Environment Impact of Aviation and Tradeoffs

Cranfield University

Ken Rumph

The Impact of Uncertainty on Decisions and Trade-Offs in Aviation and the Environment

School of Applied Sciences

MSc Environmental Management for Business

Thesis

Cranfield University

School of Applied Sciences

Department of Sustainable Systems

MSc Environmental Management for Business

Academic Year 2006-7

Kenneth Charles RUMPH

The Impact of Uncertainty on Decisions and Trade-Offsin Aviation and the Environment

Supervisor: Dr Matthew COOK, Cranfield University

Presentation Date: 6th September 2007

This thesis is submitted in partial fulfilment of the requirements for the Degree ofMaster of Science.

© Cranfield University, 2007 All rights reserved. No part of this publication maybe reproduced without the written permission of the copyright holder.

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Cranfield University Ken Rumph, 2007

Abstract

UK air travel has grown rapidly (passenger numbers multiplied six-fold between 1970

and 2000) and is expected to continue to grow, albeit less rapidly, in coming decades

(Department for Transport forecasts are for a 250% increase between 2000 and 2030).

Interventions to abate the associated environmental impacts of aviation, specifically

noise, local air pollution and climate change are subject to uncertainties and trade-offs.

As part of the UK ‘Omega’ knowledge-transfer research programme, the study explored

the scale, nature and consequences of these uncertainties on decision-making and on the

management of trade-offs. Following a literature review, primary data was elicited from

a purposive sample of key informants in academia, NGOs and the aviation industry,

covering sub-sectors of air traffic management, airport, airlines, and airframe and

engine manufacturers. Two broad strands of responses to uncertainty, related to job

roles and worldviews, were identified, with some seeing uncertainty as a reason for

delay, others as a spur to action. Management of trade-offs in this context was found to

follow a typical hierarchy based on historical priorities, beliefs and regulatory trends.

The present limitation of regulation to noise and local air quality was commonly seen as

privileging these environmental aspects over emissions driving climate change.

Recognising changing external influences and environmental priorities, respondents

consistently appealed for ‘scientific certainty’ and/or regulators as higher authorities for

guidance in setting new priorities and procedures.

Keywords: Aviation, environment, climate change, trade-offs, uncertainty

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Acknowledgements

I would like to thank my supervisor Dr. Matthew Cook for his calm and his good

judgement in calling me back to the straight and narrow when straying. In addition, the

support and advice of Professor Joe Morris, Dr. Andrew Angus and Sophie Walker,

fellow participants in the Omega project was more valuable than they may realise, in

my thesis and future plans.

This project was carried out with the aid of the funding and knowledge base of the

Omega research project, for which I am most grateful.

Thanks to my wife Jacqueline, who has sacrificed a year with an absentee husband, and

my daughter Miranda who now knows that if you don’t get school right, they’ll make

you do it again when you’re old.

I could not have completed this thesis without the encouragement and example of the

work of fellow students at Cranfield, notably Julie, Nora and Julia, who proved to me

that there is a purpose in all this, and Kirstie and Fanda for intensive final day hand-

holding.

Contact Information:

Ken Rumph

[email protected]

+44 7785715095

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Table of contents

Abstract .......................................................................................................... i

Acknowledgements .......................................................................................ii

Table of contents ..........................................................................................iii

List of Figures ............................................................................................... v

List of Tables................................................................................................. v

Abbreviations ...............................................................................................vi

Chapter 1: Introduction ................................................................................. 11.1 Context: Aviation and the environment ........................................................... 11.2 The Research Problem: Uncertainty and Trade-offs ........................................ 11.3 Aim and objectives ........................................................................................... 21.4 Scope ................................................................................................................ 21.5 Structure ........................................................................................................... 3

Chapter 2: Literature Review ........................................................................ 42.1 Scope ................................................................................................................ 42.2 Uncertainty and Risk ........................................................................................ 52.3 Structure ........................................................................................................... 62.4 Noise................................................................................................................. 62.5 Noise Summary .............................................................................................. 122.6 Aviation and Climate Change ........................................................................ 132.7 CO2 and climate impact from aviation ........................................................... 172.8 NOx emissions and related effects (Ozone, Methane, HOx) ......................... 192.9 Contrails, Aviation-induced Cirrus and Climate Change............................... 212.10 Aviation-induced Cloudiness and Climate Change........................................ 252.11 Climate Change Summary.............................................................................. 312.12 Local Air Quality............................................................................................ 312.13 Local Air Quality Summary ........................................................................... 332.14 Interventions and Trade-Offs ......................................................................... 342.15 Abatement/Mitigation of Contrails and Aircraft-Induced Cirrus ................... 342.16 Summary......................................................................................................... 39

Chapter 3: Methodology..............................................................................403.1 Introduction .................................................................................................... 403.2 Research Design ............................................................................................. 403.3 Research quality ............................................................................................. 493.4 Summary of research design .......................................................................... 50

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Chapter 4: Article ........................................................................................51

The Impact of Uncertainty on Decisions and Trade-Offs in Aviation andthe Environment .......................................................................................... 51

Abstract....................................................................................................................... 51Introduction ................................................................................................................ 52Methodology............................................................................................................... 58Analysis and Discussion............................................................................................. 58Conclusions ................................................................................................................ 68

References (Article only) ............................................................................72

References (Thesis) .....................................................................................84

Appendix 1: Guidelines for Authors, Business Strategy and theEnvironment ................................................................................................ 99

Appendix 2: Interview Guide....................................................................102

Appendix 3: Transcript of An Interview...................................................105

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List of FiguresFigure 2.1: Schematic of ideal and non-ideal products of combustion……….………..13

Figure 2.2: Radiative Forcing from aircraft in 1992 from IPPC, 1999....…….………..15

Figure 2.3: Update RF from aircraft for 2000………………………………...………..16

Figure 2.4: Illustrative figure relating location and lifetime of different

aviation climate impacts ......……………………………..…………...………..17

Figure 2.5: Six scenarios for projected global CO2 emissions……….……….………..18

Figure 2.6: Regional variation in aircraft fuel consumption ………………....………..25

Figure 2.7: CO2 and non-CO2 radiative forcing …………………………..….………..30

Figure 4.1: Influences given (primary and secondary) for listing of environmental

impacts of aviation …………………………………………………....………..60

Figure 4.2: different influences of those ranking noise or climate change as most

important environmental influence of aviation …………………...….………..61

List of TablesTable 2.1: Forecasts of Contrail Cover ……….………………………………………..23

Table 2.2: Radiative Forcing from contrails, comparisons of study values…..………..24

Table 2.3: Typical emission levels for different engine operating regimes ….………..33

Table 3.1: Respondents Interviewed and job/role description ......……………...……..46

Table 3.2: Codes for Data Analysis ……….………………………………….………..48

Table A.1: Interventions and Trade-offs ……….……………………..…….………..103

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AbbreviationsACARE Advisory Council for Aeronautics Research in Europe

AGWP Absolute Global Warming Potential

AHP Analytical Hierarchy Process

AIC Aviation induced cloudiness

ANERS Aircraft Noise and Emissions Reduction Symposium

ATC/ATM Air Traffic Control/Management

CDA Continuous Descent Approach

CH4 Methane

CO2 Carbon Dioxide

DEFRA Department for Environment, Food and Rural Affairs

DfT Department for Transport

ETS Emissions Trading Scheme

EWF Emissions Weighting Factor

FAA Federal Aviation Authority

GCM Global Climate Model (also known as General Circulation Models)

GDP Gross Domestic Product

GHG Greenhouse Gas

GWP Global Warming Potential

H20/HOx Water, oxides of hydrogen

ICAO International Civil Aviation Organisation

IPCC Intergovernmental Panel on Climate Change

ISSR Ice super-saturated region

LTO Landing and Take-Off

NGO Non-governmental organisation

NOx Oxides of nitrogen

O3 Ozone

RCEP Royal Commission on Environmental Pollution

RF/RFI Radiative Forcing/Radiative Forcing Index

SOx/SO2 Oxides of sulphur/sulphur dioxide

UHC Unburnt hydrocarbons

UTLS Upper Troposphere/Lower Stratosphere

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Chapter 1: Introduction

1.1 Context: Aviation and the environment

“Air transportation is certainly not environmentally benign … It is essentially

industry with wings. It is noisy, generates local air pollution, ... and emits global

warming gases” (Button, 2002)

Aviation is rapidly growing, and alongside recognition of its benefits to society and

economic importance comes concern over its rising environmental costs. In terms of

growth, global forecasts for compound annual passenger air traffic growth of 4.8 - 5.0%

and freight tonnage by 6.0 - 6.8% over the next two decades (Airbus, 2006; Rolls-

Royce, 2006; Boeing, 2007) compare to global Gross Domestic Product (GDP) growth

forecasts in the same sources of around 3%. Longer term global growth forecasts used

in IPCC (1999) show growth continuing to exceed that predicted for the wider economy

to 2050 in the majority of the economic scenarios considered. Part of the global growth

in aviation is driven by rapid penetration of aviation in developing regions such as

China and India (for example, see Airbus, 2006). For the UK itself, a more mature

aviation market, growth is expected to slow from the rate of the past three decades

(1970-2000) when passenger numbers multiplied six fold, (DfT, 2006) and yet still see

an increase of 250% between 2000 and 2030 if unconstrained

Such growth in activity contrasts with various policy objectives from the UK

government, to reduce emissions driving climate change and affecting local air quality

and to reduce noise impact (DfT, 2003; DfT, 2006). Other bodies, international, public

or private sector have similar concerns and aims: for example Advisory Council for

Aeronautics Research in Europe (ACARE, 2001) and Greener by Design, (2003). Bows

and Anderson, 2007 question whether these growth expectations are consistent with the

UK government’s aims of a 60% reduction in national CO2 emissions under draft

climate change legislation.

1.2 The Research Problem: Uncertainty and Trade-offs

Research suggests that uncertainty is an important influence on decision-making and

that trade-offs are a pervasive feature of the aviation sector’s environmental impacts

(IPCC, 1999; ACARE, 2001). A generic example from literature is the tendency for the

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pursuit of reduced fuel consumption (and hence reduction of climate change impact

through CO2 emissions) via higher temperatures and pressures to lead, other things

being equal, to high NOx emissions (Greener by Design, 2003), affecting both local air

quality at low altitudes and climate change itself at higher altitudes – a trade-off against

two environmental impacts. The uncertainties over the scale of some impacts also

hinders decision-making and management of trade-offs. Interventions to reduce the

climate change impact of contrails and cirrus, which entail increased fuel burn and CO2

emissions (Williams et al., 2002) – and yet the climate impact of contrails and cirrus is

highly uncertain versus the much better understood and quantified CO2 effects,

complicating choices.

1.3 Aim and objectives

In view of the importance of uncertainty and trade-offs, this study has the aim of

identifying the uncertainties and trade-offs involved in aviation’s environmental impacts

and their consequences for decision-making. Four objectives were enumerated in

pursuit of this aim:

To identify the environmental impacts of aviation

To identify the importance of selected environmental impacts of aviation

To identify and analyse the uncertainties associated with the selected

environmental impacts, and how these impact upon decision-making within the

aviation sector and associated bodies

To identify and gain insights into the trade-offs involved in measures to abate

aviation’s environmental impacts, and how these trade-offs are managed in

theory and practice

1.4 Scope

This study focuses on the subsonic civil aviation market, and on larger planes 1, which

make up the bulk of global emissions (IPPC, 1999). Local air quality in particular is

affected by sources other than aircraft such as ground transportation and airport

equipment, as well as the transportation of passengers to and from the airport. However,

a wider study encompassing integrated travel planning is beyond the constraints of time

1 Large defined as per IPCC, 1999 as those above approximately 9 tonnes take-off weight

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and resources available to this study, which therefore focuses on aircraft in flight and on

the ground.

Although the structure of the industry is not the subject of this study, some

characteristics are relevant to behaviours in dealing with uncertainty and trade-offs.

These include the oligopolistic nature of the airframe and engine industries, both of

which feature two or three major industrial groups dominating the market (IPCC, 1999;

Doganis, 2002; Doganis, 2006) and effective separation, albeit with co-operation, of

engine design and manufacture from airframe design and manufacture (Airbus, 2006;

Mecham and Wall, 2006; Rolls-Royce, 2006; Boeing, 2007). The high capital outlay

entailed in aircraft purchases and their long design timescales (5-10 years), and even

longer lives in use (25-40 years, IPCC, 1999) mean that the fleet of aircraft turns over

only slowly – changes to the environmental performance of new aircraft thus take a long

time to shift the aggregate environmental characteristics of the fleet.

1.5 Structure

The literature on the environmental impacts of aviation, focussing on the particular

issue of uncertainty was reviewed and the results of this reported in Chapter 2 The

particular issue of trade-offs associated with abatement measures is given emphasis in

the literature review. The research design follows, with methods for data collection and

analysis (Chapter 3). The article submitted for publication forms Chapter 4, and

includes the analysis and discussion of findings and conclusions of the study, with

related references. The thesis is completed by a full reference list, plus appendices

containing the guidelines for authors for the article (Appendix 1), interview guideline

used for interviews (Appendix 2) and a transcript of one of the interviews (Appendix 3).

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Chapter 2: Literature Review

The objectives of this study can be briefly summarised as exploring the perceptions of

uncertainty associated the environmental impacts of aviation, the trade-offs involved in

interventions to abate these environmental impacts and the consequences for decisions

over such interventions. The literature review begins with introductory comments on

scope and the general topic of risk and uncertainty, before the main review is

introduced.

2.1 Scope

This study is part of a wider research project (within the wider Omega project) with the

aim of generating abatement cost curves for interventions to reduce environmental

impacts of aviation). In line with the wider Omega project the scope of the study covers

commercial subsonic aircraft, both passenger and freight. However, we note that over

80% of freight was carried on passenger aircraft (IPCC, 1999) and hence focus on

passenger aircraft (respondents include airlines with large freight operations). This

scope decision does cover a large part of aviation-sourced emissions – for example,

IPCC, (1999) estimate that military consumption of fuel (a reasonable proxy for many

emissions, particularly CO2, important in climate change impacts) was around 18% of

the world aviation total in 1992 and used scenarios for forecasting which implied that

this share would shrink to 7% by 2015 and 3% by 2050, the two forecasting periods

focussed on in that 1999 study.

As for abatement interventions, this study excludes those measures that could be

defined as ‘demand management’ – such as carbon or other taxes or tradable permit

systems, used with the aim of either incentivising abatement or reducing demand by

internalising some of the environmental externalities through pricing, rationing of

flights or of carbon generally. There is no implication that such demand management is

either ineffective or undesirable, merely that this study focuses on interventions to

address emissions for any given level of demand, whether unconstrained or not.

As below, the abatement measures considered thus include changes to the use of

airspace and to aircraft on-the-ground operations, the development of more fuel efficient

aircraft and engines, and interventions to reduce or alter the mix or quantity of

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emissions. Although airports generate emissions from (non-aircraft) ground activities

and from transportation associated with passengers, freight and workers travelling to

and from the airport, these aspects are not part of this study, which concentrates on

aviation directly and does not attempt any foray into integrated transport policy.

A presupposition of this study, based on the Omega project’s terms of reference and

priorities identified in the literature itself, is that there are three key environmental

impacts of aviation: noise, climate change, and local air quality. The validity of this

scope decision is examined in the interview phase, below.

2.2 Uncertainty and Risk

Although one of the objectives of this study is the impact of uncertainty on decisions,

rather than the nature of uncertainty itself, it is necessary to make a brief review of the

extensive literature concerning uncertainty, risk and perceptions of risk and uncertainty:

the following represents only a selection of some widely references works in the field.

In 1921, Knight defined the terms risk and uncertainty as follows (Knight, 2006): it’s

risk if you don’t know for sure what will happen, but you know the odds, whereas if you

don’t even know the odds, it’s uncertainty. However, Adams (1994) wisely observes

that this technical usage is frequently blurred in common usage, with the words used

interchangeably. Douglas and Wildavsky (1983) linked risk perception to cultural

attributes, and that individuals and cultures constructed and perceived risks according to

their own beliefs about nature. Holling (1986) and then Schwarz and Thompson (1990)

developed this into a typology of four ‘myths of nature’: nature benign, nature

ephemeral, nature perverse/tolerant and nature capricious. The application of these

myths of nature to risk and uncertainty produced a further typology of five worldviews

(Holling et al. 2002) adding nature evolving to the four above. The characteristic

behaviour of individuals facing risk, using the first four worldviews above was

described by Adams (1994) as individualist, egalitarian, hierarchist and fatalist.

Slovic (2000) described risk perception in terms of two factors: ‘dread’ and ‘unknown’.

Dread included perceptions of the risk as being uncontrollable, potentially catastrophic,

dangerous to future generations and involuntary. A second factor, labeled ‘unknown’,

combined characteristics related to the observability of risks, whether the effects are

immediate or delayed in time, the familiarity of the risk and whether the risks are judged

to be known to science (Slovic, 2000).

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For the purposes of this study, the key points are that risk and uncertainty are socially

constructed (Adams, 1994) and that uncertainty, which does relate to Slovic’s (2000)

factor of ‘unknown’, is a key determinant in the individual’s perception of risk. In a

business context, using the example of the similarly highly regulated utility sector, Toke

and Lauber (2007) observe that despite a general aversion to regulation as costly, firms

may prefer regulation when faced with a level of risk that threatens their returns or

hampers long term investments by raising the implied cost of capital.

2.3 Structure

The areas of noise, climate change and local air quality are considered in turn and in

each case we review the literature on the links between aviation and environmental

impacts, focussing on their significance and then the uncertainties associated with these

links, and finally covering studies of abatement or mitigation options with a particular

emphasis on trade-offs. A final section covers a broad typology of interventions and

trade-offs between them. The particular area of interventions to abate climate change

arising from contrails and change sin cloudiness are discussed, as an illuminating group

of examples of trade-offs which require little knowledge of the technicalities of

aerodynamics or aero-engine combustion to be understood. Inevitably some abatement

measures will apply to more than one environmental impact, and we note such overlaps,

but the chosen structure more closely represents the approach of researchers, who tend

to operate in silos, with say, atmospheric physicists considering, the impact of NOx on

climate change but not on local air quality, or aerospace specialists focussed on

reducing noise, but not necessarily improving fuel efficiency.




2.4 Noise

“The main concern of the aviation industry and the public has been with noise”

(Royal Commission on Environmental Pollution, 1994)

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The quotation above from the 1994 UK RCEP survey of environmental impacts for all

forms of transportation reflected the consensus view found by the authors at that time –

that air quality and climate change are relatively more recent concerns for the industry

and public. Brooker, (2006) argues that the dominance of noise, as the main

environmental design consideration, has only been questioned in the past decade.

2.4.1 Noise and Aviation: Metrics

The International Civil Aviation Organisation (ICAO, a UN specialised agency that has

global responsibility for setting standards and recommended practices for civil aviation)

set its first noise standards for aircraft in 1971, and standards have been made

increasingly stringent in successive reviews (Royal Commission on Environmental

Pollution, 1994) and further increases have recently been proposed (Greener by Design,

2003b).

Current regulations2 specify maximum noise levels at three points, to the side of, and

under. the flight path on take-off and under the flight path on final approach (Greener by

Design, 2003a).

As long ago as 1966, at the inaugural meeting of the British Acoustical Society (as

reported in Kryter, 1967), Karl Kryter stated that “the problems related to the criteria

of acceptability of aircraft noise in a community are most challenging and require the

application of many scientific disciplines and arts, including political and economic

ones, before they can be equitably settled” but went on with the optimistic view that

“present-day knowledge about the generation, measurement and effects of noise on

man are sufficiently advanced … to allow the specification of the exposures to

aircraft noise that might be considered socially acceptable”. (Kryter, 1967)

Reviewing subsequent decades of research, the challenging nature of socially acceptable

noise levels seems more durable than the subsequent optimism that a specification was

within reach.

A number of metrics are used for noise measurement: all from Greener by Design,

(2003a)

2 Chapter 3 of Annex 16 to the Convention on International Civil Aviation as referenced by Greener byDesign, 2003b

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dBA : the A-weighted Decibel3 (dBA) adjusts (weights) frequency components

of sound to conform with the normal response of the human ear at

conversational levels

EPNdB: the Effective Perceived Noise level (EPNdB) is a unit measure of

aircraft noise based on how people judge the annoyance of sound they hear

adjusted for the duration of the event and for pure tones

Intensity – the sound energy flow through a unit area in a unit time

LAmax – the maximum A-weighted sound pressure level

Leq – the ‘equivalent continuous noise level’ which is a parameter that

calculates a constant level of noise with the same energy content as the varying

acoustic noise signal being measured.

