Air pollution and climate change policies in Europe : exploring linkages and the added value of an integrated approach .
Date: 2005-07-12
Institutions: European Environment Agency
Subjects: EU environmental policy, air quality, climate change, environmental monitoring

EEA Technical report

No 5/2004

Air pollution and climate 
change policies in Europe: 
exploring linkages and 
 the added value of an 
 integrated approach

European Environment Agency

Cover design: EEA
Layout: Brandpunkt a/s

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iii

Contents

Acknowledgements ..........................................................................  

Executive summary ..........................................................................  

1.  Introduction ................................................................................  

1.1.  Aims and scope of the report .................................................... 

1.2.  Rationale ............................................................................... 

1.3.  The issues .............................................................................. 
1.3.1.  Regional and local issues ............................................... 
1.3.2.  Global issues ............................................................... 

1.4.  Categories of linkages ............................................................. 

1.5.  Structure of the report ............................................................. 

1

2

6

6

6

7
7
8

8

9

2.  Atmospheric linkages between climate change and air pollution .   11

2.1.  Atmospheric linkages: substances that affect both air pollution  

and climate change .................................................................  11
2.1.1.  Radiative forcing of air pollutants ....................................  11
2.1.2.  Aerosols and climate change ..........................................  14
2.1.3.  Tropospheric ozone pollution and climate change ..............  14
2.1.4.  Stratospheric ozone and climate change ..........................  15

2.2.  Overview of important compounds ............................................  17

2.3.  Conclusions ............................................................................  17

2.4.  Proposed linkage indicators for the EEA ......................................  17

3.  Linkages of impacts .....................................................................   19

3.1.  Introduction ...........................................................................  19

3.2.  Ecosystems and biodiversity .....................................................  20

3.3.  Human health .........................................................................  21

3.4.  Proposed linkage indicators for the EEA ......................................  23

4.  Linkages in emissions and control options ...................................   25

4.1.  Linkages in emissions and control options ..................................  25

4.2.  Conclusions ............................................................................  28

4.3.  Proposed linkage indicators for the EEA ......................................  28

5.  Current policy practices and opportunities ..................................   30

5.1.  Introduction and history ...........................................................  30

5.2.  Air quality policies and climate change .......................................  31

5.3.  Climate change policies and air pollution ....................................  31

5.3.  Policies and instruments ..........................................................  33

5.4.  Conclusions ............................................................................  34

5.5.  Proposed linkage indicators for the EEA ......................................  34

iv

Air pollution and climate change policies in Europe

6.  History of integrated assessment of air pollution and  

climate change ............................................................................   36

6.1.  History of integrated assessment of air pollution and climate  

change in Europe ....................................................................  36

6.2.  Ancillary and co-beneﬁts ..........................................................  38

6.3.  Implications for integrated assessment: discussion ......................  38

7.  Discussion and future EEA work ..................................................   41

7.1.  Barriers to integration ..............................................................  41

7.2.  Arguments in favour of integration of climate change and air  

pollution policies .....................................................................  42

7.3.  Research gaps ........................................................................  42

7.4.  Addressing linkages between air pollution and climate change  

in EEA reporting ......................................................................  43

References .......................................................................................   45

Introduction to the Annexes .............................................................   54

Annex 1:   European environmental priorities: an integrated  

economic and environmental assessment (EEP project) ..   55

Annex 2:   ‘Shared analysis air pollution and greenhouse gases’  

(ShAIR) study ..................................................................   58

Annex 3:   AIR-CLIM project .............................................................   62

Annex 4:   Approaches to analyse interactions of climate change, 

acidiﬁcation and ozone (NRP project) ..............................   67

Annex 5:   Study for Europe’s environment, the third assessment: 

Exploring the ancillary beneﬁts of the Kyoto Protocol  
for air pollution in Europe ................................................   71

Annex 6:   Ancillary beneﬁts and costs of greenhouse gas  

mitigation (proceedings of the OECD workshop) .............   75

Annex 7:   Workshop of the Task Force of Integrated Assessment 

Modelling (TFIAM) of UNECE on ‘Linkages and  
synergies of regional and global emission control’ ...........   80

Annex 8:   Overview of a selected number of workshops  

addressing the interaction of climate change and air  
quality .............................................................................   87

Annex 9:   Internet addresses containing information on the  

linkage of Climate change and air quality ........................   89

Acknowledgements

1

Acknowledgements

This report was prepared by the 
European Topic Centre for Air and 
Climate Change (ETC/ACC) of the 
European Environment Agency in 
cooperation with the Joint Research 
Centre (JRC), Ispra, Italy. Willemĳn 
Tuinstra (National Institute for Public 
Health and the Environment — RIVM, 
the Netherlands) has been co-ordinator 
of the report. The atmospheric linkages 
between climate change and air 
pollution were addressed by E.-A. 
Kalognomou and N. Moussiopoulos 
(Aristotle University Thessaloniki), H. 
Eerens (RIVM) and F. Dentener and 
F. Raes (JRC). The linkages between 
impacts of air pollution and climate 
change were addressed by H. Eerens 
and J. van Minnen (RIVM). The linkages 
between emissions of air pollutant and 
greenhouse gases and their control 
options were addressed by M. Amann, 
J. Cofala and Z. Klimont (International 
Institute for Applied Systems Analysis) 
and C. Brink (RIVM). R. Swart and T. 
Petroula (RIVM) wrote the overview 
of current policy practices as well as 

future policy opportunities. R. Swart 
and W. Tuinstra (RIVM) wrote the 
history of integrated assessment of air 
pollution and climate change. Finally, 
the discussion and proposal for future 
EEA work in these areas was developed 
and wri�en by R. Swart and H. Eerens 
(RIVM).

H. Eerens, J. van Minnen and R. Swart 
developed the preliminary indicators 
presented in Chapters 2 to 5.

This report has beneﬁted from useful 
comments kindly provided by R. 
Alkemade, K. Aunan, G.J. van den Born, 
L. van Bree, J.M. Brignon, T. Carter, J.P. 
He�elingh, A. Hinsberg, F. de Leeuw, 
M. Posch, J. Po�ing, H. Simons, G. 
Velders and J. West. We would like to 
thank them all for their contributions. 
Any errors or omissions remain the full 
responsibility of the authors.

EEA project manager was Andreas 
Barkman.

2

Air pollution and climate change policies in Europe

Executive summary

There is an increasing awareness in both 
the science and policy communities 
of the importance of addressing the 
linkages between the traditional air 
pollutants and greenhouse gases. 
Many of the traditional air pollutants 
and greenhouse gases have common 
sources, their emissions interact in the 
atmosphere, and separately or jointly 
they cause a variety of environmental 
impacts on the local, regional and global 
scales. Linkages work in two directions: 
there can be synergies and negative 
trade-oﬀs. Thus, emission control 
strategies that simultaneously address 
air pollutants and greenhouse gases 
may lead to a more eﬃcient use of the 
resources on all scales.

This report explores the linkages 
between air quality and climate change 
from a European perspective in order 
to assist the European Environment 
Agency (EEA) in approaching the issues 
of air quality and climate change in an 
integrated way. This report addresses 
atmospheric linkages, linkages of 
impacts and possible synergies in 
emission reductions and emission 
control strategies. Furthermore, it 
assesses the relevance and signiﬁcance 
of linkages for diﬀerent control options 
and deﬁnes priority issues for integrated 
assessment. Finally it proposes 
preliminary indicators that could be 
used by the EEA to approach and report 
on linkages between air quality and 
climate change in a structured manner.

Atmospheric linkages between air 
pollution and climate change
•  Air pollutants and greenhouse 

gases interact on various spatial and 
temporal scales. Many air pollutants 
contribute to radiative forcing. 
Examples are nitrogen oxides, 
carbon oxide and non-methane 
volatile organic compounds which 
are precursors to tropospheric ozone 
(an important greenhouse gas as 
well as an air pollutant). Another 

example are aerosols and particulate 
ma�er (PM), which can have either 
a positive or negative forcing eﬀect, 
dependent on their composition. 
Both ozone and PM have direct 
health eﬀects.

•  Particularly relevant for the linkages 
between climate change and air 
pollution is tropospheric ozone. 
Climate change, on the one hand, 
inﬂuences ozone concentrations 
through dynamical and chemical 
changes in the atmosphere. On the 
other hand, increasing background 
ozone concentrations in Europe 
aﬀect climate change because ozone 
is a potent greenhouse gas itself and 
indirectly inﬂuences the lifetime 
of other greenhouse gases such as 
methane.

•  The climatic eﬀects of aerosols are 
dependent on their composition. 
Black carbon (soot) enhances 
warming, while other aerosols 
constituents (sulphates, nitrates, 
organic compounds) generally 
have a cooling eﬀect. The net eﬀect 
of reducing particulate ma�er 
is probably leading to a further 
enhancement of the greenhouse 
eﬀect. However, the issue of a 
net cooling/warming by aerosols 
critically depends on the highly 
uncertain eﬀect of black carbon 
aerosol, which is at present strongly 
under debate.

•  Climate change and stratospheric 

ozone depletion interact in various 
ways. Inter alia, the disturbance of 
the atmospheric radiative balance is 
expected to delay the recovery of the 
ozone layer by some decades. 

Linkages of impacts of air pollution and 
climate change
• 

Impacts of climate change and air 
pollution on humans and ecosystems 
interact in two ways. On the one 
hand, climate change can change 
the eﬀects of exposure of humans 
and ecosystems to air pollution, 

Executive summary

3

and the other way round. On the 
other hand, climate change can 
aﬀect the sensitivity of humans and 
ecosystems to speciﬁc impacts of air 
pollution and the other way round.
•  The exposure of ecosystems to air 
pollution can change as a result 
of phenological changes induced 
by climate change (e.g. changes in 
the length of the growing season) 
as well as by changed distribution 
of air pollutants through changed 
weather pa�erns. Their sensitivity 
may change as a result of, inter 
alia, climate-induced changes in 
ecosystem vitality, soil processes and 
ecosystem composition.

•  The exposure of humans to ozone, 

particulate ma�er and other 
pollutants is likely to be aﬀected 
by climate-induced changes in 
their local and regional abundance. 
Insuﬃcient information is available 
to assess changes in the sensitivity 
of humans to air pollutants because 
of climate change.

•  Because of the long response times 
involved in impacts of climate 
change, interactions with regard to 
impacts are believed to be of lesser 
signiﬁcance in the short to medium 
term than other types of linkages 
discussed in this report. 

Linkages of emission sources and 
control options
•  From a policy perspective, the most 
important linkages between climate 
change and air pollution exist at 
the level of emission sources. Air 
pollutants and greenhouse gases are 
o�en emi�ed by the same sources 
and hence changes in the activity 
levels of these sources aﬀect both 
types of emissions.

•  Technical emission control measures 
aiming at the reduction of one type 
of emissions from a particular source 
may reduce or increase the emissions 
of other substances. In the energy 
sector, eﬃciency improvements and 
increased usage of natural gas can 
address both problems (synergies), 
while desulphurisation of ﬂue gases 
reduces sulphur emissions but can 
— to a limited extent — increase 

carbon dioxide emissions (trade-
oﬀs). In agriculture, some speciﬁc 
measures to abate ammonia 
emissions could enhance nitrous 
oxide and/or methane emissions, 
while other types of measures would 
reduce these.

•  Energy scenarios that ignore the 
linkage between emissions of 
local and regional air pollutants 
and greenhouse gases ignore the 
constraints imposed by concerns 
about local and regional air 
pollution on the development of 
the energy system and thus tend to 
overestimate the potential growth of 
greenhouse gas emissions. Similarly, 
an integrated assessment across 
economic sectors is important to 
identify possible situations in which 
emission reductions in one sector 
or region of one type of pollutant 
would lead to increasing emissions 
in another sector or region.
Implementing climate policies, e.g. in 
order to achieve the Kyoto Protocol 
targets, can signiﬁcantly reduce the 
costs of meeting air quality targets. 
In the same way, meeting stringent 
air quality targets is at the same 
point likely to require measures 
beyond end-of-pipe technological 
solutions, and require broader 
structural changes (e.g. in the energy 
mix), consistent with climate goals. 

• 

Policy practices and opportunities
•  Opportunities for synergies and 
avoiding trade-oﬀs have been 
integrated into international 
air quality policies or policy 
negotiations in Europe, such as the 
'Clean Air For Europe' programme 
(CAFE) where the links between air 
pollution and climate change are an 
integral part of the analysis which 
will lead to the adoption of the 
Thematic Strategy on Air Pollution 
in mid 2005. Neither the Convention 
on Long Range Transboundary Air 
Pollution of the United Nations 
Economic Commission for Europe 
(UNECE CLRTAP), nor the current 
climate negotiations under United 
Nations Framework Convention on 
Climate Change (UNFCCC) address 

4

Air pollution and climate change policies in Europe

these issues on policy level. At the 
technical assessment level however, 
the opportunities are increasingly 
noted (Intergovernmental Panel on 
Climate Change — IPCC, UNECE 
Task Force on Integrated Assessment 
Modelling — TFIAM).

•  Linkages can be taken into account 
when designing diﬀerent types 
of policies such as economic 
instruments, regulatory policies, 
voluntary agreements, and 
awareness and education strategies. 
Policies targeting activities that 
release air pollutants and greenhouse 
gases (e.g. combustion of fossil fuels, 
intensive agriculture) rather than the 
emissions of one speciﬁc substance 
(like carbon dioxide, sulphur 
dioxide, or ammonia) have a larger 
potential for capturing possible 
synergies.

•  Climate change policies, if developed 
independently from air pollution 
policy, will either constrain or 
reinforce air pollution policies, 
depending on the choice and 
design of the policy instruments, 
and the other way around. From 
an economic perspective, policies 
that may not be regarded as cost-
eﬀective from a climate change or an 
air pollution perspective alone may 
be found to be cost-eﬀective if both 
aspects are considered.
If climate change considerations 
were to be taken into account when 
designing policies and measures to 
abate local and regional air pollution 
(and vice versa), the cost-beneﬁt 
equation and thus the relative 
priorities of policy options could 
change considerably; there is as yet 
no agreed operational framework to 
evaluate the importance of climate 
change versus air pollution. 

• 

Integrated assessment
•  The complex atmospheric 

interactions between air pollution 
and climate change are presently not 
understood suﬃciently well to allow 
their quantitative incorporation in 
integrated assessment modelling. 
Instead, these interactions should 
be taken into account in integrated 

assessment of the two issues in a 
qualitative fashion. The same counts 
for interactions between impacts of 
air pollution and climate change.
•  Suﬃcient knowledge is available 
to include quantitatively many of 
the linkages at the level of emission 
sources and control strategies in 
integrated assessment and integrated 
assessment modelling in the near 
future.
It is important to take into account 
the linkages between climate change 
and air pollution both in cost-
eﬀectiveness analysis (how to reach 
adopted environmental quality 
goals in the cheapest manner) 
and cost-beneﬁt analysis (what is 
the economically optimal level of 
abatement?).

• 

•  Choice and design of policies and 

measures to address climate change 
can aﬀect the spatial and temporal 
distribution of emissions and hence 
their eﬀectiveness in terms of air 
pollution. This needs to be taken into 
account in integrated assessment 
studies.

•  The experience acquired with a 

framework of models in previous 
European integrated assessment 
studies provides a good basis for 
future activities to include both air 
pollution and climate change. While 
components of this framework 
focusing on the two issues can 
be further improved to include 
linkages, a ‘so� link’ rather than a 
‘hard link’ between the components 
appears to be appropriate because 
of the disparate characteristics of the 
problems in terms of time, space, 
and complexity. 

In conclusion, there are various options 
to address the linkages between 
climate change and air pollution in 
diﬀerent EEA reporting activities. 
An immediate short-term example is 
the State of the environment and outlook 
report (SoEOR2005). For eﬀective 
communication of information about the 
links to policy-makers and the public, 
translation into indicators is required. 
We have given some preliminary 
suggestions for the development and 

Executive summary

5

implementation of such indicators. Some 
of these can be implemented at short 
notice, using the integrated assessment 
framework with associated models and 
information systems available to the 
EEA. Other indicators require further 
reﬂection, discussion with external 
experts, and elaboration.

6

Air pollution and climate change policies in Europe

1.  Introduction

1.1.  Aims and scope of the report

This report explores the linkages 
between air quality and climate change 
from a European perspective in order 
to assist the European Environment 
Agency (EEA) in approaching the issues 
of air quality and climate change in an 
integrated way. The report addresses 
the linkages between air pollution and 
climate change by:

(1)  collecting and summarising existing 
information from the literature on 
linkages between air pollution and 
climate change;

(2)  identifying gaps in current 

knowledge on linkages between air 
pollution and climate change;

(3)  assessing the relevance and 

signiﬁcance of linkages for diﬀerent 
control options;

(4)  prioritising issues for integrated 

assessment;

(5)  proposing preliminary indicators for 
the EEA for reporting on linkages.

1.2.  Rationale

Air pollution abatement policies in 
Europe have resulted in a number 
of protocols (Convention on Long-
Range Transboundary Air Pollution 
(CLRTAP) of the United Nations 
Economic Commission for Europe 
— UNECE CLRTAP) and directives 
(EU). These policies have increasingly 
been designed to be cost-eﬀective, i.e. 
meeting environmental requirements 
at minimum emission abatement costs. 
However, reaching cost-eﬀectiveness 
also depends on externalities in other 
areas, such as climate change. There 
is an increasing awareness in both 
the science and policy communities 
of the importance of addressing the 
linkages between the traditional air 
pollutants and greenhouse gases. 
Many of the traditional air pollutants 
and greenhouse gases have common 
sources, their emissions interact in the 

atmosphere, and separately or jointly 
they cause a variety of environmental 
impacts on the local, regional and 
global scales. Linkages work in two 
directions: there can be synergies and 
negative trade-oﬀs. Thus, emission 
control strategies that simultaneously 
address air pollutants and greenhouse 
gases may lead to a more eﬃcient use 
of the resources on all scales. The EEA 
seeks to address these linkages in an 
integrated manner in its reporting, 
scenario development and indicator 
development. 

The increasing awareness of the 
importance of addressing the linkages 
between the various environmental 
problems is reﬂected by a number of 
workshops that were organised  
around this topic in recent years 
(see Annex 8). The UNECE CLRTAP 
Task Force on Integrated Assessment 
Modelling (TFIAM), together with 
the European Topic Centre on Air and 
Climate Change (ETC-ACC) of the 
EEA, held a workshop on the linkages 
between air pollution and climate change 
at the International Institute for Applied 
Systems Analysis (IIASA) in Laxenburg, 
Austria (27 to 29 January 2003), to 
explore future directions for integrated 
assessment modelling under CLRTAP. 
The workshop reviewed the present 
scientiﬁc activities that investigate 
linkages between air pollution and 
climate change, pointing out the need 
for a systematic analysis of the synergies 
and trade-oﬀs throughout the full DPSIR 
(drivers, pressures, state, impacts, 
responses) chain.

This report takes the insights from this 
workshop into account. It addresses 
several aspects of the linkages between 
local and regional air pollution and 
stratospheric ozone depletion and 
climate change. It addresses atmospheric 
linkages, linkages of impacts and 
possible synergies in emission 
reductions and emission control 

Introduction

7

Box 1.1 Terminology (W.Tuinstra)

In this report we use the term linkages when referring to the connection between air 
pollution and climate change. We consider linkages in the broadest sense, ranging from 
atmospheric linkages to linkages in emission control and policies. Different terms to refer to 
these linkages exist in the literature, reﬂecting different disciplinary or policy perspectives. 
Below we provide an overview. However, sometimes the terms are used interchangeably in 
practice, and thus ambiguity exists.

In the ﬁeld of climate change the term ancillary beneﬁts or secondary beneﬁts is often 
used by economists to refer to monetised beneﬁts incidentally resulting from mitigation of 
greenhouse gas emissions, the primary beneﬁts being the reduction of climate change.

The term ancillary beneﬁts may also be used in a more general sense to indicate incidental 
beneﬁts resulting from the mitigation of a certain environmental problem other than the 
abatement of the environmental problem itself. Thus, air pollution mitigation may have 
ancillary beneﬁts in the area of climate change mitigation and the other way around or in 
other (non-environmental) policy areas. Ancillary effects may also be negative, thus being 
ancillary costs. The term ancillary beneﬁts and costs is used in the literature mostly to 
indicate incidental monetised effects, thus referring to the monetised value gained or lost to 
society by a positive or negative physical or social effect. However, the term is also used to 
describe physical impacts, such as reduced health risks.

According to Davis et al. (2000) the term co-beneﬁts (sometimes also referred to as 
multiple beneﬁts) refers to (possibly monetised) intentional effects of the combination of 
policy objectives (e.g. mitigating air pollution and climate change) looking at the costs and 
beneﬁts from an integrated perspective.

Other terms to indicate linkages between different environmental problems or other 
issues are side effects, knock-on effects, spin-off and synergies. Synergies implicate 
intentional (not monetised) effects and often refer to policies or reduction strategies from an 
integrated perspective.

strategies. Furthermore, it proposes 
preliminary indicators that could be 
used by the EEA to approach and report 
on linkages between air quality and 
climate change in a structured manner.

This report does not address co-
beneﬁts for other social, economic and 
environmental issues, such as waste 
disposal, traﬃc congestion, energy 
security and employment. In Box 1.1 we 
provide some deﬁnitions of the terms 
used.

1.3.  The issues

1.3.1. Regional and local issues

the early 1970s. The main acidifying 
compounds are sulphur dioxide (SO2), 
nitrogen oxides (NOx) and ammonia 
(NH3), which are mainly emi�ed during 
fossil fuel combustion (SO2 and NOx) 
and agricultural production (NH3). Once 
in the atmosphere, these pollutants are 
transformed, transported through the 
atmosphere and subsequently deposited 
on the earth’s surface. Acidifying 
deposition may be harmful to 
ecosystems of soil, water and forests and 
may also cause corrosion of metals and 
damage to buildings and monuments. 
Because of the long-distance 
atmospheric transport, acidifying 
deposition and its environmental impact 
in one country originates to a large 
extent from emissions in other countries.

Regional and local issues considered in 
this report are acidiﬁcation, tropospheric 
ozone, urban air pollution and 
eutrophication.

Acidiﬁcation has been recognised as 
a major environmental problem since 

Tropospheric ozone or ground 
level ozone formation is another 
transboundary air pollution problem 
that can have negative impacts on 
human health, agricultural crops 
and vegetation. NOx, volatile organic 
compounds (VOCs), CO and CH4 

8

Air pollution and climate change policies in Europe

contribute together to the formation 
of ground level ozone. Emissions are 
mainly caused by fossil fuel combustion 
(NOx and VOC), solvents (VOC) and 
agriculture (CH4). There is a non-linear 
relation between the concentration 
of ozone in the air and its precursors 
NOx, VOC, CO and CH4. Abatement 
of NOx emissions can lead to an 
increase or decrease in tropospheric 
ozone concentrations at ground 
level, depending on the NOx/VOC 
concentration ratio (Barre� and Berge, 
1996), but will always reduce ozone in 
the free troposphere.

Urban air pollution: NOx, benzene, 
PAHs, SO2, tropospheric ozone, 
particulate ma�er as well as other 
pollutants (e.g. CO, 1.3 butadien) all 
contribute to ‘urban air pollution’, 
which can cause damage and more 
speciﬁcally soiling to monuments 
and buildings; ozone and particulate 
ma�er (PM, but also called aerosols) 
in particular have shown to have 
adverse impacts on human health and 
are strongly related to the other air 
pollution problems (Lükewille et al., 
2001). Particulate ma�er is a complex 
conglomerate of water, particulates 
from natural origin (sea salt, wind-
blown dust) and primary and secondary 
organic (EC, OC) and inorganic (SO4, 
NO3, NH4) formed particulates. There 
is a non-linear relationship between the 
concentration of secondary particulate 
ma�er and its precursors. There are 
complex and poorly understood 
chemical linkages between ozone and 
secondary particulate ma�er formation 
in and around the urban atmosphere.

Eutrophication is the strong enrichment 
of ecosystems by nutrients (mainly 
nitrogen and phosphorus), which causes 
changes in ecosystems. NOx and NH3 
contribute to eutrophication.

1.3.2. Global issues

Global issues considered in this report 
are stratospheric ozone depletion and 
climate change.

Stratospheric ozone depletion is 
caused by increased levels of chlorine 
and bromide compounds in the 
stratosphere. These compounds 
result mainly from the emission of 
chloroﬂuorocarbons (CFCs) used as 
the coolant in refrigerators and air 
conditioners, aerosol propellants and 
foaming and cleaning agents, as well as 
bromoﬂuorocarbons (halons) used in 
ﬁre extinguishers. Stratospheric ozone 
depletion can be harmful as it results 
in higher ultraviolet (UV-B) radiation 
at ground level. UV-B can initiate a 
number of chemical and biological 
processes, which can damage living 
organisms (UNEP, 1994). CFCs but also 
their substitutes (HFCs) are powerful 
greenhouse gases.

Anthropogenic induced climate change 
is caused by an increasing concentration 
of greenhouse gases and changes of 
aerosol content in the atmosphere. Some 
greenhouse gases and aerosols occur 
naturally in the atmosphere, although 
certain human activities add to the levels 
of most of these naturally occurring 
gases, while others result solely from 
human activities. Greenhouse gases and 
aerosols are formed in or emi�ed into 
the atmosphere as a result of several 
human activities including fossil fuel 
burning, agricultural activities and 
deforestation. Important greenhouse 
gases are carbon dioxide (CO2), 
methane (CH4), ozone (O3), water 
vapour, nitrous oxide (N2O) and several 
ﬂuorinated compounds (such as CFCs, 
HCFCs, HFCs, PFCs and SF6). Unlike 
air pollutants and aerosols, the main 
greenhouse gases are uniformly mixed 
in the atmosphere because of their 
relatively long atmospheric lifetime. 
Therefore, the environmental impact of 
greenhouse gases does not depend on 
the location of the emissions. Ozone, 
however, has a medium lifetime.

1.4.  Categories of linkages

There are several interrelations between 
regional air pollution and climate 
change. White et al. (1989) provide an 
early overview of possible linkages. 

Introduction

9

Brink (2003) subdivides interrelations 
between air pollution and climate 
change into four categories: (i) emissions 
of one pollutant may contribute to 
regional air pollution as well as climate 
change; (ii) climate change and regional 
air pollution may have an eﬀect on 
each other and on emissions; (iii) air 
pollutants and greenhouse gases may 
be emi�ed by the same source; and (iv) 
technical measures to reduce emissions 
of greenhouse gases may aﬀect 
emissions of air pollutants and measures 
to reduce emissions of air pollutants 
may aﬀect greenhouse gas emissions.

An example of interrelations in category 
(i) is the role of SO2, which contributes 
to acidiﬁcation and also plays a role 
in climate change, partly oﬀse�ing 
the greenhouse eﬀect due to increased 
amounts of sulphate aerosols in the 
atmosphere. Examples of interrelations 
in category (ii) are the eﬀect of 
acidiﬁcation and nitrogen deposition 
on emissions of CH4 and N2O in some 
ecosystems and the eﬀect of increased 
temperatures on nitrate leaching. 
Moreover, linkages between regional 
air pollution and climate change may 
exist because climate change may 
alter atmospheric transport pa�erns 
of air pollutants and the sensitivity of 
ecosystems for acidifying deposition. 
Category (iii) contains another 
important linkage between regional air 
pollution and climate change. Because 
emissions contributing to regional 
air pollution and climate change are 
to a large extent emi�ed by the same 
sources, policies focusing on these 
sources to reduce one of these problems 
may have an impact on the other. This 
is in particular the case with policies for 
climate change, which largely focus on 
reducing CO2 emissions. CO2 emissions 
are almost entirely produced by burning 
fossil fuels, which is also an important 
source of several air pollutants. CO2 
emissions can be limited by reducing 
the use of fossil fuels through energy 
eﬃciency improvements and a shi� to 
renewable sources of energy. Climate 
policies leading to reduced fossil fuel 
use will have side beneﬁts, because 
emissions of air pollutants such as 

SO2, NOx and VOC will also decrease. 
Interrelations in category (iv) occur if 
technical measures to reduce emissions 
of air pollutants have an eﬀect on 
emissions of greenhouse gases and the 
other way around. Technical measures 
may have beneﬁcial as well as harmful 
side eﬀects. Examples are installing 
scrubbers in power plants to reduce SO2 
emissions causing an increase in CO2 
emissions through increased coal use, 
and three-way catalysts in cars reducing 
NOx and VOC but at the same time 
causing an increase in N2O emissions.

1.5.  Structure of the report

We will use the subdivision as presented 
in the former section to structure the 
remainder of this report. First we will 
discuss the physical and chemical 
linkages in the atmosphere between 
diﬀerent forms of air pollution and 
climate in Chapter 2 (category (i)). In 
Chapter 3 we will discuss linkages in 
impacts on humans and ecosystems 
(category (ii)) and in Chapter 4 we 
will discuss sources of emissions and 
linkages in control options (categories 
(iii) and (iv)). Chapter 5 discusses 
current policy practices and challenges. 
Chapter 6 provides an overview of 
recent European-scale projects that 
addressed linkages between several 
environmental issues in an integrated 
way. 

Each of the Chapters 1 to 6 starts with 
the key messages of that chapter. At the 
end of each of the Chapters 1 to 5 we 
propose indicators to assess and express 
linkages between climate change and 
air pollution issues with respect to 
atmospheric interactions, impacts, 
control options and international 
policies respectively. The EEA may 
ﬁnd the indicators useful to report on 
linkages between air pollution and 
climate change in a structured manner.

We conclude in Chapter 7 by proposing 
priority issues for further development 
of integrated assessment tools and 
summarising the proposed indicators. 

10

Air pollution and climate change policies in Europe

The Annexes provide summaries of 
selected European studies that adopted 
an integrated approach towards climate 
change and air pollution, as well as 
summaries of workshops on the issue 
and references to relevant websites.

