Chemistry-Climate Modelling: Impacts of climate change on tropospheric chemical composition David Stevenson Institute of Atmospheric and Environmental Science School of GeoSciences The University of Edinburgh Thanks to: Ruth Doherty (Univ. Edinburgh) Dick Derwent (rdscientific) Mike Sanderson, Colin Johnson, Bill Collins (Met Office) Frank Dentener (JRC Ispra), Markus Amann (IIASA)

STOCHEM Global Lagrangian 3-D 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 detailed oxidant photochemistry Interactive lightning NOx, C5H8 from veg. ~1 year/day on 36 processors (Cray T3E)

Model experiments Two transient runs: 1990 → 2030 Driving meteorology 1. Fixed SSTs (mean of 1978-1996) 2. SSTs from a climate change scenario (is92a) shows ~1K surface warming 1990s-2020s New IIASA* global emissions scenario: Business as usual (BAU) [aka CLE Current Legislation] Stratospheric O3 is a fixed climatology Vegetation (land-use) also a fixed climatology *IIASA: International Institute for Applied Systems Analysis (Austria)

IIASA Emissions scenarios Global totals – there are significant regional variations Courtesy of Markus Amann (IIASA) & Frank Dentener (JRC)

Compare changes between the 1990s and 2020s Model experiments BAU, fixed SSTs 1990-2030 Compare changes between the 1990s and 2020s BAU, is92a SSTs 1990-2030 1990 2030

Decadal mean values 1990s

BAU 2020s

BAU Change in surface O3, BAU 2020s-1990s +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, BAU 2020s-1990s BAU

BAU+climate change 2020s

MRF BAU BAU+cc Change in surface O3, BAUcc 2020s-1990s Look at the difference between these two to see influence of climate change Change in surface O3, BAUcc 2020s-1990s MRF BAU BAU+cc

destruction over the oceans ΔO3 from climate change Warmer temperatures & higher humidities increase O3 destruction over the oceans But also a role from increases in isoprene emissions from vegetation?

Isoprene emissions 1990-2030

Lightning NOx 1990-2030

Zonal mean H2O increase 2020s (climate change – fixed climate)

Zonal mean C5H8 change 2020s (climate change – fixed climate) Increased emissions from veg as T increases

Zonal mean lightning NOx change 2020s (climate change – fixed climate) More convection in N mid-lats? Less, but higher, tropical convection? No overall trend in Lightning NOx emissions

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

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

Zonal mean O3 NCP change 2020s (climate change – fixed climate) Looks quite like NOx + H2O increase C5H8 increase Longer O3 lifetime in MT/UT means reduced NCP there dominates globally.

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

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

CH4, CH4 & OH trajectories 1990-2030 Current CH4 trend looks like MRF – coincidence? All scenarios show increasing OH

Conclusions Anthropogenic emissions will be the main determinant of future tropospheric O3 Ship NOx looks important Climate change will introduce feedbacks that modify air quality