DNL: day night level (also known as ldn) as for Leq except that 10 dB is added

to those noise events occurring at night (between 10 p.m. and 7 a.m.), to reflect

the added intrusiveness of night-time noise events when community background

noise levels typically decrease by about 10 dB.

Airport studies of noise disturbance typically use contours of equal noise (Leq) around

airports and make calculations of the area within, or number of people living (or

working) within, a given contour (Royal Commission on Environmental Pollution,

1994).

2.4.2 Health Impacts of Noise

As a summary of the health impacts of noise, on which there is a large technical

literature, the World Health Organisation’s 2004 peer-reviewed report into the Large

Analysis and Review of European housing and health Status (LARES) which covered 8

European cities concludes that:

“for noise induced sleep disturbances, traffic noise annoyance and neighbourhood

noise annoyance, the identified health effects are independent of socio-economic

status and housing conditions. The elevated relative risks are expressed in the

cardiovascular system, the respiratory system and the musculoskeletal system, as well

as through depression”. (World Health Organisation, WHO, 2004).

3 Decibels (dB) are a logarithmic measure of sound energy – doubling of decibels thus means a 10 foldincrease in energy levels.

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2.4.3 Noise and Perception: a source of uncertainty, but of alternative abatements?

Aside from its long history as an environmental issue for aviation, noise has other

particularities: most importantly there is a psychological, non-acoustic aspect of

perceived noise annoyance, where ‘acoustic’ is taken to mean the energy-based aspect

of noise and ‘non-acoustic’ the perception aspect. As Maris et al., (2007) note, “noise is

unwanted sound, and therewith a subjective description”.

Purely acoustic aspects of noise (loudness, pitch etc) only explain part of the annoyance,

with non-acoustic variables (Fields, 1993; Job, 1988) such as perceived control, noise

sensitivity and attitudes towards the source accounting for another part of the

explanation (only 25-40% was acoustic, in Job’s 1988 meta-analysis). Fields (1993)

found that isolation from sound at home and five other attitudes determined annoyance:

fear of danger from the source, noise prevention beliefs, general noise sensitivity,

beliefs about the importance of the noise source and annoyance with non-noise impacts

of the noise source. Clearly residents near airports could be affected by a number of

non-noise attitudes to air travel. In a practical test of this, surveys of residents near

Vancouver airport before and after an additional runway produced a step change in

noise levels that was ‘markedly’ greater than could be explained by dose-response

(Fidell et al., 2002).

Noise sensitivity is a human characteristic independent of other factors – some people

are more sensitive to noises at all levels as Miedema and Vos (2003) found, and

explained 26% of the perceived annoyance in a van Kamp et al., (2004) study of 3

international airports.

Many authors treated the non-acoustic aspect of annoyance as a blurring or error item in

dose-response studies (Schultz, 1978; Fidell et al., 1988; Schomer, 1989; Green and

Fidell, 1991; Miedema and Vos, 1998;).

Insofar as sound annoyance has a non-acoustic, psycho-social (Stallen, 1999) side, this

can be part of the abatement solution. As Stallen, (1999) argues, perceived control is a

key factor when noise is seen as a ‘you expose me’ relationship between the source and

auditor. Maris et al., (2007) open the door to potential new avenues of thought about

abatement of perceived noise in an empirical study that found that subjects perceived

less noise when they also perceived themselves to be treated fairly. As Stallen (ANERS,

2007) noted, sound management through engagement with the community to achieve a

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perception of fair treatment can be an effective tool in reducing perceived noise

annoyance separate to acoustic measures.

Noise disturbance varies not only according to level but also time of day, as Hume et

al., (2003) found. There are diurnal variations in other emissions and their impacts but

the strong significance of night-time versus daytime noise annoyance is reflected in the

typical weightings in noise metrics where night flights attract a scaling compared to the

same flight in daytime (as in DNL/ldn above). Hume et al., (2003) found the average

propensity to complain about night flights (2300-0600) more than five times that for

flights during other periods. In a medical study of noise effects, Quehl, (2005) found not

only that rising volume was correlated with sleep disturbance, but that the number of

events was the most critical factor, confirmed in laboratory and field tests (Quehl and

Basner, 2006).

2.4.4 Noise Abatement: ‘balanced approach’ - airports and operating measures

The ICAO ‘balanced approach’ to noise consists of action via reduction at source

(quieter aircraft), land-use planning and management, noise abatement operational

procedures and operating restrictions, “with the goal of addressing the noise problem

in the most cost-effective manner” (ICAO, 2004). The questions immediately arising

over how a process such as this is managed in practice and what trade-offs are made is

part of the purpose of this study. Quieter aircraft issues are dealt with below, and land-

use planning falls outside the scope of this review – however, as with the non-acoustic

perception related points above, abatement of perceived noise through these non-

aviation routes may offer attractive cost-benefits versus operating procedures,

restrictions and quieter aircraft, if these have other unattractive environmental trade-off

consequences (e.g. quieter engines at the expense of fuel efficiency and hence emissions

as below).

As an example of an operating measure to reduce noise, on the approach procedure,

when airframe, rather than engine noise is the key aspect, Van Boven, (2004) describes

Airbus’ studies of the continuous descent approach (CDA) which also has fuel saving

benefits. CDA involves descending from cruise or intermediate altitudes without

levelling out (which is the normal procedure). Noise reductions in the optimal descent

profile were reduced by 5dBA. However, Clarke, (2003) argues that to obtain the

maximum noise and fuel benefits of using CDA and other advanced noise abatement

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procedures, aircraft require to be scheduled and spaced according to their noise and

aerodynamic characteristics, adding to ATC workload and implying a shift to

automation in ATC.

Although ground transportation is outside the scope of this study, the ground

movements of aircraft is not, and an example study shows that additional taxiways can

cut taxiing times and distances and reduce noise and fuel consumption (Daniel, 2002).

In terms of airport planning, capacity and economics, Ignaccolo, (2000) included the

relationship between noise and, amongst other factors, fleet composition, in a tool to

determine the environmental capacity and compatibility (for local residents) of airport

activities.

Doganis (2002) notes that noise reduction is one of the factors driving a trend towards

smaller aircraft, despite the apparent attractions of larger planes – smaller planes are

typically quieter, as well as being quicker to turn around, offering higher frequencies

and being preferred as airports become congested (Doganis, 2002; Doganis, 2006).

Measures which favour larger aircraft may thus run counter to these environmental

(noise) and economic drivers.

As with the proposed inclusion of aviation in the EU ETS (European Commission,

2006), regulatory and economic measures are already in place at a number of airports

(e.g. Amsterdam Schiphol, Morrell and Lu, 2000), adding to the environmental pressure

to reduce noise. Measures include regulatory noise restrictions (some planes cannot

operate at certain times or certain airports) and fiscal measures such as noise charging to

airlines. The benefits of noise reduction, typically calculated through hedonic pricing

studies of house values near airports suffer from wide variations (Schipper et al., 1998)

introducing uncertainties into making cost benefit calculations for noise charging.

Studies and reports into the technological development and prospects of aviation

(ACARE, 2004a; Greener by Design, 2003b) observe that since the 1950s introduction

of commercial jets noise from aircraft has halved in energy emission terms, but that the

rate of reduction is diminishing. Both of these forward-looking studies argue that

breakthrough or radical innovations are needed for further progress, such as new

airframe shapes or major changes to engine configurations.

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2.5 Noise SummaryLimiting noise has been a key design factor in the aviation industry for decades – the

dominant environmental factor until at least the last decade. Aircraft are certified under

international standards for their noise energy output, and successively more stringent

regulations have restricted the use (and thus economic attractiveness) of noisier aircraft.

Individual localities (usually airports) have also introduced regulations and fiscal

measures to limit noise. The scope to reduce noise through incremental changes to the

current standard configuration of aircraft appears to be diminishing, requiring

breakthrough technological changes. Rising flight frequencies act in opposition to a

reduction in ‘per-plane’ noise levels: many more planes, even if quieter, may well

generate more annoyance. The local and temporary nature of noise annoyance are also

noted in contrast to other environmental impacts (ACARE, 2004a; ACARE, 2004b;

Brooker, 2006; Greener by Design, 2003b).

Although there are nuances to the measurement of noise in energy terms, the main

source of uncertainty in assessing the environmental impact of noise arises from the

non-acoustic aspect. Perception of annoyance is determined by a range of factors

beyond physically quantifiable energy levels. These non-acoustic elements may offer

alternative routes for abatement (e.g. fair treatment of auditors) but may also raise

barriers to abatement: reducing energy levels may not reduce the perceived annoyance

as expected from a simple dose-response model.

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2.6 Aviation and Climate Change

IPCC (1999) provides a comprehensive review of aviation and its impact on climate

change (and on ozone in its own right) with a 1992 baseline for calculations and

estimates. Figure 2.1 shows schematically the in- and out-flows of a typical turbojet

engine, both in idealized and actual terms (including the unintended products of

incompletion combustion).

Figure 2.1: Schematic of ideal and non-ideal (all existing) products of combustion in a

typical current jet engine, adapted from (IPCC, 1999). UHC is unburned hydrocarbons

(fuel).

14


As a measure of climate change impact, IPCC, (1999) used radiative forcing (RF), a

measure of the impact on the Earth’s energy budget in terms of energy flow across a

square metre at the top of the tropopause (see below) in units of W m-2 (or mW m-2)- for

further details of the definition see IPCC, 1990; IPCC, 1995; IPCC, 1999, however it is

sufficient to note at this stage that RF is a first order indicator of climate change impact

(avoiding the need for complex climate modelling for each element) but that this

concept has

“significant limitations for spatially inhomogeneous perturbations to the climate

system and can be a poor predictor of the global mean climate response” (Wuebbles,

2006).

Further discussion of metrics for climate change drivers, a source of uncertainty in its

own right, follows below.

In addition to describing the processes by which aviation affects climate, the IPCC

(1999) produced, where possible, best estimates for the RF of each emission source or

factor, with ranges of uncertainty in estimates where available, as well as a description

of the level of scientific understanding (a different form of uncertainty4) on the topic.

Briefly, the climate impacts from aviation can be listed as (adapted from IPCC, 1999;

Sausen et al., 2005; Wuebbles, 2006):

CO2 and H2O: direct impacts through the emission of CO2, a greenhouse gas

(GHG) product of combustion.

NOx and related Ozone (O3), methane (CH4) and HOx (water and OH)

interactions

Aerosols and soot: liquid particles containing sulphate and organics plus carbon

soot particles: these can be radiatively active themselves by scattering or

absorbing radiation, or indirectly through triggering contrails or altering

cloudiness – cloudiness affects radiative forcing.

Contrails and Cirrus: in certain atmospheric conditions, the warm moist air

emitted by engines burning hydrocarbons (or hydrogen Marquart et al., 2005)

causes contrails to form and may also alter cloudiness.

4 The meaning of the terms used for the level of scientific understanding here and below, follow theIPCC, (1999) definition as representing the amount of supporting evidence available, degree ofconsensus and scope of analysis.

15


The IPCC, (1999) summarised its results in chart form Figure 2.2. Note that the

significance, even allowing for uncertainty, of the H2O, direct soot and aerosol factors is

low compared to CO2, contrails and cirrus (despite the lack of a best estimate) and the

combined items related to NOx. As below, these four areas (CO2, NOx-related, contrails

and cirrus) remain the significant issues in updated studies. Uncertainty was high for all

of these items except CO2 and level of scientific understanding was also only good for

CO2, but ranged from fair (ozone, contrails) through poor (methane/NOx) to very poor

(cirrus).

Figure 2.2: Radiative Forcing from Aircraft in 1992 from (IPCC, 1999).

How have levels of scientific understanding, significances and uncertainties developed

since IPCC (1999)?

In a study to update these results (Sausen et al., 2005) summarised the new results in a

modified chart as in Figure 2.3. The IPCC (1999) 1992 baseline estimates were scaled

using air traffic growth to a 2000 level (interpolated from 2015 forecasts in the same

16


source), and then compared to new results from the European TRADEOFF programme

and Minnis et al., (2004).

Figure 2.3: Updated RF from aircraft for 2000 from (Sausen et al., 2005)

As Figure 2.3 shows, the scale in RF terms of the main sources have not changed

significantly as studies progressed except in the single case of contrails, where, as

discussed below, the previous best estimate has reduced by a factor of 3, and which is

the main cause of the total RF excluding cirrus having reduced versus the scaled IPCC

(1999) conclusions. Best estimates remain elusive for cirrus.

Since the (Sausen et al., 2005) updating study, a workshop held in June 2006 (reported

in (Wuebbles, 2006) and papers from participants, including a number of the referenced

authors in this section, at an Aircraft Noise and Emissions Reduction Symposium

(ANERS, 2007) in June 2007, did not propose notable changes to the views set out in

Figure 2.3.

In terms of uncertainty and levels of scientific understanding, (Sausen et al., 2005)and

(Wuebbles, 2006) concur that the understanding of NOx and related species has

improved to a level described as fair, and cirrus from very poor to poor, but the non-

CO2 items remain subject to large ranges of uncertainty, particularly since the NOx –

17


related items generate a net RF that is the combination of two items of different sign,

and of different timescales, as below, Figure 2.4.

Figure 2.4: Illustrative figure relating location and lifetime of different aviation climate

impacts (Baughcum, at ANERS, 2007)

2.7 CO2 and climate impact from aviation

Given our focus on the significance and uncertainties in aviation’s environmental

impacts, CO2 merits less discussion in this review – its magnitude and importance are

large, but the mechanisms of its production (combustion of hydrocarbons), its quantity

(Olsthoorn, 2001) and its influence on climate change (Sausen and Schumann, 2000) are

relatively well understood and estimated to relatively precise degree. Abatement

measures involving reductions in CO2 emissions (directly proportionate to reduced fuel

burn by whatever means) are thus highly important but not subject to great uncertainty -

except, as noted below, when traded off or measured against other less certain aspects

(see below, and Forster et al., 2006; Wuebbles, 2006; Wuebbles et al., 2007), especially

where different lifetimes of species make RF comparisons unsuitable.

CO2 emissions are a freely mixing and long-lived part of the much larger anthropogenic

emissions of CO2 from fossil fuel combustion, deforestation, cement manufacture, etc –

aviation is notable not so much because of its current importance as a source (about 2%

18


of global anthropogenic CO2 emissions in 1992, IPPC, 1999) but rather because of

projected growth (Figure 2.5) against a background of policies to reduce CO2 emissions

from all sources. For the UK, as Bows and Anderson, 2007 argue, the government’s

own forecasts for aviation, would, if the rest of the UK’s emissions were meeting the

trend towards a 60% reduction by 2050 as the draft Climate Change bill envisages,

imply that aviation would become the dominant emitter of CO2 by 2030

Figure 2.5: Six scenarios for projected global CO2 emissions (Gt/yr and increase vs. 1990)

from IPPC, 1999

From an abatement and features of aviation point of view, aviation participants (engine

and airframe manufacturers) have been assumed to have strong economic incentives to

improve fuel efficiency5 if not to reduce total fuel consumption: as the IPPC, 1999,

noted, “[some] improvements [in fuel efficiency] are expected to take place for

commercial reasons”. IPCC, 1999

This view has been repeated in various sources of which Doganis, 2002; DfT, 2003;

ACARE, 2004a are a sample, with a recent example from Flight International’s June

2007 Environment Special, where the author notes that

5 Fuel efficiency is used in the literature in a number of ways, without a settled definition – sometimestaken to mean measure fuel consumption per unit distance flown, but at other times measured in terms ofthrust generated per unit of fuel consumed, or fuel consumed per passenger-kilometre flown.

19


“aircraft and engine manufacturers have long been committed to driving down the

cost of flying [by improving fuel efficiency and other means and ] …have toiled away

for years tackling fuel consumption… achieving a respectably steady, albeit

incidental, reduction in emissions” (Turner, 2007)

These economic incentives are potentially to be strengthened by the planned inclusion

of aviation into the European Union Emissions Trading Scheme (EU ETS) (Bows and

Anderson, 2007).

2.8 NOx emissions and related effects (Ozone, Methane, HOx)

Oxides of nitrogen (NOx) are emitted from the combustion process in jet engines as a

by-product (IPCC, 1999). Higher by pass ratios (the ratio of the volumes of air passing

trough the turbofan versus the core6) with higher pressure/temperatures in the

combustor have been a feature of engine designs for increased fuel efficiency: the side

effect tends to be higher NOx from reactions between the nitrogen in the air during

combustion (IPCC, 1999).

NOx emitted at low levels or on the ground during idling or taxiing contributes to local

air pollution and has direct and indirect impacts on human health (Wellburn, 1994),

covered below, but emissions at higher altitudes, in the upper troposphere and lower

stratosphere (UTLS)7 have an effect on reactions involving the production and

destruction of ozone (O3) and methane (CH4) (Sausen and Schumann, 2000). Ozone is a

GHG affecting radiative balance through both its absorption of incoming shortwave

radiation8 and of outgoing infrared radiation, while methane is also a significant GHG

(IPCC, 1999) (Wuebbles and Hayhoe, 2002).

NOx encourages the production of ozone at ground level, but emissions of NOx at higher

altitudes in the troposphere are more effective in this process (IPCC, 1999). The ozone

produced due to NOx emissions in the stratosphere is somewhat offset by the tendency

of aircraft sulphur and water emissions to reduce ozone (IPCC, 1999), although the

6 For a useful introduction for non-experts to the modern aero engine, see IPCC, 19997 between 9 and 13 km typically, although the boundary between the layers, the tropopause, variesaccording to local conditions, season (lower in winter) and latitude (lower at the poles, higher at theequator)8 Hence the role of the stratospheric ozone layer in shielding the earth’s surface from ultravioletshortwave radiation, and its related human health impacts (IPCC, 1999). The historic addition ofstratospheric ozone by aviation is overwhelmed by the destruction of ozone due to CFCs etc leading to anet reduction in stratospheric ozone and its related greenhouse effect (IPCC, 2007).

20


latter effects are now believed to be small (Wuebbles, 2006). A further step in the

chemical process is that ozone takes part in reactions that destroy methane – hence the

NOx climate effect is a combination of increased radiative forcing through net increases

in tropospheric and stratospheric ozone, but a reduction in radiative forcing through the

reduction in methane.

Bernsten et al., (2005) found that NOx emissions varied in their climate impact

according to location, implying that a single metric for NOx impacts on climate globally

would be inadequate – another source of uncertainty in aviation’s environmental

impacts.

As above, advances in scientific understanding have been achieved in the UTLS

chemical processes, more data has been gathered on conditions in this region (Sullivan

and Prather, 2005) and improved models of the UTLS transport and chemistry

developed (Sausen et al., 2005; Wuebbles, 2006; IPCC, 2007). Programmes such as the

European MOZAIC have contributed to this process, with water and ozone

measurement instruments carried on commercial aircraft in operation (Wuebbles et al.,

2007).

As above in Figure 2.3, the best estimates for both the positive ozone forcing and

negative methane effect have been reduced, although the net positive (warming)

contribution of the two has increased slightly from IPCC, (1999) to the latest studies

(Sausen et al., 2005): in terms of significance, NOx remains among the major impacts

on climate change from aviation.

Uncertainties remain in two broad areas (Wuebbles, 2006): model formulation and

chemistry/meteorology. In the former, data on aircraft emissions (amount, type, location

in terms of altitude, longitude and latitude) can be further improved, the understanding

of the fundamental chemistry of NOx and HOx reactions in the upper troposphere where

models deviate from observations, and in the background naturally occurring levels of

NOx from lightning (Grewe et al., 2002; Grewe et al., 2004; Wuebbles, 2006).

In the latter, coupling and feedbacks in the tropospheric NOx/ozone/methane reactions

remain to be fully understood (Grewe et al., 2001; Grewe et al., 2004), as do the

impacts on these processes of climate change itself (Grewe, 2007). Also in the

chemistry/meteorology group are questions over the correlation of flight routings and

metrological conditions (often treated as independent but interdependent in practice)

21


and issues of transport and mixing in atmospheric regions that often exhibit slow or

stagnant flows (Wuebbles, 2006)

2.8.1 Abatement of NOx via changed flight routing and altitude.

Measures to reduce NOx emissions are discussed under the wider heading of engine fuel

efficiency and emissions below, due to the trade-offs typically present in improving fuel

consumption as discussed above. An exception to this is the (Gauss et al., 2006) study

as part of the European TRADEOFF programme, where the impact of higher or lower

flight paths and polar routes was modelled. Polar routes are increasingly used for long

haul flights where they more closely match the shortest great circle routing9, hence

reducing distances, flight times and fuel consumption (Gauss et al., 2006). The study

found polar routes resulted in significantly higher ozone in summer, although not in

winter, and in altitude terms, higher cruise altitudes increased ozone in both the UT and

LS, while lower altitudes were found to cause a net reduction in total ozone, with

reduction in UTLS ozone and increases in lower tropospheric ozone which however was

more likely to be washed out.

