Leif Backman HENVI Seminar February 19, 2009

Transcription

1 Methane Sources and Sinks Leif Backman HENVI Seminar February 19, 2009

2 Background Atmospheric methane Sources & Sinks Concentration variations & trends Objective & methods Objective & Goals Research plan Methods Tools Previous research, cooperation & progress Open questions & recent findings Methane growth rates Partitioning between sources Lifetime, BVOC & OH Soil freezing

3 Background Atmospheric methane Sources & Sinks Concentration variations & trends

4 Atmospheric methane The natural range is 320 to 790 ppb, determined from ice cores of the last years CH 4 concentrations have more than doubled since preindustrial times 700 ppb -> 1780 ppb Sources identified, but partitioning poorly known More than half from anthropogenic sources Main sink, tropospheric OH IPCC, 2007

5 Change in radiative forcing > 2005 Methane (CH 4 ) is the 2 nd most important anthropogenic greenhouse gas after CO 2 CH 4 is a ca. 20 times more potent greenhouse gas than CO 2 (per mass) IPCC, 2007

6 Methane sources Biogenic CH 4 sources (> 70% of the global total) wetlands rice agriculture livestock landfills biomass burning forests oceans termites Non-biogenic CH 4 sources emissions from fossil fuel mining and burning natural gas, petroleum and coal waste treatment geological sources fossil CH 4 from natural gas seepage geothermal/volcanic CH 4 IPCC, 2007

7 Methane sources Natural sources Tg/a Wetlands Termites Oceans 4 15 Hydrates 4 5 Geological sources 4 14 Wild animals 15 Wildfires 2 5 Anthropogenic sources Tg/a Energy & industry (fossil fuels) Landfills & waste Ruminants Rice agriculture Biomass burning Total sources Tg/a IPCC, 2007

8 Methane sinks Sinks Tg/a Tropospheric OH Stratosphere (OH, Cl, O 1 D, hv) Soils Methane chemistry Decreases the amount of tropospheric OH Precursor for ozone production Stratosphere Source of water vapor Terminates ozone loss cycles by converting Cl to HCl Affects ozone through OH

9 Greenhouse gas concentrations NOAA global flask sampling network,

10 Consistently higher CH 4 emissions in the NH CH 4 emissions from wetlands mostly during warm seasons OH concentration increases with sunlight => The maximum of atmospheric CH 4 in the NH reached in late autumn or even in winter Seasonal changes in CH 4 emissions and photochemical oxidation, causes the seasonal cycle and a shift in phase between NH and SH

11 Objective & methods Objective & Goals Research plan Methods Tools

12 Objectives and goals The main objective is to improve the understanding of how sources and sinks influence the atmospheric abundance and growth rate of CH 4, and the subsequent effect on the climate The principal tool for these studies will the ECHAM5- HAMMOZ, and the practical goal is to improve the parameterization of CH 4 sources Long-term goals Improved Earth system models To develop a coupled biosphere-ccm including a realistic description of the response of CH 4 emissions from wetlands for different hydrological conditions

13 Research plan I) Implementation of the chemistry climate model (ECHAM5- II) III) IV) HAMMOZ) to the high performance computing facilities at FMI Methane lifetime studies CH 4, OH, CO, BVOC Review of in situ data Review of remote sensing data soil melting/freezing land use snow cover trace gas data (CH 4, CO, CO 2 ) V) Parameterization of methane source emissions VI) Effect of meteorology on global and local methane growth rates (comparison to observations) nudged model runs (ECMWF) Inverse modelling VII) VIII) Coupled biosphere-chemistry-climate model

14 ECHAM5-HAMMOZ CCM Chemistry & Aerosol coupled GCM (Pozzoli et al., 2008)

15 Methane lifetime Reaction with tropospheric OH (85-90%) OH formed when ozone is photo-dissociated: O 3 + hv -> O 1 D + O 2 O 1 D + H 2 O -> OH + OH OH concentrations affected by CH 4, CO and BVOCs Increase in methane leads to positive feedback Variations in UV (stratospheric ozone, aerosols) affects OH Urban areas, NOx -> O 3 -> OH production The distribution of OH can be estimated using compound that have known sources and sinks e.g. methyl chloroform (CH 3 CCl 3 )