Atmospheric linkages between climate change and air pollution

11

2.  Atmospheric linkages between 
climate change and air pollution

Key messages

•  Air pollutants such as ozone and particles contribute substantially to the radiative forcing 

of the atmosphere.

•  Particularly relevant for the linkages between climate change and air pollution is 

tropospheric ozone. Climate change, on the one hand, inﬂuences ozone concentrations 
through dynamical and chemical changes in the atmosphere. On the other hand, 
increasing background ozone concentrations in Europe affect climate change because 
ozone is a potent greenhouse gas itself and indirectly inﬂuences the lifetime of other 
greenhouse gases such as methane.

•  Particles have important health effects and are direct and indirect contributors to radiative 
forcing. The climatic effects of aerosols are dependent on their composition. Black carbon 
(soot) enhances warming, while other aerosol constituents (sulphates, nitrates, organic 
compounds) generally have a cooling effect. The net effect of reducing particulate matter 
(as required by the European national emission ceilings directive, mainly for health 
reasons) is probably leading to a further enhancement of the greenhouse effect. However, 
the issue of a net cooling/warming by aerosol critically depends on the highly uncertain 
effect of black carbon aerosol, which is at present strongly under debate. 

•  Methane is a greenhouse gas (GHG) and a precursor for tropospheric ozone; its lifetime is 
determined by the OH radical, a key trace gas in removing air pollutants and greenhouse 
gases from the troposphere.

•  Important feedbacks and interrelations between the gases (e.g. NOx–O3–N2O–CO2 cycle) 
and their effects on each other exist. However, they are quite complex and are often 
poorly understood.

•  Climate change induced stratospheric cooling is likely to delay the recovery of the 
stratospheric ozone layer by approximately 20 years. In turn stratospheric ozone 
determines tropospheric OH levels, important for air pollution, and the amount of 
detrimental UV radiation arriving at the earth’s surface.

•  More research is needed in order to understand the various atmospheric linkages and their 

distribution (e.g. ozone and particles) in the troposphere.

2.1.  Atmospheric linkages: 

substances that affect both 
air pollution and climate 
change

2.1.1. Radiative forcing of air pollutants

Emissions of one pollutant may 
contribute to regional air pollution as 
well as climate change. Important in 
this respect is the contribution of air 
pollutants to radiative forcing (see 
Box 2.1).

Air pollutants contribute to radiative 
forcing in direct and indirect ways. We 
distinguish:

•  air pollutants with direct radiative 

forcing like CO2, O3, CH4, N2O, NO2, 
HFCs, PFCs and SF6, and aerosols 

like sulphate aerosols and black and 
organic carbon and PM2.5;

and
•  air pollutants with indirect eﬀects 
on radiative forcing: all gases that 
inﬂuence OH (NOx, CO, VOC, H2O, 
etc.), O3 precursors (NOx, VOC, CH4, 
CO) and aerosol precursors (primary 
and secondary, including NH3). 

Many air pollutants can be seen as 
short-lived greenhouse gases and 
the control of radiative eﬀects of air 
pollutants may therefore oﬀer a faster 
response of the climate system than 
the control of major greenhouse gases, 
which are usually long-lived. However, 
the distribution of the short-lived gases 
varies highly in space and time and 
consequently it is diﬃcult to quantify 
their global radiative forcing eﬀects. 
Furthermore, the interrelations and 
feedbacks between the gases and their 

12

Air pollution and climate change policies in Europe

Box 2.1. Radiative forcing

The earth absorbs solar energy from the sun, redistributes it through atmospheric and 
oceanic circulations and radiates it back to space at longer wavelengths. Any factor that alters 
the radiation received from the sun or lost to space, or that alters the redistribution of energy 
within the atmosphere and between the atmosphere, land and ocean, can affect climate. 
A change in the energy available to the global earth-atmosphere system due to external 
changes is called radiative forcing (Wm–2) of the climate system. Radiative forcing of climate 
change constitutes an index of the relative global mean impacts on the surface-troposphere 
system due to different natural and anthropogenic causes.

Radiative forcing arises from changes in the atmospheric composition, alteration of surface 
reﬂectance by land use, and variation in the output of the sun. Except for solar variation, 
some form of human activity is linked to each. Positive radiative forcing tends to warm the 
earth’s surface and lower atmosphere and negative radiative forcing tends to cool. Increases 
in the concentrations of greenhouse gases will reduce the efﬁciency with which the earth’s 
surface radiates to space. Consequently more of the outgoing terrestrial radiation from 
the surface is absorbed by the atmosphere and re-emitted at higher altitudes and lower 
temperatures, which results in a positive radiative forcing that tends to warm the lower 
atmosphere and surface. The amount of radiative forcing depends on the size of the increase 
in concentration of each greenhouse gas, the radiative properties of the gases involved, and 
the concentrations of other greenhouse gases already present in the atmosphere.

Figure 2.1  The global mean radiative forcing of the climate system for the year 

2000, relative to 1750

3

2

1

0

i

g
n
m
r
a
W

g
n

i
l

o
o
C

-1

-2

)
2
-
m
W

(

g
n
i
c
r
o
F

e
v
i
t
a
d
a
R

i

Halocarbons

N2O

CH4

CO2

Tropospheric
ozone

Aerosols

Fossil
fuel
burning
(black
  carbon)

Mineral
Dust

Aviation-induced

Solar

Contrails 

Cirrus

Stratospheric
ozone

Sulphate

Fossil
fuel
burning
(organic
  carbon)

Biomass
burning

Land-
use
(albedo)

Tropospheric 
aerosol
indirect 
effect

(1st type)

High Medium Medium Low

Very
Low

Very
Low

Very
Low

Very
Low

Very
Low

Very
Low

Very
Low

Very
Low

Level of Scientific Understanding

Note: The rectangular bars represent estimates of the contributions of these forcings, some of which yield 

warming, and some cooling.

Source: Ramaswamy et al., 2001.

eﬀects on each other are quite complex. 
For example, an increase in NOx leads 
to a decreased lifetime of CH4 and HFCs 
(via OH) and thus to reduced radiative 
forcing (see also Box 2.2).

 
 
 
Atmospheric linkages between climate change and air pollution

13

Box 2.2  The OH radical (F. Dentener)

The main oxidant removing atmospheric trace gases from the troposphere is the hydroxyl 
(OH) radical (Levy, 1971). A net source of OH is the reaction of ultraviolet (UV) sunlight with 
ozone (O3) (R1), and water vapour (H2O) (R2):

O3 + hv  O(1D) 

O (1D) + H2O  2 OH 

R1

R2

O3 is produced by in situ photochemistry within the troposphere (formation of ‘air pollution’) 
and is also transported from the stratosphere (background ozone). UV radiation ﬂuxes are 
strongly dependent on the solar zenith angle and the overhead O3 column. Therefore OH 
levels are highest in the tropics where the stratospheric ozone layer is thinnest and the 
absolute humidity is highest.

The lifetime of OH is very short (1 second) and determined by a multitude of reactions and 
trace gas concentrations. The most important loss process of OH is the reaction with CO, CH4 
and hydrocarbons in general according to the following initial reactions:

CO + OH  CO2 + HO2 

RH + OH  RO2   

CH4 + OH  CH3O2 

R3a

R3b

R3c

Although CH4 and CO constitute efﬁcient OH sinks, these reactions do not necessarily strongly 
deplete OH because part of the radicals (e.g. HO2) can be recycled, e.g. by the action of 
nitrogen oxides (NOx ≡ NO + NO2) if sufﬁciently available.

OH can now be measured in situ on the local scale, but there exist no in situ or remote 
sensing techniques that provide insight on the concentrations and trends of OH on regional, 
hemispheric or global scales. The only indirect method to determine large-scale OH utilises 
information on emissions and concentrations of the anthropogenic trace gas methyl-
chloroform. However, especially the long-term and large-scale OH trends, derived using this 
method, are highly uncertain.

Therefore we have to rely on atmospheric models that include all abovementioned processes 
to estimated changes of the OH concentrations.

These models suggest that global OH decreased in the last century by – 9 to – 15 %. Further 
decreases by – 10 to – 20 % are expected to happen in the 21st century as indicated in the 
IPCC Third assessment report (Prather et al., 2001)

However, the exact impact of changing emissions on OH, and therefore on the concentrations 
of a number of short- and long-lived trace gases, will depend on the magnitude and mix of 
the emissions of precursor gases, such as NOx, CH4, non-methane-hydro-carbons (NMHC), 
and CO. Generally, NOx emissions will increase OH concentrations, and CH4, NMHC and CO 
reduce large-scale OH. A recently emerging policy option is the possibility of reducing CH4 
emissions, which would lead to less ozone formation, and to higher OH concentrations (Fiore 
et al., 2002).

An increase in NOx also leads to an 
increase in O3 which increases radiative 
forcing. At the same time a higher 
concentration of NOx in the atmosphere 
may lead to increased N-deposition 
causing higher soil fertilisation which 
can lead to more CO2 uptake by surface 
vegetation (depending on the level of N-
deposition and the type of vegetation), 
which leads to reduced radiative 
forcing. Furthermore, increased N-
deposition leads itself to increasing 

N2O emissions (see also Chapter 3 for 
linkages in impacts).

The net eﬀect of these processes on 
climate change is not clear. We elaborate 
in the next subsections on a limited 
selection of linkages: the role of aerosols, 
the linkage between tropospheric ozone 
pollution and climate change and 
vice versa, and the linkage between 
stratospheric ozone depletion and 
climate change. 

 
 
 
 
 
 
 
 
 
 
 
14

Air pollution and climate change policies in Europe

2.1.2. Aerosols and climate change

Aerosols are (sub)micron particles 
suspended in the air, also referred to 
as particulate ma�er. Atmospheric 
aerosols and clouds play a substantial 
role in the radiative forcing of the earth’s 
climate as they inﬂuence the radiation 
balance of the earth mostly through 
sca�ering and absorption processes. 
They have a residence time of few days, 
and are thus not evenly distributed 
in the atmosphere, with maximum 
concentrations close to their sources. 
There are still many uncertainties 
concerning the spatial distribution, 
the chemical composition of the 
tropospheric aerosols and especially 
the chemical coupling between PM and 
O3. Furthermore, and perhaps most 
importantly, aerosols have an important 
impact on health (see Boxes 2.3 and 3.3).

Aerosols can aﬀect the abundance of 
other greenhouse gases such as O3, since 
their presence reduces the amount of 
UV-radiation that reaches the lower 
troposphere (Papayannis et al., 1998, 
Dickerson et al., 1997 and section 2.1.4), 
however this eﬀect plays only a minor 
role in the overall radiative forcing of 
aerosols.

2.1.3. Tropospheric ozone pollution and 

climate change

Ground-level ozone is the major 
component of photochemical smog 
and elevated ozone concentrations. 
Tropospheric O3 is a direct greenhouse 
gas and has an extremely variable 
chemical lifetime ranging from weeks to 
months in the dry upper troposphere, 
to hours or less in the shallow nocturnal 
atmospheric boundary layer (ABL). The 
average lifetime in the troposphere is of 
the order of weeks.

The limited number of surface 
measurements in Europe, which date 
back to the late 19th century, suggest 
that the concentration of O3 has more 
than tripled in the 20th century. The 
lack of global information on pre-
industrial tropospheric O3 distributions 
is, however, a major uncertainty in the 

evaluation of the forcing of this key gas 
(Prather et al., 2001).

Ozone background concentrations
Ozone levels in the troposphere 
typically vary from less than 10 ppb over 
remote tropical oceans up to about 100 
ppb in the upper troposphere (Prather 
et al., 2001), and o�en exceed 100 ppb 
downwind of polluted metropolitan 
regions. The reason for this variation 
is the rapid chemical turnover, which 
makes it impossible to determine the 
tropospheric burden from the available 
surface sites only.

Ozone levels in Europe and global inﬂuences
Ozone peak values have been 
decreasing signiﬁcantly over the last 10 
years, whereas, on the other hand, the 
lower percentiles in the ozone values 
have increased in polluted areas and 
there is evidence of a general increase 
in the tropospheric O3 background. 
As ozone concentrations depend on 
the increasing emissions of ozone 
precursor gases, the observed ozone 
concentrations in Europe are also 
increasing, since emissions of these 
precursors are increasing. This increase 
in O3 concentrations is not only due 
to an increase in local emissions, but 
also due to the long-range transport of 
precursor emissions (a regional/global 
scale phenomenon), giving rise to 
the concentrations observed far from 
their initial source (or formation) area 
(Midgley et al., 2002).

Finally, another parameter (related 
to climate change) inﬂuencing the 
observed surface O3 levels in urban 
areas is the presence of aerosols. Since 
radical reactions in the atmosphere are 
driven by sunlight, they are directly 
aﬀected by temperature variations 
which change the rate of chemical 
reactions and by aerosols and clouds 
which a�enuate the intensity of 
ultraviolet radiation (see Subsection 
2.1.4). Moreover, O3 also inﬂuences 
the presence of other GHGs, since, for 
example, through the chemical impact 
of O3 on OH, the lifetime of CH4 is 
modiﬁed and although CH4 is much 
less abundant than CO2 in the earth’s 

Atmospheric linkages between climate change and air pollution

15

Box 2.3  Aerosols (F. Raes)

Aerosol particles in the atmosphere arise from natural sources such as wind-borne dust, 
sea-spray and emission of biogenic volatile organic compounds. They also arise from a 
range of anthropogenic activities, such as agriculture (e.g. tilling, waste burning), residential 
wood combustion and construction, road transport, but in particular the combustion of 
fossil fuels. Emitted directly as particles (primary aerosol) or formed in the atmosphere by 
(often photochemical) conversion of gaseous precursors (secondary aerosol), atmospheric 
particles range in size from a few nanometers (nm) to tens of micrometers (µm). A detailed 
description of the atmospheric processes leading to the formation of aerosols can be found in 
Raes et al., 2000.

Today, the interest in aerosols is high mainly because of their effect on human health and 
their role in climate change. They also have a determining effect on visibility and contribute 
to the soiling of monuments. They can also have effects on ecosystems and crops, both by 
contributing to deposition of toxic material to soils and foliage and by interception of UV 
(Bergin et al., 2001).

Aerosols and health
Epidemiological studies show that an increase in PM10 mass concentration by 10 µg m-3 results 
in an increase of 0.5–1.5 % in premature total mortality in case of short-term/episodic 
exposure, and in an increase up to 5 % in premature total mortality in case of long-term/
lifelong exposure (Wilson and Spengler, 1996). As yet, there is no indication which physical 
or chemical PM characteristic is responsible for these effects. However, recent research seems 
to indicate that PM10 is associated with respiratory responses and PM2.5 with cardiovascular 
diseases (Wyzga, 2002). Legislation in the EU and US is therefore expressed in terms of 
target values for PM10 and PM2.5 ( = the mass of particles with a diameter below 10 µm or 2.5 
µm, respectively).

Aerosols and climate
Observations and model calculations show that the increase in the atmospheric aerosol 
burden is delaying the global warming expected from the increase in greenhouse gases. 
Whereas the increase in GHGs since pre-industrial times is producing a warming of 2.4 Wm-2, 
the overall cooling effect of aerosols might be up to — 2.5 Wm-2 (Ramaswamy et al., 2001; 
Penner et al., 2001). The latter value is composed of contributions by, for example, sulphate 
and organic particles, which cool, and black carbon (BC), which heats. Modelling studies 
suggest that the abundance of BC (soot) relative to non-absorbing constituents has a strong 
inﬂuence on the magnitude of the cooling or warming effect (e.g. Hansen et al., 1997; Penner 
et al., 1998). Furthermore, an important parameter for the sign and magnitude of the effect 
is the state of mixing between BC and sulphate aerosols (Jacobson, 2001). Combustion 
processes are the dominant source for black carbon (e.g. Penner et al., 1993) and organic 
carbon (OC) is the largest single component of biomass burning aerosols (see e.g. Andreae 
et al., 1988). It should also be noted that the size of those particles mentioned largely 
corresponds with the PM2.5 fraction considered in relation to the health problem. International 
and EU climate change policies aim at reducing the emissions of greenhouse gases by 
implementing the Kyoto Protocol. It is expected that negotiations of reductions beyond the 
Kyoto Protocol might consider also the role of aerosols (Hansen et al., 2000).

Linkages
European air pollution policies such as the EC’s national emission ceilings directive, and the 
implementation of the EU standards for PM, are expected to reduce aerosol burdens by 50 % 
or more. The need to reduce PM pollution in the developing world is even larger. Taking the 
IPCC at face value, it is expected therefore that PM policies will aggravate the global warming 
problem, and more stringent climate change policies (i.e. GHG emission reduction policies) 
are required. However, more detailed analyses will be required that consider the effect of 
speciﬁc PM reduction policies, e.g. those focusing on black carbon, and that consider the 
regional climate effects of PM, before deﬁnite statements can be made.

atmosphere, the total warming eﬀect of 
CH4 is substantial.

2.1.4. Stratospheric ozone and climate 

change

The stratospheric ozone layer eﬀectively 
serves as a protective shield that reduces 

the harmful ultraviolet radiation 
(UV) reaching the earth’s surface and 
modulates outgoing IR radiation 
from the earth. As a consequence, 
the depletion of stratospheric ozone 
observed over the last two decades, 
probably caused by the emission of 
man-made halocarbons (CFCs, halons), 

16

Air pollution and climate change policies in Europe

Table 2.1 

Interaction stratospheric ozone-climate change 

e
d
u
t
i
t
a
l
-
d
m

i

l
a
c
i
m
e
h
C

x

x

x

x

x

e
d
u
t
i
t
a
l
-
d
m

i

l
a
c
i
m
a
n
y
D

x

x

x

r
a
l
o
p

l
a
c
i
m
e
h
C

r
a
l
o
p

l
a
c
i
m
a
n
y
D

l

o
c
o
t
o
r
P

l
a
e
r
t
n
o
M

X

x

x

l

o
c
o
t
o
r
P
o
t
o
y
K

x

x

x

x

x

?

Description

Catalytic ozone destruction in the stratosphere: 
decreased depletion is anticipated due to lower 
emissions of CFCs, halons, CCl4, CH3CCl3, HCFCs
Chemical destruction of ozone by NOx cycle; 
anticipated increase in N2O emissions
Formation of reservoir species HC1 decreases ozone 
destruction

Temperature dependence of the Chapman cycle: 
anticipated decrease in temperature in the 
stratosphere

Additional polar ozone loss by cooling and a stronger 
vortex combined with spread-out of ozone-depleted 
air into mid-latitudes
Increase in stratospheric H2O as a result of changes 
in dynamics and methane 
oxidation, and consequent chemical reactions that 
affect ozone

An increase of the stratospheric circulation intensity, 
leading to: 
• increase of tropopause height
• accelerated removal of CFCs from the atmosphere
• increase of transport subtropical air into mid-

latitudes

Source:  Kelfkens et al., 2002.

Process/ 
component

CFCs, halons

N2O

CH4

T (gas chem)

Polar vortex

H2O increase

Dynamics

has probably led to higher UV levels. 
Increased penetration of UV-B radiation 
leads among others (see Table 2.1) to 
more rapid photochemical destruction 
of CH4, thereby reducing its radiative 
forcing (Houghton et al., 2001).

Since the Montreal Protocol of 1987, 
a phase-out of ozone-depleting 
substances has been agreed upon. These 
countermeasures are expected to lead to 
a slow recovery of the ozone layer over 
the next century. It is expected that a slow 
recovery of the ozone layer will occur 
with a return to ‘normal’ (1980) levels 
around 2050 (WMO/UNEP, 2002; Slaper 
et al., 1996). Excess skin cancer risk, 
caused by ozone depletion, are in those 
scenarios expected to rise until 2050–70.

Growing insight into the radiative 
balance of the atmosphere and its 
disturbance by the continuous increase 
in greenhouse gas emissions indicates 
cooling of the stratosphere and a change 
in dynamical processes. These changes 

can have eﬀects on the ozone levels 
and furthermore they can interact with 
the chemical breakdown processes 
(Kel�ens et al., 2002).

Kel�ens et al. (2002) concluded, under 
the uncertainties given by the risk 
assessment, that climate change induced 
stratospheric cooling is likely to delay 
the recovery of the stratospheric ozone 
layer by approximately 20 years and as 
a consequence results in a higher and 
more persistent increase in (eﬀective) 
UV levels over Europe. In north-western 
Europe the increase in eﬀective UV 
(with ozone climate interactions) is 
expected to peak at 9.4 % (relative to the 
1980 level) around 2020 as compared to 
8.7 % extra UV (in 2000), with no ozone-
climate interaction assumed. 

Kel�ens et al. (2002) concluded that 
research on depletion of stratospheric 
ozone and research on climate 
change follow separate tracks. But the 
interactions between climate change 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Atmospheric linkages between climate change and air pollution

17

Table 2.2 

Illustration of the linkages between climate change and air pollution

SO2

NOx

NH3

VOC

CO

Primary 
PM+BC

CH4

CO2+ 
GHGs

Ecosystems

• Acidiﬁcation

• Eutrophication

• Ground level ozone

Health impacts

• Direct

• Indirect by sec. aerosols 

and ozone

Radiative forcing

• Direct

• Via aerosols

• Via OH

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

and ozone layer, summarised above, 
are so complex and may induce such 
(potential) important eﬀects that 
integration of these lines of research is 
recommended. Internationally, this asks 
for a closer cooperation of the panels 
active under the Montreal Protocol and 
the Intergovernmental Panel on Climate 
Change (IPCC).

2.2.  Overview of important 

compounds

In the previous subsections a selection of 
linkages has been presented following 
a thematic approach. In this section we 
present an overview of the involved 
compounds and their contributions to 
the diﬀerent environmental problems. 
Table 2.2 illustrates how the linkages 
between air pollution and climate 
change can be seen as a multi-pollutant/
multi-eﬀect problem extended towards 
radiative forcing.

Overall, although there is signiﬁcant 
scientiﬁc understanding of the chemical 
interactions between individual air 
pollutants, long-lived greenhouse gases 
and aerosols, the understanding of 
the complete relationship between the 
quantities emi�ed or formed and the 
concentrations eventually measured at 
diﬀerent time scales is low. Also, more 
precise determination of the chemical 
composition of aerosols is necessary in 
order to assess the overall net warming 
or cooling eﬀect, as this is the largest 
source of uncertainty among the 
radiative forcing, as described in the 
IPCC 2001 reports.

Moreover, tropospheric ozone 
background concentrations play an 
important role in the concentration 
of greenhouse gases and they also 
signiﬁcantly aﬀect urban scale air 
quality modelling. Hence, further 
studies aiming to determine ozone 
background concentrations in various 
locations should be conducted.

2.3.  Conclusions

The examples in the preceding 
paragraphs illustrate that air pollutants 
and greenhouse gases interact at 
various scale levels and that there is 
a clear link between air pollution and 
climate change. In particular, the fact 
that air pollutants can act as short-lived 
greenhouse gases and the complex 
contribution of aerosols to the overall 
greenhouse eﬀect deserve special 
a�ention.

2.4.  Proposed linkage indicators 

for the EEA

In order to assist the EEA to approach 
and report on linkages between 
air quality and climate change in a 
structured manner we propose here, 
as a ﬁrst, very preliminary step, some 
potential indicators that could be 
relevant for describing the linkages. 
As noted, not all identiﬁed linkages 
can be assessed and described yet with 

 
18

Air pollution and climate change policies in Europe

the current state of knowledge and 
modelling framework available.

Below we propose ‘state’ linkage 
indicators to describe the linkages 
between climate change and air 
pollution.

•  Contribution of European air 
pollutants to global climate 
change over time in Europe — This 
indicator can be developed on the 
short- to medium-time scale for most 
pollutants with the exception of 
black carbon. The proposed indicator 
can be expressed in diﬀerent ways: 
in concentrations terms (ppb/ppm), 
in CO2-equivalents (ppm-CO2 equiv.) 
or in their contribution to the global 
radiative forcing (W/m2).
•  Half-life time of the various 

air pollutants — This indicator 
describes the development of the 
half-life time of the various air 
pollutants and thereby indirectly 
provides a measure of the eﬀect that 
changes in atmospheric composition 
can have on the global warming 
potentials (GWPs). In the Kyoto 

Protocol, scaling factors are used 
to establish a common base for the 
eﬀect of a unit of CO2 reduction 
compared to other GHGs (GWP). 
This scaling factor is, among others, 
dependent on the half-life time of 
the air pollutant in the atmosphere. 
The half-life time is variable, 
depending on the development of 
the concentration of the OH radical 
in the troposphere. The development 
of this indicator is foreseen for the 
medium to the long term.

•  Climate change induced changes in 
weather pa�erns leading to changes 
in air pollution — This indicator 
refers to the change of frequencies 
of stagnant high pressure systems 
leading to high pollution events. 
Meteorological data (e.g. on high 
press. occ., and precipitation) are 
available. The development of this 
indicator is foreseen for the medium 
to the long term. Quite a number of 
research groups in Europe are trying 
to link climate change induced 
changes in weather pa�erns to ‘air 
pollution’.

3.  Linkages of impacts

Linkages of impacts

19

Key messages

•  Climate change can enhance but also lower the impacts of regional air pollution such as 

ozone and particles, and vice versa. 

•  Climate change is likely to impact natural emissions of ozone precursor gases (NOX, VOC) 
and of particles (mineral dust) and will therefore change the background concentrations of 
particles and ozone.

•  Impacts of climate change and air pollution on humans and ecosystems interact in 

two ways. On the one hand, climate change can change the exposure of humans and 
ecosystems to impacts of air pollution, and the other way round. On the other hand, 
climate change can affect the sensitivity of humans and ecosystems to speciﬁc impacts of 
air pollution and vice versa.

•  The exposure of ecosystems to air pollution can change as a result of phenological 

changes induced by climate change (e.g. changes in the length of the growing season) 
as well as by changed distribution of air pollutants through changed weather patterns. 
Their sensitivity may change as a result of, inter alia, climate-induced changes in soil 
processes, plant growth (both determining ecosystem vitality) and ecosystem composition.
•  The exposure of humans to the ozone, PM and other pollutants is likely to be affected by 
climate-induced changes in their local and regional abundance. Insufﬁcient information 
is available to assess changes in the sensitivity of humans to air pollutants because of 
climate change.

•  In general, linkages regarding impacts are surrounded by a relative high uncertainty. 
•  Because of the long response times involved in impacts of climate change, interactions 
with regard to impacts are believed to be of lesser signiﬁcance for the short to medium 
term than other types of linkages discussed in this report.

3.1.  Introduction

Climate change and regional air 
pollution may have an eﬀect on each 
other and on emissions.

In this chapter we summarise the 
interactions between climate change 
on the one hand and (i) regional air 
pollution and (ii) stratospheric ozone on 
the other hand regarding their impacts. 
The impacts of the three issues are o�en 
assessed separately. Many reasons exist 
for such a separate treatment (e.g. air 
pollution impact studies frequently 
focus on the term of one or two decades 
whereas studies of climate change 
o�en focus on the longer term, i.e. from 
decades to even centuries). However, 
there are also many interactions between 
the abovementioned issues, resulting 
in an ampliﬁcation or mitigation of 
impacts of acid and nitrogen deposition 
and stratospheric ozone by climate 
change and vice versa. Because of 
this interdependency, an integrated 
assessment of the impacts of the issues 
is desirable.

The interactions between climate 
change, air pollution and stratospheric 
ozone consist of two parts, both 
resulting in changed vulnerability of 
ecosystems and human beings. The 
approach is also used in other studies 
like the ‘Millennium assessment on 
biodiversity’ in which the vulnerability 
of the ecosystem to environmental 
changes will be assessed. Firstly, 
changes in climatic conditions may alter 
the (level of) exposure to air pollution 
and air pollution may inﬂuence climatic 
conditions (e.g. through the cooling 
eﬀect of sulphur aerosols). Likewise, 
climate change aﬀects the breakdown 
of the stratospheric ozone layer and 
therefore the UV-B exposure. Secondly, 
one environmental problem may change 
the sensitivity of human and natural 
systems to other issues, negatively or 
positively. We describe the linkages 
for both the exposure and sensitivity, 
including some examples. Firstly, the 
linkages are described for the impacts 
on ecosystems and biodiversity, 
followed by an assessment of impacts on 
human health. We also add statements 

20

Air pollution and climate change policies in Europe

Box 3.1  Examples of interactions between climate change and regional air 
pollution regarding the exposure to ecosystems (J. van Minnen)

•  Changing weather patterns may alter atmospheric distribution of air pollutants. Such 
changes are caused by changing wind patterns and changes in precipitation amounts 
and intensities. Alcamo et al. (2002) have shown that changes in precipitation amounts 
might be limited (this conclusion was based on climate change projections of a single 
climate model). Further research is needed on this issue. The intensity of precipitation will 
determine the atmospheric concentration and deposition of acidifying compounds on soils 
and water and as such the exposure of plants (Seip and Menz, 2002). 

•  Climate change parameters that lead to a longer growing season (e.g. higher temperature) 
increase the exposure of plants to air pollutants like SO2 and O3, whereas parameters that 
shorten the growing season (e.g. water stress) reduce the exposure and damaging effects 
of air pollutants (Guardans, 2002; Mauzerall, 2002).

•  Climate change affects ecosystem structure (e.g. growth stimulation under temperature 

increase or more frequent forest ﬁres under precipitation decrease). Ecosystem structure 
is one of the determinants of surface roughness (Claussen, 1994), which affects the 
deposition pattern of air pollutants (Draaiers, 1993).

•  Aerosols likely affect the CO2 uptake of plants and thus plant growth, for example through 
its effect on the quantity of radiation that reaches plants (Mauzerall, 2002). The net effect 
is species speciﬁc. 

about the uncertainties of the linkages, 
because the uncertainties are in general 
high.