2.9 Contrails, Aviation-induced Cirrus and Climate Change

In addition to its impact on climate change through emissions of GHGs and effects on

ozone above, aviation has a specific impact through persistent condensation trails

(contrails) and cirrus – potentially significant, but not well understood and complex to

abate given the trade-offs typically entailed in interventions.

2.9.1 Contrails: formation, coverage and climate change impact

Schumann, (2005) provides a thorough review of the contrail issue, beginning with an

explanation of the formation of contrails due to the mixing of moist, warm air from

aircraft engines with colder super-saturated ambient air – helpfully illustrating this with

the human analogy of the fog visible when breathing out on a cold winter day. He also

notes that both jet and prop engines produce contrails due to their engine exhaust, and

that contrails can also occur due to air flows around wings, although noting that the

latter are rare and of little practical importance Schumann, (2005). The warm, moist air

9 City pairs between western Europe and western North America or between the Far East and easternNorth America both fall into this category (Gauss et al., 2006)

22


arises inevitably from the burning of hydrogen-containing fuels, with implications for

possible abatement from different fuel types below.

Referring to his earlier study Schumann, (2000) he notes that higher engine efficiency,

defined in specific thrust terms, a desirable trait from a CO2 emissions standpoint,

means more of the energy in a unit quantity of fuel is converted to thrust, and the

exhaust is cooler for the same rate of water emissions, and so higher in relative

humidity. This leads to the formation of contrails at higher ambient temperatures, and

thus to greater overall contrail cover – another trade-off. Note that this would not apply

for aerodynamic or other non-engine-related efficiency gains – it is a thermodynamic

feature of the combustion process.

Contrails always form when particular conditions of temperature and humidity are met –

typically in the high troposphere and also, although less commonly in the lower

stratosphere Schumann, (2005) (as above, the boundary between these regions, the

tropopause, varies in altitude according to season, latitude and other factors). Gierens et

al., (1999b), using data gathered from instruments aboard commercial aircraft, found

that approximately 15% of flight time occurs in air masses where contrails form.

Contrail cover, the proportion of the earth’s surface (or a region of it) covered by

contrails. was initially estimated manually, with researchers identifying contrails and

distinguishing them from other cloud formations by their linear form on satellite

images. This was the method by which (Bakan et al., 1994) found contrails covered on

an annual average 0.5% of the daytime sky over the Eastern North Atlantic and Western

Europe. Using automated techniques developed by Mannstein et al., (1999) these

findings were refined and have been extended to other regions Schumann, (2005).

Sausen et al., (1998) extended this process to a global coverage estimate, calibrated to

the original (Bakan et al., 1994) regional study, and reached a global annual average

contrail cover for 1992 of 0.087% (lower than the Bakan result due mainly to lower air

traffic levels globally versus western Europe and to lower night time cover). Gierens et

al., (1999a) extrapolated this result for different future air traffic scenarios, calculating

that cover could reach 0.25% by 2015 (a near threefold increase versus 1992) and

between 0.26% and 0.75% by 2050 depending on the scenario for air traffic. Contrail

cover grows more quickly than air traffic due to assumed higher fuel efficiency:

remember that counter-intuitively contrail formation (and associated climate change

23


impacts) increase with rising fuel efficiency even as specific CO2 emissions decrease.

Gierens et al., (1999a) assumed in the 2050 scenarios fuel efficiency ratios ranging from

0.3 to 0.5 versus the average for the 1992 fleet of around 0.3 and the 1950s level of 0.2:

for further discussion of efficiency and the derivation of this ratio see (Schumann,

2000).

Marquart et al., (2003) rebased these figures for the updated satellite data results above,

and also allowing for a changing climate, whereby higher temperatures themselves

reduce contrail formation, and found lower results as shown in Table 2.1. As we shall

see below, these coverage figures are much lower than for aviation-induced cirrus.

Study 1992 2015 2050

Gierens et al., (1999a) 0.087% 0.25% 0.46%

Marquart et al., (2003) without

allowing for climate change

0.06% 0.15% 0.28%

Marquart et al., (2003) including

effect of climate change

0.06% 0.14% 0.22%

Table 2.1: Forecasts of Contrail Cover (global annual average) from different studies

(using the IPCC FA1 scenario, related air traffic forecasts and 2050 fuel efficiency factor

of 0.5, IPCC, 1999)

Taking these contrail cover estimates and forecasts, and converting them into climate

change impacts involves the calculation of radiative forcing (RF). Contrails (and cirrus)

reduce the incoming short wave solar radiation (albedo effect) and reduce the outgoing

long-wave radiation (greenhouse effect) (IPCC, 1999). The net result of these two

countervailing effects depends on contrail (and cirrus as below) optical depth and

temperature (Schumann, 2005), and in turn on particle properties and ice water content -

characteristics which remain subject to uncertainty in measurement and modelling.

Meerko tter et al., (1999) and Meyer et al., (2000) note that RF values can even be

negative (i.e. acting against global warming) depending on the characteristics of the

contrail particles and earth’s surface beneath.

As the difference between two numbers, positive and negative as above, and both

subject to uncertainties, the net RF of contrails is subject to large uncertainties.

24


As Schumann, 2005 observes, the values for RF (measured as energy flux across a

square metre) from contrails for 1992 traffic conditions vary across a wide range, as

summarised in Table 2.2.

1992 traffic conditions 2000 (Sausen et al., 2005)

Minnis et al., 1999 +17 mW m-2 +20 mW m-2

Myhre and Stordal, 2001 +9 mW m-2 +15 mW m-2

Marquart et al., 2003 +35 mW m-2 +6 mW m-2

Table 2.2: Radiative Forcing from contrails, comparisons of study values

The IPCC in 1999 used the high end of this 1992-basis range (IPCC, 1999) at +17 mW

m-2 but by the latest Assessment Report, used the updated results from Sausen et al.,

(2005) of +10 mW m-2 for 2000 Because of the low traffic growth between 2000 and

2005, the same figure was seen as a best estimate for 2005 as well. The best estimate

has thus halved, due to a combination of reduced contrail cover estimates and reduced

optical depth estimates (IPCC, 2007), underlining the uncertainty in this area, with

scientific understanding still seen as low. Examples of un- or incompletely explained

anomalies include the difference between US and European contrail optical depths

discussed in Meyer et al., (2002); Ponater et al., (2002) and Palikonda et al., (2005).

Concluding on the climate change impact of contrails, it can be noted that although the

uncertainties are large Sausen et al., (2005) conservatively estimates a factor of three for

the range of uncertainty in RF values) the best estimate RF of +10 mW m-2 compares to

a RF from CO2 of +25mW m-2 as above. Contrails thus appear, even with their wide

potential range of RF outcomes, to be markedly less significant in driving climate

change globally than CO2 emissions. However, unlike freely mixing CO2 and other

long-lived GHGs, contrails (and cirrus below) are not evenly distributed: local effects

could be significant given that contrail cover is expected to be highly concentrated over

certain air traffic intensive regions such as Western Europe and North America, and

northerly latitudes generally, as illustrated in various studies such as that of (Sausen et

al., 1998) shown in Figure 2.6.

25


Figure 2.6: Regional variation in aircraft fuel consumption (and hence contrails):

vertically integrated mean annual fuel consumption above 500hPa from DLR 2 data set:

(Sausen et al., 1998). Note contour spacing varies logarithmically.

2.10 Aviation-induced Cloudiness and Climate Change

As the IPCC, (1999) described, contrails are observed to shear and spread (Minnis et al.,

1998) to cover larger areas with cirrus cloud: indeed, contrails are an anthropogenic

form of thin cirrus, both consisting of ice crystals. Aviation exhaust aerosols and

particles could also lead to cirrus formation IPCC, (1999) and IPCC, (2007) defines

aviation-induced cloudiness (AIC) as the sum of all aviation-induced cloud changes. As

noted already, no best estimate for the RF due to AIC was possible for IPCC, (1999) nor

in the updates of Sausen et al., (2005) or IPCC, (2007). However, the range of estimates

in these studies suggests that AIC could be a significant factor in total aviation RF.

2.10.1 Contrails and Cirrus

Unlike contrails, AIC cannot be distinguished observationally from natural cirrus, and

estimates of the ratio of AIC cover to contrail cover ranges from 1.8 to 10 (Minnis et al.,

2004; Mannstein and Schumann, 2005). Estimating the scale of AIC using trends in

cirrus cloudiness correlated against aircraft fuel consumption regionally does suggest a

26


rising trend as Zerefos et al., (2003) and Stordal et al., (2005) found a moderate

correlation between air traffic and cirrus trends, but clearly separating anthropogenic

from other causal factors was not possible. Stordal et al., (2005) extrapolated their study

to global scale and over time for all aircraft activity and came to an RF mean estimate of

+30mW m-2, close to the upper limit in IPCC, (1999). Cirrus trends over the USA (but

not Europe) were found to be correlated with changes in contrail cover and frequency

(Minnis et al., 2004). Eleftheratos et al., (2007) in a 20 year study of global trends in

cirrus analyse natural and anthropogenic factors and further confirm the link between

cirrus trends and air traffic.

As a measure of the potential significance and continuing uncertainty in the AIC climate

impact, we note the studies and associated dialogue from Minnis et al., (2004) and

Shine and Minnis, (2005). Initial estimates that AIC could be responsible for 1973-1994

surface warming in the USA equal in scale to the total warming observed over the same

period i.e. a highly significant source of climate change. Subsequent studies (Hansen et

al., 2005; Ponater et al., 2005) found the AIC effect to be smaller by one or two orders

of magnitude, although with large uncertainties remaining, with the reduction in impact

due to the lower efficacy (scope to influence climate change) of contrail RF versus CO2

RF.

Another notable focus of study was the increase observed in diurnal temperature range

(DTR) during the short period after 11th September 2001 when almost all air traffic in

the USA was grounded. Travis et al., (2002; 2004) show that DTR rose across the USA

due to rises in daytime temperatures not matched by rises in nighttimes temperatures,

that this effect was largest in areas with previously the greatest contrail cover. However,

as Schumann, (2005) notes, as these results are not based on a quantitative model, but

on correlation indicating only association not causation, the (necessarily) limited data is

a weakness in any conclusion. Kalkstein and Balling, (2004) proposed that unusually

clear weather (not contrail related) could account for the observed DTR changes.

In a meeting convened in June 2006 (“Workshop on the Impacts of Aviation on Climate

Change”, reported in Wuebbles, 2006) the uncertainties relating to contrails and AIC

were summarised as concerning the characteristics of the cirrus and contrail ice crystals

(and hence the optical properties) which required further empirical work, the detection

and prediction of ice supersaturation (both for modelling and potential abatement

27


through avoidance as in Mannstein et al., 2005), the incorporation of contrails and cirrus

into General Circulation Models (GCMs) on finer scales of resolution and in more

sophisticated form and finally the need for further study into long term trends in cirrus,

including improvements to the current satellite data and record.

2.10.2 Aerosols, particles and Cirrus

In addition to the observed source of AIC from spreading contrails, cirrus and other

clouds may form from the aerosol and particulate (carbon soot, etc) emissions in jet

engine exhaust.

Compared to the contrail formation process, or even the less well understood contrail-

cirrus link, the role of aerosols and particles in ice nucleation and other cloud formation

processes remains subject to a low level of understanding and large uncertainty.

Hendricks et al., (2005) found that such emissions could cause cirrus far from flight

paths due to transport of aerosols and particles in the atmosphere and that there was the

potential for significant cirrus modification from black carbon particles (soot) from a

modelling study, whereas aerosols could either increase or decrease the likelihood of ice

nucleation depending on assumptions about the cloud formation process. IPCC, (2007)

noted that studies of the correlation between trends in cirrus cover and in air traffic

would not distinguish between contrail cirrus and aerosol/particle related cirrus and

continues to be unable to conclude on a best estimate or range for RF from this source

of cloudiness.

The Wuebbles, (2006) workshop report summarised the uncertainties over the

aerosol/particle influence on AIC as being due to observational difficulties in measuring

the wide range of aerosol, particle and ice crystal sizes and habits, the general area of

ice nucleation from natural and other anthropogenic sources being not well understood

or observed, as well as the uncertainties already mentioned relating to contrails and

cirrus above.

2.10.3 Uncertainty and Dispute in Comparing Drivers of Climate Change

The authors of the sets of simulation studies (Williams et al., 2002; Fichter et al., 2005;

Williams and Noland, 2005) all note that the RF from contrail cover, and any reduction

in it via reducing contrail formation by reducing cruise altitudes entail a trade-off in

terms of increased RF from the additional emissions associated with increased fuel burn

at lower cruise altitudes. Both allude to the point that contrails have different, and much

28


shorter, lifetimes than species such as CO2. Fuglestvedt et al., (2003) examine RF and

emissions indices in the context of their use as metrics of climate change.

The relevance of this point for aviation is expanded upon in Forster et al., (2006) paper.

Although the argument made by Forster et al. specifically address the issue of including

non-CO2 effects of aviation (as above, from NOx and its effects on ozone and methane,

from contrails and from cirrus below) in emissions-trading schemes, it is equally

relevant in our context of abatement. It concerns the significance and uncertainty of

different environmental impacts of aviation, and how they may be compared or traded-

off. Whether the intervention is an emissions trading scheme (ETS) or technological or

operational changes (e.g. changed cruise altitudes) similar issues of comparing CO2-

derived climate change impacts and non-CO2 derived impacts arise.

Noting the use of the radiative forcing index (RFI), the ratio of total RFs for all sources

over the RF from CO2 alone, in various policy studies, as a multiplier to be potentially

used to include non-CO2 impacts in the EU ETS, the authors forcefully make a number

of points concerning RFs and climate change impacts, and hence the issues involved in

including non-CO2 effects in an ETS. An RFI of 2.5 is found in various sources, traced

to the 1999 IPPC report where for 1992, CO2 RF was assigned a best estimate value of

0.22 W m-2 and total RF from all sources (excluding cirrus, for which no best estimate

was found) a best estimate of 0.055 W m-2 , hence the 2.5 RFI ratio.

Firstly, they note that the RF is a time dependent measure, of the cumulative effect of

past emissions up to a given point in time, of the emissions on the Earth’s energy

budget. The pattern of past emissions of species, their history, as well as their current

quantities in the atmosphere, are thus needed to calculate the RFI. The authors note that

when climate change impacts now and in the future are being assessed or comparing, as

for the Kyoto Protocol, global warming potentials, (GWPs), have been used rather than

RFIs (IPCC, 1990).

“[GWPs] consider the time-integrated [author’s italics] RF from a pulse emission

rather just the RF alone” (Forster et al., 2006)

The authors go on to give an example, paraphrased here, of the emission on the same

day of equal masses of two different climate change agents, with similar RFs, yet one

with a lifetime of a few days and the other of 100 years: clearly the latter would have a

larger climate change impact than the former, despite their similar initial RF, due to

29


their different residence lifetimes. When the initial RFs are different, as well as the

lifetimes, the impact on climate change will depend on the period considered: a smaller

initial RF but a longer lifetime could soon lead to a larger climate change impact from

the lower initial RF source. Forster et al., (2006) note the use of a 100 year period for

GWPs for non-CO2 species such as methane and nitrous oxide in the Kyoto Protocol.

Using the specific example of aviation, and setting the starting point such that the RFI is

25, in line with the IPCC (1999) finding, Forster et al., (2006) illustrate the time

dependence of RF values for different agent life spans graphically (Figure 2.7), by

assuming that the 1992 level of aviation activity remains constant, and plotting the

forecast CO2 and non-CO2 RF values over the next century, and hence the RFI. On the

assumption that all of the non-CO2 effects are shorter lived and thus in equilibrium,

(noting that this assumption is weakest for methane, with a 10 year life, but still would

cause negligible impact beyond about 20 years of stable emissions), as time passes, the

non-CO2 RF is constant in line with air traffic in this illustration, whereas the CO2 RF

continues to rise, as more CO2 is added to the atmosphere each year. Hence the RFI

declines over time, the importance of long-lived CO2 in driving climate change becomes

increasingly apparent relative to shorter-lived species, even if the latter have initially

higher RF.

30


Figure 2.7: CO2 and non-CO2 radiative forcing, plus RFI as a function of time for constant

aviation traffic from (Forster et al., 2006): the figure shows the RF from CO2 and non-CO2

sources (excluding cirrus) over time, with emissions held constant at 2000 levels from that

year. The RFI (ratio of total RF to CO2 RF) is also shown (solid line, RHS).

Forster et al., (2006) go on to attempt to derive the equivalent of a GWP for aircraft

emissions, recognising the difficulties in doing so for contrails and for the

methane/NOx/ozone group (cirrus was not included) – without reiterating the

complexities and uncertainties of the latter, the outcome illustrates for the authors, the

unsuitability of RFI as a metric to trade off non-CO2 versus CO2 effects. The derived

ratio of AGWP (absolute global warming potential, the version of GWP used) from CO2

to the total, named the Emissions Weighting Factor (EWF) would be 16 for a 1 year

time horizon (i.e. the total impact of contrails, Tropospheric chemicals and CO2 would

be 16 times greater than that of the CO2 alone) but would decline to 18 after 20 years

and 12 after 100 years, as the long-lived nature of CO2 versus the other factors gained

weight. Note that these figures include the corrections made in Forster et al., (2007).

Any trade-off or cost effectiveness analysis of interventions effecting CO2 emissions

and non-CO2 effects differentially would have to take account of this question of time

31


periods – an additional layer of uncertainty on top of the uncertainties in the current RF

estimates.

2.11 Climate Change SummaryAviation’s impact on climate change was extensively discussed in the IPCC’s 1999

‘Aviation and the Global Atmosphere’, and arises from CO2 emissions due to fuel

combustion, plus other engine emissions such as NOx, soot and aerosols, the latter two

also being associated with variations in cloud formation, together with an effect from

contrails. The location, vertically within the atmosphere as well as geographically, also

effects the impact of these emissions The range of study estimates and level of scientific

understanding, (two different although often related forms of uncertainty) rise in the

same order: CO2 being best understood and quantified, clouds least well understood and

quantified. Research since IPCC (1999) has generated changes to best estimates for

each element, and reduced some error ranges, as well as improving the levels of

scientific understanding in some areas, but the ranking of increasing uncertainty remains

the same.

Sources of uncertainty range from quantification and characterisation of source

emissions, through dispersion and atmospheric chemistry and physics, including cloud

formation, and into the fine-scale modelling of climate. There are further complexities

in gauging impacts which arise from the regional nature of drivers such as cloudiness,

which are concentrated in regions of high traffic, such as northern Europe, unlike CO2

which mixes freely on global scale, whatever its point of origin.

Uncertainties arising from the different lifetimes of these drivers of climate change,

represent a final layer of complexity and source of dispute and uncertainty.

2.12 Local Air Quality

Aircraft engines contribute, along with ground support vehicles and non-airport sources

to local air pollution, with the same types of emissions as described in Figure 2.1 above:

CO2, NOx, SO2, unburnt hydrocarbons (UHC), and carbon monoxide CO. Particulates,

both from engines and from brake and tyre wear, are another pollutant. There is a large

literature concerning the emissions and their health effects, of which some UK focussed

32


reports are Bickel et al., 1997; Lampert et al., 2004; DEFRA, 2007a; DEFRA, 2007b

and a summary of recent research in Brooker, (2006).

In a recent study at Zurich Airport, Schu rmann et al., (2007) on the sources of different

pollutants, carbon monoxide concentrations were found to be highly dependent on

aircraft movements whereas NOx concentrations were in fact dominated by ground

support vehicles.

As Table 2.3 shows, emissions of pollutants (except CO2 and SO2, as effectively all of

the carbon and sulphur are oxidised) vary according to the engine operating situation –

idling (and taxiing) generate relatively more CO and UHC as found in the Schu rmann et

al., (2007) study whereas NOx is most strongly emitted (per kg of fuel burnt) in the high

power mode of take-off (and climb out) (Brasseur et al., 1998).

