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Atmospheric Methane Distribution and Trends: Impacts on Climate and Ozone Air Quality

Atmospheric Methane Distribution and Trends: Impacts on Climate and Ozone Air Quality. Arlene M. Fiore Larry Horowitz (NOAA/GFDL) Jason West (Princeton) Ed Dlugokencky (NOAA/GMD) Earth, Atmospheric, and Planetary Sciences Department Seminar Massachusetts Institute of Technology

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Atmospheric Methane Distribution and Trends: Impacts on Climate and Ozone Air Quality

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  1. Atmospheric Methane Distribution and Trends: Impacts on Climate and Ozone Air Quality Arlene M. Fiore Larry Horowitz (NOAA/GFDL) Jason West (Princeton) Ed Dlugokencky (NOAA/GMD) Earth, Atmospheric, and Planetary Sciences Department Seminar Massachusetts Institute of Technology December 16, 2005

  2. Atmospheric CH4: Past Trends, Future Predictions IPCC [2001] Projections of Future CH4Emissions (Tg CH4) to 2050 Variations of CH4Concentration (ppb) Over the Past 1000 years [Etheridge et al., 1998] Scenarios 1600 900 A1B A1T A1F1 A2 B1 B2 IS92a 1400 800 1200 700 1000 800 600 1500 1000 2000 2020 2040 2000 Year Year

  3. More than half of global methane emissions are influenced by human activities ~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] BIOMASS BURNING + BIOFUEL 30 ANIMALS 90 WETLANDS 180 LANDFILLS + WASTEWATER 50 GLOBAL METHANE SOURCES (Tg CH4 yr-1) GAS + OIL 60 COAL 30 TERMITES 20 RICE 40

  4. hn Global Background O3 NO NO2 OH HO2 VOC,CH4, CO air pollution (smog) NOx NMVOCs O3 NOx NMVOCs O3 air pollution (smog) Air quality-Climate Linkage:CH4, O3 are important greenhouse gasesCH4 contributes to background O3in surface air O3 Free Troposphere Boundary layer (0-3 km) Direct Intercontinental Transport CONTINENT 1 CONTINENT 2 OCEAN

  5. Observations indicate historical increase in background ozone; IPCC scenarios project future growth Change in 10-model mean July surface O3 [Prather et al., 2003] Ozone at European mountain sites 1870-1990 [Marenco et al., 1994]. 2100 SRES A2 - 2000 Attributed mainly to increases in methane and NOx [Wang et al., 1998; Prather et al., 2003] Adapted from J. West

  6. Rising background O3 at northern mid-latitudes has implications for attaining air quality standards Pre-industrial background Current background new CA standard 8-hr avg Europe seasonal 20 40 60 80 100 O3 (ppbv) WHO/Europe 8-hr average U.S. 8-hr average Analyses of surface O3 from North American and European monitoring sites indicate increasing background [Lin et al., 2000; Jaffe et al., 2003,2005; Vingarzen et al., 2004; EMEP/CCC-Report 1/2005 ]

  7. Radiative Forcing of Climate from Preindustrial to Present:Important Contributions from Methane and Ozone Hansen, Scientific American, 2004

  8. Approach: Use 3-D Models of Atmospheric Chemistry to examine climate and air quality response to emission changes GEOS-CHEM [Bey et al., 2001] MOZART-2 [Horowitz et al., 2003] • GEOS GMAO meteorology • 4°x5°; 20 s-levels • GEIA/Harvard emissions • Uniform, fixed CH4 • NCEP meteorology • 1.9°x1.9°; 28 s-levels • EDGAR v. 2.0 emissions • CH4 EDGAR emissions for 1990s 3-D model structure

  9. Double dividend of Methane Controls: Decreased greenhouse warming and improved air quality Number of U.S. summer grid-square days with O3 > 80 ppbv Radiative Forcing (W m-2) 50% anth. CH4 50% anth. NOx 50% anth. VOC 2030 A1 2030 B1 1995 (base) 50% anth. VOC 50% anth. CH4 50% anth. NOx 2030 A1 2030 B1 GEOS-Chem Model Simulations (4°x5°) CH4 links air quality & climate via background O3 Fiore et al., GRL, 2002

  10. Response of Global Surface Ozone to 50% decrease in global methane emissions (actually changing uniform concentration from 1700 to 1000 ppbv) • Ozone decreases by 1-6 ppb • ~3 ppb over land in US summer ** ~60% of reduction in 10 yr; ~80% in 20 yr.

