GAO Report to Congressional Committees

United States Government Accountability Office

AVIATION AND 

CLIMATE CHANGE 

Aircraft Emissions 

Expected to Grow, but 

Technological and 

Operational 

Improvements and 

Government Policies 

Can Help Control 

Emissions

June 2009 

GAO-09-554 
What GAO Found

United States Government Accountability Office

Why GAO Did This Study

Highlights

Accountability Integrity Reliability

 June 2009

AVIATION AND CLIMATE CHANGE 

Aircraft Emissions Expected to Grow, but 

Technological and Operational Improvements and 

Highlights of GAO-09-554, a report to Government Policies Can Help Control Emissions

congressional committees 

Aircraft emit greenhouse gases and 

other emissions, contributing to 

increasing concentrations of such 

gases in the atmosphere. Many 

scientists and the 

Intergovernmental Panel on 

Climate Change (IPCC)—a United 

Nations organization that assesses 

scientific, technical, and economic 

information on climate change—

believe these gases may negatively 

affect the earth’s climate. Given 

forecasts of growth in aviation 

emissions, some governments are 

taking steps to reduce emissions. In 

response to a congressional 

request, GAO reviewed (1) 

estimates of aviation’s current and 

future contribution to greenhouse 

gas and other emissions that may 

affect climate change; (2) existing 

and potential technological and 

operational improvements that can 

reduce aircraft emissions; and (3) 

policy options for governments to 

help address commercial aircraft 

emissions. 

 

GAO conducted a literature review; 

interviewed representatives of 

government agencies, industry and 

environmental organizations, 

airlines, and manufacturers, and 

interviewed and surveyed 18 

experts in economics and aviation 

on improvements for reducing 

emissions from aircraft. 

GAO is not making 

recommendations. Relevant 

agencies provided technical 

comments which we incorporated 

as appropriate and EPA said 

emissions standards can have a 

positive benefit to cost ratio and be 

an important part of policy options 

to control emissions. 

According to IPCC, aviation currently accounts for about 2 percent of humangenerated global carbon dioxide emissions, the most significant greenhouse 

gas—and about 3 percent of the potential warming effect of global emissions 

that can affect the earth’s climate, including carbon dioxide. IPCC’s mediumrange estimate forecasts that by 2050 the global aviation industry, including 

aircraft emissions, will emit about 3 percent of global carbon dioxide 

emissions and about 5 percent of the potential warming effect of all global 

human-generated emissions. Gross domestic product growth is the primary 

driver in IPCC’s forecasts. IPCC also made other assumptions about future 

aircraft fuel efficiency, improvements in air traffic management, and airport 

and runway capacity. IPCC’s 2050 forecasts for aviation’s contribution to 

global emissions assumed that emissions from other sectors will continue to 

grow. If other sectors make progress in reducing emissions and aviation 

emissions continue to grow, aviation’s relative contribution may be greater 

than IPCC estimated; on the other hand, if other sectors do not make progress, 

aviation’s relative contribution may be smaller than estimated. 

While airlines currently rely on a range of improvements, such as fuel-efficient 

engines, to reduce emissions, some of which may have limited potential to 

generate future reductions, experts we surveyed expect a number of additional 

technological, operational, and alternative fuel improvements to help reduce 

aircraft emissions in the future. However, according to experts we interviewed, 

some technologies, such as advanced airframes, have potential, but may be 

years away from being available, and developing and adopting them is likely to 

be costly. In addition, according to some experts we interviewed, incentives 

for industry to research and adopt low-emissions technologies will be 

dependent to some extent on the level and stability of fuel prices. Finally, given 

expected growth of commercial aviation as forecasted by IPCC, even if many 

of these improvements are adopted, it appears unlikely they would greatly 

reduce emissions by 2050. 

A number of policy options to address aircraft emissions are available to 

governments and can be part of broader policies to address emissions from 

many sources including aircraft. Market-based measures can establish a price 

for emissions and provide incentives to airlines and consumers to reduce 

emissions. These measures can be preferable to other options because they 

would generally be more economically efficient. Such measures include a capand-trade program, in which government places a limit on emissions from 

regulated sources, provides them with allowances for emissions, and 

establishes a market for them to trade emissions allowances with one another, 

and a tax on emissions. Governments can establish emissions standards for 

aircraft or engines. In addition, government could increase government 

research and development to encourage development of low-emissions 

improvements. To view the full product, including the scope 

and methodology, click on GAO-09-554. 

For more information, contact Susan Fleming 

at (202) 512-2834 or flemings@gao.gov. 
Page i GAO-09-554 

Contents 

Letter 1

Background 3 

Aviation Emissions Represent a Small but Growing Share of All 

Emissions 10 

Experts Believe Future Technological and Operational 

Improvements Are Likely to Help Reduce Emissions from 

Commercial Aircraft, but Likely Not by Enough to Fully Offset 

Estimated Market Growth 22 

Governments Can Use a Variety of Policy Options to Help Reduce 

Commercial Aircraft Emissions, but the Costs and Benefits of 

Each Vary 35 

Agency Comments and Our Evaluation 49 

Appendix I Legal Implications of European Union Emissions 

Trading Scheme 53 

Appendix II List of Experts 70 

Appendix III Detailed Survey Results 71 

Part 1: Technology Options 72 

Part 2: Operational Options 76 

Part 3: Alternative Fuel Options 83 

Appendix IV Scope and Methodology 87 

Appendix V Comments from the National Aeronautics and Space 

Administration 90 

Appendix VI Comments from the Environmental Protection 

Agency 91 

 Aviation and Climate Change 
Appendix VII GAO Contact and Staff Acknowledgments 94 

Tables 

Table 1: Types of Aviation Emissions and Their Effects at Cruising 

Altitude 13 

Table 2: Selected Potential Aircraft Engine Improvements to 

Reduce Emissions 23 

Table 3: Selected Aircraft Improvements to Reduce Emissions 25 

Table 4: Selected Operational Improvements to Reduce Emissions 27 

Table 5: Selected Air Traffic Management Improvements to Reduce 

Emissions 29 

Table 6: NASA’s Subsonic Fixed-Wing Research Fuel-Reduction 

Goals 48 

Figures 

Figure 1: Selected Greenhouse Gas and Other Emissions from 

Aircraft at Cruising Altitude 4 

Figure 2: Total Fuel Consumption and Fuel Efficiency of U.S. 