An example of the implications of this can be seen in the study of four Turkish airports

(Kesgin, 2006) which found that 71-73% of emissions (by weight) of four species

(UHC, CO, NOx and SO2) of pollutant were emitted during taxiing, versus 22-23% on

take-off and climb-out and the remaining 5-6% on approach. The implications of the

benefits of reducing taxiing/idling are clear.

In terms of toxicology, Tesseraux, (2004) found that the risks from jet fuel were not

significantly different than diesel, or other urban sources, with health and environmental

impact therefore dependent on dosage and exposure.

The key areas of uncertainty in local air quality impacts of aviation concern the mixing

of sources (Schu rmann et al., 2007), wherein ground transportation and industrial

activities contribute to concentrations of all of the same pollutants. The health effects of

the various species emitted are also under continued epidemiological investigation

(Brooker, 2006) and uncertainty remains.

33


Operating Condition

Species Idle Take-off Cruise Comments

CO2 3,160 3,160 3,160

H2O 1,230 1,230 1,230

CO 25 (10-

65)

<1 1-35

Unburned Hydrocarbons (UHC:

as Methane)

4 (0-12) <05 02-13

NOx (as NO2) 4,5 (3-6) 32 (20-

65)

79-119 Short haul

45 (3-6) 27 (10-

53)

111-154 Long haul

SOx (as SO2) 10 10 10

Table 2.3: Typical emission levels for different engine operating regimes – units are g of

pollutant per kg of fuel burnt (g kg-1) adapted from (Brasseur et al., 1998), with reference

to (Baughcum et al., 1996a; Baughcum et al., 1996b; Gardner et al., 1997)

2.13 Local Air Quality SummaryAircraft engines contribute, along with ground support vehicles and non-airport sources

to the deterioration of local air quality, with the same types of emissions as described

for climate change above: CO2, NOx, SO2, unburnt hydrocarbons (UHC), and carbon

monoxide CO. Particulates, both from engines and from brake and tyre wear, are

another pollutant. A key area of uncertainty in local air quality impacts of aviation

concern the mixing of sources (Schu rmann et al., 2007), wherein ground transportation

and industrial activities contribute to concentrations of all of the same pollutants.

Aircraft also emit different quantities of the species affected local air quality according

to the engine state – taxiing, idling, taking off or landing (Brasseur, 1998). The sources

and impacts of NOx are relatively well understood but the emissions and health impacts

of other species, notably particulates, are under continued epidemiological investigation

(Brooker, 2006) and uncertainty in these areas remains large.

34


2.14 Interventions and Trade-Offs

The literature suggests that trade-offs are pervasive in aviation’s environmental impacts

(RCEP, 1994; IPPC, 1999; Greener by Design, 2003b; ACARE, 2004a). The focus of

this study is not the technicalities of the trade-offs themselves but rather the way that

they are managed and how uncertainty affects their management.

However, in order to gain an understanding of the issues, have concrete examples and to

aid the generation of questions for primary data collection, a selection follows with

examples of studies of specific abatement measures and the trade-offs they involve.

2.15 Abatement/Mitigation of Contrails and Aircraft-Induced Cirrus

As noted above, Schumann, (2005) any aircraft burning hydrogen-containing fuel

generates warm, moist air and will produce contrails and potentially cirrus in certain

atmospheric conditions. This applies therefore to traditional kerosene (jet fuel), any

biofuel hydrocarbon and would also apply to hydrogen-fuelled planes (cryoplanes)

(Marquart et al., 2001; Ponater et al., 2006;).

2.15.1 Abatement via Cruise Altitude Changes

A mitigation option is thus to avoid, wholly or partially, flight paths through

atmospheric regions where contrails form – ice supersaturated regions (ISSRs). A

number of authors have examined the potential and implications for such strategies.

Williams et al., (2002) , using actual air traffic data on one day in Western Europe as a

baseline and an air traffic control (ATC) simulation model, applied various increasingly

stringent altitude reductions to enforce flying below the typical cruise altitude around

29,000 ft or nearly 9km where contrail formation conditions are likely. Blanket

restrictions of this kind have implications for fuel consumption and related emissions,

which are typically increased due to the aircraft flying below its optimal design cruise

altitude, through denser air, and may also increase flight times and affect air traffic

control: Williams et al., (2002) examines each of these trade-offs. Varying the altitude

restrictions with the aim of avoiding most contrail formation also implied seasonal

variations in altitude restrictions, as winter colder conditions are more conducive to

contrail formation than hotter summer periods, and winter altitude limits were thus

lower – taking this into account, Williams et al., (2002) found that the average

additional fuel burn (and thus CO2 emissions) averaged 39% annually, ranging from

35


72% above the control baseline in February to 16% above control in the June-

September period. A reduction in contrails to a 5% probability of formation threshold,

or a 95% reduction on average, for a 39% increase in fuel burn appears an attractive

trade-off, although Williams et al., (2002) note, in line with the comments of Forster et

al., (2006), that the different lifetimes of CO2 and contrails complicate the assessment.

Journey times in the Williams et al., (2002) simulation averaged under 1 minute longer,

with some flight times reduced and other increased, which could lead to scheduling

problems and economic implications for operators. A bigger problem emerged in the

ATC system – ‘dramatic’ increases in the number of sectors exceeding thresholds for

severe loading. From 7 out of 81 sectors in the control experiencing severe loading, this

rose to 31 sectors in the most stringent altitude restriction scenario, under which the

total number of centres and sectors would actually be reduced as some centres/sectors

dealing only with higher altitude flights would not be required to operate. More flights

were being squeezed into a smaller space and at the same time, fewer air traffic staff

were handling them. Another measure of ATC stress is the number of ‘conflicts’, where

flight paths require intervention to avoid aircraft coming too close together – the most

stringent scenario generated 35 more such events than the control.

The same strategy and modelling was developed further Williams and Noland, (2005) to

allow for variable altitude restrictions within six hour slots each day, allowing actual

weather conditions to be factored into altitude restrictions, refining the more rigid

monthly patterns used in the 2003 study. Williams and Noland, (2005) found that this

more sophisticated approach did optimise the fuel burn trade-off, as well as avoiding the

risk that a blanket altitude restriction rigidly applied could actually increase contrail

production on some days. Varying the altitude restriction so as to maximise the ratio of

contrail reduction to additional fuel burn reduced the contrail formation versus the fixed

policy by between 65 and 95% for similar fuel burn to the fixed policy, showing the

variable policy to be more effective. However, as the authors discuss, the cost

effectiveness of the variable versus fixed policy would be impacted by the additional

demands on ATC (already strained as above) of the more frequent altitude limit

changes, and the more frequent transitions between time periods (the latter not being

fully modelled in the simulation).

36


A similar study carried out by Fichter et al., (2005) used a detailed database of

aircraft/engine pairings, related emissions inventories and mission/operational

characteristics combined with actual Eurocontrol and FAA mission data (over 53,000

flights), and applied the resulting emission and location data to a GCM model to assess

the impact on contrails of reductions or increases in cruise altitude in increments of

2,000 ft. Increasing cruise altitude by 2,000 ft was found to slightly increase expected

contrail coverage (by 6%) whereas reductions in altitude lead to reduced expected

contrail cover, broadly proportionate to altitude reduction, with the largest reduction of

45% in cover for the largest altitude reduction (6,000 ft). This Fichter et al., (2005)

study was global but focussed only on contrails, confirming the reduction expected in

contrail cover for altitude reduction, and also that the RF would be reduced in a very

similar way to contrail cover. It also found strong seasonal and regional variations in

contrail cover. The Williams et al., (2002) and Williams and Noland (2005) studies are

regionally narrower, but do examine the trade-offs in terms of fuel burn, ATC stress and

journey time changes.

Mannstein et al., 2005 use operational radiosonde data that show ISSRs to be relatively

shallow (typically 500m in vertical extent) to develop in illustrative form (without ATC

simulation or fuel burn calculations) a strategy for avoiding contrails that would be

more effective than that of Williams et al., (2002), Fichter et al., (2005) and Williams

and Noland, (2005). The core of the argument is that general changes in flight altitude

without precise knowledge of whether the aircraft is in an ISSR or if so, where, in

altitude terms, the nearest ‘dry’ region is are sub-optimal, and may, as Williams and

Noland, (2005) found, actually increase contrail formation in some circumstances.

Mannstein et al. (2005) suggest an approach where pilots and ATC would be alerted to

the formation of contrails, by hygrometers installed onboard, or by visually observing

contrails from their own or nearby aircraft, and would then rise or descend only if

contrail formation was occurring or expected. Given the shallowness of ISSRs, a 50%

reduction in contrails could be achieved with around 2,000 ft (600m) altitude changes

only when needed, versus a blanket altitude restriction approach, where around 6,000 ft

(1,800m) altitude changes would be needed for the same contrail reduction. Mannstein

et al., (2005) suggest two further refinements. The first was that evasion action would

only be taken if other conditions indicated that their formation would have a positive

37


RF. For instance, and as above (Meerko tter et al., 1999; Meyer et al., 2002), lower level

albedo can affect this – so a plane flying over a low-level cloud deck (high albedo)

might take evasive action whereas one flying over cold dark water might not. Mannstein

et al.’s (2005) second refinement was that if either the ATC system, through

assimilation of the data from aircraft, or through refined meteorological models and

forecasts, could predict where the nearest ‘dry’ air was located, the altitude adjustment

could be refined still further, perhaps to an average of only 1,000 ft for a 50% contrail

reduction. The authors accept that the kind of free flight and/or more sophisticated ATC

required, plus instrumentation, meteorological knowledge and pilot training are all new

and entail additional costs and international standards and agreements, but argues that

they are in many cases already being developed or validated.

2.15.2 Abatement via Night/Day rescheduling

Stuber et al., (2006) in a study of a site in SE England, near the start of the North

Atlantic flight corridor, found that flights during the hours of darkness account for only

25% of the daily traffic, but contribute 60-80% of the RF due to contrails. Furthermore,

the seasonal effect was also large, due to both lower mean temperatures and longer

nights, meaning that winter flights, at 22% of annual air traffic, contributed half of the

mean annual RF. The authors conclude that rescheduling flights could be a means of

climate change abatement.

2.15.3 Contrails in Long vs. Short haul flights

Williams and Noland, (2006) compared the CO2 and contrail impact of short- and long-

haul flights from London Heathrow and found that although contrail generation per

passenger km increased with flight distances from short to medium ranges, it was lower

on average for long haul flights: contrail per passenger-kilometre flown was higher, but

the number of passengers more than offset this. As above, different scheduling

approaches to abatement would affect operators in different ways according to their

operating and business model: as Doganis, (2006) describes, charter airlines make

particular use of night flights as part of their business model.

2.15.4 Changes in Cruise Altitude

Williams et al., (2002) in the simulation study of a possible strategy to abate contrail

formation by reducing cruise altitudes made a number of observations about the

potential impact on the operations of airlines that could arise as by-products of the

38


altitude restriction plan (as well as the additional burden on ATC of any such scheme).

The scheme had a general effect of lengthening flight times, and although on average

this was by less than 1 minute, the results of the simulation (based against actual historic

traffic on a specific day over Western Europe) showed a skewed distribution, with some

flights actually becoming quicker, although typically by tens of seconds, and a range of

lengthened flight times reaching as high as 12 minutes for the less stringent 31,000 ft

altitude limit, and over 17 minutes for the most stringent 24,000 ft limit – all differences

measured against the actual baseline. Although these times appeared to the authors to lie

within normal day-to-day variability in flight times, low cost scheduled operators’

business model is reliant on high utilisation of aircraft and crew via quick turnarounds

and high levels of punctuality and could therefore be more severely impacted than low

cost charter operators or other operators (Williams et al., 2002; Doganis, 2006). For

long haul flights, particularly if the same kind of restrictions on cruise altitude applied at

all points, as Williams et al., (2002) observe, longer flight times could exceed crew

operating hours, requiring either double staffing or a stop-over. Likewise, fuel and range

constraints could come into play, once again either requiring stop-overs or in some

circumstances, and for some aircraft, making routes non-viable.

A specific example from Williams et al., (2002) study was the impact of the reduced

altitude scheme on flight times for flights by the McDonnell Douglas MD80, of which

there were 401 among the over 9,000 flights in the data used for the simulation. The

authors found that for the most stringent altitude limit (24,000 ft) more than 90% of the

MD80 flights had a reduced journey time, versus 21% for the whole sample. The

complexities of the issue are highlighted by the same data for the least stringent 31,000

ft altitude limit: in this scenario, almost half of the MD80 flights were faster (reduced

journey time) but two of the MD80 flights showed long delays, over 11 minutes, the

longest delays to journey times in the sample and more than double the next longest

delays. Williams et al., (2002) draw the conclusion that not just aircraft type but also

route are factors in differentiating changes to flight times. Versus the faster travel times

for the MD80, the study found the largest increases in flight time among the Boeing 757

and 777 and the Airbus A310, 320 and 340 As an example, the authors state that in the

24,000 ft scenario, of the 406 Boeing 757 flights in the sample, 364 showed increased

journey times and 160 of these were more than 5 minutes.

39


2.15.5 Changes in Day/Night and Winter/Summer scheduling

Above, Stuber et al., (2006) showed that nighttimes and winter flights (and thus

especially winter nighttime) flights had a disproportionate contribution to RF from

contrails (and it may be assumed, from AIC). The tentative proposal to use rescheduling

to minimise this effect would have significantly different impacts on the various airline

operators and potentially on airports and ATC. One example would be low cost charter

operators, one of whose sources of cost advantage is the use of night flights (Doganis,

2006).

2.16 Summary

Key findings of the literature survey are firstly that the perception of risk and

uncertainty (which are often interchangeable in common usage) and decisions under

uncertainty are subject to individual’s (or society’s) perspective and beliefs about

nature. For noise, climate change and local air quality, there are aspects in each area

which are better understood, with less uncertainty, and other areas with greater

uncertainty. In some cases, such as the climate change impact of aviation-induced

cloudiness, the importance may be large but is highly uncertain despite a large ongoing

research effort. Cross-disciplinary and trade-off studies are developing but remain in the

minority.

40


Chapter 3: Methodology

3.1 Introduction

The methods selected and deployed in pursuit of the research aim and objectives are

detailed within this chapter. A research design is presented and the rationale for its

development is described. Details of how the research design was applied in the study

are provided and the limitations and validity of the research design discussed.

3.2 Research Design

This section is concerned with the development of an appropriate research method to be

deployed in the study: a research design. There are many methods available to social

scientists, which may be combined in various ways to produce many different forms of

research design. It is therefore necessary to employ a systematic approach to the

selection of methods to form the basis for a coherent and appropriate research design.

Robson (2002) states that when developing a research design, the following items

should be considered (with examples):

The purpose of the study: exploratory, explanatory, descriptive

The research strategy: case study, experiment, survey

The type of data collected: qualitative and quantitative

The data collection techniques used: interviews, ethnography, checklists

The approach to data analysis used: coding and clustering, content analysis,

discourse analysis

This section is structured to enable consideration of these items in turn.

3.2.1 Purpose of the study

According to Robson (2002), there are three classifications of research purpose; namely,

exploratory, descriptive and explanatory. In broad terms, Robson (2002) suggests that

explanatory research is undertaken when an explanation of a situation or problem is

required, which is usually conceived in terms of causal relationships. A detailed

understanding of the problem or situation to be researched is required before

41


undertaking this type of enquiry. Considerable knowledge of the relationships to be

investigated is required. Descriptive research is undertaken when an accurate profile of

persons, events or situations is required. As above, considerable knowledge of the

situation is required, particularly of appropriate aspects of a situation on which to gather

information. Finally, exploratory research is undertaken when little is known about a

situation, topic or problem or when new insights are required. Little knowledge of the

focus of the inquiry is required, and such research often acts as a precursor to

descriptive and explanatory research. Outputs from exploratory research include among

other things hypotheses, conceptual frameworks and research questions.

Little is known about the impacts of uncertainty and trade-offs on decision-making in

the field of aviation and the environment. Insufficient information is available to

complete research which is explanatory or descriptive in nature, and thus the research

presented in this study is exploratory in nature.

3.2.2 Research Strategy

According to Robson (2002) and Neuman (2003) there are three traditional research

strategies: experiment; survey; case study. The characteristics of these are presented

below:

Case Study - development of detailed, intensive knowledge about a single case,

or of a number of related cases.

Experiment - measuring the effects of manipulating one variable on another

variable

Survey - Collection of information in standardised form from groups of people

The purpose of the research plays a key role in determining the selection of the research

strategy (Robson, 2002). Typically experiments are used in explanatory studies, surveys

in descriptive studies and case studies in exploratory research. In similarly vein,

according to Yin (2003) the research questions also play a key role in selection of the

research strategy, research questions which begin with ‘how’ or ‘why’ may be most

efficiently answered using experiments. Those beginning with ‘who’ or ‘what’ are

typically answered via survey and ‘how’, ‘why’ and ‘what’ by case study research.

Research questions take the form, restating from Chapter 1 in Yin’s (2003) terms, of

firstly, what are aviation’s environmental impacts, and what is the importance of each of

these impacts. A second group of research questions ask how do uncertainties affect

42


decision-making, and how are trade-offs managed. Thus the research is exploratory in

nature and a case study research strategy was adopted. Case study research is

undertaken to study a phenomenon in its context and in instances where these are

difficult to separate (Robson, 2002; Yin, 2003). In this study, the phenomena are

environmental impacts, and particularly the uncertainties associated with these impacts,

and the context is that of the aviation sector.

3.2.3 Type of data collected

There are two options available to social science researchers: qualitative data and

quantitative data. According to Robson (2002) in social science research, qualitative

data are based on meanings expressed through words and quantitative data are based on

meaning derived from numbers.

The exploratory aim of discovering deeper insights into evolving issues that are not

fully understood, as described above, made the collection of qualitative data most

suitable.

3.2.4 Data collection techniques

Case study research entails the use of multiple methods to elicit data from multiple

sources. The type of methods selected to elicit data in this study are presented in this

section, as well as the rationale for their selection. The sources from which data were

collected are also described.

In case study research, data may be elicited using a variety of methods such as: small

surveys, content analysis, interviews. A selection of research methods were used in this

study.

Primary data collection

As Robson (2002) observes, a survey is a common tool for data collection, in a case

study and other formats. However, a survey is best suited to the collection of a small

amount of standardised data from a large population. Neither of these characteristics

applies in this case. Firstly, access to large population of stakeholders was not available,

given the concentrated nature of many of the aviation industry sub-sectors (single

national ATC organisations, engine and airframe manufacture both duopolies, airport

ownership concentrated in the UK, etc). Secondly, the requirement for standardised

questions to elicit standardised data could not be met for this exploratory study, where

knowledge of appropriate questions was insufficient at the time of initiation of the study

43


to generate a suitable questionnaire. In addition, the constraints of time and risks of

inadequate response rates both weighed against the survey route.

There are three types of interviews: structured, semi structured and unstructured.

Structured interviews elicit data in standardised form via a set of pre-determined

questions, semi structured interviews elicit data via an interview guide which comprises

pre-determined questions, which may however be deviated from, with new questions

being added, questions dropped and the order changed. Unstructured interviews are

completely informal and usually involve a conversation about the topic or situation

under investigation.

Semi-structured interviews are used in this study, a choice consistent with the

exploratory nature and flexible structure of the study (Robson, 2002). Semi-structured

interviews were employed as insufficient knowledge was available to develop fully

structured interviews, which are, as above, typically used as part of surveys.

Conversely, unstructured interviews were deemed unnecessary given the secondary data

that could be elicited from the literature review as below. The strengths of targeted

enquiry, capable of providing insights into perceived causal inferences from expert

informants (Yin, 2003) are key reasons for the choice of semi-structured interviews in

this research.

Secondary data

The context of the study, the environmental impacts of aviation, has been the subject of

a wide ranging and comprehensive academic literature, and also of a number of other

reports, commercial studies and governmental documents. Given the aims of the study

include the identification of the environmental impacts of aviation, a critical review of

the literature was a necessary and valuable step in the data collection process. The

review was carried out with the specific aim of extracting data concerning these

impacts, their importance and the uncertainties associated with them.