3.2.  Ecosystems and biodiversity

The impacts of air pollution and climate 
change on ecosystems and biodiversity 
have been issued in many studies in 
the last decades. The studies showed, 
for example, that climate change 
impacts are already visible (e.g. plant 
distribution, reviewed by Gitay et al., 
2001) or that nitrogen deposition had 
large impacts on ecosystem composition 
(e.g. Van Breemen et al., 1998). The 
impacts on ecosystems are o�en treated 
separately for air pollution and climate 
change. However, recent studies show 
that climate change aﬀects various 
processes in the vegetation (e.g. growth) 
and soil compartment (e.g. weathering) 
of ecosystems that are important 
in determining the exposure levels 
(Box 3.1) and sensitivity (Box 3.2) of 
ecosystems to air pollutants and vice 
versa. Thus the combined eﬀect might 
diﬀer from the sum of separate eﬀects 
due to the interactions.

Some recent studies (such as those 
presented at the UNECE workshop 
on linkages and synergies; see 
Annex 7) concluded that climate 
change, air pollution and ozone all 
aﬀect ecosystems and biodiversity. 
Secondly, they concluded that a 
number of linkages exist between these 
stress factors, but that the net eﬀect is 
uncertain and can even go in diﬀerent 
directions. Impacts of acid deposition 
can be ampliﬁed or mitigated by climate 
change and vice versa (Skelly, 1993). The 
changes can be expressed in changed 
critical loads (Posch, 2002) or critical 
climate change (1) (Van Minnen et al., 
2002). Thirdly, various compounds 
are involved in the linkages between 
climate change and air pollution. 
Ozone and nitrogen are two important 
ones (Box 3.2). Fourthly, the studies 
concluded that the linkages vary over 
spatial and temporal scales. On a local 
scale, for example, climate change 
eﬀects on the surface roughness and 
therefore deposition pa�erns of air 
pollutants might be important, but on a 
regional scale these eﬀects will be less 
relevant for the total deposition. Finally, 
because of the complex interactions, 

(1)  Critical climate has been deﬁned as a ‘quantitative magnitude of climate change above which unacceptable 
long-term effects on ecosystems may occur, according to current knowledge’ (Van Minnen et al., 2002). 
The method in the current stage only deﬁned thresholds for changes in monthly mean temperature and 
precipitation.

Linkages of impacts

21

Box 3.2  Examples of the interactions between climate change and regional air 
pollution regarding the sensitivity of ecosystems (J. van Minnen)

Soils
•  Climate change most likely alters many soil processes, having consequences for the entire 
ecosystem. For example, climate change (especially temperature) affects the weathering 
rate of soils and thus the cation availability. Cations are important drivers of the buffer 
capacity of soils and thus the sensitivity of plants to air pollution (Posch, 2002). Posch 
showed for a number of climate change scenarios that climate change increases the 
weathering rate in many regions of Europe, resulting in higher critical loads (i.e. lower 
sensitivity of ecosystems to air pollutants). In some other areas, however, ecosystems 
might become more sensitive to air pollution with climate change, especially regions 
projected to become drier.

•  Likewise, climate warming may increase the mineralisation process in soils. This leads to 
more nitrogen in the soil. The nitrogen availability also increases by deposition (through 
air pollution). On the one hand, the increased nitrogen availability results in more nitrogen 
available for plants. This, in turn, increases plant growth and thus the C sink (especially 
if nitrogen is the limiting compound; Bazzaz and Sombroek, 1996), and enhances the 
response of an ecosystem to increased CO2 levels in the atmosphere and changes in 
temperature. On the other hand, an overload of nitrogen leads to eutrophication and 
changed ecosystem composition (Alkemade et al., 1998; Van Oene and Berendse, 2002), 
decreased vitality of ecosystems, and increased emissions (N2O) and leaching of nitrogen 
(Grennfelt et al., 1994; Van Breemen et al. 1998; Bouwman and van Vuuren, 1999) 
The changes in ecosystem composition and vitality may increase the sensitivity of an 
ecosystem to other stress factors. 

Direct effects on plants
•  Ozone affects the stomatal activity of leaves and as such increases the sensitivity of plants 

to reduced moisture availability (e.g. Mortensen et al., 1995; Emberson et al., 2000).
•  Climate change parameters that trigger stomata opening (e.g. increasing temperature, 
humidity) increase the sensitivity of plants to air pollutants like SO2 and O3. Parameters 
that lead to stomata closure (e.g. water stress, increased CO2) help to protect the plant 
from damaging effects of air pollutants. The net effect varies for different ecosystem types 
(natural and managed), type of interaction, the concentration of the pollutants and regions 
(Bazzaz and Sombroek, 1996; Mauzerall, 2002). 

•  Ozone decreases the winter hardiness of many agricultural and natural species. Thus, 

increased ozone levels may increase the risk of frost damage (reviewed by Bazzaz and 
Sombroek, 1996).

Ecosystem composition
•  Temperature and precipitation are factors that determine ecosystem composition directly 
(details, for example, in Leemans et al., 1996; Leemans and Hootsman, 1998). As such 
climate change may result in changes in ecosystem composition. Such changes have 
been observed under historic climate change (e.g. Prentice et al., 1998) and are also 
projected for the future (e.g. White et al., 1998; Sitch et al., 2003). Since critical loads 
of air pollution are species speciﬁc, the critical loads in a region may change if ecosystem 
composition changes, meaning that the sensitivity to air pollution changes.

•  Also air pollution (especially nitrogen) affects ecosystem composition (e.g. Alkemade 

et al., 1998; Van Oene and Berendse, 2002). This may change the sensitivity of 
an ecosystem to climate change (e.g. the response to increasing CO2 levels in the 
atmosphere). 

new environmental impact models 
should be developed that are capable 
of assessing changes in multiple stress 
factors on diﬀerent scales.

3.3.  Human health

Numerous publications exist regarding 
the impacts of air pollution (e.g. through 
particles and ozone) and climate change 
(e.g. through heat-related mortality and 

vector-borne diseases) on human health. 
In this report we will not describe the 
separate relationships, but focus on the 
interactions between air pollutants and 
climate change and the consequences 
for human health. Similar to ecosystems, 
the linkage between climate and air 
pollution can be categorised in linkages 
with respect to the exposure and 
sensitivity of humans to one of the 
issues. Regarding the former, various 
linkages are described in Box 3.3. 

22

Air pollution and climate change policies in Europe

Box 3.3  Examples of interactions between climate change and regional air 
pollution regarding the exposure of humans (J. van Minnen and H. C. Eerens)

•  Climate change may affect distribution patterns and atmospheric mixture of pollutants. 
This may lead to changes in the frequency and extent of episodes (e.g. ozone and PM10) 
and thus damages to human health.

•  Ozone exposure changes under climate change. The changes are initiated in two ways. 

Firstly, climate change may result in increased emissions of pollutants. Secondly, 
temperature is one of the drivers of ozone exposure. Increased temperatures, especially 
in the summer, will result in a higher background concentration and in more and longer 
ozone episodes. Anderson, Derwent and Stedman (2001) show that elevated O3 episodes 
in the UK especially occur when the daily temperature exceeds 25 oC. Such conditions 
will occur more frequently under climate change. This can have severe consequences for 
human health both in the short and long term (Van Bree, personal communication).

•  Increased (annual) temperatures result in less extreme winters, resulting in less exposure 

to ﬁne particulates. The exposure to particulates may also be reduced by various 
greenhouse gas mitigation policies. Reduced exposure to these particulates can increase 
life expectancy by two to three years (Kovats et al., 1999; Mechler et al. 2002). Vice 
versa, policies to reduce particulate emissions (e.g. because of health reasons) might 
contribute to climate change control, depending on the type of particles that are reduced 
(see section 2.1.2).

•  Particulates are both drivers of climate change and air pollution. Their spread and 

concentration depend on climate conditions. The concentration in the lower atmosphere 
can, for example, largely increase under cold weather conditions with less wind. In Europe 
such cold periods might occur less frequently under climate change (Kovats et al., 1999).
•  In Subsection 2.1.4 we discussed the effect of climate change on the recovery process of 
the stratospheric ozone layer, including some of the uncertainties. Climate change may 
slow down the recovery, causing more UV-mediated skin cancer (Figure 2.4). Kelfens et 
al. (2001) quantiﬁed the excess skin cancer risk in 2070 for the mid-latitudes in Europe, 
considering some of the uncertainties. They showed that between 50 and 150 extra cases 
per million inhabitants per year may occur (compared to the situation of no delayed 
recovery of the ozone layer).

Figure 2.4 Increase in skin cancer incidence in 2070

Skin cancer: 2070 relative to 1980; 
with ozone-climate interaction

Extra skin cancer in 2070; 
with ozone-climate interaction rel. to no interaction

action spectrum: 
SCUPh excess cases
per milion per year

< 0
0–25
25–50
50–75
75–100
100–125
125–150

action spectrum: 
SCUPh excess cases
per milion per year

< 0
0–10
10–20
20–30
30–40
40–50
50–60
60–70

Note: The change in risk is expressed as the number of extra cases per million inhabitants per year 

(comparing projected number of cases with ozone–climate interaction and without ozone–climate 
interaction). Computations are based on the UV sensitivity of the Dutch population.

Source: Kelfkens et al., 2001.

With respect to exposure, particles are 
critical for the linkages between air and 
climate change because the net eﬀect of 
reduction on climate change is unclear 
whereas the net eﬀect on human health 
is positive (see Box 3.4 for details). We 
deﬁned one indicator for this linkage to 
quantify the climate change eﬀect on the 
frequency of ozone and PM episodes.

Regarding the sensitivity of humans 
to air pollution and climate change, 
only a limited amount of information 
is available regarding the linkage. One 
example of a linkage is that humans 
may become less prone to respiratory 
infections (e.g. inﬂuenza) under 
increasing temperatures, resulting, 
in turn, in a lower sensitivity to air 

 
    
  
 
 
 
 
 
 
 
    
  
 
 
 
 
 
 
 
 
   
  
  
  
 
 
 
 
   
  
  
  
 
 
Linkages of impacts

23

Box 3.4  Health risks of ﬁne particulates

Introduction
Particles such as sulphate have a negative radiative force (cooling) and compensate some 
of the positive radiative forcing of GHGs (see Box 2.3) From an air pollution point of view, 
further reductions of certain particles are important. 

Expected health effects
The ‘Global burden of disease’ project has recently expanded its analysis of the impact of 
common risk factors on health to include environmental factors. It has been estimated that, 
worldwide, close to 1 000 000 premature deaths occur due to long-term exposure to high PM 
concentrations (Ezzati et al., 2002).

Such effects are to be seen as a reduction of life expectancy by a few years, and increased 
infant mortality in the more highly exposed areas (Brunekreef, 1997; Bobak and Leon, 1999), 
increased bronchitis rates, reduced lung function and perhaps other chronic effects. For 
almost all types of health effects, data are available not only from studies conducted in the 
US and Canada (Dockery et al., 1996; Raizenne et al., 1996), but also from Europe (Braun-
Fahrlander et al., 1997; Nyberg et al., 2000), which adds strength to the conclusions. 

Vulnerable groups
The very young and the very old, as well as persons with lower socioeconomic status, are 
apparently especially affected by PM air pollution (Gwynn and Thurston, 2001; Krewski et 
al., 2000; Pope et al., 2002). In the time-series studies, it has been well established that 
elderly subjects (and, possibly, very young children) are more at risk than others (Schwartz, 
1994). Subjects with pre-existing cardiovascular and respiratory disease are also at higher 
risk (Dockery, 2001; Goldberg et al., 2001). This is remarkably similar to the experiences 
of the populations exposed to the London 1952 smog episode. Children with asthma and 
bronchial hyper-responsiveness have also been shown to be more susceptible to ambient PM 
(Boezen et al., 1999; Pope and Dockery, 1992) although effects have been observed in non-
symptomatic children as well. 

Main sources contributing to the health effects of particulates
The short-term studies suggest that a number of source types are associated with mortality, 
including motor vehicle emissions, coal combustion, oil burning and vegetative burning. Some 
studies have also implicated trafﬁc as one important source of PM related to morbidity and 
mortality in time-series studies (Hoek et al., 2002; Janssen et al., 2002; Roemer and van 
Wijnen, 2001a; Roemer and van Wijnen, 2001b).

Source:  Brunekreef and Dybing, 2003.

pollutants and particulates (Kovats et 
al., 1999). The relationship is, however, 
still uncertain. Therefore this aspect 
and other aspects need to be further 
researched. In contrast, climate change 
may result in increased temperatures in 
summer, potentially causing a higher 
sensitivity to ozone.

3.4.  Proposed linkage indicators 

for the EEA

In order to assist the EEA to approach 
and report on linkages between 
air quality and climate change in a 
structured manner we propose here, 
as a ﬁrst, very preliminary step, some 
potential indicators that could be 
relevant for describing the linkages. 
As noted, not all identiﬁed linkages 

can be assessed and described yet with 
the current state of knowledge and 
modelling framework available.

We identiﬁed various indicators 
to illustrate the linkages between 
air pollution and climate change 
regarding the impacts and to assess 
the eﬀectiveness of diﬀerent policies 
(see Table 3.1). A ﬁrst criterion to 
deﬁne the indicators was, obviously, 
the assessment of linkages. As such, 
separate indicators for both issues 
(as they are currently developed for 
climate change state and impacts) 
(Erhard, Voigt and Van Minnen, 
2002) are excluded. Secondly, the 
indicators should be easy to understand 
and relevant to both scientists and 
stakeholders. Therefore a number of 
policy eﬀectiveness indicators (e.g. the 

24

Air pollution and climate change policies in Europe

Table 3.1 

Impact and response indicators for the relationship between climate change 
and air pollution

Indicator

Climate change effect on percentage area 
exceedance of critical loads (total acidity)

Climate change effect on percentage area 
exceedance critical loads (total nitrogen)

Climate induced change of emissions

Climate change effect (esp. temperature) on 
frequency of episodes of air pollutants

Unit

DPSIR 

Development 
time (1)

Type (2)

 % change

 % change

 % change

 % change

I

I

I

I

I

S

S

S

M

M

Mo

Mo

Me, Mo

Mo

Mo

Nitrogen effect on climate change induced changes 
in ecosystem composition

Additional % 
change

DPSIR = ‘Driving forces, pressure, state, impacts, response’; note that the type of indicator can be different from a 
climate change or air pollution perspective.

(1)  Development time means the time period that an indicator becomes applicable for assessments.  

S = short (0–2 years), M = medium (3–5 years), L = long (6–10 years).

(2)  Indicator type illustrates the main source of information. Me = measurements (past trends),  

Mo = modelling (scenarios).

CC eﬀect on the eﬀectiveness of air 
pollution policies) have been selected. 
A ﬁnal criterion was the scientiﬁc 
soundness and related uncertainty. As 
mentioned before, linkages of climate 
change and air pollution impacts are in 
general surrounded by a relative high 
uncertainty. Some exceptions exist, 
however, such as the climate change 
eﬀect on critical loads. Therefore the 

climate change eﬀect on critical loads 
(both acidity and nitrogen) have been 
deﬁned as indicators that are applicable 
in the short term, whereas the eﬀects of 
air pollution on climate change impacts 
are less clear. An example of the la�er 
type of indicator is the ‘nitrogen eﬀect 
on climate change induced changes in 
ecosystem composition’ that has been 
deﬁned as a medium-term indicator.

Linkages in emissions and control options

25

4.  Linkages in emissions and control 

options

Key messages

•  From a policy perspective, the most important linkages between climate change and 

air pollution exist at the level of emission sources. Air pollutants and greenhouse gases 
are often emitted by the same sources and hence changes in the activity levels of these 
sources affect both types of emissions.

•  Technical emission control measures aiming at the reduction of one type of emission 
from a particular source may reduce or increase the emissions of other substances. 
In the energy sector, efﬁciency improvements and increased usage of natural gas can 
address both problems (synergies), while desulphurisation of ﬂue gases reduces sulphur 
emissions but can — to a limited extent — increase carbon dioxide emissions (trade-offs). 
In agriculture, some speciﬁc measures to abate ammonia emissions could enhance nitrous 
oxide and/or methane emissions, while other types of measures would reduce these.
•  Energy scenarios that ignore the linkage between the emissions of local and regional 

air pollutants and greenhouse gases ignore the constraints imposed by concerns about 
local and regional air quality on the development of the energy system and thus tend to 
overestimate the potential growth of greenhouse gas emissions. Similarly, an integrated 
assessment across economic sectors is important to identify possible situations in 
which emission reductions in one sector or region of one type of pollutant would lead to 
increasing emissions in another sector or region.

•  Implementing climate policies, e.g. in order to achieve the Kyoto Protocol targets, 

can signiﬁcantly reduce the costs of meeting air quality targets. Conversely, meeting 
stringent air quality targets is likely to eventually require measures beyond end-of-pipe 
technological solutions, and require broader structural changes (e.g. in the energy mix), 
consistent with climate goals.

4.1.  Linkages in emissions and 

control options

Many measures to abate air pollution 
also beneﬁt the climate through 
reduction of GHG emissions, and 
vice versa. For achieving overall 
cost-eﬀectiveness, it is necessary to 
understand these synergies in emission 
controls and to address local, regional 
and global objectives simultaneously 
rather than separately. As marginal 
costs of further air pollution abatement 
measures tend to increase rapidly 
once a certain reduction level has 
been achieved, any potential for cost 
savings for strategies to reach air quality 
objectives must be explored. Synergies 
may free resources that allow reaching 
more ambitious targets. Many of the 
driving forces underlying air pollution 
and climate change are identical: 
economic growth, consumption and 
production processes, and demography. 
A sustainable development strategy 
must address these issues in an 
integrated manner.

Emissions of air pollutants and 
greenhouse gases may be interlinked in 
various ways:

•  Air pollutants and greenhouse gases 
are simultaneously emi�ed from 
the same sources. Any measure 
modifying the activity level of a 
source (e.g. energy conservation, fuel 
substitution, change in production 
level, etc.) thus inﬂuences emissions 
of air pollutants and greenhouse 
gases simultaneously.

•  Certain technical emission control 

measures have eﬀects on more than 
one pollutant. Thus, measures aimed 
at the reduction of one pollutant may 
lead to reductions or increases of 
other pollutants.

A number of studies have addressed the 
synergies and trade-oﬀs emerging from 
these linkages.

Energy emission models have been 
used to demonstrate that the structural 
changes of energy strategies that are 

26

Air pollution and climate change policies in Europe

implemented to control CO2 emissions 
(e.g. less coal use) result in many cases 
also in lower emissions of air pollutants 
(Barker and Rosendahl, 2000; RIVM et 
al., 2001, Rentz et al., 1994; Syri et al., 
2001).

to enhance natural gas infrastructure, 
while reducing global CO2 emissions, 
may increase SO2 emissions in other 
regions due to the possible risk of 
switching to coal in gas-exporting 
countries.

It has also been shown that global 
energy scenarios that ignore the linkage 
between the emissions of local and 
regional air pollutants and greenhouse 
gases overlook the constraints imposed 
by concerns about local and regional 
air quality on the development of 
the energy system and thus tend to 
overestimate the potential growth of 
greenhouse gas emissions (Nakicenovic 
et al., 1995; Amann et al., 1995).

If air quality is safeguarded by 
appropriate provisions (such as national 
emission ceilings), emissions of air 
pollutants and emissions of greenhouse 
gases can, up to a certain extent, be 
decoupled through the application of 
emission control technologies. However, 
it has been demonstrated that in such 
a case energy strategies that result 
in lower GHG emissions enable the 
compliance with emission ceilings at 
signiﬁcantly lower costs due to the 
lower volume and diﬀerent structure of 
energy consumption.

For Europe, Syri et al. (2001) and the 
EEA (2004) have estimated that the costs 
of controlling regional air pollution, 
including the costs of implementation 
of the emission ceilings of the national 
emission ceilings directive and of the 
Gothenburg Protocol, could be reduced 
by up to 10 %. These cost savings 
compensate 20 to even more than 50 % 
of the additional costs incurred by the 
constraint on carbon emissions. Similar 
results were obtained by Alcamo et al. 
(2002).

To be eﬃcient, such strategies must 
be considered in their full context. A 
limited focus (e.g. on single countries) 
might invoke even counterproductive 
eﬀects in an international context.

For instance, Klaassen et al. (2002) have 
pointed out that a regional strategy 

It is also important that such an analysis 
include all economic sectors. The 
increased use of biomass in the domestic 
sector that occurred in recent years in 
some EU countries has contributed 
to the reduction of CO2 emissions but 
has increased emissions of PM, CO, 
VOC and PAH emissions from this 
sector (compare, for example, IIASA, 
2002). In Asia, a replacement of coal by 
renewables in the electricity sector may 
result in higher use of coal in some other 
sectors, where less technical potential 
for emission controls exists, so that, as 
a consequence, SO2 and PM emissions 
might increase (Klaassen et al., 2002).

A recent EEA study (EEA, 2004) points 
out that economic instruments, such 
as GHG emissions trading systems, 
can have signiﬁcant eﬀects on the 
distribution and levels of air pollution 
emissions. While carbon trading within 
Europe can reduce the overall costs of 
emission reductions for given carbon 
targets, it tends to shi� the signiﬁcant 
co-beneﬁts of abatement measures 
from western Europe to other regions. 
Unconstrained trading of GHG may 
not be cost-eﬀective, if air quality 
objectives are taken into account. In 
some countries, GHG trading may not 
make sense, as the structural measures 
for CO2 abatement may be necessary to 
achieve the emission reductions (e.g. 
for NOx) that are required to comply 
with the national emission ceilings. 
The other linkage between emissions of 
air pollutants and greenhouse gases is 
related to the eﬀect of technical emission 
control measures on multiple pollutants.

There are a number of emission 
control technologies that reduce both 
air pollutants and greenhouse gases. 
For instance, some of the measures 
in the agricultural sector that reduce 
NH3 emissions (e.g. dietary changes, 
improved storage of manure) also 

Linkages in emissions and control options

27

lead to lower N2O emissions (Brink et 
al., 2001a). Under certain conditions, 
new engine technologies that improve 
fuel eﬃciency and thus reduce CO2 
emissions also have, at the same time, 
lower NOx emissions. Selective catalytic 
reduction (SCR) on gas boilers reduces 
not only NOx, but also N2O, CO and CH4 
(IPCC, 1997). The three-way catalysts 
on cars reduce NOx, CO and CH4. 
Regular inspection and maintenance 
programmes on oil and gas production 
and distribution facilities will reduce 
losses of CH4, but also of other VOCs.

There are, however, several examples 
where, at least in principle, emission 
control technologies aimed at a certain 
pollutant could increase emissions of 
other pollutants. This is the case for 
all emission control measures that 
increase energy consumption and thus 
the related emissions of greenhouse 
gases. Desulphurisation techniques 
involving CaCO3 increase CO2 emissions 
(IPCC, 1997), and catalysts that are 
used to reduce NOx, VOC and CO 
emissions from vehicles tend to cause 
higher N2O and NH3 emissions (e.g. 

Becker et al., 1999; Baum et al., 2000). 
Also the substitution of gasoline 
engines with more fuel-eﬃcient diesel 
engines might lead to higher PM/
black carbon emissions (EC, 1998). 
A similar eﬀect holds for the new 
direct injection gasoline (GDI) engines 
(Kwon et al., 1999; Lappi et al., 2001). 
Options to reduce losses of NH3 from 
the application of manure (e.g. deep 
injection) may result in an increase of 
emissions of N2O from soils (Brink et al., 
2001a).

While some of these eﬀects are well 
documented, their quantitative 
relevance in an overall emission 
control strategy needs to be examined. 
Not many studies are available that 
have addressed such issues. Brink 
et al. (2001b) have analysed for the 
agricultural sector the spillover eﬀects 
of NH3 controls on CH4 and N2O 
emissions, and vice versa, and found 
that the impact of cost-eﬀective NH3 
abatement strategies on N2O and CH4 
emissions diﬀers between countries, 
depending on the NH3 control options 
applied. Most importantly, Brink (2003) 

Box 4.1  Integrated studies (C. Brink)

For some countries, integrated studies have been carried out addressing the joint abatement 
of CO2 emissions and air pollutants. The two studies below monetise the effects of CO2 
abatement.

Interactions in reducing energy-related emissions in Belgium
Proost and Van Regemorter (2001) perform an integrated optimisation analysis for reducing 
energy-related emissions of air pollutants and greenhouse gases. They adapted the Markal 
model for Belgium to include atmospheric transport and location speciﬁc damages from 
pollution, including damage across the border. They consider monetary values of impacts 
of Belgian emissions on public health, terrestrial ecosystems and materials. Like most of 
the literature on ancillary beneﬁts of CO2 abatement, interactions between greenhouse gas 
reduction policies and air pollution occur because energy efﬁciency improvements reducing 
CO2 emissions simultaneously reduce emissions of SO2, NOx, VOC and PM. In addition, they 
include speciﬁc abatement technologies for air pollutants.

Beneﬁts of energy saving in Hungary
The potential importance of beneﬁts related to public health resulting from CO2 mitigation 
policies is indicated in an assessment of the cost and beneﬁt of energy saving in Hungary, 
originally designed to reduce CO2 emissions (Aunan et al., 1998; Aaheim et al., 1999). 
Aunan et al. (1998) give an extensive overview of the various effects of energy saving in 
Hungary, namely reduced damage to public health, building materials and agricultural crops 
obtained from reducing emissions of air pollutants, as well as reductions in greenhouse gas 
emissions. The beneﬁts (i.e. avoided damages) are monetised in order to be able to add up 
various effects of reduced energy consumption. They conclude that the dominant beneﬁt of 
the energy-saving programme relates to public health through reduced concentrations of air 
pollutants. Reduced damage to materials also gives signiﬁcant beneﬁts. Compared to the 
reduction in the local and regional effects, the beneﬁts from reducing GHGs are likely to be 
minor (Aaheim et al., 1999).

28

Air pollution and climate change policies in Europe

has shown that it is possible to cut 
ammonia emissions signiﬁcantly and at 
the same time reduce nitrous oxide and 
methane emissions.

Thus, in order to maximise the synergies 
and to avoid negative spillover eﬀects 
from emission control strategies to other 
pollutants, it is necessary to carefully 
design the basket of measures and the 
timing of their application. Example 
studies are presented in Box 4.1.

This temporal aspect is important 
because of the diﬀerent lifetimes of air 
pollutants and greenhouse gases in the 
atmosphere, the diﬀerent time scales 
of their impacts and the need to avoid 
‘locking in’ into short-term strategies 
that disable the long-term structural 
changes that are necessary for managing 
sustainable climate futures (Gritsevskyi 
and Nakicenovic, 2000).

Integrated assessment of linkages 
between climate relevant gases and 
air pollutants in Europe requires 
building a new model that will capture 
interactions among pollutants and allow 
systematic exploration of co-beneﬁts at 
the continental as well as at the national 
level (Amann et al., 2003). This model 
needs to be linked with tools used for 
designing longer-term energy and 
climate policies. When building such 
links it is necessary to harmonise the 
methodologies and the assumptions 
used by diﬀerent modelling tools. 
Depending on the purpose of the 
analysis, models applied in the climate 
policy debate use diﬀerent cost concepts 
(welfare loss due to imposition carbon 
constraint, or the increase in the energy 
system cost). They also use diﬀerent 
interest rates. In many studies oriented 
towards identiﬁcation of the reaction 
of energy consumers to higher energy 
prices induced by the carbon constraint, 
the market interest rate is used. Since 
the expenditures on air pollution control 
are usually treated as infrastructure 
investments, a much lower social 
discount rate is used. Some energy 
system models include the expenditures 
on air pollution control, some do not. 
Thus, in order to avoid double counting, 

it is necessary to check the scope of costs 
included in the two types of models and 
also to unify other assumptions. More 
remarks on problems with linking air 
pollution and climate change models are 
to be found in EEA (2004).

4.2.  Conclusions

Air pollutants and greenhouse gases are 
o�en emi�ed by the same sources, and 
changes in the activity of these sources 
aﬀect both types of sources. Technical 
control measures to reduce a pollutant 
may reduce or increase the emissions of 
other substances.

From a policy perspective, the most 
important linkage between climate 
change and air pollution exists at the 
emission sources.

Integrated assessments across economic 
sectors, taking into account all relevant 
pollutants, are important to identify 
possible options to simultaneously reach 
air pollution and climate change goals in 
the most cost-eﬀective way, and to avoid 
one-issue solutions with unknown side 
eﬀects.

Implementing climate policies, for 
example in order to achieve the Kyoto 
Protocol targets, can signiﬁcantly 
reduce the costs of meeting air quality 
targets. Conversely, meeting stringent 
air quality targets is likely to eventually 
require measures beyond end-of-pipe 
technological solutions, and require 
broader structural changes (e.g. in the 
energy mix), consistent with climate 
change goals.

4.3.  Proposed linkage indicators 

for the EEA

In order to assist the EEA to approach 
and report on linkages between 
air quality and climate change in a 
structured manner we propose here, 
as a ﬁrst, very preliminary step, some 
potential indicators that could be 
relevant for describing the linkages. 
As noted, not all identiﬁed linkages 

Linkages in emissions and control options

29

Table 4.1  Driving forces and pressure indicators for climate change and air pollution

Indicator

Unit

DPSIR

Development 
time (1)

Type (2)

Structural changes affecting both GHG and AP 
emissions (sectoral economic changes)

EUR, %

Technological changes affecting both GHG and AP 
emissions, e.g. development speciﬁc technologies

e.g.
% in fuel mix

Emissions of air pollutants and GHGs presented 
together

Tonnes/
year

D

D

P

S

S

S

Me

Me

Mo/Me

DPSIR = ‘Driving forces, pressure, state, impacts, response’; note that the type of indicator can be different from a 
climate change or air pollution perspective.

(1)  Development time means the time period that an indicator becomes applicable for assessments. S = short  

(0–2 years), M = medium (3–5 years), L = long (6–10 years).

(2)  Indicator type illustrates the main source of information. Me = measurements (past trends),  

Mo = modelling (scenarios).

can be assessed and described yet with 
the current state of knowledge and 
modelling framework available.

In Table 4.1 two driving force indicators 
and one pressure indicator are proposed 
to describe the linkages for climate 
change and air pollution.