Airlines 5 

Figure 3: Energy use per Passenger-mile, by Mode of 

Transportation 6 

Figure 4: Forecasted Fuel Consumption by U.S. Airlines 7 

Figure 5: Global Transportation’s and Global Aviation’s 

Contributions to Carbon Dioxide Emissions, 2004 12 

Figure 6: Estimated Relative Contribution of Aviation Emissions to 

Positive Radiative Forcing 15 

Figure 7: Changes in Global and U.S. Aviation Passenger Traffic, 

1978 through 2008 16 

Figure 8: IPCC’s Scenarios for Global Aviation Carbon Dioxide 

Emissions 18 

Figure 9: A Potential Cap-and-Trade Program Regulating Airlines 

and Other Emissions Sources 38 

Page ii GAO-09-554 Aviation and Climate Change
Abbreviations 

ACARE Advisory Council for Aeronautics Research in 

 Europe 

ADS-B Automatic Dependent Surveillance-Broadcast 

ATA Air Transport Association 

CDA Continuous Descent Arrival 

CER certified emissions reduction 

CO2 carbon dioxide 

DG Environment Directorate-General of the Environment 

EEC European Economic Community 

EPA Environmental Protection Agency 

ERU emission reduction unit 

EU European Union 

EU ETS European Union Emissions Trading Scheme 

FAA Federal Aviation Administration 

GDP gross domestic product 

GIACC Group on International Aviation and Climate 

 Change 

ICAO International Civil Aviation Organization 

IETA International Emissions Trading Association 

IPCC Intergovernmental Panel on Climate Change 

NASA National Aeronautics and Space Administration 

NextGen Next Generation Air Transportation System 

NOx nitrogen oxides 

RNAV area navigation 

RNP Required Navigation Performance 

SESAR Single European Sky Air Traffic Management 

 Research Program 

UNFCCC United Nations Framework Convention on Climate 

 Change 

This is a work of the U.S. government and is not subject to copyright protection in the 

United States. The published product may be reproduced and distributed in its entirety 

without further permission from GAO. However, because this work may contain 

copyrighted images or other material, permission from the copyright holder may be 

necessary if you wish to reproduce this material separately. 

Page iii GAO-09-554 Aviation and Climate Change
Page 1 GAO-09-554 

United States Government Accountability Office

Washington, DC 20548 

 

June 8, 2009 

Congressional Requesters 

Many sources, including manufacturing, residential, and transportation 

sources, emit greenhouse gases that contribute to the accumulation of 

these gases in the earth’s atmosphere. Greenhouse gases disperse and trap 

heat in the earth’s atmosphere. This heat-trapping effect, known as the 

greenhouse effect, moderates atmospheric and surface temperatures, 

keeping the earth warm enough to support life. However, according to the 

Intergovernmental Panel on Climate Change (IPCC)—a United Nations 

organization that assesses scientific, technical, and economic information 

on the effects of climate change—global atmospheric concentrations of 

these greenhouse gases have increased markedly as a result of human 

activities over the past 200 years, contributing to a warming of the earth’s 

climate. These trends, if unchecked, could have serious negative effects, 

such as rising sea levels and coastal flooding worldwide. 

Aircraft emit a variety of greenhouse and other gases, including carbon 

dioxide—the most significant greenhouse gas emitted by aircraft—and 

nitrogen oxides, as well as other substances such as soot and water vapor 

that are believed to negatively affect the earth’s climate. Airlines have a 

financial incentive to reduce carbon dioxide emissions, as those emissions 

are a direct result of fuel burn, which represents a large portion of their 

operating costs—about 30 percent for U.S. airlines in 2008. Some experts 

expect aviation to grow at a fast rate until 2021, when the Federal Aviation 

Administration (FAA) forecasts that U.S. domestic commercial aviation 

will serve over 1 billion passengers a year. While the current economic 

downturn could delay this growth somewhat, experts believe that growth 

in the aviation sector means greater productivity and mobility, but is also 

likely to increase emissions. To counteract expected increases in 

emissions, many governments and international organizations have set 

goals for future emissions reductions. For example, a number of 

developed countries have set a goal to reduce carbon dioxide emissions by 

50 percent by 2050. In addition, the Kyoto Protocol, an international 

agreement to minimize the adverse effects of climate change, set binding 

targets for the reduction of greenhouse gases for 37 industrialized 

countries and the European Economic Community (EEC) to achieve 

 Aviation and Climate Change 
 

during the 2008 through 2012 commitment period.1 Although the United 

States is a signatory to the Kyoto Protocol, it is not bound by its terms or 

emissions target because it has not ratified the Protocol. The Protocol also 

requires industrialized nations and the EEC to pursue “limitations or 

reduction of emissions of greenhouses gases... from aviation... working 

through the International Civil Aviation Organization.”2

 Finally, some 

governments have taken actions designed to control aviation emissions. 

For example, in 2003, the European Union (EU) established a cap-andtrade program known as the EU Emissions Trading Scheme (EU ETS) to 

control carbon dioxide emissions from various energy and industrial 

sectors. The EU ETS was first implemented in 2005 and was amended in 

2008 to include aviation. Beginning in 2012, the ETS will include all 

covered flights into or out of an EU airport.3

You asked us to provide information on aviation emissions of greenhouse 

gases and other emissions that may affect climate change. To do so, we 

identified (1) aviation’s current and estimated future contribution to the 

emissions of greenhouse gases and other emissions that may affect climate 

change, (2) existing and potential future technological and operational 

improvements that the commercial aviation industry can use to reduce 

commercial aircraft emissions, and (3) policy options for the U.S. 

government and other governments to help reduce commercial aviation 

emissions and the potential costs and benefits of each option. You also 

asked that we describe the EU’s plans to add the aviation industry to its 

existing ETS and the potential legal implications of doing so. (See app. I 

for this description.) To address these objectives, we reviewed studies on 

the impact of aviation on climate change. We also collaborated with the 

National Academy of Sciences to identify and recruit experts with 

experience in climate change and the aviation industry. We interviewed 18 

such experts (see app. II for a list of the experts). After these interviews, 

 

1

Kyoto Protocol to the United Nations Framework Convention on Climate Change 

(hereinafter the Kyoto Protocol). The Kyoto Protocol was adopted in December 1997 and 

was open for signature between Mar. 16, 1998, and Mar. 15, 1999. As of Jan. 14, 2009, 183 

countries and the EEC had ratified the Kyoto Protocol. The binding emissions targets 

varies by country and is generally higher for more highly developed countries. For instance, 

the EEC has agreed to reduce their aggregate emissions by 8 percent from 1990 emissions 

levels. 

