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Climate feedbacks on tropospheric ozone

Climate feedbacks on tropospheric ozone. David Stevenson Institute of Atmospheric and Environmental Science University of Edinburgh

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Climate feedbacks on tropospheric ozone

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  1. Climate feedbacks on tropospheric ozone David Stevenson Institute of Atmospheric and Environmental Science University of Edinburgh F.J. Dentener, M.G. Schultz, K. Ellingsen, T.P.C. van Noije, O. Wild, G. Zeng, M. Amann, C.S. Atherton, N. Bell, D.J. Bergmann, I. Bey, T. Butler, J. Cofala, W.J. Collins, R.G. Derwent, R.M. Doherty, J. Drevet, H.J. Eskes, A.M. Fiore, M. Gauss, D.A. Hauglustaine, L.W. Horowitz, I.S.A. Isaksen, M.C. Krol, J.-F. Lamarque, M.G. Lawrence, V. Montanaro, J.-F. Müller, G. Pitari, M.J. Prather, J.A. Pyle, S. Rast, J.M. Rodriguez, M.G. Sanderson, N.H. Savage, D.T. Shindell, S.E. Strahan, K. Sudo, and S. Szopa

  2. Introduction • Tropospheric O3 is the no.3 GHG • Closely coupled to OH and CH4 lifetime • Ground-level O3 is a major air pollutant • Most studies of future O3 focus on emissions trends (NOx, CO, VOCs etc.) • BUT climate feedbacks may also be important

  3. ACCENT Intercomparison • Target IPCC-AR4 • 25 models participated • Simulations: • Year 2000 (reference or base year) • Three year 2030 scenarios: • IIASA CLE (medium) • IIASA MFR (low) • IPCC SRES A2 (high) • Plus one climate change case: • 2030 CLE + prescribed 2030 climate • (Performed by nine models) ACCENT: ‘Atmospheric Composition Change: the European Network of Excellence’

  4. Year 2000 Annual Zonal Mean Ozone (24 models)

  5. Year 2000 Ensemble meanof 25 models AnnualZonalMean Annual TroposphericColumn

  6. Year 2000 Inter-model standard deviation (%) AnnualZonalMean Annual TroposphericColumn

  7. Comparison of ensemble mean model with O3 sonde measurements UT250 hPa Model ±1SD Observed ±1SD J F M A M J J A S O N D MT 500 hPa LT 750 hPa 30°S-Eq 30°N-Eq 90-30°N 90-30°S

  8. +10 ppbv +5 ppbv -5 ppbv 2030 A2 - 2000 2030 MRF - 2000 2030 CLE - 2000

  9. CLE +ΔClimate Change in tropospheric O3 burden (2000-2030) ΔO3 / Tg(O3)

  10. Loss increasesby more thanproduction Stratospheric influx increases

  11. Positive stratosphericinflux feedback Negative watervapour feedback Impact of Climate Change on Ozone by 2030(ensemble of 9 models) Mean + 1SD Mean - 1SD Mean Positive and negative feedbacks – no clear consensus

  12. Tropospheric water vapour in 6 GCMs Differences of ± 10% in tropics Tropospheric H2O column / g(H2O) m-2 90S Eq 90N

  13. Conclusions • Two important feedbacks of climate on tropospheric ozone: • Negative feedback due to water vapour, via the ozone loss process: O3 + hν → O(1D) + O2 O(1D) + H2O → 2OH (also leads to a negative feedback on CH4) • Positive feedback due to an increase in the stratospheric influx of O3, mainly due to enhanced Brewer-Dobson circulation, but also possibly because LS O3 increases. • Models show no consensus on which process dominates • Need to reduce uncertainties in modelling water vapour and STE of O3 to further constrain these feedbacks • Feedbacks on lightning and isoprene emissions appear less important globally • There are other potential feedbacks not yet analysed, e.g. wetland CH4, biomass burning emissions…

  14. Radiative forcing implications Forcings (mW m-2) 2000-2030 for the 3 scenarios: +37% -23% CO2 CH4 O3

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