Interactions Among Air Quality and Climate Policies: Lectures 7 and 8 (abridged versions)

1. Interactions Among Air Quality and Climate Policies: Lectures 7 and 8 (abridged versions)

2. Radiative forcing of climate (1750 to present):Important contributions from air pollutants IPCC, 2007

3. Methane: Connecting global climate and ozone pollution Arlene M. Fiore (GFDLNOAA) Jason West (University of North Carolina) Larry Horowitz (GFDL/NOAA) Vaishali Naik (GFDL/NOAA)

4. Historical increase in atmospheric methane Variations of CH4Concentration (ppb) Over the Past 1000 years [Etheridge et al., 1998] 1600 1400 1200 1000 800 1500 1000 2000 Year

5. Global Methane Emissions <25% uncertainty in total emissions Clathrates? Melting permafrost? PLANTS? 60-240 Keppler et al., 2006 85 Sanderson et al., 2006 10-60 Kirschbaum et al., 2006 0-46 Ferretti et al., 2006 [EDGAR 3.2 Fast-Track 2000; Olivier et al., Wang et al., 2004] BIOMASS BURNING + BIOFUEL 30 ANIMALS 90 WETLANDS 180 LANDFILLS + WASTEWATER 50 GAS + OIL 60 COAL 30 TERMITES 20 RICE 40 GLOBAL METHANE SOURCES Natural ~200 (Tg CH4 yr-1 ) Anthro ~300 (Tg CH4 yr-1 )

6. Modern Methane cycle • The cycle is relatively simple since the dominent sink is well known (over 90% due to oxidation by OH radicals). The sources are another story. • The total atmospheric burden is ~5Pg (~1,780ppbv) with an atmospheric lifetime of ~9 years, which is modestly dependent on [CH4] itself. • Interestingly for a greenhouse gas with over 50% anthropogenic sources, its level in the atmosphere has stopped increasing over the last decade.

7. Observed trend in surface CH4 (ppb) 1990-2004 Global Mean CH4 (ppbv) • Can we explain this? • Many hypotheses : • 1. Approach to steady-state • 2. Source Changes • Anthropogenic • Wetlands/plants • (Biomass burning) • 3. Transport changes • 4. Sink Changes (CH4+OH) • Humidity • Temperature • OH precursor emissions • overhead O3 columns NOAA 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

8. 100 Year IPCC scenarios for methane emissions Longterm Projections Are Very Uncertain (Tg CH4) to 2100 2100 SRES A2 - 2000

9. Double dividend of methane controls: Improved air quality and reduced greenhouse warming CLIMATE: Radiative Forcing (W m-2) NOx OH  CH4 20% anth. NMVOC 20% anth. CO 20% anth. CH4 20% anth. NOx 20% anth. NMVOC 20% anth. CO 20% anth. CH4 20% anth. NOx AIR QUALITY: Change in population-weighted mean 8-hr daily max surface O3 in 3-month “O3 season” (ppbv) Steady-state results from MOZART-2 global chemical transport model West et al., 2006

10. MOZART-2 [West et al., PNAS 2006; this work] TM3 [Dentener et al., ACP, 2005] GISS [Shindell et al., GRL, 2005] GEOS-CHEM [Fiore et al., GRL, 2002] IPCC TAR [Prather et al., 2001] X Tropospheric O3 responds approximately linearly to anthropogenic CH4 emission changes across models Anthropogenic CH4 contributes ~50 Tg (~15%) to tropospheric O3 burden ~5 ppbv to global surface O3 A.M. Fiore

11. 0.7 1.4 1.9 How much can methane be reduced? (industrialized nations) 10% of anth. emissions 20% of anth. emissions 0 20 40 60 80 100 120 Methane potential reduction (Mton CH4 yr-1) 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

12. July surface O3 reduction from 30% decrease inanthropogenic CH4 emissions Globally uniform emission reduction Emission reduction only in Asia Take Home 1. Ozone reduction is independent of location of methane reduction [pick the cheapest option] 2. Ozone reduction is generally largest in polluted regions [high nitrogen oxides] 3. Methane reduction is a win-win for climate and air quality Fiore et al., JGR, 2008

13. CONCLUSIONS • Methane reduction is a win-win for climate and air quality. This is a robust result across global chemical transport models. • A 10% reduction should pay for itself and another 10% can be paid for with modest carbon credits. • The maximum impact on air quality is in high NOx regions. • The location of the methane reduction is not important for either climate or air quality, so pick the least expensive options.

14. On To Lecture 8

15. Surface Methane Abundance (ppb) DTropospheric O3 Burden (Tg) Characterizing the methane-ozone relationship with idealized model simulations Reduce global anthropogenic CH4 emissions by 30% Simulation Year Model approaches a new steady-stateafter 30 years of simulation Is the O3 response sensitive to the location of CH4 emission controls? A.M. Fiore

16. Multi-model study shows similar surface ozone decreases over NH continents when global methane is reduced Full range of 12 individual models EUROPE N. AMER. S. ASIA E. ASIA • >1 ppbv O3 decrease over all NH receptor regions • Consistent with prior studies TF HTAP 2007 report draft available at www.htap.org

17. Will methane emissions increase in the near future? Anthropogenic CH4 emissions (Tg yr-1) A2 Dentener et al., ACP, 2005 B2 Current Legislation (CLE) Scenario MFR

18. Possible Emission Trajectories in the Near Future (2005 to 2030) Surface NOx Emissions 2030:2005 ratio 0.3 0.8 1.4 1.9 2.5 Anthropogenic CH4 Emissions (Tg yr-1) CLE Baseline A B C • Control scenarios reduce 2030 CH4 emissions relative to CLE by: • A)-75 Tg (18%) – cost-effective now • -125 Tg (29%) – possible with current technologies • -180 Tg (42%) – requires new technologies A.M. Fiore

19. Summary: Climate and Air Quality Benefits From CH4 Control • Significant CH4 reductions can pay for themselves • Benefits are independent of reduction location • Target cheapest controls worldwide • Complementary to NOx, NMVOC controls and maximum benefit in high NOx regions • Robust response over NH continents across models • ~1 ppbv surface O3 for a 20% decrease in anthrop. CH4 • Decreases hemispheric background O3 •  Opportunity for joint international air quality-climate management