Overlaps of AQ and climate policy

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)

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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 TM3others)
• 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 doesnt
  change.
• For 3, climate is forced by the is92a scenario,
  and shows a global surface warming of 1K between
  1990 and 2030.

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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)

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Global NOx emissions
SRES A2
CLE
MFR
Figure 1. Projected development of IIASA
anthropogenic NOx emissions by SRES world region
(Tg NO2 yr-1).
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Global CO emissions
SRES A2
CLE
MFR
Figure 2 Projected development of IIASA
anthropogenic CO emissions by SRES world region
(Tg CO yr-1).
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Global CH4 emissions
SRES A2
CLE
MFR
Figure 3 Projected development of IIASA
anthropogenic CH4 emissions by SRES region (Tg
CH4 yr-1).
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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
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Surface O3 (ppbv) 1990s
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CLE
A large fraction is due to ship NOx
Change in surface O3, CLE 2020s-1990s
BAU
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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.
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Surface ?O3 2030CLE2000(NB July)
18 Models from IPCC-ACCENT intercomparison
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Change in surface O3, MFR 2020s-1990s
MRF
BAU
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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
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Surface ?O3 2030MFR2000(NB July)
18 Models from IPCC-ACCENT intercomparison
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CH4, ?CH4 OH trajectories 1990-2030
CLE
CLEcc
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If the world opts for MFR over CLE, net reduction
in radiative forcing of 0.2-0.3 W m-2 for the
period 2000-2030
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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

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?O3 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
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Zonal mean ?T (2020s-1990s)
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Zonal mean H2O increase 2020s-1990s
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Zonal mean change in convective updraught flux
2020s-1990s
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C5H8 change 2020s (climate change fixed climate)
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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
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Zonal mean PAN decrease 2020s (climate change
fixed climate)
Colder LS
Increased PAN thermal decomposition, due
to increased T
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Zonal mean NOx change 2020s (climate change
fixed climate)
Increased N mid-lat convection and lightning
Less tropical convection and lightning
Increased PAN decomposition
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Zonal mean O3 budget changes 2020s (climate
change fixed climate)
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Zonal mean O3 decrease 2020s (climate change
fixed climate)
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Zonal mean OH change 2020s (climate change
fixed climate)
Complex function F(H2O, NOx, O3, T,)
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Influence of climate change on O3 4 IPCC ACCENT
models
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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