3.2.5 Development of interview guide

The interview guide (Appendix 2) was developed with the twin aims of developing a

rapport with the respondents as well as eliciting information – on the basis that the

former would aid the latter, allowing respondents to reflect freely on the wider issues

raised by questions. This ensured that insights which a more formal process would have

missed were raised. Therefore the interview guide began with warm-up questions

44


concerning the respondents’ job role and moved onto an initial group of questions

arising from the literature review, concerning the nature and ranking of importance of

environmental impacts of aviation, and how this ranking has in the past, and might in

future, change. Having established this groundwork, it was then possible to move onto

more complex questions of influences on respondents’ views, and to uncertainty in the

environmental impacts, and its impact on decision-making.

Although the literature produced data on these issues, the interview was structured

flexibly, with open questions and invitations to respondents to propose lists of factors,

before any prompting, in order to capture the insights of expert informants. As an

example, for the fourth research objective, concerning the management of trade-offs,

again based on issues arising from the literature, the interview guide invited respondents

to use their own experience to provide examples of trade-offs encountered, and how

they were managed. As with the earlier questions on impacts, this approach served the

double purpose of confirming or contradicting the results of the literature review, as

well as gaining fresh insights into these issues.

At all times, the format allowed for the flexibility to return to previous questions or

responses for amplification or clarification, if subsequent comments demanded this.

Such feedback loops are a recommended means of validating the quality of the data

collected (Miles and Huberman, 1994)

3.2.6 Sampling

The sampling strategies available for use are divided by Robson (2002) into probability

and non-probability and given that the likelihood of selection of each candidate was not

known (the defining characteristic of probability sampling) the approach was one of

non-probabilistic sampling, which is, as Robson (2002) noted, suitable for small surveys

and where there is no intention to make a statistical generalization from the results. Both

of these criteria were met by the study.

Forms of non-probabilistic sampling enumerated by Robson (2002) include quota,

dimensional, convenience, purposive and snowball. To meet the exploratory

requirements of the study, and gain insights from all of the stakeholders in the aviation

sector, purposive sampling was most suitable. An element of snowball sampling was

used, in that some of the respondents first identified where used to elicit further

candidates in the sectors required. The alternatives of quota sampling or the related

45


dimensional approach were not appropriate, as there was no requirement for relative

proportions of the case study population to be replicated, only that at least one

respondent from each stakeholder sector be included. Convenience sampling, whose

weaknesses are in any case noted by Robson (2002), was not required as the purposive

approach was able to generate a suitable panel.

Within the purposive approach adopted, selection of respondents was based on a

stakeholder analysis (Robson, 2002) derived from a wide review of the literature

concerning aviation and the environment (Button, 1993; RCEP, 1994; IPCC, 1999;

ACARE, 2001; DfT, 2003; Green, 2003; Greener by Design, 2003; Hensher and Button,

2003; Noland, 2005; Brooker, 2006; Doganis, 2006). The sample was thus drawn to

include aviation industry participants, regulators, academics and NGOs. Among

industry participants, the breadth of participants across sub-sectors was specifically

intended to cover the different specialisations within the aviation sector, as identified by

among others, Doganis (2002, 2006) or the Acare reports (2001, 2004a). Thus, engine

manufacturers, airframe manufacturers, component suppliers, airlines, airport operators

and air traffic management groups were all included. Given the exploratory nature of

the study, no attempt was made to weight the numbers of respondents to achieve a

representative sample, but rather to ensure that all perspectives were heard. Academic

researchers in the corresponding fields of aero-engines, aerodynamics and air traffic

management were also included.

Respondents were invited to participate in an interview by email, and for those willing

to participate a face to face or telephone interview was conducted, or in two case, a

combination of written answers by email and additional comments by telephone. Notes

were taken, and the interviews recorded when possible. An example transcript of one

telephone interview is included in Appendix 3. 14 respondents were interviewed as

described in Table 3.1.

46


Respondent Description

A Consultant to aviation industry, visiting professor in Air Traffic

Management

B Researcher in engine turbomachinery design

C Environmental dept chief, airport operator

D Chief executive, Airport environmental pressure group

E Environmental manager , national air traffic control organisation

F Environmental department chief, airport operator

G Design engineer with environmental responsibilities, major aero-engine

manufacturer

H Private sector researcher in atmospheric chemistry/physics, adviser to

aviation industry on environmental metrics

I Academic researcher, aviation economics

J Environmental manager, major international airline

K Academic researcher, combustion and aero engines

L Noise/environment design engineer, component supplier to aviation

sector

M Spokesman, aviation/environment national NGO

N Chairman of local environmental NGO

Table 3.1: Respondents Interviewed and job/role description

3.2.7 Data analysis

To structure the analysis of the qualitative and rich data arising from the interviews,

clustering (Miles and Huberman, 1994) and coding to extract key concepts from data

and eventually discover relationships between them. As Corbin and Strauss (1998)

describe, the purpose of coding is:

To build rather than test theory

To provide researchers with analytic tools for handling masses of raw data

To help analysts to consider alternative meanings of phenomena

To be systematic and creative simultaneously

To identify, develop and relate the concepts that are the building blocks of

theory

47


The admonition of Rubin and Rubin, 2005, when analysing qualitative interview data

was also kept in mind, that “intuition and memory do not substitute for systematic

examination” (Rubin and Rubin, 2005)

Initial provisional codes were established based on categories and themes identified

from the literature, and then, using the procedure described in Miles and Huberman

(2004) the summaries of the interviews where examined and codes applied to describe

each ‘chunk’ of data that seemed to the researcher to be potentially relevant. Themes

and ideas that emerged during the course of the interviews and analysis were used to

modify the initial list of codes, to give the codes shown in Table 3.2.

For that part of the analysis which collated the views of respondents on such subjects as

the listing of environmental impacts of aviation, ordered by importance, tabulation of

the responses was sufficient to generate graphical outputs for the findings and

discussions – coding was used for the more complex qualitative responses on

uncertainty, changes in uncertainty, actions/reactions to uncertainty, and management of

tradeoffs required the clustering and coding approach to draw out common themes. As

an example based on Table 3.2 codes, a ‘chunk’ (to use Miles and Huberman’s 1994

term) of speech referring to a respondent’s reasons for allocating a specific level of

uncertainty to the topic of noise might be coded as NOI-ENERGY-UNC-ACA if the

respondent saw lack of academic research as the reason for uncertainty over the energy

aspect of noise (the original single category of noise was subdivided into energy and

non-acoustic after the first round of coding). Some items, such as examples of trade-offs

were simply collected as memo items due to their diverse nature, as recommended by

Miles and Huberman (1994).

48


Codes for topic code SubcodeGeneral –throughout thesurveyresponses, thesecodes were used

CC climate change

LAQ local airquality/pollution

NOI noiseUNC uncertaintyT/O trade offs

Under CCCO2 carbon dioxideNOX nitrogen oxidePART particulates, soot, aerosolsCLOUD contrails, cirrusOr NONCO2 forNOX/PART/CLOUD in combinationUnder LAQNOX, PART as aboveHAZORG hazardous organicsUnder NOIENERGY energy aspect of noiseNONACC non-acoustic aspect ofnoise

3 influences INFLU influences incoming to a given opinion

PUB general publicMED mediaACA academic sourcesLAW law, regulationGOV government, politicsCOMM commercial factors,customersFUEL fuel pricesNGO non-governmental organisationsBRISK business riskto any of which further qualificationsof LOCAL or GLOBAL could beapplied

Uncertainty, andreasons for it

UNC uncertaintyLabelled asVH very highH highNOP no opinion/neutralLOW lowVLOW very low

ACA academic researchDATA data needed, to be collected?SOURCE uncertainTIME time (for research) neededFUND fundamental difficulty inunderstandingEFFORT effort needed (or previouslylacking)

9 tradeoffs T/O trade-offs Y for positive response on means formanagement, N for negative, DN fordon’t know – examples below use xxwhere either Y or N or DN would beinsertedT/O-xx-MON monetaryT/O-xx-NEED a tool/managementmethod is neededT/O-xx-COMM commercial pressuresguide – etc using codes as ininfluences above

Table 3.2: Codes for Data Analysis

49


3.3 Research quality

A key weakness of the case study approach is that the context-dependency of the

method means that the results are not generalisable (Robson, 2002; Yin, 2003).

However, an exploratory case study such as this can lead to further research which can

produce generalisable findings – the potential and nature of further research is discussed

in Chapter 4.

Writing in the context of case study research, Yin (2003) highlights the strengths and

weaknesses of interviews in qualitative research. The weaknesses Yin (2003) notes as

needing attention are:

Bias due to poorly constructed questions

Response bias

Inaccuracies due to poor recall

Reflexivity: the interviewee says what the interviewer wants to hear

Given that the interviews seek to examine the opinions and perceptions of different

experts, it does not attempt to eliminate the risk of respondent bias – but rather to allow

it to be expressed and then compared with other responses. Inaccuracies due to poor

recall should not represent a major problem, as the respondents are all experts working

currently in the field of aviation and environment, and thus are not being asked to recall

past or unfamiliar information. There was an exception to this statement in initial

formulations of the interview guide (Appendix 2), when respondents were asked how

they felt the importance of different environment issues had changed over the past five

years. Whether because of difficulty in recollection or more likely because of

continuously changing importance levels, initial respondents commonly preferred to

reply in terms of ‘in the past’ or ‘a few years ago’. The question was thus reformulated

as to ask how importance levels had changed ‘over the last few years’, with subsequent

probing to determine whether more precision was available. Similar changes were made

to forward-looking questions (see Appendix 2), where the original formulation in asked

for revised answers in 2 years time, 5 years time, 20 years time – the revised formula

was to ask about the direction of future changes, and to probe answers to establish any

timescale available.

50


3.4 Summary of research design

In summary, the purpose of the study was established by the nature of the research

questions as being exploratory, and these factors together with the requirement for

flexibility made the choice of a case study research strategy most suitable. The

requirement for fresh insights into a poorly understood area required that qualitative

data be collected. There were two means of data collection. Secondary data were

acquired through a critical literature review focussing on the issues of uncertainty and

trade-offs in aviation’s environmental impacts, and which formed a basis for research

design decisions on sampling, constructing the initial interview guide and coding for

analysis in the later stages of the study.

Primary data was collected through semi-structured interviews, due to the insufficient

knowledge prior to the interview stage for structured interviews or survey approaches.

The flexibility of the semi-structured interview allowed the insights of the expert

respondents to be elicited. The sampling for interviews was purposive, in order to meet

the exploratory aim of the study, and was based on a stakeholder analysis, although with

some snowballing used to ensure that all of the stakeholder groups were represented at

least once. Analysis of primary data was through clustering and coding.

The interview guideline and a transcript of one of the recorded telephone interviews are

included in Appendices 2 and 3 respectively.

51


Chapter 4: Article

The Impact of Uncertainty on Decisions and Trade-Offs

in Aviation and the Environment

Author: Ken Rumph, Cranfield University

Email: [email protected]

Phone: +44 7785 715095

Abstract

Rapid growth in aviation raises concerns over its environmental impacts. These impacts,

specifically noise, local air pollution and climate change, are subject to uncertainty. The

study explored the consequences of these uncertainties for decision-making and for the

management of trade-offs in abatement measures. Primary data was elicited from key

informants in aviation industry, academia and NGOs. Two strands of responses to

uncertainty were identified, with some seeing uncertainty as a reason for delay, others

as a spur to action. Management of trade-offs in this context was found to follow a

typical hierarchy based on historical priorities, beliefs and regulatory trends. The

present limitation of regulation to noise and local air quality was seen as privileging

these environmental aspects over emissions driving climate change. Recognising

changing external influences and environmental priorities, respondents consistently

appealed for ‘scientific certainty’ and regulators as higher authorities for guidance in

setting new priorities and procedures.

Keywords: Aviation, environment, climate change, trade-offs, uncertainty

52


Introduction




Aviation is rapidly growing, and alongside recognition of its benefits to society and

economic importance comes concern over its rising environmental costs. In terms of

growth, global forecasts for compound annual passenger air traffic growth of between

48% and freight tonnage by 60-68% over the next two decades (Airbus, 2006; Rolls-

Royce, 2006; Boeing, 2007) compare to global Gross Domestic Product (GDP) growth

forecasts in the same sources of around 3%. Longer term global growth forecasts used

in IPCC (1999) show growth continuing to exceed that predicted for the wider economy

to 2050 in the majority of the economic scenarios considered. Part of the global growth

in aviation is driven by rapid penetration of aviation in developing regions such as

China and India (for example, see Airbus, 2006). For the UK itself, a more mature

aviation market, growth is expected to slow from the rate of the past three decades

(1970-2000) when passenger numbers multiplied six fold, (Department for Transport,

DfT, 2006) and yet still see an increase of 250% between 2000 and 2030 if

unconstrained.

Such growth contrasts with various policy objectives from the UK government, to

reduce emissions driving climate change and affecting local air quality and to reduce

noise impact (DfT, 2003; DfT, 2006). Other bodies, international, public or private

sector have similar concerns and aims: for example Advisory Council for Aeronautics

Research in Europe (ACARE, 2001), Greener by Design, (2003b). Bows and Anderson

(2007) question whether these growth expectations are consistent with the UK

government’s aims of a 60% reduction in national CO2 emissions under draft climate

change legislation.

Academic literature (Bickel et al., 1997; Brasseur et al., 1998; Brooker, 2006) and

national and international public sector reports (DfT, 2003; ACARE, 2004a, ACARE,

2004b) highlight three main environmental impacts of aviation: noise, climate change

and local air quality. These environmental impacts are all subject to uncertainty to some

degree.

53


Risk and Uncertainty

In 1921, Knight defined the terms risk and uncertainty as follows (Knight, 2006): it’s

risk if you don’t know for sure what will happen, but you know the odds, whereas if you

don’t even know the odds, it’s uncertainty. However, Adams (1994) wisely observes

that this technical usage is frequently blurred in common usage, with the words used

interchangeably. Douglas and Wildavsky (1983) linked risk perception to cultural

attributes, and that individuals and cultures constructed and perceived risks according to

their own beliefs about nature. Holling (1986) and then Schwarz and Thompson (1990)

developed this into a typology of four ‘myths of nature’: nature benign, nature

ephemeral, nature perverse/tolerant and nature capricious. The application of these

myths of nature to risk and uncertainty produced a further typology of five worldviews

(Holling et al. 2002) adding nature evolving to the four above. The characteristic

behaviour of individuals facing risk, using the first four worldviews above was

described by Adams (1994) as individualist, egalitarian, hierarchist and fatalist.

Slovic (2000) described risk perception in terms of two factors: ‘dread’ and ‘unknown’.

Dread included perceptions of the risk as being uncontrollable, potentially catastrophic,

dangerous to future generations and involuntary. A second factor, labelled ‘unknown’,

combined characteristics related to the observability of risks, whether the effects are

immediate or delayed in time, the familiarity of the risk and whether the risks are judged

to be known to science (Slovic, 2000).

For the purposes of this study, the key points are that risk and uncertainty are socially

constructed (Adams, 1994) and that uncertainty, which does relate to Slovic’s (2000)

factor of ‘unknown’, is a key determinant in the individual’s perception of risk. In a

business context, using the example of the similarly highly regulated utility sector, Toke

and Lauber (2007) observe that despite a general aversion to regulation as costly, firms

may prefer regulation when faced with a level of risk that threatens their returns or

hampers long term investments by raising the implied cost of capital.

Noise from aviation has been a topic of study since the early days of commercial

aviation (RCEP, 1994) so that by the time of the inaugural meeting of the British

Acoustical Society, Karl Kryter (1967) felt able to present the optimistic view that

although

54


“the problems related to the criteria of acceptability of aircraft noise in a community

are most challenging … present-day knowledge about the generation, measurement

and effects of noise on man are sufficiently advanced … to allow the specification of

the exposures to aircraft noise that might be considered socially acceptable”. (Kryter,

1967).

Reviewing subsequent decades of research, the challenging nature of socially acceptable

noise levels seems more durable than the subsequent optimism that a specification was

within reach. The development of metrics for aviation noise has advanced (Brooker,

2006), with recognition along the way that noise measurement has to allow for the

variable sensitivity of auditors, both in terms of frequencies (Royal Commission on

Environmental Pollution, 1994; Greener by Design, 2003a; Hensher and Button, 2003)

and such factors as the effect of night-time vs. daytime noise annoyance (Hume et al.,

2003).

There are two aspects of perceived noise annoyance, ‘acoustic’, the energy-based aspect

of noise above but also ‘non-acoustic’, a perception or psychological aspect: as Maris et

al., 2007 note, “noise is unwanted sound, and therewith a subjective description”

(Maris et al., 2007)

Many authors treated the non-acoustic aspect of annoyance as a blurring or error item in

dose-response studies (Schultz, 1978; Fidell et al., 1988; Schomer, 1989; Green and

Fidell, 1991; Miedema and Vos, 1998;), but purely acoustic aspects of noise (loudness,

pitch etc) only explain part of the annoyance, with non-acoustic variables (Job, 1988;

Fields, 1993) such as perceived control, noise sensitivity and attitudes towards the

source accounting for another part of the explanation (only 25-40% was acoustic, in

Job’s 1988 meta-analysis). Fields (1993) found that isolation from sound at home and

five other attitudes determined annoyance: fear of danger from the source, noise

prevention beliefs, general noise sensitivity, beliefs about the importance of the noise

source and annoyance with non-noise impacts of the noise source. In a practical test of

this, surveys of residents near Vancouver airport before and after an additional runway

produced a step change in noise perception levels that was ‘markedly’ greater than

could be explained by dose-response (Fidell et al., 2002). Noise sensitivity is a human

characteristic independent of other factors – some people are more sensitive to noises at

55


all levels as Miedema and Vos (2003) found, a factor explaining 26% of the perceived

annoyance in a van Kamp et al. (2004) study of 3 international airports.

Compared to the mature and stable state of research into the acoustic or energy aspect of

noise, uncertainty remains significant in the measurement, characterisation and

understanding of the non-acoustic aspects of noise above.

Aviation’s impact on climate change was extensively discussed in the IPCC’s 1999

‘Aviation and the Global Atmosphere’, and arises from CO2 emissions due to

hydrocarbon fuel combustion, but also other engine emissions such as NOx, soot and

aerosols, the latter two also being associated, together with contrails, with variations in

cloud formation. The location, vertically within the atmosphere as well as

geographically, also effects the impact of these emissions (Wuebbles and Kinnison,

1990; Grewe et al., 2001; Wei et al., 2001; Grewe et al., 2002; Bernsten et al., 2005).

The range of study estimates and level of scientific understanding, (IPCC, 2007), two

different although often related forms of uncertainty, rise in the same order: CO2 being

best understood and quantified (Vedantham and Oppenheimer, 1998; Sausen and

Schumann, 2000; Olsthoorn, 2001), and NOx effects subject to a moderate level of

uncertainty (Gardner et al., 1997; Kühlwein et al., 2002; Wuebbles and Hayhoe, 2002;

Herndon et al., 2004; Gauss et al., 2006). Contrail and cloud effects are least well

understood and quantified, and despite the extensive and ongoing research effort,

subject to the greatest uncertainty (Sausen et al., 1998; Gierens et al., 1999; Meerkotter

et al., 1999; Myhre and Stordal, 2001; Marquart and Mayer, 2002; Ponater et al., 2002;

Marquart et al., 2003; Zerefos et al. 2003; Minnis et al., 2004; Hendricks et al., 2005;

Ponater et al., 2005; Schumann, 2005, a useful summary; Stordal et al., 2005; Williams

and Noland, 2005; Atlas et al., 2006; Stuber et al., 2006; Eleftheratos et al., 2007).

Research since IPCC (1999) has generated changes to best estimates (Sausen et al.,

2005; Wuebbles, 2006) for each element, and reduced some error ranges, as well as

improving the levels of scientific understanding in some areas, but the ranking of

increasing uncertainty remains the same.

Sources of uncertainty range from quantification and characterisation of source

emissions (Pitari et al., 2001; Ka rcher and Schumann, 2003; Scha fer et al., 2003),

through dispersion and transport (Grewe et al., 2004 ; Burkhardt and Becker, 2006;

Becker and Burkhardt, 2007), atmospheric chemistry (Grewe et al., 2002; Sullivan and

56


Prather, 2005; Wei et al., 2001) and physics, including cloud formation (Liu and

Penner, 2005; Mangold et al., 2005; Mohler et al., 2005), and into the fine-scale

modelling of climate (Marquart and Mayer, 2002; Ponater et al., 2002). There are

further complexities in gauging impacts which arise from the regional nature of drivers

such as cloudiness, which are concentrated in regions of high traffic (Bakan et al., 1994;

Sausen et al., 1998; Mannstein et al., 1999; Minnis et al., 1999; Meyer et al., 2002;

Stubenrauch and Schumann, 2005) such as northern Europe (Mannstein and Schumann,

2005), unlike CO2 which mixes freely on global scale, whatever its point of origin

(IPPC, 1999, Olsthoorn, 2001).

