How will changes in emissions and climate affect tropospheric composition in 2050? David Stevenson University of Edinburgh Markus Amann, Peter Rafaj, Jim Corbett, Veronika Eyring, Peter Braesicke, Veronica Montenaro, John Pyle, Mike Sanderson, Twan van Noije, Oliver Wild, Guang Zeng Thanks to all the ACCENT Photocomp & Royal Society modellers

What controls tropospheric O3? Chemistry (global precursor emissions, year 2000): ? Anthropogenic Biomass burning Natural NOx 62% 16% 11% Soils 11% Lightning CH4 57% 6% 37% (mostly wetlands) VOCs 4% 80% Veg. C5H8 CO 44% 47% 9% (Veg/ocean) Main human controls Likely to be affected by climate change

What controls tropospheric O3? Physical climate variables/processes Temperature and humidity (chemical fluxes) Stratosphere-troposphere exchange Clouds & precipitation (UV fluxes, wet removal) General circulation (long range transport) ENSO, NAO, blocking frequency, storm tracks, BL ventilation Biological processes Vegetation amount, distribution, speciation Stomatal functioning Many will/may change as climate changes

Anthropogenic NOx emission scenarios 2000-2100 SRES B2 SRES A2 IIASA CLE IIASA CLE 2050 (+Climate Change) IIASA ‘current legislation’ IIASA MFR ACCENT Photocomp runs Royal Society runs Courtesy Markus Amann, IIASA

Ship and aircraft emissions Both have essentially no legislation to regulate them Likely to keep increasing if nothing is done Ships a particularly large NOx source In the 2050 scenario used here, we optimistically assumed that ship emissions will be controlled…

Future projections of ship NOx emissions 4 lines for each colour are different economic growth scenarios. SRES B2 (=CLE basis) is 2nd line down I chose to use TS2 (green) This gives a 50% reduction in ship NOx 2000 to 2050. Upper scenario is more consistent with ‘current legislation’ Eyring et al 2005

NOx emissions 2050-2000 Ships x 0.5 W. Europe x 0.41 N. America x 0.23 China x 1.03 Reduce almost everywhere – global total down ~40%

Anthropogenic NOx emission scenarios 2000-2100 SRES B2 SRES A2 IIASA CLE IIASA CLE 2050 (+Climate Change) IIASA ‘current legislation’ IIASA MFR ACCENT Photocomp runs Royal Society runs Courtesy Markus Amann, IIASA

ACCENT models ensemble mean JJA surface O3 changes 2000-2030 under three scenarios: IIASA CLE IIASA MFR SRES A2 IIASA CLE IIASA MFR SRES A2

Anthropogenic NOx emissions scenarios 2000-2100 SRES B2 SRES A2 IIASA CLE IIASA CLE 2050 (+Climate Change) IIASA ‘current legislation’ IIASA MFR ACCENT Photocomp runs Royal Society runs Courtesy Markus Amann, IIASA

Peak surface O3 season changes Impact of IIASA CLE 2050 emissions changes only (relative to 2000) Impact of climate change from 2000-2050 only (HadGEM SRES A1B)

Impact of climate change (via increased water vapour) is NOx dependent High NOx Low NOx More water vapour in high NOx environments increases O3 More water vapour in low NOx environments reduces O3

Compare responses to climate change in 3 models Strong increases in lightning NOx in mid-latitudes (up to +50%). Smaller increases/ little change/ decreases in tropics. Global increase of +1 to +10%

Upward mass fluxes through ~70 hPa level in the tropics Strengthening Brewer-Dobson circulation is a robust feature of transient climate runs Upward mass fluxes through ~70 hPa level in the tropics (Butchart et al., 2006) The stratospheric source of tropospheric ozone will increase

Conclusions Anthropogenic emissions will be the main control on near-future tropospheric ozone Stringent controls would bring major benefits for AQ and climate Ships (and aircraft) not currently regulated Climate change influence is complex and uncertain More water vapour will reduce O3 in remote regions, but increase O3 in polluted regions STE will increase Lightning will increase in mid-lats (decrease in tropics?) Changes in the biosphere (biomass burning, land-use change) only just starting to be modelled