2

Kyoto Protocol, art. 2(2). 

3

This would also include those airports in non-EU countries currently participating in the 

EU ETS—Norway, Iceland, and Liechtenstein. See app. I for further explanation of the EU 

ETS. 

Page 2 GAO-09-554 Aviation and Climate Change
 

we asked the experts to complete a survey in which they assessed a list of 

options to reduce emissions on a variety of predetermined factors, such as 

potential for emissions reductions and costs (see app. III for complete 

results). In addition, we spoke with government, airline, and interest group 

officials in the United States, the EU, and the United Kingdom, focusing on 

commercial aviation. (See app. IV for a more detailed description of our 

scope and methodology.) We conducted our work from March 2008 

through June 2009 in accordance with generally accepted government 

auditing standards. Those standards require that we plan and perform the 

audit to obtain sufficient, appropriate evidence to provide a reasonable 

basis for our findings and conclusions based on our audit objectives. We 

believe that the evidence obtained provides a reasonable basis for our 

findings and conclusions based on our audit objectives. 

Emissions from a variety of human-generated sources, including 

commercial aircraft, trap heat in the atmosphere and contribute to climate 

change. During flight operations, aircraft emit a number of greenhouse gas 

and other emissions, including carbon dioxide, nitrogen oxides (NOx), 

soot, and water vapor. Figure 1 shows the primary emissions from 

commercial aircraft. Carbon dioxide emissions from aircraft are a direct 

result of fuel burn. For every gallon of jet fuel burned, about 21 pounds of 

carbon dioxide are emitted. Reducing the amount of fuel burned, 

therefore, also reduces the amount of carbon dioxide emitted. Water vapor 

emissions and certain atmospheric temperature and humidity conditions 

can lead to the formation of contrails, a cloudlike trail of condensed water 

vapor, and can induce the creation of cirrus clouds. Both contrails and 

cirrus clouds are believed to have a warming effect on the earth’s 

atmosphere. Aircraft also emit other pollutants that affect local air quality. 

Finally, airport operations are sources of greenhouse gas and other 

emissions, which we are not examining in this report. 

Background 

Page 3 GAO-09-554 Aviation and Climate Change
 

Figure 1: Selected Greenhouse Gas and Other Emissions from Aircraft at Cruising 

Altitude 

Air

Exhaust Jet engine

Carbon dioxide

Nitrogen oxides

Water vapor

Sulphate

Soot 

Source: GAO.

Fuel

Combustion

Historically, the commercial aviation industry has grown substantially in 

the United States and worldwide and is a contributor to economic growth. 

Between 1981 and 2008, passenger traffic increased 226 percent in the 

United States on a revenue passenger mile basis and 257 percent globally 

on a revenue passenger kilometer basis.4

 According to the FAA, in 2006 

the civil aviation industry in the United States directly and indirec

contributed 11 million jobs and 5.6 percent of total gross domestic product 

(GDP) to the U.S. economy. Globally, the International Air Transport 

Association estimated that in 2007 the aviation industry had a global 

economic impact of over $3.5 trillion, equivalent to about 7.5 percent of 

worldwide GDP. Recently, however, the airline industry has experienced 

declining traffic and financial losses as the result of the current recession. 

tly 

 

The fuel efficiency of commercial jet aircraft has improved over time. 

According to IPCC, aircraft today are about 70 percent more fuel efficient 

on a per passenger kilometer basis than they were 40 years ago because of 

improvements in engines and airframe design.5

 The cost of jet fuel is a 

large cost for airlines. In the 2008, when global fuel prices were high, jet 

fuel accounted for about 30 percent of U.S. airlines’ total operating 

expenses, compared with 23 percent during 2007. Fuel efficiency 

(measured by available seat-miles per gallon consumed) for U.S. carriers 

increased about 17 percent between 1990 and 2008, as shown in figure 2. 

Internationally, according to the International Air Transport Association, 

4

Fuel consumption of U.S.-based airlines roughly doubled during that same period. 

5

However, some aircraft available in the 1950s were about equally as fuel efficient as jets 

currently available today. 

Page 4 GAO-09-554 Aviation and Climate Change
 

fuel efficiency (measured by revenue passenger kilometers) improved 16.5 

percent between 2001 and 2007. According to FAA, between 2000 and 

early 2008 U.S. airlines reduced fuel burn and emissions while transporting 

more passengers and cargo. 

Figure 2: Total Fuel Consumption and Fuel Efficiency of U.S. Airlines 

Gallons consumed (in billions) Available seat miles per gallon

Source: U.S. Department of Transportation.

Year

Gallons of fuel per available seat mile

Gallons of fuel consumed

0

2

4

6

8

10

12

14

16

18

20

2008200720062005200420032002200120001999199819971996199519941993199219911990198919881987198619851984198319821981

0

44

46

48

50

52

54

56

58

60

In addition, commercial aviation has become less energy intensive over 

time—that is, to transport a single passenger a single mile uses less energy 

than it previously did, measured in British thermal units. See figure 3 

showing energy intensity over time of aviation and other modes of 

transportation. 

Page 5 GAO-09-554 Aviation and Climate Change
 

Figure 3: Energy use per Passenger-mile, by Mode of Transportation 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005

BTUs/passenger mile

Year

Air

Cars

Intercity rail

Buses

Transit rail

Source: Department of Energy.

However, despite these efficiency improvements, overall fuel burn and 

emissions of U.S. airlines are expected to grow in the future. FAA 

forecasts that between 2008 and 2025 fuel consumption of U.S.-based 

airlines will increase an average of 1.6 percent per year while revenue 

passenger miles will increase an average of 3.1 percent per year over the 

same period. As seen in figure 4, FAA forecasts that between 2008 and 

2025 fuel consumption of U.S.-based airlines will increase an average of 

1.6 percent per year. 

Page 6 GAO-09-554 Aviation and Climate Change
 

Figure 4: Forecasted Fuel Consumption by U.S. Airlines 

0

5

10

15

20

25

30

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

2022

2023

2024

2025

Gallons consumed (billions)

Source: FAA Aerospace Forecast, FY 2009-2005.

