Overlaps of AQ and climate policy – global modelling perspectives

1. Overlaps of AQ and climate policy – global modelling perspectives David Stevenson Institute of Atmospheric and Environmental ScienceSchool of GeoSciencesThe University of Edinburgh Thanks to: Ruth Doherty (Univ. Edinburgh) Dick Derwent (rdscientific) Mike Sanderson, Colin Johnson, Bill Collins (Met Office) Frank Dentener, Peter Bergamaschi, Frank Raes (JRC Ispra) Markus Amann, Janusz Cofala, Reinhard Mechler (IIASA) NERC and the Environment Agency for funding

2. Material mainly from 2 current publications: The impact of air pollutant and methane emission controls on tropospheric ozone and radiative forcing: CTM calculations for the period 1990-2030 Dentener et al (2004) Atmos. Chem. Phys. Disc. (currently open for discussion on the web) Impacts of climate change and variability on tropospheric ozone and its precursors Stevenson et al (2005) Faraday Discussions (upcoming discussion meeting at Leeds in April)

3. Rationale • Regional-global scale AQ legislation has implications for climate forcing – quantify these for current and possible future policies (use 2 very different models to try and reduce model uncertainty) • Climate change will influence AQ – use coupled climate-chemistry model to identify potentially important interactions

4. Modelling Approach • Global chemistry-climate model: STOCHEM-HadAM3 (also some results from TM3+others) • Three transient runs: 1990 → 2030, following different emissions/climate scenarios: 1. Current Legislation (CLE) Assumes full implementation of all current legislation 2. Maximum Feasible Reductions (MFR) Assumes full implementation of all available current emission reduction technology 3. CLE + climate change For 1 and 2, climate is unforced, and doesn’t change. For 3, climate is forced by the is92a scenario, and shows a global surface warming of ~1K between 1990 and 2030.

5. STOCHEM-HadAM3 • Global Lagrangian chemistry-climate model • Meteorology: HadAM3 + prescribed SSTs • GCM grid: 3.75° x 2.5° x 19 levels • CTM: 50,000 air parcels, 1 hour timestep • CTM output: 5° x 5° x 9 levels • Detailed tropospheric chemistry • CH4-CO-NOx-hydrocarbons (70 species) • includes S chemistry • Interactive lightning NOx, C5H8 from veg. • these respond to changing climate • ~3 years/day on 36 processors (SGI Altix)

6. Global NOx emissions SRES A2 CLE MFR Figure 1. Projected development of IIASA anthropogenic NOx emissions by SRES world region (Tg NO2 yr-1).

7. Global CO emissions SRES A2 CLE MFR Figure 2 Projected development of IIASA anthropogenic CO emissions by SRES world region (Tg CO yr-1).

8. Global CH4 emissions SRES A2 CLE MFR Figure 3: Projected development of IIASA anthropogenic CH4 emissions by SRES region (Tg CH4 yr-1).

9. 1990 2000 2030 CLE 2030 MFR Regional NOx emissions Figure 4. Regional emissions separated for sources categories in 1990, 2000, 2030-CLE and 2030-MFR for NOx [Tg NO2 yr-1]

10. Surface O3 (ppbv) 1990s

11. +2 to 4 ppbv over N. Atlantic/Pacific >+10 ppbvIndia CLE A large fraction is due to ship NOx Change in surface O3, CLE 2020s-1990s BAU

12. CLE Surface Annual Mean O3 2020s-1990s TM3 (top) and STOCHEM (bottom) Figure 13. Decadal averaged ozone volume mixing ratio differences [ppbv] comparing the 2020s and 1990s for (a) TM3 CLE and STOCHEM CLE.

13. Surface ΔO3 2030CLE–2000(NB July) 18 Models from IPCC-ACCENT intercomparison

14. Up to -10 ppbvover continents Change in surface O3, MFR 2020s-1990s MRF BAU

15. MFR Surface Annual Mean O3 2020s-1990s TM3 (top) and STOCHEM (bottom) Figure 13(b) Decadal averaged ozone volume mixing ratio differences [ppbv] comparing the 2020s and 1990s for TM3 MFR and STOCHEM MFR

16. Surface ΔO3 2030MFR–2000(NB July) 18 Models from IPCC-ACCENT intercomparison

17. CH4, CH4 & OH trajectories 1990-2030 CLE CLEcc

18. Methane controlsare the most effective for RF If the world opts for MFR over CLE, net reduction in radiative forcing of 0.2-0.3 W m-2for the period 2000-2030

19. Part 1 Summary • Co-benefits for both AQ and climate from some emissions controls • Methane offers the best opportunity (also CO and NMVOCs) • NOx controls (alone) benefit AQ, but probably worsen climate forcing (via OH and CH4) (Similarly for SO2) • AQ policies influence climate – this study gives a quantitative assessment • Use of many models shows results are quite consistent

20. ΔO3 from climate change Warmertemperatures & higher humidities increase O3 destruction over the oceans But also a role from increases in isoprene emissions from vegetation &changes in lightning NOx 2020s CLEcc- 2020s CLE

21. Zonal mean ΔT (2020s-1990s)

22. Zonal mean H2O increase 2020s-1990s

23. Zonal mean change in convective updraught flux 2020s-1990s

24. C5H8 change 2020s (climate change – fixed climate)

25. HadCM3 Amazon drying Lightning NOx change 2020s(climate change – fixed climate) More lightning in N mid-lats Less, but higher, tropical convection No overall trend in Lightning NOx emissions

26. Zonal mean PAN decrease 2020s (climate change – fixed climate) Colder LS Increased PAN thermal decomposition, due to increased T

27. Zonal mean NOx change 2020s (climate change – fixed climate) Increased N mid-lat convection and lightning Less tropical convection and lightning Increased PAN decomposition

28. Zonal mean O3 budget changes 2020s (climate change – fixed climate)

29. Zonal mean O3 decrease 2020s (climate change – fixed climate)

30. Zonal mean OH change 2020s (climate change – fixed climate) Complex function: F(H2O, NOx, O3, T,…)

31. Influence of climate change on O3 – 4 IPCC ACCENT models

32. Part 2 Summary • Climate change will introduce feedbacks that modify air quality • These include: • More O3 destruction from H2O • More stratospheric input of ozone • More isoprene emissions from vegetation • Changes in lightning NOx • Increases in sulphate from OH and H2O2 • Wetland CH4 emissions (not studied here) • Changes in stomatal uptake? (``) • These are quite poorly constrained – different models show quite a wide range of response: large uncertainties