1. The Double Dividend of Methane Control Arlene M. Fiore IIASA, Laxenburg, Austria January 28, 2003 ANIMALS 90 LANDFILLS 50 GAS 60 COAL 40 RICE 85 TERMITES 25 WETLANDS 180 BIOMASS BURNING 20 (Fiore et al., GRL, October 2002) GLOBAL METHANE SOURCES (Tg CH 4 yr -1 )

2. Year 600 800 700 Scenarios A1B A1T A1F1 A2 B1 B2 IS92a 900 Variations of CH 4 Concentration (ppbv) Over the Past 1000 years [Etheridge et al., 1998] Year 20001000 800 IPCC [2001] Projections of Future CH 4 Emissions (Tg CH 4 ) to 2050 1200 1600 1400 1000 1500 2000 2020 2040 Atmospheric CH 4 : Past Trends, Future Predictions

3. NO x NMVOCs NO x NMVOCs CONTINENT 2 OCEAN O3O3 Boundary layer (0-2.5 km) Free Troposphere CONTINENT 1 CH 4 itself is an important greenhouse gas, and links climate with air pollution via its influence on tropospheric ozone OH HO 2 VOC, CH 4, CO NO NO 2 h O3O3 O3O3 Global Background O 3 Direct Intercontinental Transport greenhouse gas air pollution (smog)

4. Summer 1995 1- 5 p.m. Observations at Harvard Forest, Massachusetts Data from Munger et al., [1996, 1998] r 2 = 0.74 U.S. Ozone Standard Range of observed background (Index of Aged Pollution) Ozone (ppbv) NOy-NOx (ppbv) Intercept 30 ppb background (clean air) Mean Afternoon O 3 Background (ppbv) in GEOS-CHEM Model, Summer 1995 Background is tagged as ozone produced outside the N. American boundary layer (surface-700 hPa) What is background O 3 over the United States? Fiore et al., JGR, August, 2002.

5. APPROACH: Sensitivity simulations in GEOS-CHEM Model [Bey et al.,2001] (uses assimilated meteorology; 20  ; 4ºx5º or 2ºx2.5º horiz. resn.) Perturbations to total emissions when anthropogenic are halved What is the anthrop. contribution to global emissions? NO x ~ 65% 33% CO ~ 50% 25% VOCs ~ 12% 6% CH 4 ~ 60% 30% 1. Reduce various combinations of anthrop. emissions by 50% globally relative to 1995 base year CH 4 fixed at steady-state global uniform concentration (1700 ppbv for 1995) 1000 ppbv CH 4 )( QUESTION: Can we simultaneously mitigate air pollution and greenhouse warming by reducing CH 4 emissions?

6. METHOD (continued): NOx COCH 4 VOCs Percent change in anthrop. emis. from 1995 base case to 2030 simulations: GLOBAL increase USA decrease A1 2030 2. Implement IPCC A1/B1 future emission scenarios for 2030 B1 2030

7. Change in radiative forcing* (W m -2 ) from O 3 and CH 4 relative to 1995 base case *calculated from changes in global CH 4 concentrations [IPCC, 2001] and changes in the mean tropospheric O 3 column [Mickley et al., 1999] NO x  OH  CH 4 50% anthr. NO x 2030 A1 50% anthr. CH 4 50% anthr. NMVOC 2030 B1

8. Change in summer afternoon O 3 in surface air over the U.S. Mean O 3 Background O 3 * 50% anthr. NMVOC 50% anthr. CH 4 50% anthr. NO x 2030 A1 *produced outside the North American boundary layer (surface-700 hPa) Change in O 3 (ppbv) Relative to 1995 base year (mean 51 ppbv, background 23 ppbv) Degradation of U.S. air quality from rise in global emissions despite domestic reductions 2030 B1

9. Impacts of Emissions Perturbations on U.S. Air Quality 1995 (base ) 50% anthr. VOC 50% anthr. CH 4 50% anthr. NO x 2030 A1 Increase in U.S. pollution events despite domestic decline in anthrop. emissions Number of summer grid-square days with O 3 > 80 ppbv 2030 B1

10. Rising emissions from developing countries lengthen the O 3 pollution season in the United States 2030 A1 1995 Base Case

11. CH 4 NO x NMVOCs NO x NMVOCs O3O3 Chemical loss Deposition CONTINENT 2 OCEAN O3O3 O3O3 NO x emissions local impact; little effect on climate Boundary layer (0-2.5 km) Free Troposphere CH 4 emissions global impact: Lower background O 3 Negative radiative forcing Intercontinental transport, global O 3 background increases in 2030 A1 simulation CONTINENT 1 Double dividend of methane emissions reductions: lower global O 3 background and improve air quality everywhere