Fiscal year

To develop a better understanding of the effects of human-induced climate 

change and identify options for adaptation6

 and mitigation,7 two United 

Nations organizations established IPCC in 1988 to assess scientific, 

technical, and socio-economic information on the effects of climate 

change. IPCC releases and periodically updates estimates of future 

greenhouse gas emissions from human activities under different economic 

development scenarios. In 1999, IPCC released its report, Aviation and the 

Global Atmosphere, conducted at the request of the International Civil 

Aviation Organization (ICAO)—a United Nations organization that aims 

to promote the establishment of international civilian aviation standards 

and recommended practices and procedures. In 2007, IPCC released an 

 

6

According to IPCC, adaptation is an adjustment that occurs in response to expected or 

actual climatic stimuli or effects in order to moderate damages or exploit beneficial 

opportunities. 

7

IPCC defines mitigation as technological change and substitution that reduce resource 

inputs, such as energy use, and emissions per unit of output. Although several social, 

economic, and technological policies would produce an emissions reduction, with respect 

to climate change, mitigation means implementing policies to reduce greenhouse gas 

emissions. 

Page 7 GAO-09-554 Aviation and Climate Change
 

update on emissions from transportation and other sectors called the 

Fourth Assessment Report of the Intergovernmental Panel on Climate 

Change. These reports were developed with input from over 300 experts 

worldwide and are internationally accepted and used for policy-making. 

A variety of federal agencies have roles in addressing aviation emissions. 

In 2004, FAA and other organizations including the National Aeronautics 

and Space Administration (NASA) released a report, Aviation and the 

Environment: A National Vision Statement, Framework for Goals and 

Recommended Actions, through the collaborative PARTNER program,8

stating a general goal to reduce overall levels of emissions from 

commercial aviation and proposing actions to deal with aviation 

emissions. FAA also is involved in a number of emissions-reduction 

initiatives—including work on low-emissions technologies and low-carbon 

alternative fuels; the implementation of a new air traffic management 

system, the Next Generation Air Transportation System (NextGen);9

 and 

climate research to better understand the impact of emissions from 

aviation. NASA has been involved in research that has led to the 

development of technologies that reduce aircraft emissions. Currently, 

NASA’s Subsonic Fixed-Wing project, part of its Fundamental Aeronautics 

program, aims to help develop technologies to reduce fuel burn, noise, and 

emissions in the future. Both FAA and NASA are involved in the Aviation 

Climate Change Research Initiative, whose goals include improving the 

scientific understanding of aviation’s impact on climate change. Also, as 

mandated under Title II of the Clean Air Act, the Environmental Protection 

Agency (EPA) promulgates certain emissions standards for aircraft and 

aircraft engines10 and has adopted emission standards matching those for 

aircraft set by ICAO.11 While neither ICAO nor EPA has established 

standards for aircraft engine emissions of carbon dioxide, ICAO is 

 

8

The PARTNER program—the Partnership for AiR Transportation Noise and Emissions 

Reduction—is a cooperative research organization sponsored by FAA, NASA, and 

Transport Canada, with members including universities and other organizations with 

expertise. 

9

NextGen is a new, satellite-based air traffic management system that is expected to 

increase the safety and enhance the capacity of the air transport system. NextGen will 

transform the current radar-based air traffic control system. 

1042 U.S.C. § 7571. 

11However, EPA has the authority to set emissions standards. As the technical agency with 

responsibility for international civil aviation in the United States, FAA, in consultation with 

EPA, works with representatives of other ICAO member countries to formulate the 

standards. 

Page 8 GAO-09-554 Aviation and Climate Change
 

currently discussing proposals for carbon dioxide emissions standards and 

considering a global goal for fuel efficiency.12 In addition, in 2007 a 

coalition of environmental interest groups filed a petition with EPA asking 

the agency, pursuant to the Clean Air Act, to make a finding that 

“greenhouse gas emissions from aircraft engines may be reasonably 

anticipated to endanger the public health and welfare” and, after making 

this endangerment finding, promulgate regulations for greenhouse gas 

emissions from aircraft engines.13

International concerns about the contribution of human activities to global 

climate change have led to several efforts to reduce their impact. In 1992, 

the United Nations Framework Convention on Climate Change 

(UNFCCC)—a multilateral treaty whose objective is to stabilize 

greenhouse gas concentrations in the atmosphere at a level that would 

prevent dangerous human interference with the climate system—was 

signed.14 By 1995, the parties to the UNFCCC, including the United States, 

realized that progress toward this goal was not sufficient. In December 

1997, the parties reconvened in Kyoto, Japan, to adopt binding measures 

to reduce greenhouse gas emissions. Under the resulting Kyoto Protocol, 

which the United States has not ratified, industrialized nations committed 

to reduce or limit their emissions of carbon dioxide and other greenhouse 

gases during the 2008 through 2012 commitment period.15 The Protocol 

 

12In addition, H.R. 2454, the American Clean Energy and Security Act of 2009, § 221(b), 

111th Cong. (2009), would require EPA to issue standards for greenhouse gas emissions 

from new aircraft and new engines used in aircraft by Dec. 31, 2012. 

13In addition, in 2007, the Supreme Court ruled that greenhouse gases meet the Clean Air 

Act’s definition of an air pollutant and that EPA has the statutory authority to regulate 

greenhouse gas emissions from new motor vehicles under the Act. Massachusetts v. 

Environmental Protection Agency, 549 U.S. 497 (2007). As a result of the opinion, EPA 

must take one of three actions: 1) issue a finding that greenhouse gas emissions cause or 

contribute to air pollution that may endanger public heath or welfare; 2) issue a finding that 

greenhouse gases do not endanger public health or welfare; or 3) provide a reasonable 

explanation as to why it cannot or will not exercise its discretion to issue a finding. In 

response to this case, EPA issued an Advance Notice of Proposed Rulemaking, “Regulating 

Greenhouse Gas Emissions Under the Clean Air Act,” 73 Fed. Reg. 44354 (July 30, 2008). 

EPA subsequently issued a proposed finding that carbon dioxide, methane, nitrous oxide, 

and hydrofluorocarbon emissions from new motor vehicles are contributing to air pollution 

which is endangering public health and welfare. 74 Fed. Reg. 18886 (Apr. 24, 2009). EPA is 

moving forward with the proposed finding while it develops proposed standards for 

regulating greenhouse gas emissions from motor vehicles. 

14To date, 192 countries have ratified the UNFCCC. 

15The emissions reduction goal varies by country and is generally higher for more highly 

developed countries. Some European countries, for example, agreed to reduce emissions 

by 8 percent compared to 1990 levels. 

