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METHANE

METHANE. TOPICS FOR TODAY. Why do we care about methane? What are the sources and concentrations of methane in the atmosphere? Uncertainties in the current methane budget Methane in a changing climate. WHY DO WE CARE ABOUT METHANE?. GHG #2 (22 times more effective than CO 2 ).

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METHANE

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  1. METHANE

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

  3. WHY DO WE CARE ABOUT METHANE? • GHG #2 • (22 times more effective than CO2) (2) Contributes to background O3(GHG #3 and air quality) (3) Controls oxidizing capacity of troposphere (via OH) (4) Source of stratospheric water vapour (enhances HOx catalyzed O3 depletion) (5) Methane in stratosphere can reduce O3 depletion (termination of ClOx cycling) IPCC [2007]

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

  5. LOOKING BACK EVEN FURTHER…

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

  7. GLOBAL METHANE EMISSIONS ~300 Tg CH4 yr-1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; Olivier et al., 2005] ~200 Tg CH4 yr-1 Biogenic sources [Wang et al., 2004] >25% uncertainty in total emissions BIOMASS BURNING + BIOFUEL 30 ANIMALS 90 WETLANDS 180 Clathrates? Melting permafrost? Plants? LANDFILLS + WASTEWATER 50 GAS + OIL 60 COAL 30 TERMITES 20 GLOBAL METHANE SOURCES (Tg CH4 yr-1) RICE 40 Slide c/o Arlene Fiore (GFDL) A.M. Fiore

  8. SINKS OF ATMOSPHERIC METHANE • Transport to the Stratosphere (40 TgCH4/yr) • Only a few percent, rapidly destroyed  BUT the most important source of water vapour in the dry stratosphere • II. Tropospheric oxidation (511 TgCH4/yr) • CH4 + OH  CH3O2CO + other products • III. Biological oxidation in soil (30 TgCH4/yr) O2 OH estimated to have decreased by 10-30% from PI to PD  trend in CH4 therefore related to sources not sinks [Wuebbles and Hayhoe, 2002] Tropospheric Lifetime ~ 9 years IPCC [2007]

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

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

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

  12. ESTIMATES OF CURRENT METHANE EMISSIONS Total CH4 source ~600 Tg yr-1, ~60% anthropogenic [IPCC AR-4]>25% uncertainty in present-day CH4 sources Plants? anthropogenic c/o Michael Raupach, CSIRO, Australia; studies cited in IPCC TAR, AR-4 Methane sink (OH) also ~30% uncertain [Stevenson et al., 2006] Slide c/o Arlene Fiore (GFDL)

  13. WHY HAVE METHANE CONCENTRATIONS LEVELED OFF?How well do we understand interannual variability? CH4 (ppb) Major driver for 97-98 anomaly? -- Biomass burning (CH4 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] CH4 growth rate (ppb yr-1) Slide c/o Arlene Fiore (GFDL)

  14. MODEL STUDIES INDICATE DIFFERENT DRIVERS FOR OBSERVED DECADAL TRENDS * Many of these studies also identify a large role for wetlands and BB on IAV

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

  16. METHANE EMISSION FROM PLANTS? SCIAMACHY-TM3 Model •  Scale lab observations to estimate a global source of 62–236 Tg yr-1. • Suggest that this can reconcile high CH4 observed over tropical forests • Production mechanism unknown • VERY CONTROVERSIAL Frakenberg et al., Science 2005 Following this, Houweling et al. [2006] set 125 Tg CH4 yr-1 as an upper limit (inverse modeling) Kirschbaum et al. [2006] estimate source at 10-60 Tg CH4 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 • Why do we care about methane? • What are the sources and concentrations of methane in the atmosphere? • Uncertainties in the current methane budget • Methane in a changing climate

  18. PROJECTIONS OF FUTURE METHANE EMISSIONS (Tg CH4yr-1) Only accounting for growth in anthropogenic emissions (not feedbacks) IPCC SRES, 2001

  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 CO2-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, H2Ovap, 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? Methane emitted from thaw lakes and soils • How much of permafrost carbon pool will be converted to methane? • What fraction of the pool will thaw under anaerobic vs aerobic conditions? Zhuang, EOS, 2009 Chapman and Thurlow [1996] extrapolated the relationship between methane fluxes and temperature at bogs in Scotland to predict a CH4 emission increase of 17, 30 and 60% for warmings of 1.5°C, 2.5°C, and 4.5°C

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