Presentation on theme: "Understanding Methane Concentrations"— Presentation transcript:
1Understanding Methane Concentrations Nicola Warwick1,Euan Nisbet2, John Pyle11- Centre for Atmospheric ScienceUniversity of Cambridge2 – Royal Holloway, University of LondonQuest CH4 Workshop, June 2004
2Outline CH4 observations Understanding the global distribution and seasonal cyclesUnderstanding variability and trendsOutlook
3Factors controlling CH4 Emissions (natural and anthropogenic)Sinks (OH, soil)Meteorology (winds, temperatures, rainfall)July model surface CH4 (ppbv)July Surface OH in model (106molecules/cm3)
4Methane Measurements In-situ and flask data: Global network of stations mainly including:US-NOAA-CMDLAustralian CSIRONew Zealand NIWAMeth-MonitEUr – European NetworkSatellite observationsIce-cores
5Observed CHNorthern HemisphereSouthern HemisphereObserved CH4 mixing ratios (Marine Boundary Layer) from 1992 to 2001, NOAA-CMDL
7Ny-AlesundMace HeadMeth-MonitEUr: Methane monitoring in the European region.
8Royal Holloway College, W London (provided by E. Nisbet, D. Lowry) Ny-AlesundMace HeadRoyal Holloway College, W London (provided by E. Nisbet, D. Lowry)Meth-MonitEUr: Methane monitoring in the European region.
9Testing our understanding of CH4 Global modelling (forward and inverse)Regional modellingBack trajectory analyses / diurnal experimentsIsotopes
10December surface CH4 by MATCH model (provided by Kim Holmen, NILU)
1113C-CH4 Isotopic Fractionation of CH4 Sources Methane sources have a wide range of distinct 13CH4 signatures further constraint on emission scenarios.-47%KIEAdapted from Chanton et al. Light Heavy
12Global CH4 and 13CH4 Distributions Fossil FuelSurface CH4 (ppbv) - January monthly meanRiceSurface 13CH4 (‰) - January monthly meanWetlands
13How well do measurements describe the CH4 burden? Houwelling et al. (1999): relative contribution of NH sources decrease from 77% to 67%.Blue line: modelled zonal mean CH4 and 13C-CH4Red Circles: modelled CH4 and 13C-C-CH4 at measuring station locationsBlack squares: observed CH4 and 13C-CH4 [Dlugokencky et al., 1998, Miller et al., 2002]
14Breakdown of seasonal cycles by source Northern Hemisphere(Modelled CH4 at Alert, Canada, 82°N)Southern Hemisphere(Modelled CH4 at Ascension Island, Atlantic, 7°S)
17Understanding Interannual Variability and Trends
18Year-to-Year Millennial and Longer… Feedback TimescalesYear-to-Year Millennial and Longer…Petit, J.R., et al., 2001, Vostok Ice Core Data for 420,000 Years, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # NOAA/NGDC Paleoclimatology Program, Boulder CO, USA.Dlugokencky et al., 1998, 2003
19NOAA Observed Interpolar Gradient Dlugokencky et al., GRL, 2003
20CH4 Variability due to Meteorology Black line = observed growth rateDashed line = modelled growth rateCorrelation Coefficients:Key Biscayne, r=0.61 Ascension, r=0.59
21Modelled and Observed CH4 Variations Simulated CH4 interannual variability arising from changes in the circulationObserved CH4 growth rate (NOAA CMDL Carbon Cycle Greenhouse Gases)Changes in modelled interpolar gradient resulting from meteorology: ~up to 0.5%
22Influence of Meteorology on CH4 Tropics:OH (will vary with humidity)Tropical forest fires / wetlandsEl NiñoMeasured CH4 at Ascension Island (D. Lowry, E. Nisbet)Influence of el Nino on fire emissions – van der Werf et al., 2004.
23Influence of Meteorology on CH4 Tropics:OH (will vary with humidity)Tropical forest fires / wetlandsEl NinoWinds (alter inter-hemispheric mixing)Northern Latitudes:Northern wetlandsCH4 measurements at Yamal Peninsula compared to Teriberka background level
24Problems and OutlookModel simulations still have trouble reproducing CH4 observationsNeed more continental data (e.g. South America, Africa Asia) to test modelsSatellites:look for abrupt changes (e.g tropical fires)infer surface fluxes (need high precision)Isotopes:High-precision ground-based isotope measurements can distinguish sources (help quantify wetland source)
26The global CH4 burden may be higher than previously thought..... Use modelled radon concentrations to distinguish between ‘clean’ and ‘dirty’ airTrue global mean = 1.3% greater than ‘clean’ global meanBy , Kyoto Protocol envisages reduction in GHG emissions of ~5% w.r.t valuesModelled annual mean surface CH4 / ppbv