Uncertainties arising from the different lifetimes of these drivers of climate change,

represent a final layer of complexity (Fuglestvedt et al., 2003; Hansen et al., 2005;

Wuebbles et al., 2007) and source of dispute and uncertainty (Shine et al., 2005; Forster

et al., 2006; Forster et al., 2007; Wuebbles et al., 2007).

Aircraft engines contribute, along with ground support vehicles and non-airport sources

to the deterioration of local air quality, with the same types of emissions as described

for climate change above CO2, NOx, and products of incomplete or non-ideal

combustion and fuel contaminants, such SO2, unburnt hydrocarbons (UHC), and carbon

monoxide CO. Particulates, both from engines and from brake and tyre wear, are

another pollutant. There is a large literature concerning the emissions and their health

effects, of which some UK focussed reports are Bickel et al., 1997; Lampert et al.,

2004; DEFRA, 2007a; DEFRA, 2007b and a summary of recent research in Brooker

(2006). A key area of uncertainty in local air quality impacts of aviation concern the

mixing of sources (Schu rmann et al., 2007), wherein ground transportation and

industrial activities contribute to concentrations of all of the same pollutants. Aircraft

also emit different quantities of the species affected local air quality according to the

engine state – taxiing, idling, taking off or landing (Brasseur, 1998). The sources and

impacts of NOx are relatively well understood but the emissions and health impacts of

other species, notably particulates, are under continued epidemiological investigation

(Brooker, 2006) and uncertainty in these areas remains large.

Research suggests that uncertainty is an important influence on decision-making and

that trade-offs are a pervasive feature of the aviation sector’s environmental impacts. A

generic example from literature is the tendency for the pursuit of reduced fuel

57


consumption (and hence reduction of climate change impact through CO2 emissions)

via higher temperatures and pressures to lead, other things being equal, to high NOx

emissions (Greener by Design, 2003), affecting both local air quality at low altitudes

and climate change itself at higher altitudes – a trade-off against two environmental

impacts. The uncertainties over the scale of some impacts also hinders decision-making

and management of trade-offs. Interventions to reduce the climate change impact of

contrails and cirrus, which entail increased fuel burn and CO2 emissions (Williams et

al., 2002) – and yet the climate impact of contrails and cirrus is highly uncertain versus

the much better understood and quantified CO2 effects, complicating choices.

In view of the importance of uncertainty and trade-offs, this study has the aim of

identifying the uncertainties and trade-offs involved in aviation’s environmental impacts

and their consequences for decision-making. Four objectives were enumerated in

pursuit of this aim:

What are the environmental impacts of aviation

What is the importance of each selected environmental impact of aviation

What are the uncertainties associated with the selected environmental impacts,

and how do these impact upon decision-making within the aviation sector and

associated bodies

What are the trade-offs involved in measures to abate aviation’s environmental

impacts, and how are these trade-offs managed in theory and practice

This study focuses on the subsonic civil aviation market, and on larger planes 10, which

make up the bulk of global emissions (IPPC, 1999). Local air quality in particular is

affected by sources other than aircraft such as ground transportation and airport

equipment, as well as the transportation of passengers to and from the airport. However,

a wider study encompassing integrated travel planning is beyond the constraints of time

and resources available to this study, which therefore focuses on aircraft in flight and on

the ground.

Although the structure of the industry is not the subject of this study, some

characteristics are relevant to behaviours in dealing with uncertainty and trade-offs.

These include the oligopolistic nature of the airframe and engine industries, both of

which feature two or three major industrial groups dominating the market (IPCC, 1999;

10 Large defined as per IPCC, 1999 as above approximately 9 tonnes take-off weight

58


Doganis, 2002; Doganis, 2006) and effective separation, albeit with co-operation, of

engine design and manufacture from airframe design and manufacture (Airbus, 2006;

Mecham and Wall, 2006; Rolls-Royce, 2006; Boeing, 2007). The high capital outlay

entailed in aircraft purchases and their long design timescales (5-10 years), and even

longer lives in use (25-40 years, IPCC, 1999) mean that the fleet of aircraft turns over

only slowly – changes to the environmental performance of new aircraft thus take a long

time to shift the aggregate environmental characteristics of the fleet.

Methodology

The purpose of the study was established by the nature of the research questions as

being exploratory (Robson, 2002), and these factors together with the requirement for

flexibility made the choice of a case study research strategy most suitable (Yin, 2003).

The requirement for fresh insights into a poorly understood area required that qualitative

data be collected. There were two means of data collection. Secondary data were

acquired through a critical literature review summarised above and focussing on the

issues of uncertainty and trade-offs in aviation’s environmental impacts, and which

formed a basis for research design decisions on sampling, constructing the initial

interview guide and coding for analysis in the later stages of the study.

Primary data was collected through semi-structured interviews (Robson, 2002), due to

the insufficient knowledge prior to the interview stage for structured interviews or

survey approaches. The flexibility of the semi-structured interview allowed the insights

of the expert respondents to be elicited (Neuman, 2003). The sampling for interviews

was purposive (Robson, 2002), in order to meet the exploratory aim of the study, and

was based on a stakeholder analysis although with some snowballing used to ensure that

all of the stakeholder groups were represented at least once. Analysis of primary data

was through clustering and coding (Miles and Huberman, 1994).

14 interviews were carried out with experts in all of the sub-sectors of the aviation

industry and with related bodies: NGOs, and air traffic control.

Analysis and Discussion

Perceptions of the Environmental Impacts of Aviation?

When invited to volunteer their own lists of key environmental issues, 12 out of 14

respondents named these three aspects without any prompting, with another 2 naming

59


two of the three. Only two respondents mentioned any other environmental impacts, and

in both cases characterised the three areas above as the major issues. There was much

less consensus in current importance rankings amongst the three – although local air

quality was typically placed third in importance, respondents were equally split as to

whether noise or climate change ranked first.

Whatever the rank applied to climate change versus noise currently, all respondents saw

climate change rising in importance relative to noise. Respondents also note that noise

was the dominant environmental issue at some time in the past, although opinions

differed on the timescale attached to this change. Climate change, in contrast, is the

“new kid on the block” (consultant), “coming up on the inside track” (airport

environmental manager) and the reason “why we’re on the front pages of the

newspapers”. (airline environmental manager).

The global and long-term influence of climate change were frequently cited as a reason

for the rising importance of climate change: “even if you shut down the airport today,

the consequences of [emissions leading to climate change] will still be felt over a long

period of time … [but on noise] then within five minutes we have solved all the noise

problems, completely” (airport environmental manager)

What influences these perceptions?

When asked to offer the influences that determine both the constituents and rankings of

their lists of environmental issues, a wide range of factors were given, including laws

and regulations, media (local and national), public opinion (local and national or even

global), shareholders/proprietors, staff opinions, business risk, commercial opportunity,

NGOs, scientific opinion, and politics and these responses are displayed graphically in

Figure 4.1. Some respondents voluntarily divided their responses into major or primary

influences and minor or secondary ones.

60


0

1

2

3

4

5

6

7

8

9

Generalpublic

opinion

LocalPublicopinion

Law,regulations

Media Commercialreasons

Businessrisk

Fuel price Scientificopinion

NGOs

No

ofre

spon

dent

s

secondary

primary

Figure 4.1: Influences given (primary and secondary) for listing of environmental impacts

of aviation (total of 14 respondents, each giving from one to seven influences)

The commercial influence on environmental issues (specifically climate change) was

expressed by one respondent in the following way “customers don’t want to feel guilty

about their summer holidays, … and our corporate customers need to carry on flying

to maintain the economic benefits that aviation does bring but they don’t want to feel

guilty, … need to demonstrate to them that we are reducing our impact” and the same

respondent added, as an airline environmental manager, “I wouldn’t want aviation to be

one of those industries that people don’t want to work for, for ethical reasons”.

There were many influences shared by respondents, but contrasting those respondents

ranking noise as most important versus those ranking climate change as most important

highlights some differences. Typically those most concerned about noise mentioned

local media or local public opinion, plus law/regulation as key influences, while these

influences were not less commonly mentioned by those ranking climate change higher

than noise. The local nature of noise annoyance makes the link with local influences

seem intuitive, but the significance of regulation as an influence on noise but not

climate change is revisited below. Figure 4.2 illustrates the contrasting influences of the

two groups. A respondent within the local NGO community commented that “if noise

ceased to be a problem, I suspect [name of NGO] would go out of business” while

another respondent felt that local NGOs might find their agenda “squeezed out”

61


(aviation consultant) by the rise of climate change as a wider concern. For those ranking

climate change as the most important environmental impact of aviation scientific

opinion was cited, whereas this category was not mentioned at all by those rating noise

as most important (Figure 4.2). Indeed, scientific opinion was only added as a possible

influence after arising in two of the first three interviews, an advantage of the flexible

format of semi structured interviews.

0

1

2

3

4

5

6

7

Law,regulations

LocalPublicopinion

NGOs Media Fuel price Commercialreasons

Businessrisk

Generalpublic

opinion

Scientificopinion

No.

ofre

spon

dent

s

those ranking noise #1

those ranking climate change #1

Figure 4.2: different influences of those ranking noise or climate change as most important

environmental influence of aviation

Fuel prices were mentioned as a factor that increased the attention paid to fuel

consumption, and thus acted in parallel to concern over climate change given the close

correlation of fuel burn with CO2 emissions. Some respondents expressed the view that

fuel prices would tend to rise due to the limited quantity of fossil fuel reserves. To this,

the author would note in passing that as other factors (geopolitical risk, for instance)

appear to affect oil prices, hence prices may follow a rising trend, but are likely to

continue to see fluctuations, with periods of lower as well as higher prices, which may

erode, for some periods, this link.

Noise – certainty on energy, uncertainty over non-acoustic aspects

Asked about the uncertainty with respect to their assessment of noise as an

environmental issue, although there was a majority (9 of 14) characterising noise as

being subject to little or no uncertainty, there was a significant minority (5 of 14) who

divided their comments between ‘energy’ and ‘non-acoustic’ aspects of noise (terms

62


discussed in the literature review above). The ‘energy’ or acoustic part of noise, was

typically seen to be well specified and understood, therefore having low uncertainty, but

the non-acoustic side as being highly uncertain. Commenting on this uncertain non-

acoustic aspect of noise, one respondent stated that his job (as an acoustic engineer)

stopped at the noise energy output stage, and when asked about the non-acoustic aspect,

described it as the job of the airport operator or regulator.

On the non-acoustic aspect of noise, a number of respondents expressed the view that

the issue would “never be a closed book” (airport environmental manager) because of

the subjective nature of perception and its changes over time or location. One

respondent gave an example where a noisier (in certified energy terms) plane was

replaced with a larger but quieter plane flying the same route. Complaints about noise

rose, and the respondent speculated that the larger plane had a greater visual impact

and/or was perceived to be flying lower than the previous aircraft and went on to say

that his organisation had “evidence of people complaining about aircraft noise when

its not really noise that is the issue ... people are concerned about some other aspect of

the operation, it may be safety, it may be visual impact, but they can’t complain about

that, so they will complain about the noise the aircraft makes” (airline environmental

manager). Another respondent from a different country and sub-sector observed that

“[now] we have complaints … about the local air quality issues from people that …

have only been complaining about noise. … some of them have been looking for

something else to complain about” (airport environmental manager)

Uncertainty over Local Air Quality

In some ways similarly to noise and climate change (below), respondents stated that

some aspects of aviation’s impact on local air quality were subject to low levels of

uncertainty, and other were highly uncertain. Respondents who specified a division,

stated that the source part of the source-pathway-receptor chain was well specified and

understood, particularly for NOx (due to ICAO certification). There was less certainty

over the generation of particulates where ICAO only certifies a smoke number, seen as

an imprecise measure, and still less over hazardous organic compounds. Respondents

generally felt that the uncertainty associated with the characterisation of engine

emissions could relatively easily be resolved through modest new measurements and

regulations. One respondent who had a role in chairing a committee of an international

63


organisation focussed on setting standards for engine emission measurements was able

to confirm that just such new certification standards were being developed, supporting

the general view that a solution was close at hand. Four respondents raised the issue of

particulates arising from tyre and brake wear as an area where much less was

understood even compared to engine emissions and reduction in uncertainty seemed

more distant.

Where most respondents did observe greater uncertainty were in the dispersion and

effects of pollutants. The mixing of emissions from different sources (aviation, ground

transportation, industry etc), and the allocation of emissions to a source, the dispersion

in the atmosphere, and the long term health effects of pollutants were all cited as

sources of uncertainty, by one or more respondents, and as being not easily resolved.

Uncertainty and Climate Change

Whatever their speciality or job role, respondents generally divided the area of climate

change uncertainty according to the different species of emissions from aircraft

involved in driving climate change. All of the respondents who did divide the influences

in this way expressed that view that the CO2 part of aviation’s contribution to climate

change was highly certain, and was closely correlated to fuel burn, seen as a well

understood and measured area, as suggested by the literature. Several respondents

grouped all other species into a ‘non CO2’ set of emissions/effects which were classed

as uncertain or highly uncertain. For those who subdivided the non-CO2 items, next

down the scale of rising uncertainty (or declining certainty) was NOx (through its effects

on ozone and methane) seen as uncertain, with particulates and aerosols, and especially

contrails and aviation-induced cloudiness seen as subject to high levels of uncertainty.

Turning to the impacts of the different species, another area of uncertainty identified by

some respondents was that of the comparison of the climate change produced by

different species, with respondents (from industry and NGOs as well as academia)

referring to the disputes cited in the literature (Forster et al., 2006; Fuglestvedt et al.,

2003; Hansen et al., 2005; Wuebbles et al., 2007) over the appropriateness of measures

such as radiative forcing and global warming potentials given the very different

lifetimes of different species in the atmosphere.

As well as raising the issue of timescales as a source of uncertainty or a reason for

climate changes’ rising importance (as above) in terms of various drivers of climate

64


change, respondents also contrasted the timescales over which climate change had

effects versus noise and local quality: “if I cut down noise today [by stopping

operations], then everybody’s happy as from today until the eternal future… Local air

quality, … a couple of years, … and things will be fine. But in the climate change

arena … its going to be there around for the next 200 years anyway, to affect our

daily lives”. (airport environmental manager)

What would reduce uncertainty? Deference to Science

Informants anticipated that new scientific research would reduce uncertainty. Some

issues, such as better characterisation of particulate emissions from engines as above,

were seen as issues that could be resolved, subject to desire and funding, in a short

space of time and as not posing fundamental theoretical problems. Others, such as the

long term human health impacts of local air pollutants were tractable but might involve

long time scales needed for epidemiological studies to be completed. The impact of

non-CO2 species on climate change, particularly the issues around contrails and cloud

formation were the most problematical areas of uncertainty for most respondents, who

variously noted problems of the costliness of global climate models, the complexity of

inter-disciplinary work that the issue required, and the generally complex and even

chaotic nature of the global atmosphere and climate, rendering the small scale and non-

linear processes of cloud formation particularly difficult to understand and model.

Ironically, but perhaps significantly, it was a climate researcher who commented that

scientists might never reach acceptable levels of uncertainty, and that even if they did,

others would have to make decisions for society over interventions and priorities.

Only a few respondents felt that any area of uncertainty presented intractable problems,

that ‘science’ would not be able to ‘answer’. Exceptions were the non-CO2 aspects of

climate change (for one respondent) and the non-acoustic, subjective aspect of noise for

two respondents.

Reactions to Uncertainty

Every respondent had a reaction to the questions of how uncertainty affected their own,

or others’ , decisions, or should guide allocation of resources, policy-making, regulation

or design decisions – none were indifferent. However the responses dividing into two

very different types: for some uncertainty was a spur to action, for others a reason for

delay or deferral of action.

65


In the latter camp, an aerospace component design engineer was among the most

extreme, saying “these uncertainties create tremendous difficulties for a company

trying to plan for the future” and that only once certainty was established (through

scientific research, expected to take some time) “We will then be in a progressive

position to put the appropriate controls in place”. More typical was a view that

scientific research would reduce levels of uncertainty, and until this was achieved,

action had to be postponed. One respondent, who felt that climate change was now

sufficiently certain to act, reflected that in the past, actors could say that “we expect an

increase [in global temperatures], but still have an error bar of +/- 50%, so … in that

case there’s probably nothing going to happen”(airport environmental manager) and

hence action at that time was postponed. Referring to the uncertain aspect of noise, its

non-acoustic side, one respondent argued that this uncertainty “sometimes gives

governments a get-out – noise is not a problem, just some people are super sensitive”

(local environmental NGO).

On the other side of this divide in responses to uncertainty were respondents who felt

that uncertainty was a reason to focus efforts on a given topic – and this view was not

only expressed by researchers or academics, but also by industry participants. Typical of

such was the comment, “resolving uncertainty is what I’m meant to be doing”

(researcher in climate change).

The kind of division over responses to uncertainty was also visible in responses

concerning allocation of resources. One group focussed resources on what was well

understood, others on where the greatest uncertainty lay. The difference is partly

explained by job roles – it might be expected that engineers engaged in engine design

for imminent practical applications would focus on what was currently known, while

research scientists would focus on the uncertainties and gaps in knowledge, but the

division was not so neat, and some other categories, such as NGOs, fell into either

camp. Typical comments from either side of this division were respectively “noise,

because it is the most clear-cut, with most certainty, should be dealt with first, should

be prioritised” (local environmental NGO) versus “focus on where the risks and

uncertainties are, that’s my job” (airline environmental manager).

Another respondent, an airport environmental manager, contrasted a personal viewpoint

with a job-role viewpoint, or a view from a media-based versus a scientific opinion-

66


based perspective (in the respondents’ own characterization). He noted that an

allocation biased heavily to climate change (80%) over noise (5%) would, if issued as a

policy statement, “get my head chopped off”.

Trade-offs

Literature (e.g. IPPC, 1999) suggests that trade-offs, where one aspect of environmental

performance suffers or has to be sacrificed when another is improved, are pervasive in

aircraft design and operation. The interviews were used to establish whether industry,

regulatory and NGO respondents (as well as academics) also recognised trade-offs as a

significant decision-making problem. Every respondent affirmed that trade-offs were a

practical as well as a theoretical problem facing aviation. Examples were freely given,

with the most commonly cited specific illustration being that the new A380 aircraft was

designed so as to meet stringent noise restrictions at commercially important major

airports such as London Heathrow, and given the larger size and more powerful engines

required, that this noise focus had been made at the expense of a small but noticeable

reduction in fuel efficiency (quoted at 2% by a researcher in aero engine design).

More generic examples covered each aspect of aviation design and operation. In engines

the tendency for high fuel efficiency through higher temperatures and pressures to result

in higher NOx production was noted by a number of respondents, as was the general

problem that design changes to reduce either noise or NOx often increased weight

and/or drag and thus reduced fuel efficiency for the aircraft as a whole. For operations,

changes to flight routings to reduce noise or local air pollution, or to reduce contrail and

cloud formation resulted in increased fuel burn. Conversely, a proposal such as one

reportedly made that fuel economy on long haul flights could be improved by making a

series of shorter ‘hops’ (hence carrying less weight in fuel at each take-off) was seen to

result in increased local noise and air quality problems at the intervening airports.

Managing Trade-Offs

Did respondents state that they knew how to manage trade-offs between different

environmental impacts of aviation? As an airport environmental manager replied “no,

and to be honest if you can come up with that, you’re probably winning a couple of

gold medals”. The need for such tools was widely acknowledged – with scientists and

regulators, or both, expected to provide them.

67


What respondents could offer were examples of regulations driving trade-offs, as in the

A380 example above. In another example of the influences of regulations on trade-offs,

an airport environmental manager observed that if the local air quality was nearer a limit

along one flightpath but noise was not a problem (the example was for overflight of an

industrial zone, with other emission sources but few residents) then interventions that

increased noise could be pursued, and vice versa. The same respondent described this

process as heavily influenced by the local political situation.

Commenting on what environmental characteristics were prioritised in choice of planes,

one respondent started with fuel burn, then added that he also pushed for lower noise

and NOx as well, before concluding “We want an aeroplane that doesn’t make any

noise and doesn’t use any fuel either” (airline environmental manager). If everything is

a priority, is nothing a priority?

