 increasing globally: –~6 ppb yr -1 from Causes of increase: –Wetlands (tropics and Arctic) –In response to T and precip. anomalies Not yet at Arctic tipping point –Since 2008, Arctic increasing at global rate –IPD indicates emissions have not yet increased

Extra Slides

Summary of Long Term Trends in CH 4 Global burden of CH 4 ~5000 Tg (2011) Global CH 4 increased 180 ppb since 1983 Rate of increase decreasing → steady state –Constant emissions with lifetime of ~9 yr Inter-annual variability in growth rate –Exploit for process information

AI 4 obscures mid-day sun

Compliments of Paul Novelli, NOAA ESRL

Residuals for 30  N to 90  N

Residuals for 17.5  N to 17.5  S

Residuals for 30  S to 90  S