  11. Impacts of O3 Precursor Reductions on U.S. Summer Afternoon Surface O3 Frequency Distributions GEOS-Chem Model Simulations (4°x5°) West & Fiore, ES&T, 2005

  12. Tropospheric ozone response to anthropogenic methane emission changes is fairly linear MOZART-2 (this work) TM3 [Dentener et al., ACPD, 2005] GISS [Shindell et al., GRL, 2005 GEOS-CHEM [Fiore et al., GRL, 2002] IPCC TAR [Prather et al., 2001] X

  13. How Much Methane Can Be Reduced? 0.7 10% of anthrop. emissions 1.4 20% of anthrop. emissions 1.9 0 20 40 60 80 100 120 Methane reduction potential (Mton CH4 yr-1) IEA [2003] for 5 industrial sectors Comparison: Clean Air Interstate Rule (proposed NOx control) reduces 0.86 ppb over the eastern US, at $0.88 billion yr-1 West & Fiore, ES&T, 2005

  14. Ozone Abatement Strategies Evolve as our Understanding of the Ozone Problem Advances O3 smog recognized as an URBAN problem:Los Angeles, Haagen-Smit identifies chemical mechanism Smog considered REGIONAL problem; role of biogenic VOCs discovered A GLOBAL perspective: role of intercontinental transport, background Present 1980s 1950s AbatementStrategy: NMVOCs + NOx + CH4??

  15. Addressing the CH4-O3 air quality-climate linkage Methane controls are receiving attention as a means to simultaneously address climate and global air pollution [EMEP/CCC report 1/2005] • Does CH4 source location influence the O3 response? • What is driving recent trends in atmospheric CH4 ? • Sources? • Sinks? Observed Global Mean CH4 (ppb)

  16. Methane Control Simulations in MOZART-2: 30% Decrease in Global Anthropogenic CH4 Emissions Global surface CH4conc. (ppb) Change in global surface CH4 conc. from 30% decrease in anthrop. emis. BASE CASE ppb -30% anthrop. emis. Decrease in Tropospheric O3Burden Tg • Approaching steady-state after 30 years • Does O3 impact depend on source location? (1) global -30% anthrop. emissions (2) zero Asian emissions (=30% global)

  17. -34 -27 -20 -14 -7 mW m-2 (Radiative Forcing) No Asia – (30% global decrease) Tropospheric O3 column response is independent of CH4 emission location except for small (~10%) local changes DU -5.1 -3.4 -1.7 -0.7 +0.7 mW m-2 CLIMATE IMPACTS: Change in July 2000 Trop. O3 Columns (to 200 hPa) Zero CH4 emissions from Asia (= 30% decrease in global anthrop.) 30% decrease in global anthrop. CH4 emissions Dobson Units

  18. U.S. Surface Afternoon Ozone Response in Summer also independent of methane emission location MAX DIFFERENCE (Composite max daily afternoon mean JJA) MEAN DIFFERENCE NO ASIAN ANTHROP. CH4 GLOBAL 30% DECREASE IN ANTHROP. CH4 • Stronger sensitivity in NOx-saturated regions (Los Angeles), partially due to local ozone production from methane

  19. Observed trend in Surface CH4 (ppb) 1990-2004 Global Mean CH4 (ppb) • Hypotheses for leveling off • discussed in the literature: • 1. Approach to steady-state • 2. Source Changes • Anthropogenic • Wetlands • Biomass burning • 3. Transport • 4. Sink (OH) • Humidity • Temperature • OH precursor emissions • overhead O3 columns GMD Network Data from 42 GMD stations with 8-yr minimum record is area-weighted, after averaging in bands 60-90N, 30-60N, 0-30N, 0-30S, 30-90S How does BASE CASE Model compare with GMD observations?