Fuel efficiency (and hence climate change) as an economic priority

Many respondents disputed the view from literature that fuel costs were a sufficient

economic incentive for firms to prioritise climate change (via CO2, given the close

correlation between fuel burn and CO2 emissions) and that no additional intervention

was needed to encourage fuel efficiency. The common view was that fuel costs,

although important, could be passed onto customers – and that market variations in fuel

prices were large enough to drown out small differences in efficiency. Regulatory issues

like noise and LTO NOx thus took priority. However, one respondent did echo the

literature view, saying that there was “no specific need for me to actually go and tell

people … to develop procedures that are more fuel efficient : I would try to open

doors that are already open” (airport environmental manager).

Regulation and Uncertainty

Regulation was commonly presented as removing uncertainty – once a regulatory ruling

had been made, designers could then work to that rule, without concern for underlying

uncertainties. For example, on local air quality: “so now having legal compliance

topics and regulations with standards, … that have to be met the whole topic has …

moved into … focus … so it has got an increased attention” (airport environmental

manager).

68


Conclusions

The interviews generated some results that met the author’s expectations, based on the

literature and prior experience: that noise, climate change and local air quality were the

most important environmental impacts of aviation, or that climate change is a rising area

of concern versus noise or air quality (although half of the respondents still rated noise

as the most important environmental impact of aviation). Perceptions of uncertainty in

the fields of noise, climate change and local air quality closely matched the literature,

but reactions to uncertainty in decision making and allocation of resources divided

sharply, as discussed further below. Respondents saw trade-offs as pervasive in

aviation/environment decisions, indeed, the view was expressed that very few

interventions to address any one environmental impact did not entail trade-offs in

another. A final, and emergent, issue from the interviews was the role of regulation as a

key design criterion, and as a desired guide to decision-making under uncertainty. The

contrast with the economic incentive to reduce fuel consumption (and hence the climate

change impact through CO2 emissions) was marked.

Worldviews and Uncertainty

The third objective was concerned with uncertainties and their impact on decision-

making in the aviation sector and associated bodies. Research findings were consistent

with the literature in terms of the sources and levels of uncertainty in the various

environmental impacts, but generated a striking split in the reactions of participants to

uncertainty. This kind of split could reflect different worldviews of the respondents, in

the sense of Adams, (1994) above: the two worldviews evidenced in the findings are the

‘hierarchist’ and ‘egalitarian’.

“[the hierarchists] believe that nature will be good to them, if properly managed …

members of big business, big government, big bureaucracy … respecters of authority,

both scientific and administrative … they believe in research to establish ‘the facts’ ..

and in regulation for the collective good” Adams, 1994, p41, author’s own italics and

quotation marks.

“[the egalitarians] view nature as fragile and precarious …in cases of scientific doubt

invoke the precautionary principle” Adams, 1994, p40

Uncertainty was seen by one group of respondents as a reason for delay (hierarchist),

and by another as a spur to action (egalitarian).

69


Science as the arbiter

Whichever of the worldviews they appeared to operate under, respondents (and

participants at a recent conference, (ANERS, 2007) displayed a faith that science would

resolve uncertainties, that it would provide answers and evidence as the basis for

regulation and decision-making. Whatever their affiliation, respondents’ discourse

echoed Dryzek’s (1997) category of ‘administrative rationalism’, with a corresponding

appeal to regulation once ‘science’ had spoken. This theme continued in the

management of trade-offs.

Managing Trade-Offs: Regulations Rule

The final objective of the study concerned trade-offs and their management. The

literature is replete with examples of trade-offs entailed in interventions to abate any

given environmental impact of aviation. The complexity and constraints (size, weight,

aerodynamics, etc.) of airframe and engine design, and in flight operations, make it

seem to respondents as almost a zero-sum game – every intervention was seen to carry a

penalty elsewhere. Yet when asked how such trade-offs were managed, respondents

initially drew a blank. Exploring the issue further, a kind of design hierarchy, a set of

hurdles to be cleared, emerged.

An issue which emerged during the analysis of the primary data was the importance of

regulation in managing trade-off decisions. Fuel consumption is closely correlated to

CO2 emissions, the most certain of the drivers of climate change, and yet is not

regulated, unlike noise and NOx (at least in the LTO cycle). The literature tends to

follow the assumption (IPCC, 1999, ACARE, 2001, 2004a, DfT, 2003) that the

commercial economic incentive for aircraft customers to focus on fuel efficiency is a

sufficient, and indeed similar, driver to regulation. Yet as the analysis shows,

respondents, whether actually engaged in design decisions or contributing to them,

recognise a hierarchy of drivers or priorities.

Firstly come regulations with a global application – meeting ICAO noise, NOx and

smoke requirements is the first goal of designers. Next come more local regulatory or

commercial requirements which determine the commercial viability of any new

airframe or engine design: the oft-quoted example being the noise or NOx constraints

for operators at major airports such as London Heathrow. A plane unable to land at

night at Heathrow would face a serious commercial handicap, given the desire of

70


airlines to maximise the utilisation of their aircraft and the flexibility of routes this

usually requires: a local regulation becomes a de-facto international regulation.

Economic Incentives are secondary

Only after these regulatory and quasi-regulatory requirements have been met do other

environmental or commercial requirements, such as fuel efficiency, become a factor.

And the nature of fuel efficiency as an economic constraint differs importantly from the

regulatory requirements on noise and local air quality. As respondents typically

observed, without regulatory compliance, no planes get sold, whereas a slightly higher

fuel burn can be recouped through higher prices (or accepted in lower returns). Taken

together with the possibility that fuel prices continue to fluctuate, the extent to which

the economic incentive to reduce fuel consumption is an effective driver for reducing

climate change impacts from CO2 in the aviation is thus cast into serious doubt.

‘Progress Only’ rule of thumb inhibits trade-off management

From an administrative rationalist (Dryzek, 1997) point of view, the growing body of

knowledge and reducing uncertainty over the (externality) costs of climate change

compared to the more long-established externalities of noise and local air pollution,

mean that priorities should be reassessed – a plane that was noisier but emitted less

climate change driving species might now be a rational choice in minimising the newly

understood externalities. But respondents showed a strong resistance to any relaxation

of performance on any environmental aspect, and instead displayed a mindset that

required progress on all fronts, whatever the relative importance of each environmental

aspect. Comments that “noise is in the blood” of engine designers (researcher in turbo-

machinery) or that it was hard to change the “mindset” of air traffic controllers, and that

noise regulations had always been made progressively more stringent, with the

implication, confirmed, that the respondent expected this to continue indefinitely, all

display an unwillingness to sacrifice performance on one criterion for progress on

another. Industry structure and timescales may be a factor here – experimenting with

design choices that could cede market dominance in an oligopoly for decades seems too

risky for respondents to contemplate. The lower risk route is to ensure that at least some

progress is made on all fronts.

71


Further Research

The preliminary conclusions that decision makers manage trade-offs in a manner that

privileges regulation over economic incentives to the detriment of efforts to reduce the

climate change impact of aviation deserves further examination. From this exploratory

study sampling the views of a small but wide-ranging group of expert respondents, a

useful avenue of research would be to explore more deeply the design process for recent

new aircraft/engines in case study format. Such studies could describe more fully the

complexity of decision-making under uncertainty and its consequences for the

environmental performance of aviation. A Delphi panel or AHP approach could

generate further insights into how uncertainties and trade-offs affect industry

participants. The management of trade-offs in design decisions is a fertile ground for

multi-criteria decision analysis, complicated by the significance and uncertainty that

would have to be factored into any decision tool. Finally, deeper understanding of the

application of existing theories of risk perception (Slovic, 2000) to the particular

environmental impacts of aviation would aid policy-makers in designing,

communicating and implementing policy changes.

Policy Recommendations

The appeal to regulations (to be based on scientific evidence) was surprising to the

author, particularly from an industry one respondent, an airline environmental manager,

described (albeit without corroboration) as “the second most regulated industry after

nuclear power”. However, the nature of the industry (Toke and Laube, 2007) appears to

privilege regulations over economic incentives to a strong degree – a slightly noisier but

much more fuel efficient plane seems to be a possibility that only regulation on

minimum standards for fuel efficiency could turn into reality. Operating under

uncertainty, the normal concerns of firms that regulations add to costs may be

overridden by the desire for regulatory intervention to shield firms from risk. The entry

of the European aviation sector to the EU ETS would not change this situation in itself –

it merely adds to the economic incentive to improve fuel efficiency and still offers the

option to buy permits rather than intervene to abate fuel-burn related emissions. A

change in the balance of regulatory and economic incentives would probably also

require either relaxation of noise regulations or a stronger emphasis on the alternatives

72


to noise reductions at source (e.g. land use planning). Clearly this would face political

difficulties, pitting national and international priorities against vocal, local opinion.

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Appendix 1: Guidelines for Authors, Business Strategy

and the Environment

The following are the guidelines for authors for submission of papers to the Wiley

journal, Business Strategy and the Environment, downloaded from www.wiley.com on

28/08/2007 Note that although the word limits, style and referencing of Chapter 4 are

appropriate to the journal requirements, the instructions regarding removing tables and

figures to the end have been over-ridden by the required Cranfield thesis styles, and

table and figure numbering is continuous with the overall thesis.

NOTES FOR CONTRIBUTORS: Business Strategy and theEnvironment

Aims and ScopeBusiness Strategy and the Environment (BSE) is the leading academicjournal in its field with double blind refereed contributions of a high quality. Itseeks to provide original contributions which add to the understanding ofbusiness responses to improving environmental performance. Full lengthacademic papers, as well as shorter, more practitioner based “BSE Briefings” areinvited. These should be of interest to a broad interdisciplinary audience.

Initial manuscript submission.Authors must supply:

1. An electronic copy of the final version (see section below),

2. A Copyright Transfer Agreement form with original signature (TO BEMAILED SEPARATELY to: (Scott Lam, Managing Editor, ERPEnvironment, Suite A, 13th Floor, Unionway Commercial Centre, 283Queens Road Central, Sheung Wan, Hong Kong)– without this, we areunable to publish, and

3. If the article contains extracts (including illustrations) from, or is based inwhole or in part on other copyright works (including, for the avoidance ofdoubt, material from on-line or intranet sources), the Author, at theAuthor’s expense and in the form specified by the Publisher, will obtainfrom the owners of the respective copyrights, written permission toreproduce those extracts in the article in all territories and editions and inall media of expression and languages. All necessary permission formsmust be submitted to the Publisher on delivery of the article.

Submission of a manuscript will be held to imply that it contains originalunpublished work and is not being submitted for publication elsewhere at thesame time. Submitted material will not be returned to the author, unlessspecifically requested.

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Electronic submissionAn electronic copy of the manuscript must be sent to the Editor at:[email protected]. Submissions should be in Word format.

Illustrations must be submitted in electronic format where possible. Save eachfigure as a separate file, in TIFF or EPS format preferably, and include the sourcefile. Indicate the software package used to create them; we favour dedicatedillustration packages over tools such as Excel or Powerpoint.

Manuscript styleThe language of the journal is English, and the standard of English must beacceptable for an academic journal. If necessary, the English should be checkedby a linguist before submission.. All submissions, including book reviews, musthave a title, be double-line spaced and have a margin of 3 cm all round.Illustrations and tables must be on separate pages and not be incorporated intothe text. Their approximate position should be indicated in the text by the author,for example: TABLE 1 ABOUT HERE.

1. The title page must list the full title, short title of up to 70 characters, andnames and affiliations of all authors. Give the full address, including email,telephone and fax, of the corresponding author who is to check the proofs.

2. Include the name(s) of any sponsors of the research contained in thepaper, along with grant number(s).

3. Full length papers should be between 4000 and 7000 words long.4. Supply an abstract of up to 150 words for all articles except book

reviews. An abstract is a concise summary of the whole paper, not just theconclusions, and is understandable without reference to the rest of thepaper. It should contain no citation to other published work.

5. Include up to eight keywords that describe your paper for indexingpurposes.

BSE Briefings:In-depth and critically balanced articles of up to 2000 words in length areinvited for inclusion within this section of the journal. Articles should have apractical emphasis and/or contain a high level of factual and statisticalinformation.

BSE Policy and Practice Reviews. Reports and short publications ofrelevance to this journal and its editorial scope are reviewed within this sectionof the journal. Review material and proposals for reviews are invited.

Reference styleReferences should be cited in the text as name and year and listed at the end ofthe paper alphabetically. Where reference is made to more than one work by thesame author published in the same year, identify each citation in the text asfollows: (Collins, 1998a), (Collins, 1998b). Where three or more authors are listedin the reference list, please cite in the text as (Collins et al, 1998).

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All references must be complete and accurate. Online citations should includedate of access. If necessary, cite unpublished or personal work in the text or asfootnotes, but do not include it in the reference list. References should be listedin the following style:

Journal articles:Read A, Gilg A, Philips P. 1996 The future role of landfill: an assessment ofprivate and public sector opinions. Journal of Waste Management and ResourceRecovery 3: 37-46

Books:Ashworth JM, Corlett RT, Dudgeon D, Melville DS, Tang SM. 1993 Hong KongFlora and Fauna: Computing Conservation Hong Kong Ecological Database.World Wide Fund for Nature: Hong Kong.

Chapters from Books:Foy G, Daly H. 1992 Allocation, distribution and scale as determinants ofenvironmental degradation: case studies of Haiti, El Salvador and Costa Rica. InThe Earths can Reader in Environmental Economics, Markandya A, RichardsonJ (eds). Earthscan: London; 294-31 5

On-line sources:The Geriatric Website. 1999 http://www.wiley.com/oap/ [1 April 1999]

IllustrationsSupply each illustration on a separate page. Any photographs should be suppliedas originals – photocopies or previously printed material will not be used. Lineartwork must be high-quality laser output (not photocopies); grey shading is notacceptable. Lettering must be of a reasonable size that would still be clearlylegible upon reduction, and consistent within each figure and set of figures.Supply artwork at the intended size for printing. The artwork must be sized to thetext width of 7 cm (single column) and 16 cm (double column).

The cost of printing colour illustrations will be charged to the author. There is acharge for printing colour illustrations of £700 per page. If colour illustrations aresupplied electronically in either TIFF or EPS format, they may be used in thePDF of the article at no cost to the author, even if this illustration was printed inblack and white in the journal. The PDF will appear on the Wiley Interscience site.

CopyrightTo enable the publisher to disseminate the author’s work to the fullest extent, theauthor must sign a Copyright Transfer Agreement, transferring copyright in thearticle from the author to the publisher, and submit the original signed agreementwith the article presented for publication. A copy of the agreement to be used(which may be photocopied) can be found in each volume of SustainableDevelopment and on the Wiley Interscience website atwww.interscience.wiley.com Copies may also be obtained from the journaleditorial office or the publisher.

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Appendix 2: Interview GuideBelow is the guide used for the interviews.

Opening Comments

Hi, I’m Ken Rumph, and I am carrying out research as part of a Omega Project, which

stands for Opportunities for Meeting the Environmental Challenges of Growth in

Aviation, a UK government funded programme aimed at developing and exchanging

knowledge about aviation and the environment and disseminating it among academia,

industry and policymakers . Thanks for participating in this research – please feel free to

ask for clarification of any questions I ask, and do not answer any question if you prefer

not to. Questions about consent form?

Introductory question

1 Can you describe your job/role?

Environmental Impacts/Aspects

2 Concerning the environmental impacts of aviation, which would you consider to be

most important currently? How has this changed – which have become more important,

which less – have ranks changed? And do you expect changes in the future

3 What determines how you prioritise these different environmental impacts?

E.g. public opinion, law/regulation, general political climate, media, NGOs,

business risk, fuel prices, commercial/customer pressures, academic research,

etc

4 Our research focuses on three areas of environmental impact – noise, local air quality

and climate change. How do you perceive the certainty or uncertainty regarding the

importance of these environmental impacts

E.g. very certain, certain, neither, uncertain, highly uncertain

5 How do you expect these levels of uncertainty to change? Why/how? When?

6 Can you comment on how you deal with these uncertainties in

planning/designing/operating?

E.g. can you recall an instance when these uncertainties affected your work?

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Interventions, Trade-offs. etc

7 We now consider some broad areas of intervention, which might reduce these

environmental impacts. This is not intended to be an exhaustive list, and the

interventions are generic rather than specific. Interviewer discusses the table below,

asks for examples of interventions and their trade-offs. .

Intervention

type

Targeted to reduce Trade-offs with another emission

CO2 (Fuel burn)

NOx

Noise

Contrails, Cirrus

Engine

other

CO2 (Fuel burn)

NOx

Noise

Contrails, Cirrus

Airframe,

aerodynamic

changes

other

CO2 (Fuel burn)

NOx

Noise

Contrails, Cirrus

Flight path

(route changes,

ATM, altitude,

take-off/

descent)

other

Table A.1: Interventions and Trade-offs

8 If you had 100 units of resource (might be time, money, people) to allocate between

the three areas of climate change, noise and local air quality, how would you do so

currently? How do you believe that this would change in the future?

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9 If you had to choose between one environmental improvement and another (less noise

but more CO2 emissions from fuel) how would you choose? Do you have the

information, guidelines or tools to make such a choice?

Are there any other aspects of aviation and the environment that you would like to

comment on? (Other emissions/impacts, sources of uncertainty, gaps in knowledge)

Thanks for your time – closing remarks

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Appendix 3: Transcript of An InterviewTranscript of a telephone interview carried out on 08/08/2007 and recorded, with

Respondent F (Table 3.1, Chapter 3)

Text (I = Interviewer, R= Respondent)Opening and closing remarks not transcribedI: Can you describe your job?R: [here, the respondent described his job, as a manager in the environmentaldepartment of an airport operating company, details are excluded to preserveanonymity].So when I focus on environment, then together with my team I’m dealing with all theenvironmental aspects of the airport, which includes air quality, waste water, watermanagement, waste management, energy conservation, environmental managementsystems, environmental communication, contaminated sites, natural conservation areas,and non-ionising radiation. These are kind of like in brief is what my dept is doing,I: ok, that’s understood. Regarding aviation, and in this respect we’re not including theground operations, so it may be that some of the items you mentioned there don’t applyso much, but you tell me the answer, regarding aviation, what would you consider to bethe most important environmental aspects, I don’t know, a list of however many youthink is appropriate, or…R: yeah, well, when I look on that, we have social answers and we have scientificanswers and unfortunately they don’t match. The scientific answer that I see is that airquality is probably right now probably the one to me the most concerningenvironmental impact from aviation. The reasoning being is that it this a very longresidence time in space, or in the atmosphere, and even if you shut down the airporttoday, the consequences of air quality impact will still be felt over a long period of time.The social answer, probably would be that its aircraft noise, but if I shut down theairport today, and remove all the aircraft from the sky, then within five minutes we havesolved all the noise problems, completely.And so, to me, we usually say that noise is not so much leaping into environmentalimpact, more so into social impact. So that’s why I keep that a little bit apartI: it’s a useful split, from my point of view, so that’s goodR: right yeah, so the environmental impact I look at is air quality.I: I should say by the way that we should definitely discuss both, but the point that youmake, that kind of, what people say vs. what you would say scientifically is the biggestrisk is a useful piece of information for me, because it fits in , in a way, to the 3rdquestion, if you like, but let me keep to my schedule, which is to say would you say thatthose issues are changing in the way that they are perceived, either scientifically orsocially? Is anything becoming more or less important? I’m sorry I should go back,one step, I’m sorry, when you said air quality, you mean emissions of all varieties,including say CO2, which is clearly not a pollutant in the poisonous sense butcontributes to climate change, or you’re specifically talking about things like NOx, orparticulates or..R: well we talk both, that’s why I kind of left it open at that , and I wouldn’t specifylocal air quality or global local air quality I just say air quality, sort of encompassingboth aspects, and yes this issue has changed over time . there’s a number of levels thatlead to that and that include it. Trying to be a little structured on that, when looking

