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

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)

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

Modelling Approach• Global chemistry-climate model: STOCHEM-

HadAM3 (also some results from TM3+others)

• 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 changeFor 1 and 2, climate is unforced, and doesn’t change.For 3, climate is forced by the is92a scenario, and shows a global

surface warming of ~1K between 1990 and 2030.

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)

Global NOx emissions

0.0

40.0

80.0

120.0

160.0

200.0

1990 2000 2010 2020 2030

Europe North AmericaAsia + Oceania Latin America

Africa + Middle East Maximum Feasible Reduction (MFR)

SRES A2 - World Total SRES B2 - World Total

Figure 1. Projected development of IIASA anthropogenic NOx emissions by SRES world region (Tg NO2 yr-1).

CLE

SRES A2

MFR

Global CO emissions

0.0

200.0

400.0

600.0

800.0

1000.0

1990 2000 2010 2020 2030

Europe North AmericaAsia + Oceania Latin America

Africa + Middle East Maximum Feasible Reduction (MFR)

SRES A2 - World Total SRES B2 - World Total

Figure 2 Projected development of IIASA anthropogenic CO emissions by SRES world region (Tg CO yr-1).

CLE

SRES A2

MFR

Global CH4 emissions

0

100

200

300

400

500

600

1990 2000 2010 2020 2030

Europe North AmericaAsia + Oceania Latin AmericaAfrica + Middle East Maximum Feasible Reduction (MFR)SRES A2 - World Total SRES B2 - World Total

Figure 3: Projected development of IIASA anthropogenic CH4 emissions by SRES region

(Tg CH4 yr-1).

CLE

SRES A2

MFR

Figure 4. Regional emissions separated for sources categories in 1990, 2000, 2030-CLE and 2030-MFR for NO x [Tg NO2 yr-1]

Regional NOx emissions19

9020

0020

30 C

LE20

30 M

FR

Surface O3 (ppbv) 1990s

BAU

Change in surface O3, CLE 2020s-1990s

>+10 ppbvIndia

+2 to 4 ppbv overN. Atlantic/Pacific

A large fraction isdue to ship NOx

CLE

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.

Surface ΔO3

2030CLE–2000(NB July)

18 Models from IPCC-ACCENTintercomparison

MRF BAU

Change in surface O3, MFR 2020s-1990s

Up to -10 ppbvover continents

Figure 13(b) Decadal averaged ozone volume mixing ratio differences [ppbv] comparing the 2020s and 1990s for TM3 MFR and STOCHEM MFR

MFR Surface Annual Mean O3 2020s-1990s TM3 (top) and STOCHEM (bottom)

Surface ΔO3

2030MFR–2000(NB July)

18 Models from IPCC-ACCENTintercomparison

CH4, CH4 & OH trajectories 1990-2030CLE

CLEcc

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3R

ad. F

orci

ng /

W/m

2

CH4

O3

CH4 0.167 0.125 0.004 0.003 -0.039 0.221

O3 0.075 0.041 -0.073 -0.072 0.029 -0.03

CLE TM3

CLE STOC

MFR TM3

MFR STOC

MFR-CH4

MFR-pol

If the world opts for MFRover CLE, net reduction in

radiative forcing of 0.2-0.3 W m-2 for the period 2000-2030

Methane controlsare the mosteffective for RF

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

ΔO3 from climate changeWarmer

temperatures &higher humidities

increase O3

destruction over the oceans

But also a rolefrom increases

in isoprene emissions from

vegetation &changes in

lightning NOx

2020s CLEcc-2020s CLE

Zonal mean ΔT (2020s-1990s)

Zonal mean H2O increase 2020s-1990s

Zonal mean change in convective updraught flux 2020s-1990s

C5H8 change 2020s (climate change – fixed climate)

Lightning NOx change 2020s(climate change – fixed climate)

More lightning in N mid-lats

Less, but higher, tropical convection

No overall trend in Lightning NOxemissions

HadCM3 Amazondrying

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

IncreasedPANthermaldecomposition,due toincreased T

Colder LS

Zonal mean NOx change 2020s (climate change – fixed climate)

IncreasedPANdecomposition

IncreasedN mid-latconvectionand lightning

Lesstropicalconvectionandlightning

Zonal mean O3 budget changes 2020s (climate change – fixed climate)

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

Zonal mean OH change 2020s (climate change – fixed climate)

Complexfunction:

F(H2O,NOx,O3,

T,…)

Influence of climate change on O3 – 4 IPCC ACCENT models

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