Shifting seasonal cycles of surface ozone: the role of regional vs. global emission changes

1. Shifting seasonal cycles of surface ozone: the role of regional vs. global emission changes Olivia Clifton Fiore/McNeill Symposium July 17, 2013 Acknowledgments. Arlene Fiore (CU/LDEO), Gus Correa (CU/LDEO),Larry Horowitz (GFDL), VaishaliNaik (GFDL)

2. The GFDL CM3/AM3 chemistry-climate model Modular Ocean Model version 4 (MOM4) & Sea Ice Model Observed or CM3 SSTs/SIC for CMIP5 Simulations GFDL-CM3 GFDL-AM3 Forcing Solar Radiation Well-mixed Greenhouse Gas Concentrations Volcanic Emissions cubed sphere grid ~2°x2°; 48 levels Atmospheric Dynamics & Physics Radiation, Convection (includes wet deposition of tropospheric species), Clouds, Vertical diffusion, and Gravity wave Atmospheric Chemistry 86km Ozone–Depleting Substances (ODS) Chemistry of Ox, HOy, NOy, Cly, Bry, and Polar Clouds in the Stratosphere Chemistry of gaseous species (O3, CO, NOx, hydrocarbons) and aerosols (sulfate, carbonaceous, mineral dust, sea salt, secondary organic) Pollutant Emissions (anthropogenic, ships, biomass burning, natural, & aircraft) AM3 option to nudge to reanalysis winds Aerosol-Cloud Interactions Dry Deposition Donner et al., 2011,Golaz et al. 2011, Levy et al., 2013, Naik et al., revised Land Model version 3 (soil physics, canopy physics, vegetation dynamics, disturbance and land use) A. Fiore

3. Historical increase in atmospheric methane and ozone (#2 and #3 greenhouse gases after CO2 [IPCC, 2007]) CH4Abundance (ppb) past 1000 years [Etheridge et al., 1998] Ozoneat European mountain sites 1870-1990 [Marenco et al., 1994] 1600 1400 1200 1000 800 Methane has an indirect influence on climate & increases background levels of surface ozone 1500 1000 2000 Year A. Fiore

4. Monthly mean surface O3 (ppb) Observed (1988-2009 mean) vs.CM3 model (1990-2005 mean) Clean Air Status & Trends Network (CASTNet) sites: rural ground monitoring sites in the United States designed to capture background ozone levels, managed and operated by EPA

5. Changes in seasonal cycles in high-elevation mountaintop ozone: CM3 vs. observations from Parrish et al., 2013 at Hohenpeissenberg (47º48’N/9º30’W, 1.0km) CM3 ~ 30 years between 5 year periods • Wintertime bias in both earlier and later historical periods in CM3 • Agreement between changes in seasonal cycle shapes Parrish et al., 2013

6. Seasonal cycles in high-elevation mountaintop ozone: CM3 vs. observations from Parrish et al., 2013 at Zugspitze (47º25’N/10º59’E, 3.0km) ~ 20 years between 5 year periods CM3 • Bias in both earlier and later historical periods in CM3 • Agreement between changes in seasonal cycle shapes • Agreement between differences between periods in late spring through late summer Parrish et al., 2013

7. Well-mixed greenhouse gases (WMGGs) & Emissions of Short-Lived Climate Forcers (SLCFs) under “RCPs” 2050 2100 RCP8.5 “extreme” RCP6.0 RCP4.5 “moderate” RCP2.6 -50% -80% -50% -80% Anthrop. SO2 (Tg yr-1) CO2 abundance (ppm) -40% -60% -20% -60% Anthrop. BC (Tg yr-1) -25% -50% -35% -70% Methane abundance (ppb) Anthrop. NO (Tg yr-1) Figures c/o V. Naik

8. GFDL CM3 scenarios & sensitivity simulations Each scenario in GFDL CM3 includes 3 ensemble members

9. 21st Century Scenarios EMISSION PROJECTIONS 2005 to 2100 % change Future-Base NOxemiss. decreases RCP8.5 extreme RCP4.5 moderate RCP4.5_WMGG Global NOx NE US NOx Mtn. W NOx CO2 CH4 molecules/cm2/s 0 Global Mean Temperature (>500 hPa) RCP4.5_WMGG Enables separation of roles of changing climate from changing air pollutant emissions

10. Changing seasonal cycles by end of 21stcentury in RCP8.5 vs. RCP4.5; in ppb, land only 2006-2015 2091-2100 RCP4.5 2006-2015 2091-2100 RCP8.5 • Higher O3in RCP8.5 in cooler months despite NOx reductions • NOx reductions decrease O3 in most months under RCP4.5

11. Changes from 2006-2015 to 2091-2100 in monthly mean surface O3 due to CH4 in RCP8.5; in ppb, land only RCP8.5 RCP8.5_2005CH4 RCP8.5_2005CH4_chem RCP8.5_2005CH4_rad • Higher CH4 from chemistry contribution in winter • Difference between RCP8.5 and RCP8.5_2005CH4_chem (RCP8.5 but with CH4 held at 2005 levels) indicates that doubling CH4 in RCP8.5 increases surface O3 over NE & WUS by > 5-15 ppb • Increasing CH4 chemistry contributes to the high increase in O3 during winter & early spring and dampens decreasing effect of NOx emissions controls in the summer on O3

12. How is CH4 from chemistry affecting end of 21st century seasonal cycle? in ppb, land only 2006-2015 2091-2100 RCP8.5 2091-2100 mean of RCP8.5_2005CH4 & 2005CH4_chem • Magnitude of the future seasonal cycle is governed by increasing CH4 chemistry and the shifting O3 seasonal cycle is governed by NOx emissions controls • Future seasonal cycles have similar shape in NE USA and Mountainous W

13. Which month holds the decadal monthly mean O3 maximum? 2006-2015 RCP8.5 2091-2100 CH4 emissions double CH4 emissions stay at 2005 levels RCP8.5_2005CH4 2091-2100 • By end of 21st century regional NOx emissions controls shift the monthly mean maximum from summer months to winter & early spring • Doubling CH4 vs. leaving CH4 at 2005 levels doesn’t affect the month that the maximum monthly means occur DJF MAM JJA SON

14. Shifting back to RCP4.5: Change in ozone seasonal cycles by the end of the 21st century in RCP4.5; in ppb, land only • RCP4.5demonstrates large impact of NOx emissions controls, showing decreases of surface O3 in the summer >10-15 ppb • RCP4.5_WMGG (O3 precursors remain at 2005 levels) suggests that climate warming will increase O3 by a few ppb in NE USA summer and Mtn. W USA in early spring and decrease it slightly in Mtn. W summer, with little change over the other seasons.

15. Conclusions • Shifting balance of effect of regional-vs-global emissions sources on surface ozone • Present seasonal cycles governed in summer by regional NOx emissions • Future seasonal cycles governed by global CH4 emissions • Increasing CH4 from chemistry is most important player in regards to CH4 in increasing surface ozone by the end of the 21st century • Climate change may impact future surface O3, but can be offset by NOx reductions, which preferentially decrease highest O3 events (most evident in NE USA plots) • Future questions: how is methane from radiation vs. methane from chemistry affecting strat-to-trop exchange of ozone? RCP8.5 2005CH4_chem 2005CH4_rad