106


back we have areas, particularly in Europe, where local air quality regulation has beenissued not too long ago, so now having legal compliance topics and regulations withstandards, and ambient Air quality standards that have to be met the whole topic hasbeen moved into the focus of the regulator and in that case also as a consequence intothe public and of industry . so it has got an increased attention due to the fact that wenow have an EU directives where we have ambient Air quality standards to be met by2010 with zero margin, and all of that, that is one element that has fostered increasedattention, second point is that , from somewhat of the social aspect, many people have ina way sort of given up on the noise side, and so they’ve been looking into, well, whatelse, do we have that we can focus on, and bring it onto the carpet and raise it onattention and that’s then obviously the next one, air quality, and particularly the Localair quality and so when I read the papers, we have complaints then about the local airquality issues from people that maybe five years ago have only been complaining aboutnoise. but given that noise was here , and success was few and far between, then someof them have been looking for something else to complain aboutAnd at the same of course we have all the discussion of the Kyoto protocol , with globalwarming, with global climate change and that of course has pushed aviation into thespotlight as well, with the media , of scientists , of politicians, of pressure groups, or so,and as such it has changed over the past five years and I also expect it to change overthe like, next five to ten yrs from nowIts kind of difficult to say what’s the next 20 years,I: yeah I decided to perhaps change that, and simply say in the future, because I think tosay 2, 5 10 years was becoming at little bit too detailedR: but it will definitely still increase, and the reason for that I believe is that we’re stillin the progress of improving the scientific understanding, years ago when we didn’thave the modelling capabilities, computer capabilities available, computer scienceavailable, we had to work with simplifications, with sort of rough estimates etc etc andnow its getting more and more sophisticated to do modelling and things like that, so weincrease our scientific knowledge and that of course enables us to go into more precisepredictions that have to be looked at .Again years ago, you would say, well we expect an increase, but still have an error barof +/- 50% so there were enough people saying well, in that case there’s probablynothing going to happen – today we still have the increase that we see in emissions, orin the impacts that we see happening, but the error bar has been reduced from a +/- 50 tosomething less than thatAnd with that its getting more and more difficult to sort of deny the fact

I: OK, and when you comment on error bars, that’s particularly relating to climatechange or to emissions and local air quality generally?R: its basically on climate change and in the local air quality arena , the error bars arequite small, its fairly well known, there are of course a few uncertainties, we’re talkingabout hazardous aircraft pollutants there are still issues we don’t really fully understandbut it general its fairly well known on a local basis, and because also the local extent islimited and we’re talking about, I don’t know, 20, 50 a 100 kms, that’s about it, but on aglobal scale, its far more difficult and far more complex.I: but as you say, error bars getting smaller on the climate change side, so uncertaintygetting less,R: mmm

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I: yes, OKI: I was going to ask a question about how, how you come to a view of these differentenvironmental impacts, and in a way you’ve already answered that, in a way, by saying,well, there’s a social side of it, by which I guess you’re saying its how many complaintsI’m getting, its what the media are saying, and so on, so there’s the social aspect, thatdetermines part of your view, but then you said there’s also there’s a scientific aspect,where you said well I’m concerned about the long residence lives of some of theemissions, even if people aren’t complaining about them so to speak, I mean, and youalso mentioned legislation, so I feel I’ve got a few points there. Are there any othersyou’d mention, in terms of sources that influence your view of environmental impacts, Imean that could be a perfectly good list on its ownR: yeah, and there’s a fourth point to it actually, and that’s the mitigation costs, I mean,or let’s say, mitigation costs I wouldn’t put a dollar or a Euro amount to it, but also interms of let’s say, operational consequencesSo, you know, my director asks me, well, does it have any impact on the futuredevelopment of the airport ? in an economic sense, and I would have to evaluate that,and if I feel, yes there might be, then of course it has a higher priority, to deal with itand to do something with itAnd one of the most perfect examples is BAA, British airports authority, they perfectlyknow that climate change is an issue in the UK, and as such have decided to put it veryhigh on their priority list , to deal with itMaybe a little less here, maybe because we have dealt with that issue many years earlierand have implemented mitigation plans and all of thatI would say, between the scientific and the regulatory, and the public or social , there’salso the economic side of it, that sort of triggers on how I prioritise the topic and what Ido about itI: and when you say economic, it sounded like you where saying , not so much, as yousay, in the sense of how much will it cost to do something, but more what’s the cost ofnot doing something, in terms of how it would affect the airport’s operation…R: that’s it both, there’s always both sides to it, yeah.I: (coughs, apologises) we talked a little bit about the uncertainties, on noise would yousay there is a high or low level of uncertainty, whether its in measurement or the impactof it, or….Where would you say that one comes in terms of certainty or uncertainty?R: well, just as a remark in advance, given that all the noise issues are dealt with by mycolleague ..I: you mentioned thatR: so I don’t feel too too confident on the noise picture but I would think that given thatnoise has been an issue that started in the 60s when the first jets came up, that therecertainly has been a lot more work done on noise , understanding noise effect, than onair quality, I think as such that the understanding, the scientific understanding, I think, isfairly mature, if not to say its really mature, whereas the socioeconomic aspect are stillsomething which is being worked on, like for the effects now , you know, do I wake upso many more times a night because of that, does it mean that I work less or lessconcentrated in my job, these are still things that are investigated and are debated aswell. But the scientific understanding, like how to measure noise, things like that, isquite mature.

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I: OK, and I appreciate your comment that its not your area of expertise, but thatsounds like a good answerI: and I think, regarding how you would expect these levels of uncertainty to change, ina way you already commented, which was you feel that . particularly in the area ofclimate change you feel that there’s been progress in understanding it better, and thatthat continues – so its fair to say I guess that you would expect the uncertainty to reduceas we get further work done?R: yepI: I don’t want to put words into your mouth, but that seemed to be what you weresaying earlier so…?R: that; exactly the case, I expect that to happen , when I see what’s going in terns ofresearch programmes that are ongoing, the ones that are anticipated, indeed the onesthat have been finished, that have been finished in the past, then I see that … this is notsomething like where I expect that in two years time, that we lean back and say ‘now weknow everything, thank you very much’ so I think its really something that goes on, andto a larger or lesser degree, that’s kind of difficult to judge right now. There’s always acertain amount of resources available for research and development, and that’s going tobe used, but it depends a little bit on the political agenda, as well, whether thoseresources will be stocked up, and more research done if needed, or less, that’s difficultto judge, it depends a little bit on national prioritiesI: OK, and regarding things like climate change then, which is one of the areas whereyou’ve said perhaps there is more uncertainty, does that affect…For instance when you say , the economic consequences are one of the things I need totake into consideration, does that make it difficult for you… a good example, you said afew years ago , there were big error bars, and it was possible to say well maybe nothingwill happen, but does that kind of uncertainty make it difficult for you to decide sort ofwhat to focus on? Or do you feel its now, becoming sufficiently certain, that you canmake judgements about that?R: it has improved, recently the understanding has improved and that as such has alsoeased a little bit that uncertainty, for instance on my side on where to focus on. Nowagain , when I split between the global issue and the local issue, the local issue I mainlycommunicate and coordinate with our local regulator , to see well, what are the localissues here, because here, they might be completely different from say, somewhere inthe middle east, and as such, I’m looking into what are our problems that we’recurrently facing, and those are the ones that I’m addressing, and that, luckily enough, onthat, the error bars are fairly small,There are always some uncertainties and there is always a certain gap in knowledge andwe’re working hard to overcome both of them, particularly the part of gap inknowledge .On the global side its … again its we’re then going onto a scale where we communicateand coordinate on a global level, and also as an airport operator, our own infrastructureand the site that we have to operate, is very localI: uh huhR: so I’m not the airline that operate a fleet of aircraft, globally, and would have toworry about that globally, and taking decisions on whether to have long haul routes orshort haul routes or things like that , but of course it is important for us, because airlinesare our customers and the flying, travelling public are our customers, and we need to

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make sure that we can accommodate the needs they have, but definitely, the local scopeis closer to us than the global one

I: aha, hmm, OK. I mean, regarding the points in my matrix about mitigation, I mean,many of these are addressed for when I’m talking to people who are specialists inengines or in airframe design and so on, are there any… I would have guessed maybe,it’s the things like the flight path or ATC type issues … do you have any , mmm,involvement with ATC or route planning, descents and so on, because that can affectobviously, well noise, I guess, perhaps, but erm, it also affects fuel use and so on, or arethese things that are dealt with by the local ATM people? So… what scope do you havein terms of how airlines operate, to have an impact on … well I won’t… you knowwhere you can have an impact on that , so…. Which are the areas where you can dothat?R: well actually its my colleague from the noise dept which has the opportunity toparticipate in those programmes, because as you rightly say it is , it has noise impacts ,if you change flight paths, if you change departure and arrival profiles or procedures,then that more so a noise impact than it has, probably has a climate change impact or alocal air quality impact. So that’s an area where an airport can definitely cooperate withATC with an airline , together to optimise the system .In terms of local air quality, it is maybe less pronounced, because fuel savingsprogrammes are on the top priority of every airline, so there’s no specific need for me toactually go and tell people that, you know, you have to develop procedures that aremore fuel efficient : I would try to open doors that are already open.I: mm hmmR: so that’s a little limited, also when I talk local air quality I have to realise the fact thatonly emissions up to about 300 m above ground are actually locally significant , and ifyou look at that, then the big programme of CDA , continuous descent approach that’sbeing promoted left right and centre, has virtually no impact on local air quality,because by 300 m above ground the aircraft is lined up on the finals, its on the flightpath and established and from then on, it’s all a given, and soI: yeah,R: so it has effects, positive effects further out, which have a contribution to the , letssay, large regional air quality, and definitely the global side of it, but using less fuel forinstance, and it has on the noise because noise is something which is not just limited tojust flights below 300m, but whatever, 10 km out of the airport, so that’s why, whenlooking into things like that, ATC is important in the overall picture, my involvementthere is going to be limited, because I’m not…. Because I’m either pushing things thatare already on the priority list anyways, or they have very little, if at all, impact.I: one area which it occurs to me to ask about is things like taxiing, and use of engineson the ground, do you have any,… is there any.. because that’s something thattheoretically the operations of [the respondent’s] airport or [the respondent’scompany] sort of could have an impact on : what aircraft do, whether or not the airlineswant to save fuel or not so to speak, and that does affect local air quality as well asnoise and other emissions, and so on. I mean, is there anything to say on that front?Or…?R: yes, Actually, that’s now, the … once the aircraft actually touches the ground, anduntil it leaves the ground, this is the area where an airport can actually influence thebehaviour and can influence procedures, and that’s what we do and I think that’s what

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many airports try to do and the overall picture. And that’s where me myself can actuallygo into it and we actually look at it and we optimise taxi routes for instance, to minimisetaxi time and we change or influence procedures, on.. when to start up engines , to haveengine idling times as short as possible things like that and there are programmes, andthere are options available that are taken up by airlines as well, so , together withairlines and ATC and ourselves we influence that part, again until basically the aircraftlifts off the ground.I: uh huhR: after that, its that out, a little bit out the airport’s scopeI: Yeah, I understandR: [inaudible] I wanted to add that bit to it for the sake of being very precise, is, of theairport has always a say, together with ATC, in the choice of departure routes,depending on how that works it can well be that we have departure routes that are lessfrom optimum, that means that lets say, they might have to make turns and twists into ,to avoid noise sensitive areas that provide a trade-off for the fuel burn and that canhappen, and that’s where unfortunately there’s also then the balance, and you know,what do you prioritise for? Is it the noise, or to reach a global impact from fuel burn thatyou would like to mitigate.I: [coughs] is there a … how do you make that prioritisation, so to speak? You know, doyou feel that you have a clear, sort of, one decibel is worth a kilo of carbon dioxide , ora decibel is worth a kilo of NOx, whatever the units were, is that a clear calculation oris it a, an optimisation in a different wayR: its no, and to be honest if you can come up with that, you’re probably winning acouple of gold medals on that,I: [laughs], yes…R:, if you can come up and say, I’ve found out that a one decibel equals some manykilogram’s of NOx or so, or of CO2, it is the exactly trade-off, that trade-off that is tosome degree, to a large degree I would say, determined by the regulator or the social …let’s say from the political framework that’s around an airport. And that’s very difficultto manage, and that’s one of the trade-offs that no airport can really fully handle, byitself, because that’s what you have, you don’t have this clear , a clear correlation to saythat one decibel equals 1.7 kg of such and such an emission, that’s what you don’t have,and as such you can say well I can reduce noise but I have say, more NOx, now you cancome up and say well generally I don’t have an NOx problem here, so I can probablyafford to have a little increase in NOx if at the same time I can reduce noise because Ihave more of a noise problem than I have an NOx problem,I: so you’re working in a sense to a regulatory limit?R: yes, or what’s politically acceptable. Now if you were at a different part, where yousay well I don’t care about noise but I have, I do have an air quality problem becauseyou have heavy industry nearby or I don’t know what, so you might say I do the otherthing around, I’ll try to optimise on the NOx or generally on emissions and I’m not tootoo concerned about the noiseI: uh huhR: so this is, this again is besides the fact that we don’t have scientific criteria where wecan actually set them side by side , this is heavily influenced by the political agenda atyour local siteI: Ok, that’s a good point, well hopefully my colleagues are part of the process to tryand win the gold medals, but it doesn’t seem like an easy, like an easy job to me, but er,

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a lot of people that I speak to have the same point, that they want to try to improveeverything but you can’t always improve everything and managing the trade-off is oneof the difficult things.I: Almost at the end. If, I have a question here which I’m not sure whether I’m askingyou to answer it specifically in your job role, or in a more general way, decide perhapshow you feel, its this question of if you had a hundred units of resources whether that istime or money or people, however you imagine it to allocate between climate change,noise and local air quality , so I’ve divided the local and global air quality separately,how would you do that? And you’ve already mentioned that there are different sort offorces, social and scientific in making that decision, but I think it’s still a good question.I’m not sure how much I would take too much notice of particular figures so don’t feeltoo anxious , but how would you divide your resources at the moment, and how do youthink that would change, perhaps that’s the key one?.R: well first of all I found this is a very challenging questionI: yeahR: a good question, a very good question, because if you actually press people, to giveyou an answer, then, well OK, I can give you a personal answer, from myunderstanding, scientific understanding that I have, that some of my experience, so Idon’t know whether my board of directors would completely agree with that, butI: OK, we’ll take it definitely as you speaking for yourself, rather than making a policystatement for [respondent’s company]…R: if I had that today, I would probably assign about 80 units to climate change about 15units to local air quality and about 5 units to noiseI: OKR: and the reason clearly is, that if we look at the long term consequences then again,you know, on the noise side, if I cut down noise today, then everybody’s happy as fromtoday until the eternal future, you know. Local air quality, if I cut that down, then acouple of years, you know, and things will be fine. But in the climate change arena, if Icut it out today, its going to be there around for the next 200 years anyway, to affect ourdaily lives so if I need to invest then I take into that which has a long , and we’re talkingsustainability here in a way, then I have to go on climate change, that’s the one thatbothers me or my future generations the most. That’s the point, but if I use that as apolitical statement I’m going to have my head chopped offI: Yeah, I know I could have said, but its not my job to sort of, to lead comments, butprobably if you look at what sort of got people writing letters or complaining tonewspapers, or the airport, it would possibly be exactly the opposite, so..R: Yeah. I had an interesting presentation seen some time ago, when actually there wasthe case when a professor for atmospheric physics, he comes from the technicaluniversity in [this city], he said, he’s looked at that a little bit and he basically said, whatwe see scientifically is completely opposite on the public perception , so again there’sthe same basically, he said noise is the number one in public perception, althoughscientifically speaking its got the least… impact or significance so to speak.But in terms of scientific effect , that we in fact, have on the climate, or the globe so tospeak, now , the question you know, will that change in the future, if I take another 20years and you give me another hundred units and I have to use them, I guess today Iwould definitely reserve the right to postpone the answer until about 18 years timeI: [laughs]

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R: the reason for that, and I’m not just saying that to avoid a difficult question, is thatwe’re still improving our scientific understanding , so it can well be that in 18 years wemight have developed certain, either … we may have developed certain procedures,certain scientific understandings, certain technical mitigation options that might shiftthat whole thing a little bitI: yeah, no, that’s a good, actually I think it’s a very good answer, yeah, I mean, Isuppose what I could infer from your comments is that if you been asked the samequestion several years ago, you maybe wouldn’t have had quite such a high figure forclimate change, precisely because you would have been waiting for a little morescientific understanding,R: its correct, the thing is, like, say fifteen years ago, I would have taken 50% for globalclimate change, I would have taken 40% for local and 10% for noise or maybe 30 forlocal air quality and 20 for noise, but in that time we also had far more of a local airquality problem, we have solved part of it over the last fifteen years. So pressure hasgone a little bit on the local air quality, and at the same time we have increased ourknowledge on the potential consequences on the climate, global climate change, and assuch I’m more than happy to shift those resources allocation a little bit and so whyexactly the same thing can happen, so that if we take another 15 or 20 years from now,we might say, just for the sake of it, we might say that noise is definitely not an issueany more, so I’d rather use those 5 units that I now put to noise, and stick them intoglobal things as well.I: or of course, one of the other issues could have been solved by another meansperhaps, I suppose that’s a good point with climate change, that there are other effectsthat maybe I guess, other things could have changed that mean we’re less concernedabout the aviation impacts, so…OK.R: and maybe what we don’t know is whether within the next ten years there areemerging issues: I mentioned the fact of hazardous air pollutants, right now wetraditionally deal with particulates and other than that with NOx, with sulphur dioxide,and so, but who knows, if not something comes up which only now we have thescientific and technological means to discover it and to find out about it, then it couldbe that by fifteen years we have to open up another category where we have to allocateresources to deal with itI: mm, hm, no, that’s a good point – another respondent mentioned to me that anythingthat involves long term health effects, you can’t hurry the process, you know, it may taketen or twenty years for a study to identify a problem, you know. And until you’ve donethe study you don’t know if the problem’s there or not, so to speakR: and you have seen it with issues such as bromium in car brakes, or in carmanufacturing and it wasn’t done until after a few decades they found out that this ispretty bad stuffI: yeah, yeahR: so finally they had to shift some of their resources in those areas, you know, to battlethat.I: yeah, no, that’s a good point. No I thought your ‘no, if I have to decide in 20 yearsI’ll wait for 18 years and give myself the maximum knowledge to make a good decision’.Yeah, it’s the trend, that exists at the moment for one issue becoming more important ,could of course change as the information and the means to act change, so I think that’sa very sensible point . I think that answers all my questions…

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I: one thing that I’d made a note of to come back to, you’d said on local air qualitythere are still some gaps in knowledge, particularly in… do you have particular thingsin mind on that? Or…?R: we have, when we talk for instance on particulate matter, then we know a little bitnow about the aircraft engines , we still do not fully understand everything, becausewe’re not able to properly measure it on a reliable , reasonable basis. I mean we canmake a single test that are very expensive and very laboursome, and then we got someknowledge but whether this is generally applicable or not, we don’t know yet, the fulldegree, so there are, we still got a few issues to solve there , particulate matters, but alsowhen you focus on particulate matters, we usually consider emissions from combustionprocesses but how about the wear and tear. That’s something else that we have hugeuncertainties in aviation, we know a little bit about the brakes, you know, and the tyrewear, so, but these are things that we still don’t know. Now in general if we say thePM10 and PM2.5, it’s a health issue, then we need to go back and say, OK, whathappens if an aircraft touches down with a 120 tonnes of landing weight, and its tyresare accelerated to 250 km/h in flat no time, that smoke that you see coming up, what’sthere , or if you see a 747 that is trying to turn on a dime, to turn from a taxiway into agate, for instance, then you see those tyres, they rubber along the concrete, we don’tknowI: Yeah, I remember being told by somebody, because I said, oh yes, when the tyrestouch the runway, an he said actually a big part of the wear occurs when you’re turning, you knowR: yeah, if you ask with specialist from British Airways, the environmental directorthere, he’s fairly, fairly specialist I would say, the one specialist about issues of that andyes they know that most of the wear occurs when turning. And not when touching downon the runway.But again, you know, these are things that we need to better understand and go closerinto. And that’s on a local air quality issue that we still have gaps. Also , like in terms ofOK, we know what’s coming out of let’s say, an APU, but how does that impact theenvironment, how ‘s the dispersion, is this immediate very good dispersion and itsnicely diluted and so it doesn’t cause a lot of a problem, or is it not? So its not just theemission itself, its everything, you know, we can take an engine to a test bed, and putsome probes in it and measure, but what at the end of the day we are interested is theimpact - we need to understand the process between the emission and the final impact.And within that we have the dispersion, we have the mechanical and physical dispersionof everything, we have plume rise due to the hot air of the exhaust, etc etc. and overevery of those steps we can make mistakes or we have to live with assumptions..I: so that the pathway part of the sort of the source-pathway-receptor … yeahR: yeah, even though in theory you might give very well understood, to actually applyit and to confirm it in real life, that’s still a bit of a challenge.I: Ok, right, I think that completes my questions actually

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Environment Impact of Aviation and Tradeoffs

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