Page 9 GAO-09-554 Aviation and Climate Change
 

directed the industrialized nations to work through ICAO to reduce or 

limit emissions from aviation, but international aviation emissions are not 

explicitly included in Kyoto’s targets. In 2004, ICAO endorsed the further 

development of an open emissions trading system for international 

aviation, and in 2007 called for mutual agreement between contracting 

states before implementation of an emissions trading scheme. In part to 

meet its Kyoto Protocol requirements, the EU implemented its ETS in 

2005, which sets a cap on carbon dioxide emissions and allows regulated 

entities to buy and sell emissions allowances with one another. In 2008, 

the European Parliament and the Council of the European Union passed a 

directive, or law, to include aviation in the ETS. Under the directive, 

beginning in 2012 a cap will be placed on total carbon dioxide emissions 

from all covered flights by aircraft operators into or out of an EU airport.16

Many stakeholders and countries have stated objections to the EU’s plans 

and legal challenges are possible. (See app. I for a discussion of the ETS’s 

inclusion of aviation.) In December 2009, the parties to the UNFCCC will 

convene in Copenhagen, Denmark, to discuss and negotiate a post-Kyoto 

framework for addressing global climate change. 

IPCC estimates that aviation emissions currently account for about 2 

percent of global human-generated carbon dioxide emissions and about 3 

percent of the radiative forcing17 of all global human-generated emissions 

(including carbon dioxide) that contribute to climate change. On the basis 

of available data and assumptions about future conditions, IPCC 

forecasted emissions to 2015 and forecasted three scenarios—low, 

medium, and high—for growth in global aviation carbon dioxide emissions 

from 2015 to 2050. These scenarios are driven primarily by assumption 

about economic growth—the factor most closely linked historically to the 

aviation industry’s growth—but they also reflect other aviation-related 

assumptions. Because IPCC’s forecasts depend in large part on 

assumptions, they, like all forecasts, are inherently uncertain. 

Nevertheless, as previously noted, IPCC’s work reflects the input of over 

Aviation Emissions 

Represent a Small but 

Growing Share of All 

Emissions 

 

16In addition to the current 27 EU member states, other European countries not part of the 

EU, such as Norway, Iceland, and Liechtenstein, participate in the ETS. These airports are 

included in the amended ETS. 

17Radiative forcing is a measure for the change of the Earth’s energy balance due to a 

change in concentrations of greenhouse gases and other emissions that contribute to 

climate change. 

Page 10 GAO-09-554 Aviation and Climate Change
 

300 leading and contributing authors and experts worldwide and is 

internationally accepted and used for policy making.18

Aviation Contributes about 

2 Percent of Global Carbon 

Dioxide Emissions 

According to IPCC, global aviation contributes about 2 percent of the 

global carbon dioxide emissions caused by human activities.19 This 2 

percent estimate includes emissions from all global aviation, including 

both commercial and military. Global commercial aviation, including 

cargo, accounted for over 80 percent of this estimate.20 In the United 

States, domestic aviation contributes about 3 percent of total carbon 

dioxide emissions, according to EPA data.21

Many industry sectors, such as the electricity-generating and 

manufacturing sectors, contribute to global carbon dioxide emissions, as 

do residential and commercial buildings that use fuel and power. The 

transportation sector also contributes substantially to global carbon 

dioxide emissions. Specifically, it accounts for about 20 percent of total 

global carbon dioxide emissions.22 Road transportation accounts for the 

largest share of carbon dioxide emissions—74 percent—from the 

transportation sector; aviation accounts for about 13 percent of carbon 

 

18According to IPCC, the report was compiled by 107 lead authors from 18 countries. 

Successive drafts of the report were circulated for review by experts, followed by review of 

governments and experts. Over 100 contributing authors submitted draft text and 

information to the lead authors and over 150 reviewers submitted suggestions for 

improvement during the review process. 

19According to IPCC, global aviation’s global carbon dioxide emissions totaled an estimated 

480 million tons in 2000. 

20According to EPA, in 2007 commercial aviation represented about 82 percent of all 

aviation emissions, and about 2.5 percent of U.S. carbon dioxide emissions. In the United 

States, military aviation represents less than 10 percent of total aviation emissions. 

21EPA, Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2007, (March 

2009). The aviation estimates do not include fuel consumed for international air transport 

per UNFCCC’s reporting guidelines; according to the EPA, in 2006, when those 

international fuels were included, domestic and international commercial, military, and 

general aviation flights represented about 3.4 percent of U.S. carbon dioxide emissions. 

22In the United States according to EPA, carbon dioxide emissions from fossil fuel 

combustion in the transportation sector account for an estimated 31 percent of carbon 

dioxide emissions (in carbon dioxide equivalents not including fuels used for international 

flights). Carbon dioxide equivalents provide a common standard for measuring the 

warming potential of different greenhouse gases and are calculated by multiplying the 

emissions of the non-carbon-dioxide gas by its global warming potential, a factor that 

measures its heat-trapping ability relative to that of carbon dioxide. 

Page 11 GAO-09-554 Aviation and Climate Change
 

dioxide emissions from all transportation sources; and other 

transportation sources, such as rail, account for the remaining 13 percent. 

Figure 5 shows the relative contributions of industry, transportation, and 

all other sources to global carbon dioxide emissions and breaks down 

transportation’s share to illustrate the relative contributions of road traffic, 

aviation, and other transportation sources. 

Figure 5: Global Transportation’s and Global Aviation’s Contributions to Carbon 

Dioxide Emissions, 2004 

8%

13%

20%

18%

41%

Sources: GAO presentation of International Energy Agency and IPCC data.

Other sources

Residential and services

Industry

Power generation

Transportation

74% Road

13%

Aviation

13%

Rail and other

sources

Aviation Contributes about 

3 Percent of All HumanGenerated Emissions 

When other aviation emissions—such as nitrogen oxides, sulfate aerosols, 

and water vapor—are combined with carbon dioxide, aviation’s estimated 

share of global emissions increases from 2 percent to 3 percent, according 

to IPCC. However, the impact of these other emissions on climate change 

is less well understood than the impact of carbon dioxide, making IPCC’s 

combined estimate more uncertain than its estimate for carbon dioxide 

alone. 

Aviation emissions may contribute directly or indirectly to climate change. 

Although most aviation emissions have a warming effect, sulfate aerosols 

and a chemical reaction involving methane have a cooling effect. The 

warming effect is termed “positive radiative forcing” and the cooling effect 

“negative radiative forcing.” Aviation emissions also may contribute to the 

formation of cirrus clouds, which can cause atmospheric warming, but the 

Page 12 GAO-09-554 Aviation and Climate Change
 

scientific community does not yet understand this process well enough to 

quantify the warming effect of aviation-induced cirrus clouds. Table 1 

describes the direct or indirect effects of aviation emissions on climate 

change. 