•  The ﬁrst indicator describes the 
change in the mix of economic 
sectoral output levels that by 
deﬁnition aﬀect both GHG and air 
pollutant emissions.

•  The second indicator concentrates 
on technological changes aﬀecting 

both GHG and air pollution. In 
this indicator the contribution/
penetration of so-called zero-
emission technologies such as 
hydrogen and solar power in a 
certain sector can be quantiﬁed.

•  The third proposed indicator 

combines the traditional emission 
indicator from GHG and air 
pollutants in one reporting 
framework, where up to now they 
have been presented separately. 
Non-CO2 emissions can hereby 
be expressed in CO2-equivalent 
emissions.

30

Air pollution and climate change policies in Europe

5.  Current policy practices and 

opportunities

Key messages

•  Opportunities for synergies and avoiding trade-offs have been integrated into international 

air quality policies or policy negotiations in Europe, such as the ‘Clean air for Europe’ 
programme (CAFE) where the links between air pollution and climate change are an 
integral part of the analysis which will lead to the adoption of the Thematic Strategy on 
Air Pollution in mid 2005. Neither the United Nations Economic Commission for Europe 
Convention on Long-Range Transboundary Air Pollution (UNECE CLRTAP), nor the current 
climate negotiations (United Nations Framework Convention on Climate Change — 
UNFCCC) address these issues on policy level. At the technical assessment level, however, 
the opportunities are increasingly noted (Intergovernmental Panel on Climate Change 
— IPCC; UNECE Task Force on Integrated Assessment Modelling — TFIAM).

•  Linkages can be taken into account when designing different types of policies such as 
economic instruments, regulatory policies, voluntary agreements, and awareness and 
education strategies. Policies targeting the activities that release the air pollutants and 
greenhouse gases (e.g. combustion of fossil fuels, intensive agriculture) rather than the 
emissions of one speciﬁc substance (like carbon dioxide or sulphur dioxide emissions from 
energy use, or ammonia emissions from agriculture) have a larger potential for capturing 
possible synergies.

•  Climate changes policies, if developed independently from air pollution policy, will either 
constrain or reinforce air pollution policies, dependent on the choice and design of the 
policy instruments, and the other way around. From an economic perspective, policies 
that may not be regarded as cost-effective from a climate change or an air pollution 
perspective alone may be found to be cost-effective if both aspects are being considered.

•  If climate change considerations were taken into account when designing policies and 
measures to abate local and regional air pollution (and vice versa), the cost-beneﬁt 
equation and thus the relative priorities of policy options could change considerably; there 
is as yet no agreed operational framework to evaluate the importance of climate change 
versus air pollution.

5.1.  Introduction and history

In Chapter 4, the response options that 
are available to address both climate 
change and air pollution were discussed, 
focusing on technological options. What 
are the policies and measures that can 
be used to implement these options, and 
how do they play out in the two areas 
of air pollution and climate change? In 
the following, we will discuss current 
policy practices and opportunities for 
the future.

The increasing awareness of the linkages 
between diﬀerent environmental issues 
can be illustrated by the developments 
in the history of CRLTAP. Since its 
establishment in 1979, a considerable 
amount of protocols regarding 
air pollution have been adopted. 
The ﬁrst protocols focused on one 
single substance and on one main 
environmental eﬀect. The ﬁrst sulphur 
protocol in 1985 aimed at reducing 

SO2 in order to combat ‘acidiﬁcation’. 
The protocol on nitrogen oxides (NOx) 
(1988) focused on the eutrophication 
issue and the protocol on volatile 
organic compounds (VOCs) (1991) on 
the mitigation of tropospheric ozone. 
However, in the 1991 VOC protocol 
there was already a call to include 
nitrogen oxides in renegotiations of 
the protocol which had to start no later 
than six months a�er entry into force 
of the protocol. Furthermore, multi-
pollutant and multi-eﬀect approaches 
were the subject of discussion in the 
CLRTAP Working Group on Strategies 
(WGS) from 1992 on (We�estad, 2002). 
There was an increasing insight that 
important eﬃciency gains could be 
captured by simultaneously controlling 
acidiﬁcation and eutrophication risks 
and ground-level ozone concentrations. 
Finally, in 1999 the Gothenburg Protocol 
was adopted. This protocol focuses on 
the four substances nitrogen oxides, 
volatile organic compounds, sulphur 

Current policy practices and opportunities

31

dioxide and ammonia and on the three 
environmental issues acidiﬁcation, 
tropospheric ozone formation and 
eutrophication.

Also within policies in the European 
Union, a multi-pollutant, multi-eﬀect 
approach is taken, as can be seen from 
the developments of the acidiﬁcation 
and ozone strategy towards the national 
emission ceilings directive (2001) and 
the new ‘Clean air for Europe’ (CAFE) 
programme which commenced in 2001. 
With regard to the linkage to climate 
change, the EMEP Steering Body 
resulting under CLRTAP ‘…recognised 
at its 26th session in September 2002 the 
important links between regional air 
pollution and climate change’ (UNECE, 
2002). It welcomed the work initiated 
to explore such links and requested the 
Task Force on Integrated Assessment 
Modelling to aim at addressing all 
aspects of these links in its future work.

Despite these developments, 
international policy-making on climate 
change or stratospheric ozone still takes 
place independently from — and in 
other policy arenas than — air pollution. 
Negotiations on reducing greenhouse 
gas emissions take place within the 1997 
UN Framework Convention on Climate 
Change (UN FCCC) and substances that 
deplete the ozone layer are dealt with in 
the 1987 Montreal Protocol. The policy 
arena for climate change and ozone 
depletion is global, as opposed to the 
European level negotiation and national 
implementation of regional air pollution 
policy and local implementation of 
urban air pollution policies. In this 
section, we discuss current policy 
practices and future policy opportunities 
capturing co-beneﬁts and avoiding 
trade-oﬀs.

such as CAFE where the links between 
air pollution and climate change are an 
integral part of the analysis which will 
lead to the adoption of the Thematic 
Strategy on Air Pollution in mid 2005. 
On the other hand, many of the policies 
that are currently being implemented 
or considered in Europe do have the 
potential to capture the co-beneﬁts. For 
example, the IPPC directive addresses 
multiple pollutants, and sources of 
GHGs (EC, 1996). Synergies between 
the IPPC and the dra� emissions 
trading directive have been identiﬁed 
(EC, 2002). Energy eﬃciency standards 
in diﬀerent sectors, such as for those 
power plants and automobiles, that have 
been developed primarily for reasons 
other than climate change, such as air 
quality, also address climate change. 
Alcamo et al. (2002) show that, while 
regional air pollution and climate 
change may be fairly weakly coupled 
in the area of environmental impacts, 
they are strongly coupled in the area of 
environmental policy.

More explicitly, the opportunities for 
co-beneﬁts have been identiﬁed by 
scientiﬁc research (see Chapters 2 to 4) 
and are being picked up by technical 
assessment bodies, such as the UNECE 
Task Force on Integrated Assessment 
Modelling (TFIAM) under LRTAP. 
In the context of UNECE, integrating 
climate change considerations into 
regional air pollution policies appears 
to be a logical next step following the 
development and implementation of a 
multi-pollutant, multi-eﬀect approach. 
Recent integration of the issues through 
analyses with integrated assessment 
tools, such as RAINS and IMAGE, 
is starting to explore the potential 
synergies and trade-oﬀs in more detail.

5.3.  Climate change policies and 

5.2.  Air quality policies and 

air pollution

climate change

In general, the opportunities oﬀered for 
synergies between air quality policies 
and climate change responses have been 
integrated into international air quality 
policies or policy negotiations in Europe, 

Similar to the situation with respect to 
air quality policies, international climate 
change policy development to date 
did not explicitly take into account the 
potential for synergies. For example, in 
the negotiations of the United Nations 

32

Air pollution and climate change policies in Europe

Framework Convention on Climate 
Change (UNFCCC), the opportunities 
are not being considered other than that 
general references are made to the need 
to integrate climate change response 
strategies with sustainable development 
objectives. Nevertheless, many of the 
policy measures being considered to 
control GHG emissions clearly have 
beneﬁts for air pollutants. Examples 
are carbon or energy taxes, research, 
development and demonstration (RDD) 
of environmentally sound technologies, 
and voluntary programmes to reduce 
energy use and associated GHG 
emissions, which would also reduce air 
pollutants. The implications of GHG 
emissions trading programmes for other 
pollutants are more complex, since 
for local and regional air pollution the 
location of the emissions, which changes 
under a trading regime, is important 
(Pearce, 2000). The EEA (2004) shows 
that GHG emissions trading in Europe 
can have positive eﬀects on regional air 
pollution.

Also in the area of climate change, 
scientiﬁc research and technical 
assessments are starting to identify 
the potential synergies. For example, 
the Third assessment report of the 
Intergovernmental Panel on Climate 
Change (Metz et al., 2001) extensively 
discusses the concept of co-beneﬁts as 
one of the promising linkages between 
climate change response and wider 
sustainable development strategies. 
According to model calculations reported 
by Van Harmelen et al. (2002), the indirect 
eﬀects of climate policies in Europe 
targeting the stabilisation of greenhouse 
gas concentrations in the atmosphere 
were found to cut the costs of abating 
SO2 emissions by 50–70 % and for NOx 
by about 50 %. For the shorter-term 
implementation of the Kyoto Protocol, 
costs savings of 10 % of the costs of 
controlling acidiﬁcation and ground-level 
ozone were found (without emissions 
trading) by Syri et al. (2001). Outside 
Europe, the potential synergies between 
greenhouse gas mitigation options and 
abatement of local air pollution have 
received more a�ention than in Europe. 
This is especially true in developing 

countries (for Chile, Brazil, Mexico, see 
Cifuentes et al., 2001) and in the United 
States, where NGOs such as the World 
Resources Institute (McKenzie, 1996) and 
Resources for the Future (Burtraw and 
Toman, 1997) have actively promoted 
an integrated approach, primarily on 
the basis of the advantages for human 
health. In the USA, harmonised options 
for joint abatement of air pollutants 
and GHGs are being promoted at the 
State level (STAPPA/ALAPCO, 2000). 
Also at the local level the linkages are 
being considered. Several countries have 
mentioned the linkages in their national 
communications to the UNFCCC (Japan, 
United Kingdom, Czech Republic, Baltic 
States, others; see www.unfccc.int). 
Several studies suggest that the ‘ancillary’ 
beneﬁts of greenhouse gas abatement 
— usually primarily air quality related — 
may be of the same order of magnitude 
as the abatement costs (Metz et al., 2001) 
and therefore shouldn’t be ignored in 
policy development.

It is important to note that policy 
beyond climate change and air pollution 
may have an eﬀect on emissions, 
which is at least as signiﬁcant as 
these policies themselves. The general 
development pathway (the ‘baseline’) 
that societies may choose determines 
how eﬀective environmental policies 
can be. For example, the strategic goal 
of the European Union from the 2000 
Lisbon meeting ‘to become the most 
competitive and dynamic knowledge-
based economy in the world capable 
of sustainable economic growth with 
more and be�er jobs and greater social 
cohesion’ may lead to a structural 
change in the economic structure of 
European countries which can have 
lower environmental pressures as a co-
beneﬁt.

We also note that in addition to policies 
targeting emissions of greenhouse 
gases and air pollutants, there may be 
options in the area of adaptation to 
climatic changes and high levels of air 
pollution, for example a shi� to new 
crops which may be less vulnerable to 
the impacts of both climatic changes and 
air pollution. In this section, however, 

Current policy practices and opportunities

33

we only address speciﬁc environmental 
and energy policies targeting emissions 
of GHGs and air pollutants.

5.3.  Policies and instruments

The various types of policies, measures 
and instruments can be categorised 
as follows: economic instruments, 
regulatory instruments, voluntary 
agreements, and information and 
education programmes. Some of their 
characteristics are discussed below, 
with respect to the linkages between air 
pollution and climate change, with some 
emphasis on the diﬀerences between the 
European Union, the central European 
accession countries, and eastern 
European countries.

Economic instruments
•  Taxes and subsidies. The design of 

tax systems which can be considered 
to control GHG emissions can have 
a direct eﬀect on emissions of air 
pollutants. For example, an energy 
tax would induce more eﬃcient 
energy use and energy savings in 
general, with generally positive 
eﬀects on both air pollutants and 
GHG emissions. A carbon tax would 
place the heaviest burden on the 
fuels with the highest speciﬁc GHG 
emissions, from coal to oil to gas. In 
general, this priority in terms of their 
contribution to climate change is 
similar to their relative contributions 
to air pollution. Implementation 
design of a tax system primarily 
targeted at GHG emission reductions 
does aﬀect the ancillary beneﬁts. 
For example, raising an energy or 
carbon tax at the producers’ end 
of the system has implications for 
air pollutant emissions that are 
diﬀerent from a situation where 
the tax is raised at the users’ end. 
Also the use of the tax revenue 
can aﬀect emissions of both GHGs 
and air pollutants (e.g. recycling 
through reduced labour taxes can 
decrease the beneﬁts while targeted 

usage for stimulating renewable 
energy would increase the beneﬁts). 
Subsidies for energy eﬃciency or 
low-emission technologies can also 
have signiﬁcant co-beneﬁts for both 
air quality and climate change.
•  Emissions trading and emissions 
ceilings. Again, the impact of 
greenhouse gas or air pollutant 
emissions trading systems from 
one problem on the other is 
dependent on the design of the 
policy. It has been shown that the 
rules for GHG emissions trading 
can have an important impact 
on the regional distribution of 
air pollutants, possibly aﬀecting 
the ability of countries to meet 
air quality standards: it may be 
less or more costly to meet such 
targets, depending on speciﬁc 
circumstances (2). GHG emissions 
control could be targeted at those 
areas where the ancillary beneﬁts for 
regional and urban air pollution are 
the greatest. Trading systems tend to 
ignore such eﬀects (like the recently 
adopted EU CO2 emissions trading 
directive). 

Regulatory instruments
•  Standards. The design of the 

regulatory instrument determines 
if there are synergies or trade-oﬀs 
between air pollution and climate 
policy. The well-known example 
of a trade-oﬀ is a requirement for 
desulphurisation of stack gases, 
which would increase energy 
consumption and associated 
greenhouse gases. Energy eﬃciency 
standards generally have positive 
implications for both air pollution 
and climate change. Standards can 
also be technology based, such as 
BAT (‘best available technology’) 
or BATNEEC (‘BAT not entailing 
excessive costs’). This approach, 
e.g. incorporated in the EU’s 
integrated pollution prevention 
control directive (IPPC), implicitly 
integrates diﬀerent environmental 
issues. Finally, standards can be set 

(2)  In areas where air quality standards are met and critical loads not exceeded with or without trading, there are 

no cost implications.

34

Air pollution and climate change policies in Europe

on the basis of emissions, but if this 
happens on the basis of individual 
substances, trade-oﬀs are possible.
•  System targets. Target se�ing, such 
as for a particular percentage of 
renewables in the European fuel mix, 
can have signiﬁcant co-beneﬁts. 

Voluntary agreements
Voluntary agreements between 
governments, or the European Union, 
and private sector groups are becoming 
increasingly popular. In principle, such 
agreements can take potential synergies 
and trade-oﬀs easily into account. An 
example is the voluntary commitment 
to reduce the CO2 emissions from 
new vehicles by European (ACEA), 
Japanese (JAMA) and Korean (KAMA) 
car manufacturers (ACEA, 1999). This 
commitment simultaneously limits 
emissions of other fuel consumption 
related emissions.

Public information and education
Thus far, information and education 
campaigns have been more popular 
in the area of climate change than in 
the area of air pollution, since in the 
la�er area thus far most solutions were 
of a technological nature, focusing 
on production processes rather than 
consumption. However, in order to 
come to an eﬀective abatement of 
the remaining air pollution problems 
in Europe, structural socioeconomic 
and behavioural changes may 
be needed, and information and 
education campaigns can then play a 
role in supporting the control of both 
greenhouse gas emissions and air 
pollutants An example is the EU energy-
labelling strategy.

In practice, there can be no preference 
for any of the above types of policies, 
from the perspective of capturing 
co-beneﬁts, since these are dependent 
on the speciﬁc design of the policy. In 
general, a portfolio of these options will 
have to be developed. More importantly, 
the portfolio of options for either climate 
change response or air quality policies 
and the ranking of options will change if 
the other problem is added to the list of 
criteria.

5.4.  Conclusions

From the above it becomes clear that 
some policies address climate change 
and air pollution simultaneously 
by design (e.g. policies aiming at 
inﬂuencing the activity volume of 
common sources of GHG and air 
pollutants). Other policies target only 
one type of emission, with or without 
side eﬀects (e.g. promoting particular 
end-of-pipe technologies addressing 
speciﬁc emissions).

5.5.  Proposed linkage indicators 

for the EEA

In order to assist the EEA to approach 
and report on linkages between 
air quality and climate change in a 
structured manner we propose here, 
as a ﬁrst, very preliminary step, some 
potential indicators that could be 
relevant for describing the linkages. 
As noted, not all identiﬁed linkages 
can be assessed and described yet with 
the current state of knowledge and 
modelling framework available.

It would be interesting to highlight the 
co-beneﬁts of particular policies in the 
EEA’s future reporting. A few initial 
ideas of how this could be done are 
summarised in Table 5.1.

•  The ﬁrst indicator describes the 

number of policies adopted, which 
explicitly or implicitly address both 
types of pollution simultaneously 
(by Member State), possibly 
grouped according to the categories 
used above. This indicator can be 
implemented on the basis of the 
Member State submissions in the 
context of the national emission 
ceilings (NEC) and the GHG 
monitoring mechanism (MM). Until 
now, the Member States’ reporting 
on policies and measures (existing/
adopted or planned/additional) 
under the GHG MM is more 
advanced than under the NEC. 
Revised guidelines may be needed to 
have countries include appropriate 
information.

Current policy practices and opportunities

35

Table 5.1 

Policy response indicators for the relationship between climate change and 
air pollution

Indicator

Unit

DPSIR

Development 
time (1)

Type (2)

Policies adopted addressing climate change and air 
pollution simultaneously

Effects of climate change measures on air pollutant 
emissions

Effects of climate change measures on costs of air 
quality policy

Effects of climate change policies on urban air 
pollution and health

Number 

 %
reduction

 % change

DALYs

R

R

R

R

S

S

S

M/L

Me

Mo

Mo

Mo

DPSIR = ‘Driving forces, pressure, state, impacts, response’; note that the type of indicator can be different from a 
climate change or air pollution perspective.

(1)  Development time means the time period that an indicator becomes applicable for assessments. S = short  

(0–2 years), M = medium (3–5 years), L = long (6–10 years).

(2)   Indicator type illustrates the main source of information. Me = measurements (past trends),  

Mo = modelling (scenarios).

•  The second indicator describes the 
eﬀects of climate change measures 
on emissions of air pollutants, to 
be derived from integrated model-
based analyses. This indicator can be 
implemented in the short term, on 
the basis of existing information. In 
the longer term, information about 
these eﬀects may be included in 
the Member State submissions in 
the context of the GHG MM. The 
reverse — GHG emission reductions 
as a result of air pollution policies 
— appears to be less signiﬁcant, due 
to the fact that air quality purposes 
o�en address speciﬁc air pollutants 
that can be controlled through 
technological options which do not 
inﬂuence GHG emissions to a great 
extent.

•  The third indicator describes the 

eﬀects of climate change measures 
on costs of air quality policies, to 
be derived from integrated model-
based analyses on the European 

scale, as was done in the context 
of the AIR-CLIM project and for 
the Kiev report (see Annex 5). This 
indicator can also be implemented 
in the short term, on the basis of 
existing information. Cost reductions 
can be expressed in percentage 
costs saved. As in the previous 
indicator, the reverse — cost savings 
of air pollution policies for climate 
change policies — appears to be less 
signiﬁcant.

•  The fourth indicator describes the 

eﬀects of climate change policies 
on urban air pollution and health. 
This indicator could be derived from 
model-based analyses. Uncertainties 
are large, and further development 
of assessment methodologies would 
be needed, and are foreseen in the 
European Topic Centre on Air and 
Climate Change (ETC-ACC) work 
programme. This indicator may be 
seen as an option for the somewhat 
longer term. 

36

Air pollution and climate change policies in Europe

6.  History of integrated assessment 

of air pollution and climate change

Key messages

•  The complex atmospheric interactions between air pollution and climate change are 
presently not understood sufﬁciently well to allow their quantitative incorporation in 
integrated assessment modelling. Instead, these interactions should be taken into account 
in integrated assessment of the two issues in a qualitative fashion. The same counts for 
interactions between air pollution and climate change in impacts.

•  Sufﬁcient knowledge appears to be available to include many of the linkages, at the level 
of emission sources and control strategies, quantitatively in integrated assessment and 
integrated assessment modelling in the near future.

•  It is important to take into account the linkages between climate change and air pollution 
both in cost-effectiveness analysis (how to reach adopted environmental quality goals in 
the cheapest manner) and cost-beneﬁt analysis (what is the economically optimal level of 
abatement?).

•  Choice and design of policies and measures to address climate change can affect the 

spatial and temporal distribution of emissions and hence their effectiveness in terms of air 
pollution. This needs to be taken into account in integrated assessment studies.

•  The experience acquired with a framework of models in previous European integrated 
assessment studies provides a good basis for future activities, which include both air 
pollution and climate change. While components of this framework focusing on the two 
issues can be further improved to include linkages, a ‘soft link’ between the compounds 
appears to be appropriate because of the disparate characteristics of the problems in 
terms of time, space and complexity.

6.1.  History of integrated 

assessment of air pollution 
and climate change in Europe

In the previous chapters, an overview 
was given of the knowledge in the 
areas of atmospheric linkages, linked 
impacts, common sources, and technical 
options, respectively. Here, we focus on 
studies that have taken an integrated 
perspective, covering several of these 
issues at the same time. Such studies 
are few, o�en performed by the same 
institutions, and are concentrated in the 
developed countries. Annexes 1 to 7 give 
summaries of the main aspects of these 
projects.

In Europe, in 1997, the ‘European 
environmental priorities’ project (EEP) 
(RIVM, 2001) focused on 12 prominent 
environmental problems, including 
climate change and air pollution, 
analysing possible priorities in the 
context of the EU’s ﬁ�h environmental 
action programme (EAP5). The scenario-
based project looked at established and 
possible future environmental goals 
and evaluated the eﬀectiveness and 

costs of current and possible future 
responses (technical options and 
policies, and measures to implement 
those). The emphasis in the project 
was on individual problems and 
their relative importance. Linkages 
between the diﬀerent issues were 
not comprehensively analysed, but 
the project suggested that synergies 
between policy options would be 
possible. For climate change and 
air pollution, the project suggested 
that there might be room for further 
optimisation of the policy packages, if 
‘spillover’ eﬀects (lower emissions of air 
pollutants because of energy eﬃciency 
measures driven by GHG policies) were 
taken into account. Thus the eﬃciency 
of the additional policies would be 
improved. An economic analysis of an 
‘accelerated policy’ scenario showed that 
the macroeconomic costs of the direct 
costs associated with problems other 
than climate change policies are likely to 
be relatively small.

The project contributed to the report 
Environment in the European Union at 
the turn of the century (EEA, 1999) of the 

History of integrated assessment of air pollution and climate change

37

EEA. Reactions to this report, amongst 
others from stakeholders, suggested that 
the capabilities of the EEA to perform 
integrated scenario analysis could 
be strengthened, inter alia, by more 
thoroughly addressing uncertainties. In 
order to address this issue and to start 
the preparatory process for the next 
European state of the environment report 
in 2005, the so-called ‘ShAIR’ project 
was initiated (EEA, 2001). This project 
developed an updated projection of 
air pollutants and GHG emissions on 
the basis of the earlier ‘Shared analysis 
energy’ project, testing and evaluating 
the available integrated assessment 
framework. Four European research 
institutions involved in the EEP project 
discussed above also participated 
in the ShAIR project (RIVM, NTUA, 
IIASA, TNO), and thus the experience 
from the earlier project as well as the 
same analytical tools could be used. 
The ShAIR project identiﬁed a clear 
link between the eﬀects of policy and 
measures for long-range air pollution, 
urban air pollution and greenhouse 
gas emissions, notably because the 
main emission sources are the same: 
the energy, industry and transport 
sectors. Energy eﬃciency, regulations 
inﬂuencing the fuel mix, and low- and 
zero-emission vehicles were identiﬁed 
as options to address various issues at 
the same time. But also in physical and 
chemical terms, the issues were noted 
to be coupled, e.g. through hemispheric 
background concentrations of ozone, 
inﬂuenced by methane. The project 
also noted that for a be�er and more 
fully integrated assessment, gaps in 
knowledge would have to be ﬁlled, 
notably in the area of adequate data at 
national and regional level, especially on 
emissions, and models for integration 
and development of projections.

While the above studies focused on 
policy support (primarily for the 
European Commission’s Environment 
Directorate-General), in parallel the 
AIR-CLIM project funded by the 
Commission’s Directorate-General 
for Research focused much more 
explicitly on developing the scientiﬁc 
methodology to perform integrated 

assessments of air pollution and climate 
change (Alcamo et al., 2002). More 
speciﬁcally, the AIR-CLIM project 
further explored the so� link between 
the IMAGE climate model and the 
RAINS model (acidiﬁcation mainly). 
AIR-CLIM developed consistent 
scenarios of regional air pollution and 
climate change in Europe, analysed links 
between climatic changes and critical 
levels of acidiﬁcation and evaluated 
long-term reductions of the costs of 
controlling air pollution in Europe 
due to climate policy. A key ﬁnding of 
AIR-CLIM is that costs of air pollution 
abatement are reduced considerably as a 
side eﬀect of climate policies.

In a study in support of the report 
Europe’s environment, the third assessment 
of the European Environment Agency 
(EEA, 2004), the same suite of models 
as used in the projects discussed above 
(IMAGE, RAINS) was used to analyse 
the implications of GHG emissions 
trading on air quality in Europe.

In the Netherlands, in 2002 the project 
‘Approaches to analyse interactions 
of climate change, acidiﬁcation and 
ozone’ (‘National research programme’ 
— NRP; van Ierland et al., 2002) 
focused on the interactions of climate 
change, acidiﬁcation, eutrophication, 
tropospheric ozone and some other 
air pollutants, and on the approaches 
for an integrated analysis for these 
problems. Furthermore, apart from the 
examination of the existing approaches, 
the study also suggested new methods 
for scenario and optimisation analysis, 
with a focus on the European situation. 
While none of the institutions involved 
in the abovementioned European 
projects was involved in the NRP 
project, it used some of the databases 
and models that were used in these 
studies (e.g. the IMAGE and RAINS 
models). A new economic method to 
model interactions between reduction 
strategies was developed (a comparative 
static optimisation model). More 
speciﬁcally, interactions between 
ammonia abatement strategies and 
controls of N2O and CO2 in agriculture 
were analysed, as well as interactions 

38

Air pollution and climate change policies in Europe

between ozone and acidiﬁcation. The 
NRP project conﬁrms much of the 
knowledge gaps identiﬁed by the 
ShAIR project, notably the need for a 
ﬂexible database of emissions with some 
sectoral, spatial and temporal resolution, 
and the importance of taking into 
account the diﬀerent temporal scales of 
global and regional issues. The project 
recommends further developing so� 
links between various available models. 
For an integrated analysis of climate 
change and air pollution, the project 
also recognises the importance of having 
endogenous optimisation of the energy 
sector in the models used rather than 
analyse only end-of-pipe solutions to 
air pollution control with exogenous 
assumptions for energy supply.

6.2.  Ancillary and co-beneﬁts

The abovementioned projects at the 
European level generally share an 
approach in which medium to long-
term socioeconomic scenarios are 
developed, a range of environmental 
consequences is determined and 
compared with environmental goals, 
followed by an analysis of (additional) 
measures that would be needed to 
meet these goals, and their costs. The 
core research teams in most of these 
projects are the same. Several linkages 
at the level of atmospheric processes 
and impacts were taken into account. 
A completely diﬀerent approach to 
address linkages between climate 
change and air pollution dominated 
a workshop initiated by the IPCC in 
collaboration with the Resources for 
the Future Institute and the World 
Resources Institute (OECD, 2000). 
The results of this workshop played 
an important role in the IPCC’s Third 
assessment report (Metz et al., 2001). 
Most of the studies discussed in this 
workshop and by the IPCC are from the 
USA and other non-European countries. 
Here, the emphasis was on quantifying 
the ‘ancillary’ beneﬁts of greenhouse 
gas mitigation policies, preferably in 
monetary terms, using economic models 
and indicators. A wide range of ancillary 
beneﬁts was explored, but the monetary 

valuation of these beneﬁts was clearly 
dominated by reduced health impacts, 
usually related to reduced air pollution. 
Diﬀerent from the European studies 
discussed above, the studies quoted in 
the IPCC and OECD reports usually 
have the character of case studies in 
particular cities or regions, some of 
them being top-down macroeconomic 
modelling studies on country level. The 
results of the workshop and their policy 
relevance was evaluated by the OECD 
(Davis et al., 2002). It was concluded that 
ancillary beneﬁts and costs may be very 
important to the assessment of policy 
options, inﬂuencing decisions about 
both the level and the type of mitigation 
policy action, suggesting that these 
beneﬁts and costs should routinely be 
considered in climate policy decision-
making processes.

