Download Global Sulphur Cycle - School of GeoSciences

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
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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
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Interactive lightning NOx, C5H8 from veg.
~1 year/day on 36 processors (Cray T3E)
− CH4-CO-NOx-hydrocarbons
− detailed oxidant photochemistry
Model experiments
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Two transient runs: 1990 → 2030
Driving meteorology
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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:
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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)
Model experiments
BAU, fixed SSTs 1990-2030
BAU, is92a SSTs 1990-2030
1990
Compare changes between
the 1990s and 2020s
2030
1990s
Decadal mean values
BAU 2020s
+2 to 4 ppbv over
N. Atlantic/Pacific
>+10 ppbv
India
A large fraction is
due to ship NOx
Change in surface O3, BAU 2020s-1990s
BAU
BAU+climate change 2020s
Change in surface O3, BAUcc 2020s-1990s
MRF
BAU
BAU+cc
Look at the difference between these
two to see influence of climate change
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