Table 1: Types of Aviation Emissions and Their Effects at Cruising Altitude 

Direct greenhouse gases and emissions 

Carbon dioxide Carbon dioxide has a warming effect on the climate and remains in the atmosphere for 

hundreds of years. Carbon dioxide emissions from aviation have the same effect as 

those from other industry sectors because the carbon dioxide emitted from aircraft 

remains in the atmosphere long enough to be well mixed with the carbon dioxide emitted 

from ground-based sources. 

Water vapor Water vapor has a warming effect on the climate and is generated from the hydrogen 

contained in aviation fuel. It remains for only a short period in the troposphere (the 

lowest portion of the earth’s atmosphere), where most emissions from aviation occur. 

The quantity of water vapor emitted by aviation is small compared with the quantities 

emitted from natural atmospheric sources. 

Soot particles Soot particles are produced during combustion and have a small warming (positive 

radiative forcinga

) effect on the climate as they absorb incoming sunlight and heat the 

atmosphere. 

Indirect greenhouse gases and emissions

Ozone (from NOx) Nitrogen emissions do not contribute to global warming directly, but the ozone generated 

from increased nitrogen oxides (NOx) is a greenhouse gas that produces a warming 

effect on the climate. The effect is higher at cruising altitude than on the ground because 

of longer lifetimes and greater radiative forcing in the higher levels of the atmosphere. 

Methane (NOx related) Very little or no methane is emitted by aircraft, but NOx emissions initiate a destruction of 

methane molecules, which generates an overall cooling effect on the climate. Overall, 

the warming effect of NOx emissions due to ozone formation is estimated to be higher 

than the cooling that results from methane destruction. 

Sulfate aerosols Sulfate aerosols, which arise from sulfur in jet fuel, scatter incoming sunlight back to the 

atmosphere and have a relatively small cooling effect on the climate. 

Cloud formation 

Contrails Contrails are formed through emissions of water and particles under certain atmospheric 

conditions such as temperature and humidity. They mainly consist of water already 

contained in the atmosphere, and aircraft operations only trigger their formation in these 

areas. Contrails cool the climate through increased reflection of solar radiation, but also 

trap heat on the earth, which contributes to global warming. Overall, contrails have a 

warming effect, although uncertainties about the magnitude of this effect remain. 

Cirrus clouds Cirrus cloud formation might be augmented through aviation-induced contrails and cloud 

seeding from emission particles. Cirrus clouds have a warming effect, but exact 

quantifications are not yet possible. Consequently, IPCC did not include the impact of 

cirrus cloud formation in its estimates of aviation’s contribution to human-generated 

emissions.b

 

Source: IPCC, the Aviation Climate Change Research Initiative, and the European Topic Center on Air and Climate Change. 

Page 13 GAO-09-554 Aviation and Climate Change
 

a

According to the IPCC, radiative forcing has advantages over global warming potential (GWP) for 

estimating aviation’s impact from short-lived aviation emissions and aerosols and contrails. GWP is 

used to measure the heat-absorbing ability of long-lived gases using carbon dioxide as a reference. 

Each measure has limits and several other impact measures including a modified GWP are under 

consideration to address some of the limitations. 

b

University and government organizations, including NASA, are conducting research on them to 

better understand their effects. 

According to IPCC, when the positive radiative forcing effects of carbon 

dioxide and the positive and negative radiative forcing effects of other 

aviation emissions are combined, global aviation contributes about 3 

percent23 of human-generated positive radiative forcing. When the 

radiative forcing effects of the various aviation emissions are considered

carbon dioxide, nitrogen oxides, and contrails have the greatest poten

to contribute to climate change

, 

tial 

. 

 

The level of scientific understanding about the impact of particular 

aviation emissions on radiative forcing varies, making estimates of their 

impact on climate change uncertain to varying degrees. A recent report 

that described levels of scientific understanding of aviation emissions 

found that the levels for carbon dioxide were high; the levels for nitrogen 

oxides, water vapor, sulfates, and soot were medium; and the levels for 

contrails and aviation-induced cirrus clouds were low.24 Aviation’s 

contribution to total emissions, estimated at 3 percent, could be as low as 

2 percent or as high as 8 percent, according to IPCC. Figure 6 shows 

IPCC’s estimate of the relative positive radiative forcing effects of each 

type of aviation emission for the year 2000. The overall radiative forcing 

23This 3 percent radiative forcing estimate for aviation is based on more recent research, 

included in IPCC’s 2007 Fourth Assessment Report. Originally, IPCC calculated a 3.5 

percent estimate for 1992, which it published in its 1999 special report, Aviation and the 

Global Atmosphere. 

24See Aviation Climate Change Research Initiative: A Report on the Way Forward, (2008) 

citing Forster, P., et al. (2007), Changes in atmospheric constituents and in radiative 

forcing. In: IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of 

Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on 

Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. 

Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom 

and New York, NY, USA; and Sausen, R. et al., Aviation radiative forcing in 2000: An 

update on IPCC (1999), Meteorologische Zeitschrift, 14-4, 555–561, 2005. 

Page 14 GAO-09-554 Aviation and Climate Change
 

from aviation emissions is estimated to be approximately two times that of 

carbon dioxide alone.25

Figure 6: Estimated Relative Contribution of Aviation Emissions to Positive 

Radiative Forcing 

20%

22%

49%

Source: GAO presentation of IPCC reported study.

4%

Water vapor

5%

Soot

Contrails

Nitrogen oxides

Carbon dioxide

Note: This figure portrays the relative contributions of emissions that have a net positive radiative 

forcing effect. The effect of sulfate emissions, which have a negative radiative forcing, or cooling, 

effect, is not included. The result reported for nitrogen oxides is the net warming effect calculated by 

subtracting the cooling effect of methane from the warming effect of ozone. The aviation radiative 

forcing impact estimates described by IPCC in 2007 are reported as (positive) warming and 

(negative) cooling in milliwatts per meter squared: carbon dioxide (+ 25.3), ozone production from 

nitrogen oxides (+21.9), reduction of atmospheric methane as a result of nitrogen oxides (-10.4), 

water vapor (+2.0), sulfate particles (-3.5), soot particles (+2.5), and contrails (+10.0). For cirrus 

clouds, IPCC had no best estimate due to uncertainty, but a possible range of +10 to +80 was 

reported. The relative contributions of emissions in this chart are an approximation because of the 

uncertainty surrounding the non-carbon dioxide forcing estimates. 

IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to 

the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. 

Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge 

University Press, Cambridge, United Kingdom and New York, NY, USA. 

 

25The 1999 IPCC report originally estimated that aviation’s impact could be two to four 

times that of carbon dioxide alone. The use of a radiative forcing ratio of the forcing of all 

aviation emissions over carbon dioxide is an approximation and is an area for further 

research and understanding. 

Page 15 GAO-09-554 Aviation and Climate Change
 

Global Aviation Emissions 

Are Expected to Grow but 

Forecasts Vary, Primarily 

Reflecting Different 

Economic Growth 

Assumptions 

IPCC generated three scenarios that forecasted the growth of global 

aviation carbon dioxide emissions from the near-term (2015) to the longterm (2050) and described these scenarios in its 1999 report. These 

forecasts are generated by models that incorporate assumptions about 

future conditions, the most important of which are assumptions about 

global economic growth and related increases in air traffic. Other 

assumptions include improvements in aircraft fuel efficiency and air traffic 

management and increases in airport and runway capacity. Because the 

forecasts are based on assumptions, they are inherently uncertain. 

Historically, global economic growth has served as a reliable indicator of 

air traffic levels. Aviation traffic has increased during periods of economic 

growth and slowed or decreased during economic slowdowns. As figure 7 

shows, U.S and global passenger traffic (including the U.S.) generally 

trended upward from 1978 through 2008, but leveled off or declined during 

economic recessions in the United States. 

Forecasts of Global Economic 

Growth and Air Traffic 

Primarily Drive IPCC’s 

Emissions Estimates 

Figure 7: Changes in Global and U.S. Aviation Passenger Traffic, 1978 through 2008

Sources: U.S. Department of Transportation data and ICAO data from the Air Transport Association.

Year

Global passenger traffic

U.S. passenger traffic

Periods of recession

0

100

200

300

400

500

600

700

800

900

Global passenger traffic (revenue passenger kilometers, in trillions) U.S. carrier passenger traffic (revenue passenger miles, in billions)

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

0.0

1.0

2.0

3.0

4.0

5.0

Page 16 GAO-09-554 Aviation and Climate Change
 

Forecast models described in IPCC’s report incorporate historical trends 

and the relationship between economic growth and air traffic to produce 

scenarios of global aviation’s potential future carbon dioxide emissions. 

IPCC used a NASA emissions forecast for carbon dioxide emissions until 

2015. IPCC used an ICAO emissions forecasting model to forecast 

emissions from 2015 to 2050 using three different assumptions for global 

economic growth—low (2.0 percent), medium (2.9 percent), and high (3.5 

percent). As a result, IPCC produced three different potential scenarios for 

future air traffic and emissions.26 The 2050 scenarios include a 40 percent 

to 50 percent increase in fuel efficiency by 2050 from improvements in 

aircraft engines and airframe technology and from deployment of an 

advanced air traffic management system (these are discussed in more 

detail below). Figure 8 shows IPCC’s low-, mid-, and high-range scenarios 

for carbon dioxide emissions for 2015, 2025, and 2050 as a ratio over 1990 

emissions. IPCC used the medium economic growth rate scenario to 

estimate aviation’s contribution to overall emissions in 2050. 

 

26IPCC assumed a maturing global market with the above economic growth rates from 1990 

to 2025 and slightly lower economic growth rates thereafter. 

Page 17 GAO-09-554 Aviation and Climate Change
 

Figure 8: IPCC’s Scenarios for Global Aviation Carbon Dioxide Emissions 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

1990 2000 2015 2025 2050

Ratio of estimate over 1990 level

Source: IPCC.

Years

Low GDP scenario

Medium GDP scenario

High GDP scenario

Note: Includes advanced air traffic management and 40 percent to 50 percent fuel efficiency gain by 

2050. 

IPCC compared aviation and overall emissions for the future and found 

that global aviation carbon dioxide emissions could increase at a greater 

rate than carbon dioxide emissions from all other sources of fossil fuel 

combustion. For example, for the medium GDP growth rate scenario, 

IPCC assumed a 2.9 percent annual average increase in global GDP, which 

translated into almost a tripling (a 2.8 times increase) of aviation’s global 

carbon dioxide emissions from 1990 to 2050. For the same medium GDP 

growth scenario, IPCC also estimated a 2.2 times increase of carbon 

dioxide emissions from all other sources of fossil fuel consumption 

worldwide during this period. Over all, using the midrange scenario for 

global carbon dioxide emissions and projections for emissions from other 

sources, IPCC estimated that in 2050, carbon dioxide emissions from 

aviation could be about 3 percent of global carbon dioxide emissions, up 

from 2 percent. IPCC further estimated that, when other aviation 

Page 18 GAO-09-554 Aviation and Climate Change
 

emissions were combined with carbon dioxide emissions, aviation would 

account for about 5 percent of global human-generated positive radiative 

forcing, up from 3 percent.27 IPCC concluded that the aviation traffic 

estimates for the low-range scenario, though plausible, were less likely 

given aviation traffic trends at the time the report was published in 1999. 

IPCC’s 2007 Fourth Assessment Report included two additional forecasts 

of global aviation carbon dioxide emissions for 2050 developed through 

other studies.28 Both of these studies forecasted mid- and high-range 

aviation carbon dioxide emissions for 2050 that were within roughly the 

same range as the 1999 IPCC report’s forecasts.29 For example, one study 

using average GDP growth assumptions that were similar to IPCC’s 

showed mid- and high-range estimates that were close to IPCC’s estimates. 

In 2005, FAA forecasted a 60 percent growth in aviation carbon dioxide 

and nitrogen oxide emissions from 2001 to 2025. However, FAA officials 

recently noted that this estimate did not take into account anticipated 

aircraft fleet replacements, advances in aircraft and engine technology, 

and improvements to the air transportation system, nor did it reflect the 

recent declines in air traffic due to the current recession. After taking 

these factors into account, FAA reduced its estimate in half and now 

estimates about a 30 percent increase in U.S. aviation emissions from 2001 

to 2025.30 To account for some uncertainties in FAA’s emissions 

forecasting, FAA officials said they are working on creating future 

 

27This 5 percent estimate of aviation’s contribution to 2050 global radiative forcing is based 

on IPCC’s midrange estimate. IPCC did not provide this estimate for the 2050 high- and 

low-range scenarios. 

