1. METHANE

2. TOPICS FOR TODAY 1.Why do we care about methane? 2.What are the sources and concentrations of methane in the atmosphere? 3.Uncertainties in the current methane budget 4.Methane in a changing climate

3. WHY DO WE CARE ABOUT METHANE? (1)GHG #2 (22 times more effective than CO 2 ) (2) Contributes to background O 3 (GHG #3 and air quality) (5) Methane in stratosphere can reduce O 3 depletion (termination of ClOx cycling) (3) Controls oxidizing capacity of troposphere (via OH) (4) Source of stratospheric water vapour (enhances HOx catalyzed O 3 depletion) IPCC [2007]

4. HISTORICAL TRENDS IN METHANE The last 1000 years The last 20 years IPCC [2007] Currently, atmospheric concentration of methane is 1774 ppm (unprecedented in last 650 kyr)

5. LOOKING BACK EVEN FURTHER…

6. TOPICS FOR TODAY 1.Why do we care about methane? 2.What are the sources and concentrations of methane in the atmosphere? 3.Uncertainties in the current methane budget 4.Methane in a changing climate

7. GLOBAL METHANE EMISSIONS ~300 Tg CH 4 yr -1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; Olivier et al., 2005] ~200 Tg CH 4 yr -1 Biogenic sources [Wang et al., 2004] >25% uncertainty in total emissions ANIMALS 90 LANDFILLS + WASTEWATER 50 GAS + OIL 60 COAL 30 RICE 40 TERMITES 20 WETLANDS 180 BIOMASS BURNING + BIOFUEL 30 GLOBAL METHANE SOURCES (Tg CH 4 yr -1 ) Clathrates? Melting permafrost? Plants? A.M. Fiore Slide c/o Arlene Fiore (GFDL)

8. SINKS OF ATMOSPHERIC METHANE I.Transport to the Stratosphere (40 TgCH 4 /yr) Only a few percent, rapidly destroyed  BUT the most important source of water vapour in the dry stratosphere II. Tropospheric oxidation (511 TgCH 4 /yr) CH 4 + OH  CH 3 O 2  CO + other products III. Biological oxidation in soil (30 TgCH 4 /yr) O2O2 Tropospheric Lifetime ~ 9 years OH estimated to have decreased by 10-30% from PI to PD  trend in CH 4 therefore related to sources not sinks [Wuebbles and Hayhoe, 2002] IPCC [2007]

9. SPACE-BASED METHANE COLUMN OBSERVATIONS by solar backscatter at 2360-2385 nm

10. GLOBAL DISTRIBUTION OF METHANE NOAA/GMD surface air measurements MLO site

11. TOPICS FOR TODAY 1.Why do we care about methane? 2.What are the sources and concentrations of methane in the atmosphere? 3.Uncertainties in the current methane budget 4.Methane in a changing climate

12. c/o Michael Raupach, CSIRO, Australia; studies cited in IPCC TAR, AR-4 ESTIMATES OF CURRENT METHANE EMISSIONS Methane sink (OH) also ~30% uncertain [Stevenson et al., 2006] Total CH 4 source ~600 Tg yr -1, ~60% anthropogenic [IPCC AR-4] >25% uncertainty in present-day CH 4 sources anthropogenic Plants? Slide c/o Arlene Fiore (GFDL)

13. WHY HAVE METHANE CONCENTRATIONS LEVELED OFF? How well do we understand interannual variability? Major driver for 97-98 anomaly? -- Biomass burning (CH 4 emission, OH suppression via CO) [e.g.Butler et al., 2005; Duncan et al., 2003; Bousquet et al., 2006;Langenfelds et al., 2002] -- Wetlands [e.g. Dlugokencky et al. 2001; Cunnold et al., 2002; Wang et al., 2004, Mikaloff Fletcher 2004, Chen and Prinn, 2006] CH 4 (ppb) CH 4 growth rate (ppb yr -1 ) Slide c/o Arlene Fiore (GFDL)