6.3.  Implications for integrated 
assessment: discussion

A fully integrated assessment of the 
linkages between air pollution and 
climate change has not been performed 
yet. Even if the studies discussed above 
capture elements of the various types of 
linkages, many — if not most — of the 
linkages summarised in Sections 2.1–2.5 
are not yet taken into account. All 
European studies show the importance 
of the links, which seem to be most 
relevant in the area of policy options and 
somewhat less so in the area of impacts. 
The economic studies of ancillary 
beneﬁts of GHG mitigation suggest that 
the avoided damages in terms of public 
health can compensate a sometimes 
signiﬁcant part of the costs of the 
measures, sometimes all. It is important 
to note that the diﬀerent studies address 
diﬀerent questions and as a consequence 
have diﬀerent objectives, use diﬀerent 
tools and provide diﬀerent answers. 
The European studies discussed above 
take environmental goals (reduction 
of GHG emissions, meeting air quality 
objectives) as a starting point, and 
analyse policy options that would 
address multiple objectives, and 
(sometimes) their costs. In the USA and 
other countries, where there are as yet 

History of integrated assessment of air pollution and climate change

39

no GHG emission reduction objectives, 
and o�en a less systematic framework to 
meet air quality goals, the starting point 
is formed by the costs of climate policy. 
The emphasis here is on quantifying 
the ancillary beneﬁts of climate policy, 
to address an ‘earlier’ question: is it 
worthwhile to control GHG emissions? 
The diﬀerence can also be considered 
as a cost-eﬀectiveness versus cost-
beneﬁt analysis. For longer-term policy 
development, e.g. a second commitment 
period of the Kyoto Protocol (or another 
post-Kyoto regime), both approaches 
seem valid, combining a�ention for the 
avoidance of multiple environmental 
and other eﬀects of economic activities 
with an assessment of the costs of policy 
measures.

From a policy perspective, it may 
be recommended that for integrated 
assessment most a�ention is spent on 
policy linkages, and the development 
of tools for quantitatively evaluating 
the potential synergies and trade-
oﬀs between them. At the same time, 
since particular policies may have 
undesirable, possibly counterproductive 
results because of uncertain eﬀects on 
atmospheric and climatic processes, 
integrated assessment should not be 
limited to cost analysis, but should also 
take into account these risks, at least 
in a qualitative fashion. In addition, 
rather than focusing solely on cost-
eﬀectiveness or cost-optimisation, 
integrated assessment of policy options 
should also evaluate their potential 
consequences for equity.

As argued above, especially when 
traditional end-of-pipe solutions 
to reach air quality targets may be 
insuﬃcient, an integrated assessment 
of greenhouse gas and air pollutant 
emission reduction options — including 
changes in production and consumption 
pa�erns — is becoming relevant. This is 
becoming increasingly clear especially 
in countries that have diﬃculties 
meeting air quality objectives with 
traditional approaches, e.g. for NOx. 
Such an integrated analysis is not yet 
possible in the RAINS model. Therefore, 
for example in the EEA study referred 

to above (EEA, 2004), the ancillary 
beneﬁts of greenhouse gas emission 
mitigation for air pollutants were 
included, but not the potential ancillary 
beneﬁts of a full suite of air pollution 
abatement options on greenhouse 
gas emissions. An eﬀort is currently 
under way to include greenhouse gas 
emissions and abatement cost curves 
in the model. In this way, interactions 
between pollutants and co-beneﬁts 
between air pollution abatement and 
climate change mitigation can be more 
fully captured (Amann et al., 2003). 
The European Union has ratiﬁed the 
Kyoto Protocol, and in the context of its 
sustainable development strategy has 
pledged a further reduction of regional 
CO2 emissions by 1 % per year a�er the 
ﬁrst commitment period, until 2020. In 
various European countries (Germany, 
Netherlands, France, United Kingdom, 
Switzerland) longer-term reductions 
of greenhouse gases of 40–60 % of 1990 
emissions have been proposed, based 
on scenario analysis which suggest such 
goals to be credible and technologically 
feasible. Meeting such objectives 
has very signiﬁcant implications for 
air pollutant emissions. Integrated 
assessment therefore has to go beyond a 
limited analysis of the cost-eﬀectiveness 
of air pollution abatement strategies 
to fully incorporate structural changes 
(Landrieu, 2002).

Again focusing on the policy 
linkages, it is important to note that 
the importance of using economic 
instruments to achieve environmental 
goals is increasing. In December 
2002, the European Union adopted a 
proposal to introduce a CO2 emissions 
trading system, which intends to help 
achieve the Kyoto targets starting by 
2005. As the EEA (2004) illustrated, 
introducing such an instrument has 
very signiﬁcant implications for the 
regional distribution of air pollutants, 
and thus on the strategies of countries 
to meet the UNECE Gothenburg 
Protocol, and the EU NEC directive. 
The characteristics of air pollution 
and climate change are diﬀerent in 
various ways. First, the primary drivers 
behind air pollution and climate change 

40

Air pollution and climate change policies in Europe

mitigation policies are diﬀerent: public 
health and environmental protection, 
respectively. Secondly, the time scales 
and spatial scales are diﬀerent. The 
inertia of the climate problem and the 
long time scales needed for structural 
economic and behavioural changes are 
diﬀerent from the much shorter time 
scales that were characteristic of air 
pollution abatement until recently (3). 
Climate change necessitates a global 
response; air pollution can generally be 
addressed locally or regionally. Thirdly, 
the policy approaches are diﬀerent: a 
technological approach with absolute 
standards for air quality and a more 
structural approach including economic 
instruments for climate change. These 
new developments necessarily have 
implications for the further development 
of integrated assessment methods. 
Rather than a ‘hard’, full integration of 
modelling tools in the respective areas, 
a more loosely coupled framework of 
various tools may be developed and 
applied, bridging spatial and temporal 

scales, and allowing for combining the 
analysis of broad global developments 
with the policy options at the sectoral 
level. The modelling tools in both areas 
(e.g. RAINS for regional air quality 
and IMAGE for climate change) could 
be further developed to enhance the 
consistency between modelling runs 
and facilitate data exchange between 
the systems. Sectoral models (energy, 
transport) should be incorporated into 
the framework (Vainio, 2002).

As also noted at the TFIAM/ETC-ACC 
workshop, the objective of the work on 
linkages and synergies between regional 
air pollution and climate change should 
be to provide policy-makers with the 
information necessary to make choices. 
These choices need to be made with 
the objective of (1) reducing pollutants 
maximising the positive linkages and 
minimising the negative ones; and (2) 
taking those measures that are most 
cost-eﬀective and sustainable in view of 
the objectives in both policy areas.

(3)  The bridging between temporal scales is a difﬁcult issue to treat in an integrated techno-economic assessment. 

The integration of the long-term time frame of climate change and the shorter time frame of air pollution 
may require balancing long-term beneﬁts with short-term beneﬁts. The outputs of the integrated modelling 
framework such as the IMAGE/RAINS soft-linked package could highly depend on the respective depreciation 
schemes adopted in each model. Equity, speciﬁcally intergenerational equity considerations, could be a way to 
overcome the problem.

7.  Discussion and future EEA work

Discussion and future EEA work

41

Key messages

•  There are many institutional, scientiﬁc and political barriers to integration of climate 

change and air pollution in policy development. However, compelling arguments in support 
of integration suggest that these barriers should and can be overcome. These arguments 
include the increased cost-effectiveness of policies, reduced public health and ecosystem 
risks and the early identiﬁcation of potential perverse effects of single-issue policies.
•  An improving knowledge base can help the policy integration process. Further research 
needs to include the improved understanding of chemical and physical interactions of 
air pollutants and greenhouse gases in the atmosphere (e.g. ozone, PM/aerosols); the 
development of comprehensive integrated assessment frameworks based on a loose 
coupling of individual tools; case studies demonstrating the reality of co-beneﬁts; and 
analyses of policies and measures that integrate air pollution and climate change concerns.

•  The EEA can help furthering the issue of integrating air pollution and climate change in 

its reporting system. This includes the coverage of the linkages in the 2005 State of the 
environment and outlook report, but also inclusion of the linkages in reports and fact 
sheets on air pollution and climate change, respectively.

•  One example of the inclusion of linkages between air pollution and climate change in the 

EEA reporting system is to explore the introduction of a focused set of additional indicators 
on the linkages for the components of the DPSIR chain.

In the preceding chapters, we 
have provided an overview of the 
atmospheric linkages between air 
pollution and climate change, as 
well as linkages in impacts, and 
emissions and control options. We 
have also discussed current policy 
practices and opportunities and given 
examples of integrated assessment 
projects addressing linkages. In this 
ﬁnal chapter, we pull the information 
together by identifying existing barriers 
to integration, and by synthesising 
arguments in favour of integration of the 
two issues. We then provide suggestions 
for further work to ﬁll research gaps. 
Finally, we discuss how the knowledge 
on linkages between air pollution and 
climate change may be used in EEA 
reporting, notably the 2005 State of 
the environment and outlook report. We 
present as a ﬁrst, very preliminary step 
some potential indicators as proposed 
in the preceding chapters which may 
help the EEA to report on linkages in a 
structured manner.

7.1.  Barriers to integration

Despite the increasing awareness of 
the importance and beneﬁts of taking 
linkages into account, several factors 
contribute to the fact that potential 
synergies are as yet not harvested in 
international policy negotiations and 
national policy developments, and 
trade-oﬀs ignored.

•  The linkages are very complex, the 
knowledge base is still incomplete.

•  Air pollution and climate change 
eﬀects have diﬀerent time scales 
(and time preferences and target 
periods).

•  Scientiﬁc air pollution and climate 

• 

change communities show too li�le 
overlap.
If climate change considerations 
were taken into account when 
designing policies and measures to 
abate local and regional air pollution 
(and vice versa), the cost-beneﬁt 
equation and thus the relative 
priorities of policy options could 
change considerably. There is as yet 
no agreed operational framework to 
evaluate the importance of climate 
change versus air pollution.

42

Air pollution and climate change policies in Europe

•  The political negotiating networks, 
legal frameworks and format and 
timing of reporting requirements (4) 
are separated; the number of people 
with knowledge of both areas is 
very small and appropriate joint 
institutional arrangements are 
largely absent.

•  There is a latent and sometimes 
open concern in policy-making 
communities that including climate 
change in the air pollution policy 
development — and vice versa — 
may lead to a loss of control over the 
problem.

•  Detailed policy frameworks have 

• 

been developed over many years in 
ways that are not easily changeable 
to include other issues which may 
complicate further negotiations.
It is not evident at which level 
integration should take place: 
integration of air pollution and 
climate change should be addressed 
by the international conventions, 
but national and local governments 
should also take synergies and trade-
oﬀs into account when designing 
policies in both areas. 

7.2.  Arguments in favour of 

integration of climate change 
and air pollution policies

facilitate the implementation of these 
options.

•  Climate changes policies, if 

developed independently from air 
pollution policy, will either constrain 
or reinforce air pollution policies, 
dependent on the choice and design 
of the policy instruments, and the 
other way around. Integration 
will help identifying synergies, 
and avoiding unexpected perverse 
eﬀects.

•  From an economic perspective, 
policies which may not be 
regarded as cost-eﬀective from a 
climate change or an air pollution 
perspective alone, may be found 
to be cost-eﬀective if both are 
being considered. Integration thus 
improves the cost-eﬀectiveness of 
policies.

•  Air pollution and climate change 
have a signiﬁcant overlap in 
terms of sources of emissions, and 
their respective impacts through 
atmospheric chemistry, weather 
conditions and vulnerability of 
natural and human systems are 
linked. Although not always spelled 
out in detail in policy documents, 
there is general agreement that 
abatement of one environmental 
problem should not worsen another 
environmental problem. 

If there are so many barriers, why and 
how should the integration be pursued? 
The following arguments are in favour 
of increased integration of policies in 
the areas of air pollution and climate 
change.

Including the above issues both in 
international development (UNFCCC, 
UNECE CLRTAP, EU directives) and in 
national and local policy development 
and implementation would help to 
capture co-beneﬁts and avoid trade-oﬀs.

• 

Initial abatement of air pollution 
was possible largely through 
technological options such as add-on 
technologies or industrial process 
changes. It becomes increasingly 
clear that abatement of the remaining 
air pollution would need fuel shi�s 
or structural socioeconomic and/or 
behavioural changes, similar to 
most of the options for the control of 
GHG emissions. Integration would 

7.3.  Research gaps

From the above it becomes clear that 
there are very interesting opportunities 
to capture the co-beneﬁts of climate 
change and air pollution policies and 
avoid the dis-beneﬁts or trade-oﬀs, 
but that it is not easy to implement 
them. The potential in terms of 
reduced abatement costs and improved 

(4)  An exemption is formed by the emissions inventory methods, which are converging between the UNFCCC, 

UNECE and the EU (e.g. national emission ceilings directive).

human and ecosystem health is great. 
Improving the knowledge base can 
help supporting a process of increasing 
integration in policy development. Areas 
where additional research in support of 
European policy development would be 
needed include:

• 

further research in understanding 
the chemical and physical 
interactions of air pollutants and 
greenhouse gases in the atmosphere, 
with particular emphasis on:
—  the long-range transboundary 
transport of ozone precursor 
gases (NOx, VOC, CO), and the 
net eﬀect of their emissions on 
climate change;

—  a more precise determination 

of the chemical composition of 
aerosols/particulate ma�er, in 
order to assess the net warming 
or cooling eﬀect and the speciﬁc 
health impacts;
•  be�er deﬁning co-beneﬁts 

(calculation and allocation of costs 
and beneﬁts);

• 

•  developing appropriate assessment 
frameworks, taking into account 
monetary and physical aspects of co-
beneﬁts;
improve integrated modelling, e.g. 
by adding climate change elements 
to air pollution models (e.g. RAINS) 
and air pollutants to climate models 
(e.g. IMAGE) and developing a so� 
link between the two;
investigate linkages between air 
pollution and climate change and 
other environmental issues (waste, 
water, ecosystem resilience), 
and with socioeconomic issues 
(congestion, safety, distributional 
eﬀects of policies, employment);
implementing case studies which 
demonstrate the reality of co-
beneﬁts;

• 

• 

•  elaborating a transparent 

methodology to analyse and 
describe the relative importance of 
the various uncertainties in order 
to improve the quality of integrated 
environmental assessments;

•  analysing policies and measures that 
integrate air pollution and climate 
change concerns.

Discussion and future EEA work

43

7.4.  Addressing linkages between 
air pollution and climate 
change in EEA reporting

The EEA can increase the awareness of 
the importance of the linkages between 
air pollution and climate change by 
addressing them in its reporting. The 
linkages can be addressed in the EEA’s 
reporting system in various ways. 
Maybe the most important short-term 
opportunity is formed by the 2005 State 
of the environment and outlook report. 
Eventually, some of the proposed 
indicators could lead to inclusion in 
the EEA core set of indicators and the 
development of associated description 
and fact sheets. Other indicators could 
be developed and used in speciﬁc 
reports independent of the core set. 
Other possibilities include the inclusion 
of a summary of associated greenhouse 
gas emissions in the reporting of air 
pollutant emissions and air quality 
— and air pollutants in GHG reporting. 
For reporting of EU GHG emissions 
in the context of the GHG monitoring 
mechanism, and air pollutants in the 
context of the national emission ceilings 
directive and the UNECE Convention 
on Long-Range Transboundary Air 
Pollution, inclusion of ‘the other’ 
substances would directly highlight 
the linkages, but would ﬁrst require 
a discussion with the Member States 
about the usefulness and feasibility. 
Also, the linkages could be highlighted 
in EEA reports about environmental 
issues at the sectoral level, such as 
energy, transport and agriculture.

Indicators
With regard to the development of 
indicators, it will be important to 
identify what the relevant linkages 
are that the EEA would like to present 
and describe in the SoEOR2005 and 
other reports. Based on this review and 
earlier work by the ETC-ACC, as a ﬁrst, 
very preliminary step some potential 
indicators that can be relevant for 
describing the linkages are presented in 
Table 7.1.

As noted, not all identiﬁed linkages 
can be assessed and described yet with 

44

Air pollution and climate change policies in Europe

Table 7.1 

Examples of possible indicators for linkages between air pollution and climate 
change

Indicator

Unit

DPSIR

Development 
time (1)

Type (2)

Structural changes affecting both GHG and AP 
emissions (sectoral economic changes)

Technological changes affecting both GHG and AP 
emissions, e.g. development-speciﬁc technologies

Emissions of air pollutants and GHGs presented 
together

Concentrations of air pollutants which also affect 
climate change (sulphate, ozone and black/organic 
carbon) eventually expressed in CO2-equivalent 
concentration units or in their contribution to the 
total radiative forcing of GHG and air pollutants in 
the European atmosphere over time.

(Index) Half-life time changes of air pollutants such 
as CH4, NOx, CO
Climate change effect on percentage area 
exceedance of critical loads (total acidity)

Climate change effect on percentage area 
exceedance critical loads (total nitrogen)

Climate change effect (esp. temperature) on 
frequency of episodes of air pollutants

Nitrogen effect on the climate change induced 
changes in ecosystem composition

Policies adopted addressing climate change and air 
pollution simultaneously

Effects of climate change measures on air pollutant 
emissions

Effects of climate change measures on costs of air 
quality policy

Effects of climate change policies on urban air 
pollution and health

EUR, %

e.g.
 % in fuel mix

Tonnes/
year
ppb/CO2-
equival./W/m2

Year/index

 % change

 % change

 % change

Additional % 
change

number 

 %
reduction

 % change

DALYs

D

D

P

S

S

I

I

I

I

R

R

R

R

S

S

S

S (SO2) M (O3)
L (BC)

Me

Me 

 Mo/Me

Mo/Me

S/M

S

S

M

M

S

S

S

M/L

Mo

Mo

Mo

Mo

Mo

Me

Mo

Mo

Mo

DPSIR = ‘Driving forces, pressure, state, impacts, response’; note that the type of indicator can be different from a 
climate change or air pollution perspective.

(1)  Development time means the time period that an indicator becomes applicable for assessments. S = short  

(0–2 years), M = medium (3–5 years), L = long (6–10 years).

(2)  Indicator type illustrates the main source of information. Me = measurements (past trends),  

Mo = modelling (scenarios).

the current state of knowledge and 
modelling framework available. Some 
of the indicators reﬂect current and 
past trends and can be derived from 
monitoring and statistical information. 
Other indicators, especially the forward-
looking ones, require a modelling 
approach. At IIASA, currently work is 
under way to develop the RAINS model 
further to include also emissions of 
GHGs and technology options to reduce 
air pollutants and GHG simultaneously. 
In addition to the existing cost curve of 

air pollutants, IIASA will develop cost 
curves for the six GHGs (CO2, CH4, N2O, 
PFC, HFC, SF6) included in the Kyoto 
Protocol and implement an integrated 
cost approach over all pollutants. The 
time horizon for this new technology 
database, on a country-by-country 
basis for the EMEP region, will be 
2030. In parallel, IIASA is developing a 
methodology to assess structural change 
with RAINS. This kind of tool can be 
used to quantify several of the forward-
looking indicators suggested above.

References

45

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Air pollution and climate change policies in Europe

Introduction to the Annexes

Chapter 6 presented a short history of 
integrated assessment studies capturing 
elements of the various types of 
interactions between air pollution and 
climate change. In Annexes 1 to 5, these 
recent European projects are presented 
in more detail.

The following projects were selected:

•  1997–2001: European environmental 
priorities project: linkages noted 
between air pollution and climate 
change (Annex 1)

•  1998–99: ShAIR project in support 
of EEA ‘Environment in the EU’: 
opportunities for multiple-issue 
response options identiﬁed  
(Annex 2)

•  1998–2002: AIR-CLIM: costs of air 
quality policies greatly reduced 
under climate policy scenario; ﬁrst 
project including impact analysis 
(Annex 3)

•  2000–02: Netherlands national 

research programme: modelling 
interaction between response 
strategies in agriculture (Annex 4)

•  2001–03: Study in support of the 

EEA report Europe’s environment, the 
third assessment including analysis 
of eﬀects on spatial distribution by 
GHG emissions trading and  
AE/GHG abatement costs (Annex 5) 

In Annex 6 a summary is given of 
the proceedings of a recent OECD 
workshop with diﬀerent contributions 
describing the ancillary beneﬁts and 
costs of greenhouse gas mitigation.

Moreover, in Annex 7, the dra� 
conclusions of the Task Force on 
Integrated Assessment Modelling 
(TFIAM) Workshop on Linkages 
and Synergies of regional and global 
emission control are given as presented 
by the TFIAM Secretary, Henning 
Wüester.

Annex 8 presents a selected overview of 
earlier-held workshops in this ﬁeld.

Finally, Annex 9 lists a selected number 
of Internet sites giving information 
about linkages between climate change 
and air quality.

Annex 1: European environmental priorities

55

Annex 1: European environmental 
priorities: an integrated economic 
and environmental assessment  
(EEP project)

Study name:  

European environmental priorities: an integrated 
economic and environmental assessment

Year of development:  

1997–2001

Institute:  

Spatial coverage:  

RIVM (leading institute), IIASA, EFTEC and ICCS-
NTUA

Europe (mainly EU-15, while accession countries are 
partly assessed)

Spatial speciﬁcity:  

Europe as a whole

Time horizon:  

1990–2010

Focus (thematic coverage):  Diﬀerent environmental themes

Background information 
The European environmental priorities 
study has been carried out in order 
to guide the future priority se�ing of 
European environmental policies. The 
Commission funded this study because, 
a�er the review of the European 
Union’s (EU) ﬁ�h environmental 
action programme (ﬁ�h EAP), it had 
concluded that it was important to focus 
on key priorities and translate further 
the programme’s strategy into a set of 
pragmatic and operational tools.

Scope and objectives
The study is an economic and 
environmental analysis of priorities for 
a European environmental policy plan. 
It focuses on 12 identiﬁed prominent 
European environmental issues such 
as climate change, chemical risks and 
biodiversity. It incorporates information 
on targets, scenario results, and policy 
options and measures, including cost 
and beneﬁts. It aims to determine:

4.  If so, whether these targets are 

economically reasonable, and ﬁnally

5.  What policy responses and 

instruments can be recommended. 

Methodology used
The analysis is based on an examination 
of the cost of avoided damage, 
environmental expenditures, risk 
assessment, public opinion, social 
incidence and sustainability. The 
integrated assessment methodology has 
combined economic models, energy use 
models, emission data sets and models, 
environmental eﬀect models, economic 
beneﬁt models, and databases on the 
costs and eﬃciency of policy measures. 
This enables the scenario evaluation 
of Europe’s environment and the 
identiﬁcation of policy priorities.

Scenario development
To answer the research questions, three 
environmental policy scenarios have 
been evaluated:

1.  Whether the current environmental 

• 

policies are adequate

2.  What technology can contribute to 
solving the policy gaps as identiﬁed
3.  Whether the new targets chosen for 

• 

this study are achievable, and

‘baseline’ (BL), which consists of 
policies in place or in the pipeline 
(PIPP);
‘technology driven’ (TD), which 
abates proximate cause, by requiring 

56

Air pollution and climate change policies in Europe

• 

that all available ‘proven’ technology 
are to be implemented;
‘accelerated policy’ (AP) is related to 
new targets (set by the Environment 
DG) and mixes technology 
implementation with structural 
measures, where TD tends to fail the 
cost-beneﬁt test. 

Indicators
•  Greenhouse gas emissions
•  Air pollutant emissions (SO2, NOx, 

VOC and PM10)

•  Ecosystems with deposition 

exceeding critical loads for 
acidiﬁcation (percentage of 
ecosystem area)

•  Ecosystems with deposition 

exceeding critical loads for 
eutrophication (percentage of 
ecosystem area)

•  Population exposure to ozone
•  Vegetation exposure to ozone
•  PM10 exposure above target level
•  Heavy metals, dioxins and PAHs 

emissions

•  Pressure on nature
•  Beneﬁts welfare costs
•  Beneﬁt/cost ratio 

Main ﬁndings with regard to linkages
•  Full application of available 

technological solutions (‘end-of-
pipe’), without regard to costs, might 
show considerable improvements 
for some environmental problems. 
Technological means can solve 
problems, like acidiﬁcation and 
tropospheric ozone.

•  However, estimates suggest that 

yearly environmental expenditures 
may rise to about EUR 50 billion 
over the expected costs under 
baseline conditions. Acidiﬁcation 
and tropospheric ozone abatement 
policies will take a lot of the direct 
costs. Welfare costs are signiﬁcantly 
lower: about EUR 30 billion in 
2010. With the implementation of 
all available technical abatement 
measures, the environmental 
expenditures as a percentage of gross 
domestic product (GDP) will only 
be 1 % larger than in the baseline 
scenario.

• 

Implementing additional policies 
based on least-cost solutions 
and considering speciﬁc policy 
targets for climate change, 
acidiﬁcation, tropospheric ozone, 
waste management and human 
health and air quality (especially, 
particulate ma�er) might show 
considerable improvements to the 
environment, but to a lesser extent 
than applying all available ‘end-of- 
pipe’ technologies. Ecosystems and 
human health will beneﬁt from this 
improvement. Almost all the targets 
set for this study are achievable.
•  Some policies have positive eﬀects 
on other environmental problems 
without being purposely developed 
for solving them. Climate change 
policies have a signiﬁcant impact on 
acidiﬁcation, tropospheric ozone, 
chemicals, primary particulate 
ma�er and air quality. Air quality 
and tropospheric ozone will also 
beneﬁt from additional acidiﬁcation 
policies. Climate change-related 
policies make policies required to 
reach acidiﬁcation and ozone targets 
cheaper (by EUR 6 billion per year). 
Allowing ﬂexible Kyoto mechanisms 
will lead to fewer cost savings for 
these problems but is — overall 
— more cost-eﬀective.

•  Spillovers from climate change 
to other environmental issues 
are dominant, especially for 
acidiﬁcation, chemicals (i.e. heavy 
metals, PAHs and dioxins/furans) 
and primary particulate ma�er. 
It is shown that CO2 emission 
reduction of 15 % leads to emission 
reductions of 24 % for SO2, 8 % for 
NOx, 24 % for PM10, while SO2, NOx, 
and VOC control measures lead to 
auxiliary reduction of more than 7 
% PM10 emissions and signiﬁcant 
reduction of the pressures on natural 
ecosystems.
If, besides the baseline policies, 
no climate change policies were 
implemented at all, an additional 
investment in end-of-pipe measures 
of EUR 6 billion per year would 
be needed to reduce the acidifying 
emissions to a level that would 
ensure reaching the acidiﬁcation 

• 

Annex 1: European environmental priorities

57

targets. In terms of welfare loss, 
this would amount to nearly EUR 4 
billion.

•  The subsidiarity issue and the 

consequences of the EU enlargement 
have not been assessed in full detail.

•  Allowing for the Kyoto ﬂexible 

mechanisms will slightly reduce 
the total beneﬁt estimates of the 
accelerated policies scenario for 
climate change, mainly due to lower 
secondary beneﬁts. The assessment 
suggests substantial cost savings 
to EU from trading via the Kyoto 
ﬂexibility mechanisms, i.e. the trade-
oﬀ between secondary beneﬁts 
within the EU versus the cost 
advantage of trading. Considering 
the cost beneﬁts, emission permit 
trading is more advantageous. 

Study limitations
• 

In the framework of this study, not 
all spillover eﬀects and feedback 
mechanisms are taken into account.

•  Data and information presence 
is ﬁrm on air-related issues and 
weak in issues related to natural 
resources. This means that the study 
was not able to fully appraise all 
environmental issues and related 
costs and beneﬁts.

•  Consequently, indicators and policy 
targets selected in this study are 
mainly focused on those issues 
where a solid information basis is 
present. This means that ﬁndings on 
the remaining issues are less robust.
It is assumed that all measures 
and policy actions will be fully 
implemented and enforced. 
Implementation failures of actions 
(in place or identiﬁed) have not been 
assessed.

• 

•  The macroeconomic eﬀects of the 
beneﬁts have not been appraised. 
This also counts for the distributional 
eﬀects of new policies on diﬀerent 
socioeconomic groups within the 
EU.

•  Time was too limited to fully 
quantify the sensitivities and 
uncertainties of the results. 

Recommendations
In future, it will be necessary to focus on 
root causes emphasising an integrated 
and cost-beneﬁt approach not only 
within issue areas, but also recognising 
the ecological and cost-beneﬁt 
linkages between issues. For example, 
the interactions between climate 
change acidiﬁcation, eutrophication, 
tropospheric ozone, biodiversity loss, 
and soil degradation. By providing an 
integrated economic and environmental 
assessment on priority se�ing for 
European policy planning, this study 
represents a starting point towards that 
direction.

Lessons for the EEA for integrated 
assessment development with regard 
to linkages between air pollution and 
climate change
The broad integrated assessment of 
many environmental topics is too 
complex and time consuming and 
presently not within the reach of the 
EEA. However, the EEA could see this 
approach as a long-term goal, which 
could be adopted in the future.

Availability
The report was published by RIVM.

Publications
RIVM, EFTEC, NTUA, IIASA, 2001. 
European environmental priorities: an 
integrated economic and environmental 
assessment. RIVM report 481505010. 
National Institute for Public Health and 
the Environment (RIVM).

58

Air pollution and climate change policies in Europe

Annex 2: ‘Shared analysis air 
pollution and greenhouse gases’ 
(ShAIR) study

Study name:  

Shared analysis air pollution and greenhouse gases

Period of development:  

1998–99

Institute:  

RIVM, AuTh, ICCS-NTUA, IIASA and TNO

Spatial coverage:  

Europe (EU-14, seven accession countries —  
Czech Republic, Hungary, Poland, Slovenia and the 
three Baltic States, Estonia, Latvia, Lithuania —  
10 accession countries and the rest of Europe) 

Spatial speciﬁcity:  

Various European regions

Time horizon:  

1990–2020

Focus (thematic coverage):  Integrated assessment on air pollution and 
greenhouse gases

Background information
In the recent report Environment in 
the European Union at the turn of the 
century (EEA, 1999a), the European 
Environment Agency (EEA) showed 
substantial development in its 
experience in integrated assessment, 
which is considered as a primary 
process. The EEA medium- to long-term 
strategy and work programme aims 
at improving the methodologies for 
integrated assessment and prospective 
analysis in order to produce more 
transparent, be�er documented and 
more scientiﬁcally sound results for the 
next integrated assessment report in ﬁve 
years’ time. Therefore, the EEA initiated 
the ‘Shared analysis air pollution and 
greenhouse gases’ (ShAIR) study to 
evaluate and appraise its experience 
in the environmental projections 
underpinning the report Environment 
in the European Union at the turn of the 
century.

