Influence of future climate change on air quality – global model results David Stevenson Institute of Atmospheric and Environmental Science School of GeoSciences The University of Edinburgh Thanks to: Ruth Doherty (Univ. Edinburgh) Mike Sanderson, Colin Johnson, Bill Collins (Met. Office) Dick Derwent (rdscientific / Imperial College) Frank Dentener, Peter Bergamaschi, Frank Raes (JRC Ispra) Markus Amann, Janusz Cofala, Reinhard Mechler (IIASA) Martin Schultz, Guang Zeng, Kengo Sudo, Nadine Bell, Sophie Szopa, Veronica Montenaro, Jean-Francois Lamarque + All the other IPCC ACCENT modellers NERC and the Environment Agency for funding dstevens@met.ed.ac.uk

Modelling Approach Global chemistry-climate model: STOCHEM-HadAM3 (also some results from others) Two transient runs: 1990 → 2030, following same emissions, but different climate scenarios: 1. Current Legislation (CLE) Assumes full implementation of all current legislation 2. CLE + climate change For 1, climate is unforced, and doesn’t change. For 2, climate is forced by the is92a scenario, and shows a global surface warming of ~1K between 1990 and 2030.

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)

Surface O3 (ppbv) 1990s

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

destruction over the oceans vegetation & changes in ΔO3 from climate change Warmer temperatures & higher humidities increase O3 destruction over the oceans But in polluted regions, more H2O promotes O3 production; also a role from increases in isoprene emissions from vegetation & changes in lightning NOx 2020s CLEcc- 2020s CLE dstevens@met.ed.ac.uk

Zonal mean ΔT (2020s-1990s) dstevens@met.ed.ac.uk

Zonal mean H2O increase 2020s-1990s dstevens@met.ed.ac.uk

Zonal mean change in convective updraught flux 2020s-1990s dstevens@met.ed.ac.uk

C5H8 change 2020s (climate change – fixed climate) dstevens@met.ed.ac.uk

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

Zonal mean PAN decrease 2020s (climate change – fixed climate) Colder LS Increased PAN thermal decomposition, due to increased T dstevens@met.ed.ac.uk

Zonal mean NOx change 2020s (climate change – fixed climate) Less tropical convection and lightning Increased N mid-lat convection and lightning Increased PAN decomposition dstevens@met.ed.ac.uk

Zonal mean O3 budget changes 2020s (climate change – fixed climate) dstevens@met.ed.ac.uk

Zonal mean O3 decrease 2020s (climate change – fixed climate) dstevens@met.ed.ac.uk

Zonal mean OH change 2020s (climate change – fixed climate) Complex function: F(H2O, NOx, O3, T,…) dstevens@met.ed.ac.uk

Influence of climate change on O3 – 9 IPCC ACCENT models Others dominated by increased stratospheric O3 influx Influence of climate change on O3 – 9 IPCC ACCENT models Some models dominated By the water vapour feedback – less O3 dstevens@met.ed.ac.uk

Summary Climate change will introduce feedbacks that modify air quality These include: More O3 destruction from H2O (background air) More O3 production from H2O (polluted air) More stratospheric input of ozone More isoprene emissions from vegetation Changes in convection: mixing & lightning NOx Increases in sulphate from OH and H2O2 Changes in circulation 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 dstevens@met.ed.ac.uk