14. MODEL STUDIES INDICATE DIFFERENT DRIVERS FOR OBSERVED DECADAL TRENDS StudyPeriodApproachMajor driver of trends / IAV* Law and Nisbet, 19961980-19942D CTM1991 on FSU emis decline Bekki & Law, 19971980-19922D CTMwetlands & OH Dlugokencky et al, 20031984-2002Obs. analysisapproach to steady state? Karlsdottir and Isaksen, 2000 1980-19963D CTM (met fixed)OH (+anthrop SE Asian emis, -strat. o3) Johnson et al, 200220 years3D CTM (emis fixed)OH (water vapor) Warwick et al, 20021980-19983D CTM (OH fixed)transport Dentener et al, 2003ab1979-1993semi-inverse 3D CTMOH (mainly water vapor) Wang et al, 20041988-19973D CTManthrop emis & OH (-strat O 3 ) Dalsoren and Isaksen, 2006 1990-20013D CTM (only emis. vary)OH (+anthrop. CO, NOx, NMVOC emissions) Fiore et al, 20061990-20043D CTM (only met. varies)OH (lightning NO x ) + T Bousquet et al, 20061984-2003inverse 3D CTM (OH from CH 3 Cl inversion) anthrop emis; post-1998 +anthrop - wetlands Khalil et al, 200723 yearsObs. analysisconstant emis. and lifetime Drevet et al., 20081990-20053D CTMAnthrop. emis + OH * Many of these studies also identify a large role for wetlands and BB on IAV

15. TRENDS IN THE METHANE SINK? Significant interannual variability, but no clear trend OH difficult to measure directly, concentrations inferred from methyl chloroform IPCC, 2007

16. METHANE EMISSION FROM PLANTS?  Scale lab observations to estimate a global source of 62–236 Tg yr -1.  Suggest that this can reconcile high CH 4 observed over tropical forests  Production mechanism unknown  VERY CONTROVERSIAL SCIAMACHY-TM3 Model Frakenberg et al., Science 2005 Following this, Houweling et al. [2006] set 125 Tg CH 4 yr -1 as an upper limit (inverse modeling) Kirschbaum et al. [2006] estimate source at 10-60 Tg CH 4 yr -1 Kirschbaum et al. [2008] confirmed that source is not due to absorption/desorption Important implications for tree-planting to mitigate climate change!

17. TOPICS FOR TODAY 1.Why do we care about methane? 2.What are the sources and concentrations of methane in the atmosphere? 3.Uncertainties in the current methane budget 4.Methane in a changing climate

18. PROJECTIONS OF FUTURE METHANE EMISSIONS (Tg CH 4 yr -1 ) IPCC SRES, 2001 Only accounting for growth in anthropogenic emissions (not feedbacks)

19. IMPACT OF CLIMATE CHANGE ON METHANE BUDGET I. Most natural sources (wetlands, landfills, rice agriculture, biomass burning) are affected by T and moisture = positive feedback on CO 2 -induced warming  Degree of emission enhancement affected by water management and methods of cultivation (irrigated, rain-fed, deepwater, etc.) II. Feedbacks on the sink: OH = f(T, H 2 O vap, NOx)

20. METHANE HYDRATES: “ICE THAT BURNS” Increasing usage as an energy source? Destabilized with warming events? Could be a large positive feedback.

21. MELTING OF THE PERMAFROST AND METHANE RELEASE FROM PEATLANDS? Chapman and Thurlow [1996] extrapolated the relationship between methane fluxes and temperature at bogs in Scotland to predict a CH 4 emission increase of 17, 30 and 60% for warmings of 1.5°C, 2.5°C, and 4.5°C Methane emitted from thaw lakes and soils (1)How much of permafrost carbon pool will be converted to methane? (2)What fraction of the pool will thaw under anaerobic vs aerobic conditions? Zhuang, EOS, 2009