16 Methane lifetime Growth rate declined since early 1990s =>around zero during the last decade with large interannual variations Changes in main sink, OH, can be due to Changes in BVOC emissions (Pinatubo) CO emissions (e.g. biomass burning) Changes in NH wetland and anthropogenic methane emissions

17 Satellite data of CH 4, CO and CO 2 SCIAMACHY/Envisat ESA data available for GOSAT JAXA first light Feb 2009 OCO NASA to be launched in Feb 2009 Global coverage Column mixing ratio Model validation Inverse modeling?

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19 Previous research, cooperation & progress

20 Previous experience Global stratospheric chemistry modeling Process studies and long-term development of ozone PSC and aerosol processing Ozone loss rates Chemical and Dynamical effects on long-term ozone changes Past/future ozone trends Ozone recovery Chemistry-climate coupling FinROSE-ctm (ECMWF-, CCM-data) HAMMONIA-CCM

21 Multidisciplinary cooperation Measurements Local (+ network data) In situ data (FMI, UH) Concentrations Fluxes Column data (FMI) FTIR Global Satellite data (FMI) CH 4, CO, CO 2 Land use Soil melting/freezing, snow cover Atmospheric modelling (FJ-ICG, COSMOS, FMI, UH) Inverse modelling (LUT, FMI) Biosphere modelling (UH, FMI)

22 Progress ECHAM5-HAMMOZ implemented to FMI HPC facilities

23 Open questions & recent finding Methane growth rates Partitioning between sources Lifetime, BVOC & OH Soil freezing

24 Methane and BVOCs Evaluation of the interhemispheric gradient in atmospheric CH 4 at times in the past is possible because of the existence of ice cores in the high latitudes of both hemispheres (past yrs). These interhemispheric gradients may be used to imply temporal changes in the geographic distribution of CH 4 sources and sinks. In contrast to CH 4, which is relatively well mixed in the atmosphere, the short lifetimes of BVOCs mean that their effect on OH is mostly local. Differences between poles mainly due to changes in OH mainly due to changes in BVOCs Kaplan et al., Role of methane and biogenic volatile organic compound sources in late glacial and Holocene fluctuations of atmospheric methane concentrations, Global Biogeochem. Cycles., 2006.

25 BVOCs and OH Previously it was thought that, in unpolluted air, BVOCs deplete OH and reduce the atmospheric oxidation capacity Aircraft measurements of atmospheric trace gases performed over the pristine Amazon forest reveal unexpectedly high OH concentrations Natural VOC oxidation, notably of isoprene, recycles OH efficiently in low-nox air through reactions of organic peroxy radicals? Lelieveld et al., Atmospheric oxidation capacity sustained by a tropical forest. Nature, 2008.

26 Methane emissions and soil freezing The emissions fall to a low steady level after the growing season but then increase significantly during the freeze-in period The integral of emissions during the freeze-in period is approximately equal to the amount of methane emitted during the entire summer season CTM simulations of global atmospheric methane concentrations indicate that the observed early winter emission burst improves the agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 60 N In addition spring burst from trapped methane during the winter have been observed earlier Mastepanov et al., Large tundra methane burst during onset of freezing, Nature, 2008.

27 Methane emission during soil freezing Mastepanov et al., Large tundra methane burst during onset of freezing, Nature, 2008.

28 Summary The main objective is to improve the understanding of how sources and sinks influence the atmospheric abundance and growth rate of CH 4, and the subsequent effect on the climate Several open questions regarding methane Many possibilities for cooperation in the Kumpula campus in situ measurements and remote sensing data biosphere modeling tropospheric CCM modelling inverse modeling