Scope and objectives
In the ShAIR study, an updated 
projection on air pollution and 
greenhouse gases has been produced on 
the basis of the shared analysis energy 
project (Capros and Mantzos, 2000). A 
partly updated shared analysis energy 
scenario has also been developed. The 
main objectives of the study were to:

•   test and evaluate the integrated 

assessment infrastructure developed 
by undertaking sensitivity and 
uncertainty analysis of the so-called 
baseline scenario, with particular 
emphasis on air-related issues (air 
pollution and the interaction with 
climate change/greenhouse gases);

•   build on expertise, connections 

and interrelations among parties 
involved;

•   identify relevant indicators, 
particularly for prospective 
analysis and policy evaluation, and 
develop accessible methodologies, 
information ﬂows and tools for their 
implementation;

•   appraise, evaluate and further 
develop integrated assessment 
methodology. 

In summary, the study had two main 
goals. One was to learn about and 
improve the integrated assessment 
methods and tools used and the other 
was to produce an updated projection 
(ShAIR) on air pollution and greenhouse 
gases based on the shared analysis 
scenario.

Methodology used
This study made use of experiences 
gained in recent scenario studies in 
the context of policy processes in the 

Annex 2: ‘Shared analysis air pollution and greenhouse gases’ (ShAIR) study

59

European Union (EU). The economic 
and energy scenario used as a starting 
point in this study is the shared analysis 
scenario, which is a baseline scenario 
assuming existing agreed and adopted 
policies and measures. Various scenario 
assumptions have been updated, and 
the resulting scenario version, with 
a time horizon extended to 2020, is 
referred to as the ShAIR scenario. 
Based on these underlying trends, 
integrated projections have been made 
for emissions of greenhouse gases, 
long-range transboundary air pollution 
and urban air quality. The study used 
a model network that combined the 
models used in three policy ﬁelds.

Firstly, two diﬀerent methods have been 
used to make the projections of emissions 
of greenhouse gases in this study: the 
Primes model for carbon dioxide (CO2) 
emissions and information from scientiﬁc 
literature for the other greenhouse gases. 
The Primes model includes projections 
for all individual EU Member States 
(except Luxembourg) on energy-related 
carbon dioxide (CO2) emissions. CO2 
emissions from non-energy sources 
(industrial processes and waste burning) 
are not included. No emission projection 
model was available for the other 
greenhouse gases. Projections have 
been based on the literature, and data 
for individual countries are sometimes 
lacking. Emissions and removals from 
land-use change and forestry (carbon 
sinks) were excluded. For the non-
EU countries in Europe only limited 
information is available.

Secondly, the projections for precursor 
emissions, concentrations of ground-
level ozone and acidifying and 
eutrophicating depositions are made 
with the RAINS model. A TNO model 
has been applied for PM10 (breathable 
particulate ma�er emissions). PM10 
concentrations were not projected 
as part of the ShAIR scenario. The 
energy scenario for EU Member States, 
calculated with the Primes model, was 
used as an input to the RAINS model.

Finally, the model tools for assessment 
of urban air quality in the EEA’s 

generalised exposure assessment (GEA) 
as applied in the Auto-Oil II programme 
have been, speciﬁcally for this project, 
further extended for application to 
cities in central and eastern Europe. 
An updated and improved version of 
the AuTh’s OFIS model was applied 
to assess urban ozone levels in 
numerous large European cities. The 
RIVM’s UAQAM model for urban 
concentrations of inert gases (NO2, SO2) 
has been extended as well.

Scenario development
The updated shared analysis 
energy scenario draws on the same 
macroeconomic and sectoral projections 
as the shared analysis energy project. 
For the shorter term (up to 2000) 
these are mainly the projections of the 
European Commission (Research DG). 
For the period beyond 2000, ShAIR 
uses aggregate assumptions for the 
world economy derived from the OECD 
linkages project. The updated scenario 
features an increased transport growth.

In the shared analysis energy project 
an a�empt has been made to build a 
separate ‘story’ describing the evolution 
in each EU country. The projections 
were made in three steps:

•  First, gradual conditional 

convergence of the EU economies by 
2030 in terms of per capita income 
was assumed. The GDP of each EU 
country for the period 2000 to 2030 
was derived on this basis.

•  Second, the starting situation of 
each country, along with clearly 
identiﬁable trends and the 
identiﬁable driving forces of growth 
for each economy, were used to 
determine the growth rate in each 
industrial sector.

•  Third, the GEM-E3 general 

equilibrium model of the EU 
economy has been used to ensure 
consistency of sectoral and 
macroeconomic projections. 

The baseline scenario simulates a 
dynamic path for the EU economy up 
to 2030. This scenario is derived from 
exogenous assumptions on the evolution 

60

Air pollution and climate change policies in Europe

of technological progress associated 
with production factors, changes in the 
global economic and environmental 
context, and the continuation of the 
current pa�ern of public ﬁnance policy.

Indicators
Policy targets addressed are directed at 
UNECE protocols, EU directives for air 
pollution and the Kyoto obligation for 
greenhouse gases. The indicators chosen 
cover:

•  socioeconomic indicators per sector;
•  emissions;
• 

transboundary air pollution (ozone, 
acidiﬁcation, eutrophication);
•  urban air quality (urban ozone, 
urban SO2, NO2 concentrations). 

Main ﬁndings with regard to linkages
•  Emission reductions as foreseen 
in the ShAIR scenario result in a 
substantial improvement in the 
indicators for acidiﬁcation and 
ozone.

•  The focus in air pollution policy is 
now on eutrophication and health 
eﬀects (ozone and particulate ma�er 
(PM)) and less on acidiﬁcation.
•  Energy trends and climate change 

policies inﬂuencing the fuel mix (less 
coal, more gas) have a signiﬁcant 
eﬀect on the emission levels of long-
range transboundary air pollutants. 
Moreover, CH4 emission reductions 
in the northern hemisphere of about 
25 %, as projected in the ShAIR study 
for the EU countries, are expected to 
lower the background concentration 
of ozone.

• 

conditions. The required reduction 
in urban emissions needed to meet 
the air quality guidelines may vary 
up to 50–60 % depending on the 
selected meteorological year.
In calculating exceedances of air 
quality guidelines in the urban 
area, hourly regional background 
concentrations are needed as input 
for those pollutants where the limit 
value is equivalent to a percentile. 
Such data are not calculated in the 
RAINS model. 

Study limitations
•  Lack of a model on agriculture 

scenarios

•  Lack of a model on non-CO2 

greenhouse gases

•  Greenhouse gas models not used for 

all European countries

•  PM not integrated in the model 

network

•  Problems with linkages of the 

various components (models) in the 
integrated assessment, creating gaps 
and twists in smooth data ﬂow

•  Problems with diﬀerences in 
assumptions of the various 
components creating inconsistencies 
in the results

•  Gaps in the data ﬂow as a result 

of missing components due to the 
lack of institutional capacity for 
integrated assessment. 

Recommendations
This study used a model network, which 
needs several improvements, such as:

•   adding a model on agriculture 

•  Under the assumption of the 

scenarios;

ShAIR emission scenario, urban air 
quality is strongly improving but 
exceedance of (proposed) air quality 
guidelines is still expected in 2020. In 
a limited number of east European 
cities the models project a major 
deterioration in air quality between 
2010 and 2020. The estimated 
number of excess deaths a�ributed 
to sulphur dioxide (SO2) exposure 
decreases sharply.

•  Sensitivity calculations show 

that the modelled concentrations 
are sensitive to meteorological 

•   adding a model on non-CO2 

greenhouse gases;

•   expanding the greenhouse gas 

models to all European countries;

•   integrating PM in the model 

network;

•   improving the link between 

transboundary and urban air quality;

•   improving the link between the 
energy model and RAINS;

•   improving the consistency between 

energy and transport models;
•   improving the module on urban 

emissions;

Annex 2: ‘Shared analysis air pollution and greenhouse gases’ (ShAIR) study

61

•   obtaining a be�er understanding 
of the state of current policies and 
measures. 

Improvement of models themselves is 
costly and time consuming. However, 
the support of model development 
could be focused on the consistency 
and coherence of the model and 
the institutional network, and the 
interconnections between the models 
used in the policy processes on climate 
change, long-range air pollution and 
urban air quality.

Lessons for the EEA for integrated 
assessment development with regard 
to linkages between air pollution and 
climate change
The construction of the ShAIR scenario 
contributes to integrated assessment 
studies in air pollution and climate 
change. In a relatively short time frame 

and within limited budgets, projections 
on transboundary and urban air 
quality, and greenhouse gas emissions, 
were made for Europe for the next 20 
years based on a common scenario of 
economic and energy developments.

Availability
Available at: h�p://reports.eea.eu.int/
topic_report_2001_12

Publications
EEA (2001). The ShAIR scenario: Towards 
air and climate change outlooks, integrated 
assessment methodologies and tools applied 
to air pollution and greenhouse gases. Topic 
Report 12/2001.

Capros P. and Mantzos L. (2000). ‘The 
European energy outlook 2010 and 
2030’, Int. J. Global Energy Issues, Vol. 14, 
Nos 1–4.

62

Air pollution and climate change policies in Europe

Annex 3: AIR-CLIM project

Study name:  

AIR-CLIM project

Period of development:  

1998–2002

Institute:  

Spatial coverage:  

Centre for Environmental Systems Research, RIVM, 
TNO-MEP and CIEMAT

Europe (western Europe, eastern Europe and the 
European parts of the former USSR)

Spatial speciﬁcity:  

European regions

Time horizon:  

1990–2100

Focus (thematic coverage):  Regional air pollution, climate change

Background information 
The ‘Regional air pollution and climate 
change in Europe’ (AIR-CLIM) project 
was an integrated assessment project 
funded by the European Commission, 
Directorate-General for Research, which 
assessed the linkages between regional 
air pollution and climate change 
in Europe and provided scientiﬁc 
information about important policy-
relevant issues. 

Scope and objectives
The aim of this project was to assess 
the linkages between regional air 
pollution and climate change in Europe 
and to provide scientiﬁc information 
about important policy-relevant issues. 
This project analyses these issues in a 
geographically detailed and quantitative 
manner. The following questions were 
addressed.

1.  Over the long run, what is the 
relative importance of regional 
air pollution and climate change 
impacts in Europe?

2.   What are the possible linkages 

between regional air pollution and 
climate change in Europe? 

In particular:
(a)  How will climate change aﬀect the 

distribution of regional air pollution 
in Europe?

(b) How will climate change aﬀect the 
sensitivity of European ecosystems 
to regional air pollution?

(c)  How will regional air pollution in 

the form of sulphate aerosols aﬀect 
climate change in Europe?

(d) What will be the impact of climate 
change policies on the costs of 
controlling regional air pollution? 

Methodology used
The basic research tool used was an 
integrated modelling framework, 
which was part of the overall integrated 
approach taken in the project. This 
framework was integrated because it 
linked key elements of the problems 
(economy, emissions, atmospheric 
processes and terrestrial impacts) which 
were usually treated separately in long 
time scales and for all of Europe.

Under the AIR-CLIM framework, 
detailed scenarios of both air pollution 
and greenhouse gas emissions were 
developed. European scenarios of 
sulphur and nitrogen dioxides that are 
consistent with the new global IPCC 
scenarios (the ‘SRES’ scenarios) of 
greenhouse gases were also developed. 
These long-term emission scenarios 
make it possible to compare the long-
term trends of regional air pollution 
with climate change in Europe.

Annex 3: AIR-CLIM project

63

In general, to compare regional air 
pollution and climate change, A1 and 
B1 IPCC scenarios were used as a 
common basis. However, the values 
for the driving forces (including 
population, economic growth and type 
and magnitude of energy production) 
assumed by the IPCC for these scenarios 
could not be used by AIR-CLIM in 
their original form because they were 
speciﬁed for large aggregated world 
regions. Therefore, the assumptions 
were downscaled to the level of 
European regions.

Besides, the framework was created 
from the components of two existing 
integrated models, RAINS and IMAGE 
2. Therefore, ﬁrst the TIMER model 
calculated the estimates of global 
greenhouse gas emissions including 
CO2, CH4 and N2O in order to compute 
climate change. Regional concentrations 
of sulphate aerosol were also calculated. 
Finally, the TIMER model provided 
a consistent method for computing 
regional NOx and SO2 emissions.

A�er computing emissions, the resulting 
deposition of acidity and nitrogen to 
the environment was estimated. The 
AIR-CLIM framework used source-
receptor matrices derived from the 
EMEP long-range transport model of 
air pollutants in Europe to compute the 
deposition. The matrices describe the 
deposition in diﬀerent grid cells due to 
unit emissions from each country. Since 
country-scale emissions are required 
for these calculations, the European 
subregional emissions calculated by 
IMAGE 2 (TIMER) were downscaled to 
the country level using the distribution 
of emissions computed by the RAINS 
model. The question of how large 
the eﬀect of climate change is on the 
source receptor relationships in Europe 
was addressed by carrying out model 
experiments with EMEP and comparing 
the results on deposition calculated for 
current and future climate conditions.

Moreover, to quantify the impacts of 
deposition on natural vegetation the 
concept of critical loads and critical 
levels was used. The critical loads were 

corrected for changed average climate 
over the scenario period. At the same 
time, the concept of ‘critical climate 
change’ was introduced with the aim of 
assessing the impacts of climate change 
and providing a more consistent basis 
for comparing them to the impacts of 
regional air pollution.

Finally, to evaluate the eﬀects of climate 
policies on costs for reducing air 
pollution emissions, ﬁrst the costs of 
climate change policies were computed. 
Then, the costs of reducing sulphur and 
nitrogen dioxide were computed with 
the help of cost curves.

Scenario development
The AIR-CLIM version of A1 and B1 
assumed modestly increasing economic 
growth up to 2020 for western Europe 
and a decline in the second half of 
the century for B1. In eastern Europe, 
economic growth was assumed for both 
scenarios. Total population sinks slowly 
in western Europe but rises gradually in 
eastern Europe until around 2050, when 
it starts to decline.

More speciﬁcally, to compute the 
emission scenarios, further assumptions 
were made about the mitigation of 
emissions.

•  The A1-P and B1-P scenarios assume 
that present air pollution policies are 
continued in Europe indeﬁnitely.
•  The A1-A and B1-A scenarios assume 
‘advanced’ air pollution policies, that 
is, emission reductions increase over 
time up to a maximum value, and 
are achieved through end-of-pipe 
measures.

•  The A1-550-P and A1-550-A 

scenarios add climate policies to 
the assumed air pollution policies. 
For these scenarios it is assumed 
that greenhouse gas emissions are 
reduced so that the atmospheric 
concentration of carbon dioxide 
stabilises at 550 parts per million in 
the atmosphere over the long run.
•  The B1-450-P and B1-450-A scenarios 
include climate policies suﬃcient to 
stabilise carbon dioxide at 450 parts 
per million by 2100.

64

Air pollution and climate change policies in Europe

•  No reduction policies were 

assumed for ammonia emissions 
(which contribute to total nitrogen 
deposition). 

Additionally, in order to compute the 
costs of climate change policies and to 
stabilise carbon dioxide at 450 and 550 
parts per million by 2100 according to 
the climate policies, a ‘carbon tax’ was 
assumed in order to stimulate a variety 
of actions. For example:

• 

• 

investments and implementation of 
energy eﬃciency;
the substitution of high carbon 
fuels with lower carbon fuels (for 
example, coal with natural gas);
•  higher levels of world trade in lower 

• 

carbon fuels; and
investments and construction of low 
or non-carbon alternatives such as 
wind energy, solar energy, biofuels 
and nuclear energy. 

Indicators
For climate change, the indicators 
chosen for the AIR-CLIM project were 
changes in surface temperature and 
precipitation because of the large 
number of potential impacts associated 
with these parameters.

For air pollution, acid deposition and 
nitrogen deposition with some a�ention 
to air concentrations of nitrogen 
oxides (NOx) and sulphur dioxide 
(SO2) were chosen. One reason is that 
their precursor emissions have been 
controlled in Europe by a series of 
international agreements. An additional 
factor is that at least one regional air 
pollutant stemming from sulphur 
dioxide emissions in Europe (sulphate 
aerosol) has an established link to 
climate change (as explained later in 
the text). For these reasons the study is 
concentrated on sulphur and nitrogen. 
However, it was recommended that 
other important regional air pollutants, 
e.g. persistent organic pollutants and 
oxidants, be given a�ention in any 
follow-up studies.

Main ﬁndings with regard to linkages
•  By 2050, practically all of Europe’s 
area outside of northern Europe 
and Russia will be aﬀected by 
either or both regional air pollution 
and climate change. The areas of 
overlapping impacts in 2050 cover 
about 16–31 % (depending on the 
scenario) of Europe’s area.

•  Model experiments by the EMEP 
model showed a relatively small 
inﬂuence of climate change on the 
distribution of acid deposition and 
nitrogen deposition in Europe.
•  The change in critical loads because 
of climate change at a particular 
location does not exceed 10–15 %. 
Forest soils, on average, will have 
higher critical loads. Nevertheless, 
some parts of western coastal regions 
and mountainous regions become 
more sensitive.

•  The eﬀect of climate change on 

deposition is quite small compared 
to its eﬀect on critical loads. For 
example, under present climate 
conditions, the area where critical 
loads of nitrogen are exceeded 
ranges from only 55.6 to 58.1 % 
because of the inﬂuence of climate 
change on deposition pa�erns, but 
varies from 46.2 to 58.1 % because of 
its inﬂuence on critical loads.
•  Climate change increases the 

sensitivity of plants to speciﬁed 
levels of air pollutants in the boreal 
forests of northern Europe, while 
it decreases plant sensitivity in 
temperate areas.

•  For the highest and lowest AIR-

CLIM scenarios (A1-P and B1-450-
A), a wide range of SO2 emissions 
causes only a small diﬀerence 
in temperature (0.10 to 0.20 ˚C, 
European annual average). Hence, 
for these model experiments, 
the inﬂuence of sulphate in the 
atmosphere on Europe’s temperature 
is rather small.

•  Climate policies usually aim to 

reduce fossil fuel use in order to 
reduce carbon dioxide emissions. 
As a side eﬀect they also reduce 
emissions of sulphur dioxide and 
nitrogen dioxides signiﬁcantly and 
that could make it easier for Europe 

Annex 3: AIR-CLIM project

65

to comply with the Gothenburg 
Protocol. In the AIR-CLIM project 
this eﬀect was found to be very 
signiﬁcant.

•  For the A1 scenarios, the annual 

costs of reducing sulphur dioxide 
emissions (without climate policies 
in place) are estimated to be between 
0.19 and 0.31 % of Europe’s GDP in 
1995 (depending on the reduction 
level). These are the long-term (2000 
to 2100) average costs.
If climate policies are in place, then 
the costs of add-on technologies 
to control SO2 could be reduced by 
about 70 % because of decreased 
fossil fuel use.

• 

•  Cost savings are lower (around 55 

%) for the B1 scenarios, because base 
emissions are already much lower 
than under the A1 scenarios, again 
because of lower fossil fuel use.
•  For NOx emissions, the long-term 
average annual costs for emission 
reductions (without climate policies) 
are somewhat higher than for 
sulphur dioxide, being about 0.51 
to 0.75 % of European GDP in 1995. 
But climate policies would also 
lower the baseline NOx emissions 
and thereby save a substantial 
sum for add-on measures. The cost 
savings with climate policies in 
place are estimated to be 40 to 55 %, 
as compared to scenarios without 
climate policies. 

Study limitations
The conclusions are true for sulphur and 
nitrogen as regional pollutants, but are 
not necessarily true for other important 
regional pollutants such as persistent 
organic pollutants and photo-oxidants. 
These other pollutants do not have the 
same chemical characteristics as sulphur 
and nitrogen, and therefore respond 
diﬀerently to wind, temperature, 
precipitation and other aspects of 
climate. Hence, an assessment of the 
connection between these substances 
and climate change would be interesting 
from both the scientiﬁc and policy 
perspective.

it was comprehensive geographically, 
and in its coverage of economic, 
emission, atmospheric and ecological 
aspects of air pollution and climate 
change, it was nevertheless limited in 
scope.

•  Research focused only on the 

impacts on natural vegetation and 
not on any other impacts such as 
the impacts on human health, crop 
production and aquatic ecosystems, 
among other categories.

•  Cost calculations investigated only 
the side beneﬁts of climate policies 
to reductions of air pollution 
emissions and did not evaluate truly 
joint policies having the objective of 
simultaneously reducing greenhouse 
gas and air pollution emissions.
•  To include climate change in any 
analysis it was necessary to use 
climate scenarios. These scenarios 
have a high rate of uncertainty 
because they are generated by 
models that must make a large 
number of approximations to 
simulate global atmospheric 
processes. This uncertainty can be 
somewhat reduced by using output 
from the new generation of regional 
climate models that can be�er 
simulate ﬁner scale meteorological 
processes important in Europe. 

Recommendations
•  While the conclusions of the AIR-

CLIM project hold for sulphur and 
nitrogen as regional pollutants, they 
will not necessarily hold for other 
important regional pollutants such 
as persistent organic pollutants and 
oxidants. These other pollutants 
do not have the same chemical 
characteristics as sulphur and 
nitrogen, and therefore respond 
diﬀerently to wind, temperature, 
precipitation and other aspects of 
climate. Hence, an assessment of the 
connection between these substances 
and climate change would be 
interesting from both the scientiﬁc 
and policy perspective.

The AIR-CLIM project was 
comprehensive but not deﬁnitive. While 

•  Future research should focus not 
only on the impacts on natural 
vegetation, but also on the impacts 

66

Air pollution and climate change policies in Europe

on human health, crop production 
and aquatic ecosystems, among 
other categories.

•  Cost calculations should investigate 
not only the side beneﬁts of climate 
policies to reductions of air pollution 
emissions, but should evaluate truly 
joint policies having the objective of 
simultaneously reducing greenhouse 
gas and air pollution emissions.
In order to include climate change 
in any analysis it is necessary to use 
climate scenarios.

• 

•  These scenarios have a high rate 
of uncertainty because they are 
generated by models that must make 
a large number of approximations 
to simulate global atmospheric 
processes. This uncertainty can be 
somewhat reduced by using output 
from the new generation of regional 
climate models that can be�er 
simulate ﬁner scale meteorological 
processes important in Europe. 

Lessons for the EEA for integrated 
assessment development with regard 
to linkages between air pollution and 
climate change
The AIR-CLIM project introduced a 
new approach to carrying out regional 
studies of air pollution and climate 
change. For Europe, this method 
allows a comparison of future trends 
in regional air pollution and climate 
change in a consistent manner. 

Moreover, it made possible the building 
of a complex modelling framework in 
a short period of time and made more 
time available for scenario analysis and 
conducting model experiments, using 
for the ﬁrst time the detailed output 
from a climate model, as input to a long-
range transport model of pollutants.

The concept of critical climate can 
be a useful new tool for researchers 
in their assessments and analyses of 
climate impacts on natural vegetation. 
The simultaneous usage of critical 
loads, critical levels and critical climate 
in AIR-CLIM, which allows a more 
consistent comparison of impacts on 
natural vegetation due to deposition, air 
concentration and climate change, can 
also be applied to many other regional 
and subregional assessments.

Availability
The ﬁnal report is available at: 
h�p://www.usf.uni-kassel.de/usf/
forschung/projekte/airclim.en.htm

Publications
Alcamo J., Mayerhofer P., Guardans 
R., Van Harmelen T., Van Minnen J. 
G., Onigkeit J., Posch M. and De Vries 
B. (2002). ‘An integrated assessment 
of regional air pollution and climate 
change in Europe’. Findings of the AIR-
CLIM project. Environmental Science and 
Policy. 5: 257–272.

Annex 4: Approaches to analyse interactions of climate change, acidiﬁ cation and ozone

67

Annex 4: Approaches to analyse 
interactions of climate change, 
acidiﬁcation and ozone (NRP project)

Study name:  

Approaches to analyse interactions of climate 
change, acidiﬁcation and ozone

Period of development:  

2000–02

Institute:  

Wageningen University and TNO-MEP

Spatial coverage:  

Europe

Spatial speciﬁcity:  

Ranging from country level to Europe as a whole

Time horizon:  

1990–2010

Focus (thematic coverage):  Climate change, air pollution

Background information 
This project was carried out within 
the framework of the Dutch ‘National 
research programme on global air 
pollution and climate change’ (NRP), 
a strategic and long-term scientiﬁc 
research programme to strengthen and 
support Dutch policy-making in regard 
to climate change as a result of global air 
pollution, by providing policy-relevant 
information.

Scope and objectives
This project focuses on the interactions 
of various problems of transboundary 
air pollution, climate change and 
stratospheric ozone. The objective of the 
present study is to examine approaches 
for an integrated analysis (scenario and 
optimisation analysis) of climate change, 
acidiﬁcation, tropospheric ozone 
formation and stratospheric ozone 
depletion, with a focus on the European 
situation. The aims are:

•  analysing the interactions between 
the four environmental themes 
above;

•  assessing model speciﬁcations 

for these four themes considering 
limitations related to, for example, 
data on emissions, environmental 
eﬀects and emission reduction costs’ 
complexity of the model and limited 
computer resources.

To reach these aims, the following 
research questions have to be addressed:

•  Which interactions exist between 
acidiﬁcation, tropospheric ozone 
formation, climate change and 
stratospheric ozone depletion?
•  How can these interactions be 
analysed either by means of 
existing models, or by combining 
parts of these models, or by new 
model structures focusing on these 
interactions?

•  Which data are required at the 

appropriate spatial and temporal 
scales for these themes and how can 
these diﬀerent scales be integrated?

•  Which information is already 
available in existing emission 
inventories and existing models? 

Methodology used
First an introduction of what the most 
important interactions are between air 
pollutants and environmental problems 
was made. The interactions that were 
taken into account were those that 
exist in sources of emissions of various 
pollutants and greenhouse gases, 
the interactions because of reduction 
strategies and the interactions during 
the formation of acidiﬁcation and 
tropospheric ozone in the atmosphere. 
The impacts of climate change on 
the source receptor relations for 

68

Air pollution and climate change policies in Europe

acidiﬁcation and tropospheric ozone 
were also considered.

formulated as a linear programme 
including a large number of sources, 
pollutants and abatement options.

Then, the characteristics of existing 
emission databases, from the point of 
view of chemical compounds, spatial 
and temporal dimensions, emission 
source and emission estimation 
methods, were analysed. The analysis 
covered European databases, based 
on national inventories prepared 
for international databases on air 
pollution abatement. These include 
EMEP, Corinair and IPCC databases 
and the Pollutant Emission Register 
(PER) from the Netherlands, as an 
example of detailed national emission 
inventory. Databases that are used as 
input into integrated assessment models 
(IMAGE 2.0 and RAINS) and into an 
atmospheric transport model (LOTOS) 
were also analysed. These databases 
were compared to each other, and in 
a second stage a number of models 
(IMAGE, RAINS-Europe and RAINS-
Asia, LOTOS, MERGE and Markal) 
were analysed, from the point of view 
of their treatment of emission reduction 
strategies.

In addition, the basic requirements of 
emission inventory databases to be used 
in an integrated analysis of acidiﬁcation, 
eutrophication, tropospheric ozone 
and global warming related problems 
in Europe were identiﬁed. The 
hypothetical ‘ideal’ speciﬁcation of such 
databases, which combine requirements 
for policy, economic and atmospheric 
analyses, was compared with the 
existing emission inventory databases, 
in order to examine to what extent they 
fulﬁl these requirements.

Furthermore, two detailed economic 
models that focus on multi-pollutants 
were discussed. Both studies deal 
with cost minimisation given a set of 
environmental constraints. This new 
economic method to model interactions 
of reduction strategies in a comparative 
static optimisation model determined 
cost-eﬀective policies for several 
environmental targets simultaneously, 
taking into account interrelations 
between these policies. The model is 

Finally, suggestions are given for the 
structure of an integrated model on the 
basis of available emission inventories 
and existing models for atmospheric 
chemistry, taking into consideration 
the results of these two models. This 
model is able to determine cost-eﬀective 
solutions at a European level for given 
targets of acidiﬁcation, eutrophication 
and tropospheric ozone and for given 
emission targets for the emissions of 
greenhouse gases, either individually or 
aggregated by means of global warming 
potentials.

Scenario development
The ﬁrst economic model structure, 
which focuses on the economic 
modelling of a cost-eﬀectiveness 
analysis for reducing various pollutants, 
was applied to the agricultural sector in 
Europe. The model is used to analyse 
cost-eﬀectiveness of strategies to reduce 
NH3, N2O and CH4 from European 
agriculture taking into account 
interactions between abatement of these 
gases.

The second model structure deals with 
a combined cost-eﬀectiveness approach 
for acidiﬁcation and tropospheric ozone. 
Changes in energy supply were allowed. 
However, the demand and supply of 
the energy are given exogenously and 
stay outside the optimisation. This 
restricts the optimisation to end-of-pipe 
technologies for acidifying pollutants 
and precursors of ozone or some 
greenhouse gases in agriculture. Data 
from Germany and the Netherlands 
that qualitatively reﬂect some real 
world proportions were taken in order 
to provide parameters for the model. 
Source receptor matrices have been 
taken from EMEP but they have been 
adjusted for the two countries.

Indicators
•  Future emissions of NOx, SO2, 

NH3 volatile organic compounds, 
CO2, CH4, N2O, several ﬂuorinated 
compounds and soot.

Annex 4: Approaches to analyse interactions of climate change, acidiﬁ cation and ozone

69

•  Other suggested indicators for 
integrated analysis in terms of 
environmental impact: CO2-
equivalent emission targets for 
greenhouse gases, critical levels for 
tropospheric ozone concentrations, 
critical loads for deposition of 
acidifying and eutrophying 
compounds. 