  20. Captures flattening post-1998 but underestimates abundance Emissions problem? Model with constant emissions largely captures observed trend in CH4 during the 1990s OBSERVED BASE CASE MODEL Global Mean Surface Methane (ppb) • Possible explanations for observed behavior: • Source changes • Meteorologically-driven changes in CH4 lifetime • Approach to steady-state with constant lifetime

  21. Bias and Correlation vs. GMD Surface CH4: 1990-2004 r2 Mean Bias (ppb) BASE BASE simulation with constant emissions: • Overestimates interhemispheric gradient • Correlates poorly at high northern latitudes

  22. Inter-annually varying wetland emissions 1990-1998 from Wang et al. [2004] (Tg CH4 yr-1); distribution changes Apply climatological mean (224 Tg yr-1) post-1998 ANTH ANTH + BIO Estimates for Changing Methane Sources in the 1990s Biogenic adjusted to maintain constant total source 547 Tg CH4 yr-1 BASE EDGAR anthropogenic inventory

  23. Bias & Correlation vs. GMD CH4 observations: 1990-2004 Mean Bias (ppb) OBS BASE ANTH ANTHsimulation with time-varying EDGAR 3.2 emissions:  Improves abundance post-1998 • Interhemispheric gradient too high • Poor correlation at high N latitudes r2

  24. Bias & Correlation vs. GMD CH4 observations: 1990-2004 Mean Bias (ppb) OBS BASE ANTH ANTH+BIO ANTH+BIOsimulation with time-varying EDGAR 3.2 + wetland emissions improves:  Global mean surface conc.  Interhemispheric gradient • Correlation at high N latitudes r2 S Latitude N

  25. Model with BIO wetlands improves: 1)high N latitude seasonal cycle 1900 1850 1800 Alert (82.4N,62.5W) 1840 1820 1800 1780 1760 1740 2)trend Midway (28.2N,177.4W) 3)low bias at S Pole, especially post-1998 1800 1750 1700 Mahe Island (4.7S,55.2E) 1740 1720 1700 1680 1660 1640 South Pole (89.9S,24.8W) 1995 2000 2005 1990 OBS (GMD) BASE ANTH ANTH+BIO Methane Concentration (nmol/mol = ppb) Model captures distinct seasonal cycles at GMD stations

  26. Time-Varying Emissions: Summary Annual mean CH4 in the “time-varying ANTH+BIO” simulation best captures observed distribution OBS BASE ANTH ANTH+BIO Next: Focus on Sinks -- Examine with BASE model (constant emissions) -- Recycle NCEP winds from 2004 “steady-state”

  27. Methane rises again when 1990-1997 winds are applied to “steady-state” 2004 concentrations Area-weighted global mean CH4 concentrations in BASE simulation (constant emissions)  Recycled NCEP 1990-2004 •  Meteorological drivers for observed trend • Not just simple approach to steady-state

  28. CH4 Lifetime vs. Tropospheric OH Rapid transport to sink regions Candidate Processes: t = Temperature Humidity Lightning NOx Photolysis  Recycled NCEP How does meteorology affect the CH4 lifetime? Lifetime Correlates Strongly With Lower Tropospheric OH and Temperature r2 = 0.69 r2 = 0.65 105 molecules cm-3 K

  29. Hypotheses for leveling off: 1. Approach to steady-state  not the whole story 2. Source Changes  improve simulated abundances but not driving trend 3. Transport 4. Sink (OH) Global Mean CH4 (ppb) Meteorology major driver; further work needed to isolate cause Potential for strong climate feedbacks Methane Distribution and Trends: Climate and Air Quality Impacts • 20% anthrop. CH4 emissions can be reduced at low cost • Ozone response largely independent of CH4 source location • 30% decreases in anthrop. CH4 reduces radiative forcing by 0.2 Wm-2 and JJA U.S. surface O3 by 1-4 ppbv

  30. Q: How will future global change influence atmospheric CH4?Potential for complex biosphere-atmosphere interactions CH4 + OH …products BVOC NOx Soil

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