Main ﬁndings with regard to linkages
•  There are at least four types of 
interactions between economic 
sectors, atmospheric processes and 
environmental impacts that aﬀect 
emissions of air pollutants. These are 
the interactions between economic 
sectors and emi�ed pollutants, 
interactions between biogenic and 
biogeochemical processes and 
underlying emissions, between 
reduction strategies and related 
emissions and ﬁnally between 
emissions aﬀected by environmental 
problems.

•  The characteristics of an ideal 

emission inventory for integrated 
assessment have been identiﬁed, 
based on research aims of diﬀerent 
types of analysis (economic, 
atmospheric and policy analysis). 
The quality of an inventory is related 
to its accuracy, precision, uncertainty, 
error, reliability, completeness, 
comparability and transparency. 
None of the existing databases 
met all the requirements of an 
ideal speciﬁcation of an emission 
inventory database. None of the 
databases focuses on all four of the 
environmental problems that are 
studied in this project.

•  With respect to the aggregation level, 
it was concluded that the LOTOS 
database has the most detailed 
spatial and temporal speciﬁcation, 
which is closest to the ‘ideal’ spatial 
aggregation level, but only for a 
limited number of gases and years 
without detailed speciﬁcation of 
sources.

•  With respect to the source categories 
included, integrated models like 
RAINS and IMAGE are the most 
detailed and include several 
economic sectors and abatement 

strategies. However, they lack 
the temporal and spatial detail of 
atmospheric models.

•  An emission inventory database 

that satisﬁes all these requirements 
for economic, atmospheric and 
integrated assessment models may 
not be easy to realise.

•  Cost-eﬀective abatement of NH3 

according to the agreements in the 
Gothenburg Protocol could cause an 
increase in emissions of N2O.
•  Although total N2O emissions 
in Europe increased, total CH4 
emissions in Europe decreased due 
to NH3 abatement.

•  The reduction of acidiﬁcation 

requires large reductions of both 
SO2 and NOx emissions, which may 
only be reached by combination of 
end-of-pipe technologies, energy 
conservation and introduction of 
renewables. For this particular case, 
reduction of NOx may lead to an 
increase of ozone concentrations to 
the non-linearity in ozone formation.

•  Multiple reduction targets for 

acidiﬁcation and tropospheric ozone 
will not lead to cost savings when 
compared with single pollutant/
single target policies.

•  Renewable energy will only be 

used in modest quantities by the 
year 2010. This is mainly due to the 
relative high price of renewable 
energy compared to the price 
of fossil fuels and the fact that 
renewables are expensive related 
to the end-of-pipe technologies for 
emission reductions. 

Study limitations
•  Data availability: some chemical 

compounds are not well documented 
and measurements for many of them 
have a high rate of uncertainty.
•  The time scales relevant to the 

climate problem are much larger 
than the time scales for air pollution 
problems; the atmospheric residence 
time of most climate related species 
is 50 years or more and for most air 
pollution related species one year 
or less. The combination in one 
supermodel would imply enormous 
computational burdens.

70

Air pollution and climate change policies in Europe

consuming, as a ﬁrst step towards 
an integrated analysis of diﬀerent air 
pollution problems in Europe, the EEA 
could concentrate on so�ly linking 
existing models for the purpose of 
scenario analysis, addressing the ‘what 
if’ type of questions. A complete climate 
change plus air pollution model for 
scenario studies does not exit at the 
moment.

A next step could be to link models 
speciﬁcally designed for scenario 
analysis to models that have the 
possibility of optimisation analysis 
or general equilibrium modelling. It 
is proposed to ﬁrst decouple climate 
change calculations from air pollution in 
an analysis at the global level, in order 
to determine emission reduction targets 
for greenhouse gases in Europe. Next, 
the optimised emission levels should 
be used as one of the restrictions in an 
optimisation analysis at the European 
level, using a newly developed model 
based on elements of RAINS and 
the more detailed LOTOS system for 
transboundary air pollution.

Availability
Available at the Dutch ‘National 
research programme on global air 
pollution and climate change’ (NRP) 
Secretary which is located at RIVM.

Publications
Van Ierland E. C., Ignaciuk A., Kroeze C., 
Brink C., Schmieman E., Builtjes P., Roemer 
M. and Mayerhofer P. (2002). Approaches 
to analyse interactions of climate change, 
acidiﬁcation and ozone. NRP Report 
410200105. National Institute for Public 
Health and the Environment (RIVM).

•  Non-linear relationship between 
the formation of ozone and its 
precursors: the model used 
to compute the most eﬀective 
abatement strategies of ozone and 
acidiﬁcation, considering their 
interactions, was not detailed 
enough to give be�er insights.
•  Only a small number of countries 

were included in the example of the 
analysis.

•  The cost functions were not speciﬁed 

in any great detail. 

Recommendations
A combination of information from 
diﬀerent emission databases could be 
used in a series of atmospheric and 
environmental models. For a consistent 
set of scenarios, it is useful to analyse 
the impact on the climate change using 
ECHAM, for air pollution the LOTOS 
model, and for the potential impact 
of acidiﬁcation and eutrophication on 
ecosystems the RAINS model.

Furthermore, for this combined analysis 
of climate change and transboundary 
pollution, in regards to climate change, 
ﬁrstly the ECHAM model could be 
incorporated in an economic model, 
based on the MERGE modelling system; 
for transboundary pollution, the LOTOS 
model could be incorporated in a model 
with characteristics of the RAINS 
system.

Besides, considering the important 
interactions between CH4, N2O and NH3 
that exist in agriculture, considerable 
cost savings can be obtained if the side 
eﬀects of emission control options are 
explicitly included in the policy-making 
process.

Lessons for the EEA for integrated 
assessment development with regard 
to linkages between air pollution and 
climate change
Although the improvement of 
models themselves is costly and time 

Annex 5: Study for Europe’s environment, the third assessment

71

Annex 5: Study for Europe’s 
environment, the third assessment: 
Exploring the ancillary beneﬁts of 
the Kyoto Protocol for air pollution in 
Europe

Study name:  

Exploring the ancillary beneﬁts of the Kyoto Protocol 
for air pollution in Europe

Period of development:  

2002–03

Institute:  

RIVM and IIASA

Spatial coverage:  

Spatial speciﬁcity:  

Europe (western Europe, eastern and central Europe, 
and Russia and western new independent States)

Ranging from European regional level to country 
level

Time horizon:  

1990–2010

Focus (thematic coverage):  Air pollution, climate change

Background information
The EEA has publishedan indicator-
based report on the state and near-
term outlook of Europe’s environment 
for the 2003 conference of European 
environment ministers in Kiev: Europe’s 
environment, the third assessment. 
t. The European Topic Centre on Air 
and Climate Change (ETC-ACC) has 
prepared background material for this 
report. The study presents an integrated 
analysis of linkages and interrelations 
between scenarios and mitigation 
options for air pollution and climate 
change.

Objectives
The objective of this report is to 
explore the emission reductions of 
air pollutants as well as change in 
control costs and environmental 
impacts as a result of diﬀerent ways 
of implementing the Kyoto Protocol 
in Europe, including the use of Kyoto 
mechanisms. The report quantiﬁes 
the ancillary beneﬁts of reducing 
greenhouse gas emissions to meet the 
Kyoto targets in terms of reduction 
of air pollution and improvement of 
environmental quality.

Methodology used
The discussion focuses primarily on 
three country grouping/regions: western 
Europe (WE), central and eastern 
Europe (CEE) and Russia and Western 
NIS (R&WNIS). At this stage, the study 
is restricted to carbon dioxide (CO2), 
leaving the remaining ﬁve greenhouse 
gases covered by the Kyoto Protocol not 
addressed.

To cover a range of potential 
ancillary beneﬁts for the main region 
investigated, this study explores three 
mitigation scenarios with diﬀerent 
usage of Kyoto mechanisms to reach the 
Kyoto targets.

The ancillary beneﬁts from the 
mitigation scenarios are derived by 
comparison with a baseline scenario, 
which does not include any explicit 
climate change policies. The analysis is 
performed using a set of linked models 
that together simulate diﬀerent ways of 
achieving the Kyoto targets for climate 
change and targets for controlling 
regional air pollution. This study 
integrates the diﬀerent research areas 
by linking models that address climate 

72

Air pollution and climate change policies in Europe

change issues (FAIR and the energy 
model IMAGE/TIMER) and regional air 
pollution (RAINS).

The impacts of climate change scenarios 
are explored by comparing emission 
control costs and environmental impact 
indicators. The results included in the 
analysis are the trends in emissions, the 
areas of the ecosystem not protected 
against damage from acidiﬁcation and 
eutrophication, and exceedances of 
air quality targets for ozone. Control 
costs of diﬀerent scenarios will also 
be addressed, both for the policies 
to reduce greenhouse gases and for 
emission control costs for regional air 
pollution.

It should be noted that the results of 
the study should be seen as explorative 
for the ancillary beneﬁts in the larger 
European regions, for emission 
control costs, for climate policies and 
for air pollution control. The costs 
calculated by diﬀerent models should 
be compared with caution since 
they stem from diﬀerent modelling 
traditions (in fact, even within each 
particular area, considerable ranges of 
cost estimates exist). Furthermore, the 
results presented in this report are of a 
descriptive ‘what if’ character and do 
not intend to be prescriptive for any 
future implementation of the Kyoto 
Protocol and air pollution policies. 

Scenario development
A baseline scenario for the year 2010 was 
developed to assess trends in carbon 
dioxide emissions in the absence of 
explicit policies to control greenhouse 
gas emissions and to assess the eﬀect of 
previously decided control measures 
on future emissions of air pollutants 
and ecosystem protection. The baseline 
scenario includes emission and fuel 
standards in each country according 
to the current legislation (CLE) and 
emission ceilings from the national 
emission ceilings directive of the EU and 
from the Gothenburg Protocol to the 
CLRTAP. The baseline is characterised 
by a continuation of trends that were 
dominant during the 1990s: increasing 
globalisation, further liberalisation 

and average assumptions regarding 
population growth, economic growth 
and technology development (ETC-
ACC, 2002).

Furthermore, the following policy 
scenarios that are assumed to meet the 
Kyoto commitments are explored and 
compared with the baseline.

1.  Domestic action only (DAO). All 
Annex 1 parties (countries from 
western Europe, central Europe as 
well as Russia, new independent 
States, Canada, Australia, New 
Zealand and Japan) implement 
their Kyoto targets domestically, 
i.e. without use of the Kyoto 
mechanisms. The exception is the 
trade within the regions considered, 
thus for instance among the current 
EU member countries.

2.  Trade — No hot air (TNH). This 

scenario assumes full use of Kyoto 
mechanisms among Annex 1 parties, 
but without any use of hot air. This 
scenario explores the maximum 
ancillary beneﬁts that can be 
obtained under a trade case.
3.  Trade with hot air (THA). This 

scenario assumes full use of Kyoto 
mechanisms among Annex 1 parties 
and includes the use of hot air. 
However, the supply of hot- air is 
limited to the level that maximises 
the proﬁts of Russia and Ukraine 
from selling the emission permits. 
According to calculations performed 
by FAIR, the supply of tradable hot 
air permits is 25 % of total available 
potential. 

Indicators
CO2 emissions
Air pollutant emissions (SO2, NOx, VOC 
and PM10)
Emission control costs
Ecosystems with deposition exceeding 
critical loads for acidiﬁcation 
(percentage of ecosystem area)
Ecosystems with deposition exceeding 
critical loads for eutrophication 
(percentage of ecosystem area)
Population exposure to ozone
Vegetation exposure to ozone

Annex 5: Study for Europe’s environment, the third assessment

73

• 

Main ﬁndings with regard to linkages
Implementation of climate change 
• 
policies to comply with the Kyoto 
Protocol is likely to induce signiﬁcant 
ancillary beneﬁts for air pollution in 
Europe. The results of the domestic 
action scenario for western Europe 
can be compared to those of the 
earlier studies, with ancillary 
beneﬁts being slightly less as result 
of the fact that the CO2 baseline 
projection of this study is slightly 
lower — and some new (more 
stringent) policies for regional air 
pollutants have been introduced 
under the baseline. Interestingly, the 
‘coupling’ between reductions in CO2 
emissions and reduction of regional 
air pollutants is the strongest in 
central Europe, followed by Russia/
western NIS and ﬁnally western 
Europe.
In case of the trading scenarios, the 
ancillary beneﬁts of climate policies 
are partly ‘traded’ to other European 
regions. In case of the trading 
scenario without hot air, sulphur 
emission reduction in central 
Europe and the former Soviet 
Union are in the order of 20 %. In 
the more realistic scenario with 25 
% use of hot air (banking scenario) 
this emission reduction is about 
10–15 %. Interestingly, as the linkage 
between sulphur emissions and 
carbon dioxide emission reduction 
is stronger outside western Europe, 
the ancillary beneﬁts for Europe as 
a whole can be higher in the trading 
scenarios than in the domestic action 
case — depending on the question 
of how much hot air is used (more 
hot air use limits climate policy 
implementation costs in western 
Europe but reduces ancillary 
beneﬁts). 
In terms of acidiﬁcation impacts, 
similar trends can be observed. 
For Europe as a whole, emissions 
trading can lead to more reduction 
of acidiﬁcation impacts — but 
only in case the amount of hot 
air that is used is limited (in the 
scenario with 25 % use of hot air 
the impacts between the trading 
scenario and domestic action 

are more or less similar). In fact, 
even in western Europe itself the 
diﬀerences in ancillary beneﬁts 
in terms of acidiﬁcation impacts 
between the domestic action and 
trading scenario are relatively small 
despite the fact that most of the CO2 
emission reduction takes places 
outside western Europe. The reason 
for this is that sulphur reduction in 
central Europe also has an impact on 
acidiﬁcation in western Europe.
•  Climate policies can lead to large cost 
savings in reducing air pollution 
emissions. This is caused by structural 
changes in energy systems induced 
by climate policies. It should be 
noted, however, that there are a 
number of diﬃculties in comparing 
the cost estimates for climate policies 
and regional air pollution policies 
mentioned in this study. The results 
suggest that for the domestic 
action scenario about a ﬁ�h of the 
total costs to implement the Kyoto 
scenario are regained in terms of 
reduced costs for air pollution 
control. Implementation of Kyoto 
mechanisms (emissions trading) 
result in a smaller reduction of air 
pollution control costs in western 
Europe (EUR 2–3 billion), but from 
the perspective of total costs this is 
clearly compensated in reduction 
of climate policy costs (EUR 11–12 
billion). Trading decreases the 
air pollution control costs in the 
other regions, but these gains are 
considerably lower due to the fact 
that environmental policies are less 
strict.

•  Climate change policies also impact 
emissions of particulate ma�er. 
A relatively new concern in air 
pollution policies is the emissions 
of particulate ma�er. Also the 
emissions of PM10 are strongly 
coupled to climate policies. The 
ﬂat rate 10 % reduction of carbon 
dioxide emissions shows that the 
link is particularly strong in central 
and eastern Europe, with reductions 
of PM10 being even stronger 
than those of CO2. As a result, 
implementing the Kyoto Protocol 
by means of emissions trading can 

74

Air pollution and climate change policies in Europe

result in a much stronger reduction 
of European PM10 emissions (7–8 
% than domestic action (2 %)). 
Interestingly, there is growing 
interest in the role of emissions of 
particulate ma�er directly on climate 
change (both in terms of cooling and 
warming).

•  The results can be important in 

Recommendations
Overall strategies for climate change 
and regional air pollution can lead to 
cost savings and larger environmental 
beneﬁts, but further analysis of the 
interactions, and in particular of the 
diﬀerent costing methodologies, could 
help to further deﬁne strategies that 
fully harvest the potential synergies.

designing climate policies. In view 
of the ﬁnancial and environmental 
beneﬁts of climate policies, including 
emissions trading, it might be 
a�ractive to make sure that the use 
of hot air in climate policies indeed 
remains limited (as assumed in these 
scenarios). Moreover, it was shown 
that, for western Europe, using 
ﬂexible instruments with central 
and eastern Europe can have several 
a�ractive side eﬀects, such as a 
stronger improvement in the overall 
environmental situation in Europe, 
and, as a result of the transboundary 
nature of regional air pollution, even 
some improvements in the western 
European environment. Using CDM 
with developing countries foregoes 
these beneﬁts, and as a result a 
higher ‘carbon price’ for JI/emissions 
trading compared with CDM may be 
justiﬁable from a western European 
perspective. Although not analysed 
here, the opposite is obviously true 
for Japan in view of transboundary 
air pollution from China. 

Study limitations
•  The study is restricted to carbon 

dioxide (CO2), leaving the remaining 
ﬁve greenhouse gases covered by the 
Kyoto Protocol not addressed.
•  The costs calculated by diﬀerent 

models should be compared with 
caution since they stem from 
diﬀerent modelling traditions (in 
fact, even within each particular area 
considerable ranges of cost estimates 
exist).  

Lessons for the EEA for integrated 
assessment development with regard 
to linkages between air pollution and 
climate change
This technical report underpins the pan-
European environment report produced 
by the European Environment Agency 
for the ministerial conference to be 
held in Kiev, May 2003. The integrated 
analysis of linkages and interrelations 
between scenarios and mitigation 
options for air pollution and climate 
change used in this report shows that 
implementation of climate change 
policies to comply with the Kyoto 
Protocol is likely to induce signiﬁcant 
ancillary beneﬁts for air pollution in 
Europe. Therefore, it could support 
the eﬀort of identifying policies, which 
look at the cost- and environmental 
eﬀectiveness of proposed solutions in 
an integrated way, preventing ineﬃcient 
use of resources and implementation of 
sub-optimal solutions. 

Availability
The report is available on Internet at 
h�p://reports.eea.eu.int/technical_
report_2004_93/en 

Publications
EEA (2004). Van Vuuren, D. P., Cofala J., 
Eerens H. C., Oostenrĳk R., den Elzen 
M. G. J., Heyes C., Klimont Z. and 
Amann M. Exploring the ancillary beneﬁts 
of the Kyoto Protocol for air pollution in 
Europe. Technical report No 93.

Annex 6: Ancillary beneﬁ ts and costs of greenhouse gas mitigation

75

Annex 6: Ancillary beneﬁts and 
costs of greenhouse gas mitigation 
(proceedings of the OECD workshop)

Study name:  

Ancillary beneﬁts and costs of greenhouse gas 
mitigation

Year of development:  

2000

Institute:  

IPCC, OECD

Spatial coverage:  

World

Spatial speciﬁcity:  

Ranging from world level to country level

Focus (thematic coverage):  Climate change, case studies

Background information 
In March 2000, an international 
workshop was held to consider the 
development of systematic methods 
for creating and assessing policies and 
programmes to mitigate the direct and 
indirect impacts of climate change and 
for estimating costs and beneﬁts of these 
policies. It is generally understood that 
policies which tend to reduce GHGs can 
have positive and negative ‘ancillary 
eﬀects’ on public health, ecosystems, 
land use and materials, and that such 
eﬀects can appropriately be subtracted 
from (or added to) mitigation costs to 
assess the social cost of such policies.

The workshop brought together many 
experts in this ﬁeld to discuss and 
identify key issues for further analysis. 
The workshop was organised by the 
IPCC and was co-sponsored by OECD, 
RFF, Statistics Norway, USDoE, US EPA 
and WRI. This publication includes 
many of the papers presented at the 
workshop.

Scope and objectives
The workshop, results of which are 
presented in this publication, was 
designed to:

•  establish a common basis of 

understanding about the conceptual 
and empirical elements of ancillary 

• 

• 

beneﬁts and costs of climate change 
policies;
identify options for integrating 
ancillary beneﬁts/costs into policy 
design and analysis;
identify research gaps and fruitful 
areas for further research to narrow 
uncertainties about this issue and 
make the analysis more useful for 
policy-makers. 

Furthermore, the workshop facilitated a 
dialogue between analysts in this ﬁeld 
and highlighted recent case studies from 
developed and developing countries. It 
also highlighted some continuing areas 
of debate, including valuation of health 
impacts and diﬀerences in approach 
between industrialised and developing 
countries.

In summary, it conﬁrmed that positive 
and negative ancillary eﬀects could 
be crucial to the development of 
eﬀective and eﬃcient policy-making on 
greenhouse mitigation.

Methodology used
The diﬀerent terms used to depict 
ancillary eﬀects reﬂect diﬀerences in 
their entry into the policy process. Thus, 
the term co-beneﬁts (sometimes also 
referred to as multiple beneﬁts) signals 
eﬀects that are taken into account as 
an explicit (or intentional) part of the 

76

Air pollution and climate change policies in Europe

development of GHG mitigation policies. 
The term ancillary beneﬁts indicates 
impacts that arise incidental to mitigation 
policies. This publication uses the term 
ancillary eﬀects to denote those impacts 
that occur as an incidental consequence 
of changes in GHG emissions. This 
should be understood to include negative 
impacts, or costs, and does not imply 
that the ancillary eﬀects are necessarily 
of lesser importance than greenhouse gas 
abatement. The terms ‘ancillary eﬀects’ 
or ‘ancillary beneﬁts and costs’ are used 
in this paper when addressing literature 
that primarily looks at climate change 
mitigation, but also recognises there may 
be beneﬁts in other areas.

In addition, it introduced the general 
approach to ancillary eﬀect analysis, 
where climate mitigation policies 
operate through an economic and 
institutional system within a country 
that leads to reductions in GHGs, 
changes in other pollutants, and 
mitigation costs.

One vital element in this analysis of 
ancillary eﬀects is the development of 
the analytic baseline — which includes 
projections of many of these institutional 
and socioeconomic parameters — since 
these baseline issues determine 
the environment in which climate 
change policies will have their eﬀects. 
Morgenstern (2000) identiﬁes ﬁve issues 
where baselines could be signiﬁcant 
in assessing ancillary eﬀects. The ﬁrst 
three of these issues — non-greenhouse 
policies, technology and economic 
development — are all very closely 
interconnected. Changes in any of these 
will generally have direct implications for 
the others. The ﬁnal two — demography 
and natural activities — also have such 
linkages, but of a far smaller order, 
so these can usefully be treated as 
exogenous to GHG policy evaluation.

There are also other key issues that 
need to be considered in the analysis 
of ancillary eﬀects. For example, 
ancillary eﬀects should be understood 
and estimated in geographic and time-
speciﬁc contexts. As their examination 
is extended into developing countries, 

a number of diﬃculties arise. For many 
developing countries the problem is not 
simply ignorance about the existence 
of ancillary eﬀects but rather that 
decision-makers have to weigh the 
potential ancillary eﬀects of proposed 
GHG mitigation policies against other 
priorities, such as the satisfaction of the 
basic needs.

Furthermore, in order to ensure that 
analyses of potential ancillary eﬀects 
are integrated into the policy process, it 
is important to consider as many types 
of ancillary eﬀects as practicable. Four 
categories of ancillary eﬀects could be 
identiﬁed: health, ecological, economic 
and social. Comprehensive coverage is 
also important within classes of ancillary 
eﬀects as well as between them. O�en 
only a subset of the relevant pollutants 
is considered in ancillary pollutant 
studies. It is now widely recognised 
that multiple pollutants may yield 
signiﬁcant ancillary eﬀects and that 
the beneﬁts of emission reductions can 
vary tremendously depending on the 
spatial location of emission reductions 
vis-à-vis the proximity of the exposed 
population.

Moreover, much of the controversy 
surrounding ancillary eﬀects really 
concerns the issue of valuation, 
especially the risks to human health and 
loss of life. Participants at the workshop 
raised the option of performing cost-
eﬀectiveness analysis of alternative 
policies instead of cost-beneﬁt analysis 
as a way to improve policy-making 
while avoiding the controversies and 
uncertainties of valuation.

A further potential source of ancillary 
costs is the ‘ancillary leakage eﬀect.’ 
Though there is debate about the 
signiﬁcance of the eﬀect, it is widely 
observed in modelling the impacts 
of Annex I actions to reduce GHG 
emissions that carbon emissions in 
non-Annex I countries may rise, due 
to changes in relative factor prices. The 
resulting increase in coal use (and in 
use of other fossil fuels) in non-Annex 
I countries — the carbon leakage 
— brings with it an ancillary cost of 

Annex 6: Ancillary beneﬁ ts and costs of greenhouse gas mitigation

77

greater air pollution and other negative 
externalities. However, the issue is not 
well studied and the signiﬁcance of the 
eﬀect is not known.

Finally, there is general agreement 
that the uncertainty surrounding the 
estimates of ancillary impacts is at 
least as great as the value of those 
estimates as that associated with 
other mitigation costs. At the least, 
ancillary beneﬁt studies should provide 
similar qualitative information about 
uncertainty.

Scenario development
Almost all the studies of ancillary eﬀects 
reviewed here analyse the eﬀects of a 
GHG reduction policy through a tax 
on carbon. Only two studies consider 
alternative programmes: a national 
eﬃciency programme, and energy 
eﬃciency improvements, based on the 
adoption of existing technologies. The 
level of abatement of these two studies 
is relatively modest.

As far as the other policies, which 
were assumed in the diﬀerent study 
approaches, are concerned, there 
are some key diﬀerences related to 
assumptions about baseline regulatory 
policies. For instance, the abatement cost 
savings from reducing SO2 emissions 
in response to a carbon tax is counted 
because SO2 emissions are capped in 
the US. Similar adjustments are not 
made for SO2 taxation (or taxation of 
other pollutants) in Europe, where large 
diﬀerences exist in regulatory policy.

Furthermore, several of the developing 
country studies relate the values for 
health impacts with future income 
growth. In general, developed country 
studies do not. On the other hand, the 
majority of the ancillary eﬀect studies 
do not incorporate the potential impacts 
of changing demographic proﬁles. The 
level of spatial detail varies very widely, 
from the ﬁne detail to national level 
evaluations including the international 
summation of national ﬁgures.

Most of the studies in this publication 
use static or dynamic CGE models. 

One employs an econometric model, 
which provides top-down and 
sectorally aggregate estimates of 
ancillary eﬀects/costs. The modelling 
of carbon reductions as a result of a 
policy intervention, such as a tax, is 
credible though subject to key choices 
about energy substitution and demand 
elasticities. Although restricted to the 
electricity sector, there is only one 
study that provides the sole example 
of location speciﬁcity of an economic 
model. Other studies do not use an 
economic model, but follow a bo�om-
up approach, positing some increase in 
energy eﬃciency or reduction in carbon 
and estimating the ancillary eﬀects that 
would result, at a reasonably detailed 
spatial level. Finally, most of the studies 
try to quantify uncertainties. In addition, 
many conduct sensitivity analyses on 
key economic, health and valuation 
parameters to estimate the range of 
possible ancillary eﬀects.

Indicators
•  Avoided deaths and illness tied with 
exposure to particulate ma�er in 
developed countries.

•  Mortality and morbidity associated 
with ozone and particulate ma�er.
•  The amount of willingness to pay 

(WTP)/willingness to accept (WTA) 
for avoiding such health impacts.
•  Avoided costs (e.g. cost savings for 
meeting the SO2 cap in the United 
States). If the SO2 cap is binding, 
moderate policies to reduce GHG 
emissions from the power and 
industrial sectors will not lead to 
further reductions of SO2 emissions. 
As these emissions are capped, the 
result is abatement cost savings 
to those purchasing or otherwise 
acquiring SO2 permits freed up 
by the GHG policy induced SO2 
reductions). 

Main ﬁndings with regard to linkages
From the case studies reviewed some 
main conclusions were highlighted:

•  Changes in assumptions about the 
future price of oil could drastically 
change the measurement of ancillary 
beneﬁts as higher prices would 

78

Air pollution and climate change policies in Europe

themselves drive many of the 
improvements which climate change 
policies might support.

• 

•  Avoided costs may be an important 
and growing source of ancillary 
beneﬁts; it is important to identify 
and quantify their range.
•  Preliminary analysis of extant 
modelling results suggests the 
possibility of ancillary costs resulting 
from increases in conventional 
pollutants in developing country 
regions as a consequence of the 
‘leakage eﬀect’ of carbon reductions 
under the Kyoto Protocol.
•  Meteorology and other factors, 
including the potential for a 
non-linear relationship between 
emissions and pollutant 
concentrations, or between 
concentrations and health eﬀects, 
further enhance the value of 
complex, location-speciﬁc models.

•  Health eﬀects typically account 
for 70–90 % of the total value of 
ancillary beneﬁts in places where 
the unemployment rate is high, 
the amount of willingness to pay 
(WTP)/willingness to accept (WTA) 
for avoiding such health impacts 
may be lower or the estimate of loss 
of earnings due to illness may be 
lower.

•  The ‘Value of a statistical life’ (VSL) 
routine values used in the literature 
could lead to a diﬀerence of 300 % in 
ancillary beneﬁt estimates.

•  Ecological ancillary beneﬁts will 
arise from reductions in airborne 
emissions, although these have not 
yet been speciﬁcally modelled.
•  Some studies ﬁnd that the beneﬁts 
of the health eﬀects avoided by 
mitigation measures, per tonne of 
carbon, are roughly equal to the 
carbon tax/tonne needed to meet 
those goals or even exceed the tax. 
Others ﬁnd relatively small ancillary 
beneﬁts. Thus, it is diﬃcult to 
generate broad, general estimates 
of the magnitude of ancillary eﬀects 
relative to mitigation costs.

•  The broad divergence in the value 
of ancillary eﬀect estimates, even 
within the same country, is evident. 
Where studies include uncertainty 

bounds, these are o�en quite large 
relative to the central estimate.
Inclusion of ancillary eﬀects is likely 
to make design of GHG abatement 
policies more complex, especially 
in adding a geographic dimension 
which need not otherwise exist. In 
terms of selecting policy instruments, 
diﬀerent instruments do diﬀer in 
their ability to incorporate ancillary 
eﬀects. However, all instruments 
appear capable of building in 
ancillary eﬀects to some degree.
Inclusion of ancillary eﬀects can 
aﬀect not just the type of policy 
instrument put in place, but the 
sectoral targets of policies. Where 
policies are aimed at speciﬁc 
technologies, they may also aﬀect the 
choice of technological options.
If congestion is the overriding 
ancillary eﬀect (at least in peak 
hours), then measures which reduce 
traﬃc will have far greater ancillary 
eﬀects than those which reduce the 
emission intensity of traﬃc.
In the case where ancillary beneﬁts 
outweigh abatement costs, as found 
in some studies, the relative cost 
assessment could be completely 
switched around unless there are 
comparable ancillary costs in non-
energy sectors.

• 

• 

• 

Study limitations (from the case 
studies reviewed)
•  The diﬀerences in policy scenarios, 

modelling and parameters in 
addition to the real diﬀerences across 
countries, such as population size, 
regulatory diﬀerences, technological 
sophistication and baseline 
emissions of conventional pollutants, 
lead to diﬀerent estimates of the size 
and scale of ancillary eﬀects.

•  Most of the studies were concentrated 

on health ancillary eﬀects.

•  The dominance of health impacts 
in ancillary eﬀect analysis can 
qualitatively alter the analysis.

•  Lack of available studies on 

ecological ancillary eﬀects and land 
use impacts is an important gap in 
the knowledge base.

•  There was a lack of indigenous data 
in developing countries and it was 

Annex 6: Ancillary beneﬁ ts and costs of greenhouse gas mitigation

79

•  analysis that a�empts to capture 

ancillary costs;

•  consideration of the time frame over 
which ancillary eﬀects are realised, 
and the relationship to GHGs policy 
timeframes.

Lessons for the EEA for integrated 
assessment development with regard 
to linkages between air pollution and 
climate change
This publication is part of the eﬀort to 
assess potential ancillary eﬀects. It is 
important to follow the eﬀorts to ﬁnd 
suitable costing methods to quantify 
these eﬀects as they could further help 
to understand how ancillary eﬀects can 
inﬂuence choices about the stringency 
and types of GHG mitigation policies 
that may be adopted.

Availability
Papers and presentations of the 
workshop are available at h�p://www.
oecd.org/env/cc

Publications
Pearce, D. (2000). Policy frameworks for 
the ancillary beneﬁts of climate change 
policies, ancillary beneﬁts and costs of 
greenhouse gas mitigation, Proceedings of 
an IPCC co-sponsored workshop, March 
2000, OECD, Paris.

not possible to asses how accurate 
beneﬁt transfers from developed 
countries really are.

•  Aggregate models, which have 

many advantages for the study of 
GHG mitigation policies, are not 
well suited to capture the important 
detail or non-linearities involved in 
estimating ancillary eﬀects.

•  None of the studies reviewed in this 
assessment reported estimates of 
ancillary costs. 

Recommendations
High priority areas for further research:

•  more targeted case studies on non-
health ancillary eﬀects, especially 
ecological impacts, some of which 
are related to air pollution;

•  more comprehensive generation 
and use of health information on 
morbidity and mortality tied to the 
array of air pollutants of interest;
•  more sophisticated assessments of 

• 

baseline health and social conditions 
as these inﬂuence susceptibility to 
pollution in various regions;
transparent and reasonable 
speciﬁcation of regulatory baselines, 
particular with respect to future air 
pollution regulation;

•  development of integrated modelling 

which allows simultaneous 
consideration of macroscale and 
geographically speciﬁc impacts;
•  be�er modelling to incorporate 
avoided costs and integrated 
achievement of multiple policy 
goals;

80

Air pollution and climate change policies in Europe

Annex 7: Workshop of the Task Force 
of Integrated Assessment Modelling 
(TFIAM) of UNECE on ‘Linkages and 
synergies of regional and global 
emission control’

(This text is taken from the conclusions 
of the workshop on ‘Linkages and 
synergies of regional and global 
emission control’, 27–29 January 
2003, EMEP Centre for Integrated 
Assessment Modelling, Laxenburg, 
Austria, as presented to the Task Force 
on Integrated Assessment Modelling 
at its 28th meeting on 7–9 May 2003 in 
Haarlem, the Netherlands).

Introduction
1.   The workshop was a�ended by 

75 experts from Austria, Belgium, 
Denmark, Finland, France, 
Germany, Italy, the Netherlands, 
Norway, Poland, Portugal, Sweden, 
Switzerland, the United Kingdom, 
the United States of America and 
the European Community, as 
well as the Coordination Centre 
for Eﬀects (CCE), the UNECE 
secretariat, the World Health 
Organisation (European Centre 
for Environment and Health), the 
European Environment Agency, the 
European Community Joint Research 
Centre (Institute for Environment 
Sustainability), the European 
Chemical Industry Council 
(CEFIC), the Union of the Electricity 
Industry Eurelectric) and the World 
Conservation Union (IUCN).

2.   The workshop was organised by the 
Task Force on Integrated Assessment 
Modelling and the EMEP Centre for 
Integrated Assessment Modelling 
(CIAM). It was supported by 
the Topic Centre on Air and 
Climate Change of the European 
Environment Agency (ETC-ACC).
3.   The conclusions of the workshop and 
an informal report with extended 
abstracts will be presented to the 
Task Force on Integrated Assessment 
Modelling at its 28th meeting on 7–9 

May 2003 in Haarlem (Netherlands). 
The presentations of the workshop 
can be found at: www.iiasa.ac.at/
rains/meetings/AP&GHG-Jan2003/
announcement.html.

4.   Many of the traditional air pollutants 
and greenhouse gases have common 
sources, their emissions interact 
in the atmosphere, and separately 
or jointly they cause a variety 
of environmental eﬀects on the 
local, regional and global scales. 
Thus, emission control strategies 
that simultaneously address air 
pollutants and greenhouse gases 
could be beneﬁcial on all scales. The 
executive body at its 20th session 
noted with interest the plans of the 
Task Force on Integrated Assessment 
Modelling to examine the links 
and synergies between regional 
air pollution and climate change, 
recognising the importance of these 
links. Welcoming the work initiated 
to explore such links, it requested 
EMEP to address all relevant aspects 
of these links in its future work.
5.   Through a series of brief overview 

presentations, the workshop 
reviewed from the air pollution 
perspective the scientiﬁc knowledge 
on the physical linkages between 
the control of air pollution and 
greenhouse gases (atmospheric 
chemistry, impacts, emission control 
options) and examined possible 
synergies addressing sectoral 
emission control options, multi-
pollutant strategies and economic 
instruments. The objective was 
to identify future directions for 
integrated assessment modelling 
under the Convention on Long-
Range Transboundary Air Pollution 
so that the policy-relevant 
linkages and synergies could be 

Annex 7: Workshop of the Task Force of Integrated Assessment Modelling

81

systematically explored. While 
the focus of the workshop was on 
the linkages and synergies from a 
scientiﬁc perspective, the discussion 
also covered aspects relevant for 
policy-making in developing air 
pollution control strategies.

6.   The workshop recognised that the 
numerous linkages and synergies 
provide a strong argument for 
developing programmes that 
address air pollution and climate 
change simultaneously or at least 
in parallel. The ﬁrst step is to 
encourage the development of 
analytical tools to be able to analyse 
such a comprehensive programme. 
At the same time, policy analyses of 
air pollution control should consider 
the air pollution eﬀects on climate 
change, and vice versa.

I.  The physical linkages

A. Atmospheric chemistry
7.   The impact of gases and aerosols 

on climate is usefully expressed as 
radiative forcing. Radiative forcing 
is a measure (expressed in wa�s 
per square metre) to estimate, to a 
ﬁrst order, the relative impact on 
climate due to radiatively induced 
perturbations. The concept assumes 
a general relationship between 
global mean forcing and the global 
mean equivalent temperature 
response. While the concept of 
radiative forcing is useful, it does 
not encompass all the important 
impacts of changing atmospheric 
composition on climate, especially 
at the regional scale and in relation 
to variables other than surface 
temperature, such as precipitation.

8.   Radiative forcings of the six 

long-lived trace gases covered 
by UNFCCC (greenhouse gases 
— GHGs) have received much 
a�ention. Also some short-lived 
air pollutants, notably ozone 
and ﬁne particles, exert climate 
impacts. While GHGs are uniformly 
distributed at the global level, for 
ozone and ﬁne particles there are 
some high concentration regions, 
which are not necessarily close to the 

sources of the precursor emissions. 
In some parts of the world, 
signiﬁcant reductions of traditional 
air pollutants have been achieved, 
which is not the case for GHGs.
9.   The radiative forcings of ozone and 
ﬁne particles are diﬀerent, both in 
space and time, from those of the 
greenhouse gases. Model simulations 
have shown that short-lived air 
pollutants can lead to signiﬁcant 
regional climate perturbations, 
especially aﬀecting seasonal 
precipitation pa�erns, which may 
contribute regionally to ﬂoods and 
droughts. Climate control strategies 
are usually examined at long time 
horizons, sometimes up to 100 years 
or more. Air pollutants may aﬀect 
climate much more quickly and such 
impacts can also be addressed by 
policy on shorter time scales.

10.  Particulate ma�er (PM) is a diverse 
group of substances with diﬀerent 
physical-chemical properties 
and diﬀerent climate impacts. 
The eﬀects of aerosol forcing on 
precipitation pa�erns may be very 
important. Some of these eﬀects 
are very uncertain, in particular 
the indirect eﬀects of aerosols (via 
cloud coverage and cloud optical 
properties).

11.  Sulphate, nitrate and organic 

carbon particles in the atmosphere 
aﬀect the climate in the opposite 
direction than GHGs, i.e. they tend 
to have a cooling eﬀect and can 
lead to reduced precipitation. Other 
carbonaceous particles (black carbon, 
soot) are thought to have a positive 
forcing on the climate, although the 
magnitude of this eﬀect is uncertain. 
Hence, while the reduction of black 
carbon will be beneﬁcial in reducing 
climate change, this is not the case 
for the reduction of other aerosols.

12.  In Europe, black carbon constitutes 
only a small share (10–15 %) of total 
PM2.5 emissions. Emission reductions 
necessary to reduce health eﬀects 
of PM will have to reduce not 
only black carbon but also other 
components of PM. The net eﬀect of 
a PM reduction strategy to cut health 
eﬀects substantially may therefore 

82

Air pollution and climate change policies in Europe

be an increase in radiative forcing. 
To reach any given climate targets, 
such PM reductions will have to be 
compensated by further measures 
on other climate gases. At the same 
time, strategies to reduce PM should 
be developed so that they place more 
emphasis on bringing down black 
carbon emissions than measures 
do at present. Such strategies will 
target diesel emissions, biomass 
burning as well as residential 
combustion of solid fuels and should 
place greater emphasis on non-
road mobile sources. Preliminary 
estimates suggest that especially 
ships contribute increasingly to black 
carbon concentrations.

13.  Tropospheric ozone has a relatively 

strong radiative forcing and 
therefore measures to reduce 
it will be beneﬁcial in reducing 
climate change. The inﬂuence of 
tropospheric ozone on climate 
change is be�er understood than 
the role of aerosols. Regional 
ozone levels build up on top 
of a considerable hemispheric 
background ozone baseline. 
Hemispheric ozone baseline 
concentrations have been increasing 
by about 0.5 ppb per year and are 
projected, in some scenarios, to 
increase in the future. One of the 
important factors contributing to this 
increase is the rise in global methane 
emissions.

14.  Methane is important both in 
building up the hemispheric 
background of ozone and in 
enhancing intercontinental ozone 
transport. Methane also exerts 
direct radiative forcing and is 
a GHG with a relatively short 
atmospheric lifetime (12 years). A 
methane emission reduction strategy 
will therefore be very eﬀective in 
reducing both climate change and 
ozone concentrations. While natural 
methane emissions are important, 
the larger (and growing) share is 
anthropogenic. Preliminary results 
of work on introducing methane into 
the RAINS model 1 show that there 
is signiﬁcant potential for controlling 
methane emissions.

15. Climate change is likely to 

aﬀect regional circulation and 
wind pa�erns. This may aﬀect 
the accuracy of source-receptor 
relationships developed on the basis 
of historic meteorological data. For 
a relatively short time horizon, such 
as up to 2020, this eﬀect is not likely 
to be important and it would be very 
diﬃcult to quantify. 

B. Environmental impacts
16. There are a number of linkages 
between climate change and air 
pollution eﬀects, but they can go 
in diﬀerent directions and are 
not yet fully understood. Model 
results suggest, for example, 
that: (1) a temperature increase 
through climate change may 
reduce ecosystem sensitivity to 
acidiﬁcation damage and tends to 
change deposition pa�erns so that 
there will generally be less critical 
load exceedance; (2) an increase in 
nitrogen deposition (through air 
pollution) may raise the ability of 
plants to store carbon diminishing 
radiative forcing; (3) many air 
pollutants tend to weaken plant 
growth thereby reducing carbon 
storage capacity; (4) both climate 
change and air pollution may 
adversely aﬀect biodiversity. 

II. Synergies of multi-objective 
strategies

17.  Many measures to cut air pollution 
also beneﬁt the climate through 
reduction of GHG emissions and 
vice versa. Understanding these 
synergies in emission controls 
and addressing local, regional and 
global objectives simultaneously, 
rather than separately, is needed to 
achieve overall cost-eﬀectiveness. 
As marginal costs of further air 
pollution abatement measures 
tend to increase rapidly once a 
certain reduction level has been 
achieved, any potential for cost 
savings for strategies to reach air 
quality objectives must be explored. 
Synergies may free resources that 

Annex 7: Workshop of the Task Force of Integrated Assessment Modelling

83

allow reaching more ambitious 
targets. Many of the driving 
forces underlying air pollution 
and climate change are identical: 
economic growth, consumption 
and production processes, and 
demography. A sustainable 
development strategy must address 
these issues in an integrated manner.

18. While there are many synergies in 

emission control for air pollution 
and climate change, there are also 
trade-oﬀs. Some air pollution 
abatement measures tend to increase 
energy consumption thereby causing 
increases in CO2 emissions. Nitrous 
oxide (N2O) emissions may increase 
through nitrogen oxide (NOx) 
reducing catalytic converters.
19. At the global level, a stabilisation 
of GHG emissions will lead to a 
reduction of SO2 emissions. The 
extent of this depends on the type 
of CO2 measures applied, on SO2 
control measures in place, and on 
the energy scenario assumed. Single 
sector measures, may lead to an 
increase in SO2 or PM emissions. 
For instance, moving out of coal 
into renewables in the electricity 
sector in Asia may lead to higher 
use of coal in some other sectors 
increasing SO2/PM emissions. Also a 
regional strategy to enhance natural 
gas infrastructure may increase 
SO2 emissions regionally, while 
reducing global CO2, due to the risk 
of switching to coal in gas-exporting 
countries. The use of biomass (e.g. 
fuel wood) has been promoted in 
the EU. While reducing CO2, this has 
tended to increase PM, CO and VOC 
emissions in the domestic sector. In 
the industry and power sector this 
does not apply, as such emissions 
can be eﬀectively controlled.
20. The regulatory structure can 

facilitate multi-emission strategies 
in the power sector. Multi-pollutant 
approaches can provide more 
certainty and reduce costs. For 
instance, a power company may 
decide to apply diﬀerent emission 
control measures (e.g. a switch in 
fuel or process instead of some end-
of-pipe technology) when addressing 

multiple substances simultaneously 
than it would if it addressed emi�ed 
substances sequentially.

21. IIASA calculated that the costs of 
reaching the Gothenburg Protocol 
emission ceilings could be reduced 
more than EUR 5 billion per year 
by implementing the changes in the 
energy system necessary to achieve 
the reductions required by the Kyoto 
Protocol domestically (i.e. without 
international CO2 emissions trading).
22. For China, it has been estimated that 
the cost of cu�ing CO2 emissions 
by 5–10 % would be oﬀset by the 
beneﬁts resulting from reduced 
health eﬀects through air pollution. 
Including the eﬀects on crop-yield 
increase (via reduced NOx) increases 
the ‘no-regret’ level of CO2 emission 
cuts to 15–20 %.

23. Synergies and trade-oﬀs are also 

present in agriculture. For instance, 
certain ammonia abatement 
measures related to manure 
application can increase emissions 
of nitrous oxide (N2O), which is 
an important GHG also covered 
by the Kyoto Protocol. There are, 
however, abatement techniques that 
can reduce this negative impact. 
Scenario analysis has shown that it 
is possible to cut ammonia emissions 
signiﬁcantly and at the same time 
reduce nitrous oxide and methane 
emissions. An integrated approach 
tends to achieve such synergies at 
much lower cost.

24. Change in agricultural policy may 
be an eﬃcient structural measure 
to reduce environmental eﬀects 
of agriculture, although not all 
structural changes will reduce 
ammonia emission. Air pollution 
may not be a major driving force to 
bring about such structural change, 
but knowledge of the air pollution 
and climate impacts of agriculture 
has inﬂuenced the political 
process. For integrated assessment 
modelling, a clear political signal on 
feasible policy options is important 
to determine the boundaries of the 
modelling work.

84

Air pollution and climate change policies in Europe

III. Strategic aspects: The way 
forward

A. Emission ceilings and carbon 
trading
25. GHG emissions trading systems 
can have signiﬁcant eﬀects on 
the distribution and levels of air 
pollution emissions. While trading 
reduces the overall costs of emission 
reductions for given targets, it 
tends to shi� the signiﬁcant co-
beneﬁts of abatement measures from 
western Europe to other regions. 
Unconstrained trading of GHG may 
not be cost-eﬀective, if air quality 
objectives are taken into account. In 
some countries, GHG trading may 
not make sense, as the structural 
measures for CO2 abatement may 
be necessary to achieve the emission 
reduction (e.g. for NOx) required to 
meet the national emission ceilings.

26. In practice, the eﬀects of carbon 

trading are uncertain. Regional air 
pollution studies should therefore 
use diﬀerent assumptions about 
the baseline energy consumption 
(as aﬀected by the Kyoto Protocol), 
including diﬀerent assumptions 
on scope and order of magnitude 
of international carbon trading 
and, possibly, as an extreme case, a 
situation without the Kyoto Protocol.

27. In developing GHG emissions 

trading, the eﬀects on regional air 
pollutants (NOx, SO2, PM) should 
be taken into account so as to give 
realistic estimates of the net cost and 
the net environmental impacts of 
trading. 

B. Modelling linkages and synergies of 
regional and global strategies
28. A combined analysis of air pollution 
and climate change requires bridging 
diﬀerent temporal (from a 10 to a 100 
year perspective) and spatial (from 
local/urban to global) scales. To 
capture the feedbacks from climate 
change, air pollution modelling 
needs to incorporate suﬃciently 
long time horizons in order to take 
account of the inertia in climate 
change and the time required for 
structural measures and technology 

development to take eﬀect. At the 
same time, climate research should 
examine changes that may occur 
over the next 10–20 years.

29. The linkages between air pollution 

and climate change are manifold and 
not homogenous. Modelling such 
eﬀects that go in diﬀerent directions 
is possible, as long as they can be 
quantiﬁed. Including these eﬀects in 
integrated assessment models allows 
determining strategies that minimise 
the cost of reaching a given set of 
objectives.

30. It may be challenging to bring 

together very diﬀerent targets, such 
as health targets expressed in terms 
of years of lost life expectancy and 
targets related to climate change, 
but integrated assessment modelling 
can assist the policy process in this 
task. This has already been done in a 
multi-eﬀect framework before, using 
a gap closure approach, and such an 
approach could be extended to link 
to climate change targets.

31. By incorporating the most important 
linkages and synergies with climate 
change, air pollution-focused 
integrated assessment modelling will 
have to be extended to incorporate 
some aspects of sustainable 
development strategies, in particular 
to model structural change. This 
might, for instance, require general 
equilibrium macroeconomic 
modelling. The Task Force on 
Integrated Assessment Modelling 
may have to discuss whether new 
criteria, possibly going beyond a 
simple cost-eﬀectiveness approach, 
should be pursued and how to 
address equity considerations.
32. In further developing integrated 

assessment modelling to cover these 
issues, it is important not to lose 
focus. Rather than incorporating 
all into one unmanageable 
modelling framework, other 
ways of linking results should be 
explored. Growing complexity of 
models poses challenges for quality 
assurance and quality control (QA/
QC). This will require an active 
approach to uncertainty analysis 
and management. As the level of 

Annex 7: Workshop of the Task Force of Integrated Assessment Modelling

85

complexity makes the use of model 
optimisation more diﬃcult, an 
emphasis should be to ﬁnd robust 
results and to communicate the 
results.

33. CIAM should conduct this work 
closely, following discussions of 
the IPCC to make appropriate 
assumptions about the parts of the 
world and the issues not covered by 
the RAINS model. At the same time, 
eﬀorts should be made to inform 
the IPCC about EMEP’s work to 
encourage global modelling work 
to adequately cover air pollution 
related issues. 

C. The way forward
34. Focusing on the abatement 

synergies, CIAM will develop cost 
curves for the six GHGs (CO2, CH4, 
N2O, PFC, HFC, SF6) included in the 
Kyoto Protocol and incorporate them 
into the RAINS model. As for the air 
pollutants included in RAINS, this 
will be done on a country-by-country 
basis for the EMEP region with a 
time horizon of 2030. In parallel, 
CIAM will develop methodologies 
for introducing structural change 
into the model and for addressing 
the physical linkages. This work will 
be completed in 2004.

35. The objective of the work on linkages 
and synergies between regional air 
pollution and climate change should 
be to provide policy-makers with the 
information necessary to make the 
right choices: (1) to reduce pollutants 
maximising the positive linkages and 
minimising the negative ones; and 
(2) taking those measures that are 
the most cost-eﬀective in view of the 
objectives in both policy areas.
36. At this stage, work should ﬁrst 

concentrate on the scientiﬁc issues 
of linkages before addressing the 
policy process. This will be to the 
beneﬁt of both policy processes. 
The Gothenburg Protocol review 
can take some of the abatement 
synergies into account, while 
just addressing the air pollutants 
responsible for acidiﬁcation, 
eutrophication, ground-level ozone 
and PM pollution. The direct beneﬁts 

of climate change policies tend to be 
far away. Highlighting the additional 
beneﬁts of certain climate mitigation 
measures on air pollution will make 
such policies more a�ractive in 
bringing the beneﬁts closer both in 
space (e.g. to the local scale) and in 
time.

37. Contacts between experts in the 

ﬁelds of air pollution and climate 
change should be enhanced. The 
approach of the EEA in linking 
climate change and air pollution in 
one framework (the European Topic 
Centre on Air and Climate Change) 
is a good example. There is a need 
for further workshops like this 
one to bring the diﬀerent scientiﬁc 
communities closer together. Also 
at the policy level, closer contacts 
between those responsible for air 
pollution and climate change, both 
at the national and international 
level, would be beneﬁcial. In this 
connection, it is interesting to note 
that the Directorate-General for 
the Environment of the European 
Commission decided to bring its air 
quality and climate change units 
together under the same directorate 
from March 2003 onwards to further 
enhance policy coherence.

38. In pursuing the work, EMEP should 

cooperate with the IPCC. The 
linkages and synergies between 
air pollution and climate change 
should be examined both from the 
air pollution perspective and from 
the climate change perspective. 
While EMEP should cover the work 
from the air pollution side based on 
relevant ﬁndings of the IPCC, the 
IPCC could address the relevant 
scientiﬁc question from the climate 
change perspective. The secretariat 
and national experts, including the 
national focal points for integrated 
assessment modelling, should 
establish the necessary contacts 
so that relevant IPCC bodies are 
informed about this suggestion 
prior to deciding on the topics to be 
covered by the fourth assessment 
report.

86

Air pollution and climate change policies in Europe

D. Further research
39. Further research on how air 

pollutants (ozone and PM) aﬀect 
the climate is important in view of 
the signiﬁcant uncertainties. More 
research is especially needed to get 
a be�er understanding of how the 
diﬀerent components of PM impact 
climate, and this is also important 
for their eﬀects on human health. 
Part of this research must aim at 
improving the observational basis. 
Measurements are also required to 
improve emission inventories.

40. The relevant aspects of the eﬀects of 
air pollution on the regional climate 
should be further examined and this 
should be considered in connection 
with the work on hemispheric air 
pollution. As far as possible, this 
should also involve scientists from 
Asia.

41. Concerning the options to reduce 
emissions (of air pollutants and 
GHG), the workshop presentations 
and discussions focused on 
structural measures and energy 
saving. Further work should also 
explore technical measures for multi-
pollutant abatement.

42. The IPCC has established a Task 
Group on Scenarios for Climate 
and Impact Assessment that 
operates a Data Distribution Centre 
(website: h�p://ipcc-ddc.cru.uea.
ac.uk/). The DDC provides a broad 
set of climatic, socioeconomic and 
other environmental data that are 
consistent with published IPCC 
scenarios and are intended for use 
in assessing the impacts of climate 
change. These data may be useful to 
air pollution modellers.

Annex 8: Overview of a selected number of workshops

87

Annex 8: Overview of a selected 
number of workshops addressing the 
interaction of climate change and air 
quality

2000, March 

Workshop on ‘Ancillary beneﬁts and costs of greenhouse gas 
mitigation’, OECD, IPCC, RFF, CI, WRI workshop, Washington, 
D.C., USA.

2001, September  International expert workshop on the ‘Analysis of the economic 

and public health impacts of air pollution’: Garmisch-
Partenkirchen, Germany, 6 September 2001. Organised by the 
US Environmental Protection Agency, World Bank, US Agency 
for International Development, World Health Organisation, 
Organisation for Environmental Cooperation and Development, 
United Nations Environmental Programme, Health Eﬀects 
Institute, and National Renewable Energy Laboratory.

Summary results
Forty-nine experts from 18 industrial and developing countries 
met to discuss the economic and public health impacts of air 
pollution, particularly with respect to assessing the public health 
beneﬁts from technologies and policies that reduce greenhouse 
gas (GHG) emissions. Such measures would provide immediate 
public health beneﬁts, such as reduced premature mortality and 
chronic morbidity, through improved local air quality. These 
mitigation strategies also allow long-term goals, for example 
reducing the build-up of GHG emissions.

‘Air pollution as a climate forcing’, APCF workshop, 29 April–3 
May, Honolulu, Hawaii. The workshop, held at the East-West 
Centre of the University of Hawaii, was sponsored by the 
National Aeronautics and Space Administration, National 
Oceanic and Atmospheric Administration, National Science 
Foundation, Hewle� Foundation, California Air Resources 
Board, California Energy Commission, International Paciﬁc 
Research Centre, and East-West Centre.

Summary results
The workshop brought together the topics of air quality and 
climate change. The chosen scope emphasised the impact of 
air quality on climate change, and on air pollutants that cause 
substantial climate forcing. The aim was the description of what 
we know and what we need to know about the commonalties 
between the two phenomena and the communication of this 
status of understanding among the participants.

2002, May 

2002, September  ESF exploratory workshop on ‘Atmospheric pollution eﬀects 

on local, regional and global scales — An integrated approach’: 
Oslo, Norway, 26 September 2002. The workshop was sponsored 
by the European Science Foundation, Research Council of 
Norway, and NORAD (the Norwegian Agency for Development 

 
 
 
 
88

Air pollution and climate change policies in Europe

Cooperation), and was arranged by Cicero and the Department 
of Chemistry, University of Oslo.

Summary results
An integrated approach to mitigating climate change and local 
and regional environmental problems may have important 
advantages, but it also poses methodological challenges. At this 
workshop, 25 scientists from China, USA, Chile and several 
European countries discussed relevant issues.

2003, January  Workshop of the Task Force on Integrated Assessment 

Modelling (TFIAM) of UNECE on ‘Linkages and synergies of 
regional and global emission control’, 27–29 January 2003, at 
IIASA, Laxenburg

 
 
Annex 9: Internet addresses containing information on the linkage of Climate change and air quality

89

Annex 9: Internet addresses 
containing information on the linkage 
of Climate change and air quality

h�p://gssd.mit.edu/Gssd/startgssd.nsf/
startgssd Global system for sustainable 
development

h�p://www.ornl.gov/ORNL/Energy_Eﬀ 
Oak Ridge National Laboratory: Energy 
eﬃciency and renewable energy

h�p://icg.harvard.edu/~espp10/Readings 
Science, policy and environment

h�p://www.sei.se/climate/activities.html 
Stockholm Environment Institute (SEI) 
— Climate and energy programme

h�p://ucrevelle.ucsd.edu UC Revelle 
programme on climate science and 
policy

h�p://web.mit.edu/globalchange/www/
structure.html MIT global change joint 
programme structure

h�p://www.airimpacts.org/  Health and 
economic impacts of air pollution

h�p://www.cgenv.com/Narsto/
frame1new.html 

h�p://www.csa.com/routenet/cnie/
pop/air/airbib.html Air, climate and 
atmospheric change bibliography

h�p://www.giss.nasa.gov/meetings/
pollution02 NASA Goddard Institute: 
Air pollution as a climate forcing

h�p://www.igbp.kva.se/cgi-bin/php/
ﬁrst_page.php IGBP — International 
geosphere–biosphere programme

h�p://www.jhu.edu/~climate/index.
html Climate change and human health 
integrated assessment web

h�p://www.lib.kth.se/~lg/climate.htm 
Climate

h�p://www.tellus.org/seib/publications 
Tellus Institute online publications

h�p://www.tyndall.ac.uk/publications/
publications.shtml Tyndall Centre

h�p://www.4cleanair.org

h�p://www.oecd.org/env/cc 
Organisation for Economic Cooperation 
and Development, Paris

h�p://www.rﬀ.org Resources for the 
Future, Washington, D.C.

h�p://www.epa.gov Environmental 
Protection Agency, USA

h�p://www.esf.org European Science 
Foundation

h�p://ipcc-ddc.cru.uea.ac.uk/ The 
IPCC has established a Task Group 
on Scenarios for Climate and 
Impact Assessment led by Imperial 
College, which has established a data 
distribution centre

European Environment Agency

Air pollution and climate change policies in Europe:  
exploring linkages and the added value of an integrated approach

Luxembourg: Ofﬁce for Ofﬁcial Publications of the European Communities

2004 — 93 pp. — 21 x 29.7 cm

ISBN 92-9167-700-0