28B. Owen and D.S. Lee, Allocation of International Aviation Emissions from Scheduled 

Air Traffic—Future Cases, 2005 to 2050, Manchester Metropolitan University 

(Manchester, UK, March 2006) and Ralf Berghof, Alf Schmitt et al., CONSAVE 2050 Final 

Technical Report (July 2005). 

29The 1999 IPCC report included a high-growth emissions scenario for 2050 from an 

environmental organization that showed aviation contributing 9.8 percent of global carbon 

dioxide emissions. This estimate assumed air traffic levels for 2050 that were more than 

double those used in the highest IPCC estimate. IPCC concluded that such an estimate for 

2050, though not impossible, was unlikely because it would require countries to build more 

than 1,300 new airports with 15 gates each, or the equivalent of 2 new airports per month 

for 60 years, which would be unprecedented compared with historical increases in global 

airport capacity. 

30This estimate is based on emissions of carbon dioxide and nitrogen oxides. In terms of 

fuel consumption, FAA estimates a 28 percent increase in US carriers commercial aviation 

jet fuel from 2001 to 2025 (see FAA Aerospace Forecast, Fiscal Years 2009-2025, table 22). 

Page 19 GAO-09-554 Aviation and Climate Change
 

scenarios for the U.S. aviation sector to assess the influence of a range of 

technology and market assumptions on future emissions levels. 

While recent aviation forecasts are generally consistent with IPCC’s 

expectation for long-term global economic growth, the current economic 

slowdown has led to downward revisions in growth forecasts. For 

example, in 2008, Boeing’s annual forecast for the aviation market 

projected a 3.2 percent annual global GDP growth rate from 2007 to 2027. 

However, this estimate was made before the onset of negative global 

economic growth in 2009 and could be revised downward in Boeing’s 2009 

forecast. According to FAA’s March 2009 Aerospace Forecast, global GDP, 

which averaged 3 percent annual growth from 2000 to 2008, will be 0.8 

percent from 2008 to 2010 before recovering to an estimated average 

annual growth rate of 3.4 percent from 2010 to 2020.31 The International 

Air Transport Association has predicted that global air traffic will decrease 

by 3 percent in 2009 with the economic downturn. Moreover, according to 

the association, even if air traffic growth resumes in 2010, passenger air 

traffic levels will be 12 percent lower in the first few years after the 

slowdown and 9 percent lower in 2016 than the association forecasted in

late 2007. To the extent that air traffic declines, emissions also will

Other Forecasts Show 

Continued Long-term Growth, 

but Emissions Could Fall below 

Estimated Levels during the 

Current Economic Downturn 

decline. 

ecast results, as IPCC itself, 

 of 

e fuel efficiency by 40 percent to 50 percent 32

ould be in 

place worldwide by 2050,33 reducing congestion and delays. 

 

In developing its forecasts, IPCC made assumptions about factors other 

than economic growth that also affected its for

Assumptions about Other 

Factors Could Affect IPCC’s 

Forecasts experts we interviewed, and FAA have noted: 

• IPCC assumed that advances in aircraft technology and the introduction

new aircraft would increas

from 1997 through 2050.

• IPCC assumed that an ideal air traffic management system w

31Two main methods, market exchange rates and purchasing power parity are used to 

convert the GDP of a country in national currency terms to a common currency, usually the 

U.S. dollar. GDP growth rates can differ depending on the conversion method used. 

32However, the forecast doesn’t account for the possibility that some airlines might adopt 

low-carbon alternative fuels. 

33The United States is currently working on its future air traffic management system, 

NextGen, as is Europe through the Single European Sky Air Traffic Management Research 

Program (SESAR). 

Page 20 GAO-09-554 Aviation and Climate Change
 

• IPCC assumed that airport and runway capacity would be sufficient to 

accommodate future air traffic levels. 

However, if IPCC’s assumptions about improvements in fuel efficiency and 

air traffic management are not realized, aircraft could produce higher 

emissions levels than IPCC estimated and IPCC’s estimates would be 

understated. Conversely, if airports and runways have less capacity than 

IPCC assumed, then air traffic levels could be lower and, according to 

IPCC and some experts, IPCC’s forecast could overstate future aviation 

emissions. Finally, IPCC pointed out that its estimate that aviation will 

contribute 5 percent of positive radiative forcing in 2050 does not include 

the potential impact of aviation-induced cirrus clouds, which could be 

substantial.34

Because IPCC’s forecasts are based on assumptions about future 

conditions and scientific understanding of the radiative forcing effects of 

certain aviation emissions is limited, IPCC’s forecasts are themselves 

uncertain. According to FAA officials, given the numerous assumptions 

and inherent uncertainties involved in forecasting aviation emissions 

levels out to the year 2050, along with the significant shocks and structural 

changes the aviation community has experienced over the last few years, 

IPCC’s projections are highly uncertain, even for the midrange scenario. If 

emissions from aviation and all other sectors continue to grow at about 

the same relative rate, aviation’s contribution as a portion of overall 

emissions will not change significantly. However, if significant reductions 

are made in overall emissions from other sources and aviation emission 

levels continue to grow, aviation’s contribution could grow. 

 

34Other studies have estimated aviation’s share of current climate change emissions and 

find aviation’s contributions to climate change to be larger when the impact of cirrus 

clouds is included. For example, one environmental organization in a 2006 report included 

the upper range for aviation-induced cirrus clouds’ radiative forcing (from Sausen et al, 

2005, which was reported in IPCC) in its aviation radiative forcing total and calculated that 

aviation contributed 9 percent of total radiative forcing due to human activity worldwide in 

2000. 

Page 21 GAO-09-554 Aviation and Climate Change
 

According to experts we interviewed, a number of different technological 

and operational improvements related to engines, aircraft design, 

operations, next-generation air traffic management, and fuel sources are 

either available now or are anticipated in the future to help reduce carbon 

dioxide emissions from aircraft. We interviewed and surveyed 18 experts 

in the fields of aviation and climate change and asked them to assess a 

number of improvements to reduce emissions using a variety of factors, 

such as potential costs and benefits, and then used the results to inform 

the following discussion. (Complete survey results can be found in app. 

III.) The development and adoption of low-emissions technologies is likely 

to be dependent upon fuel prices or any government policies that price 

aircraft emissions. Higher fuel prices or prices on emissions—for example 

through government policies such as an emissions tax—would make the 

costs of low-emissions technologies relatively cheaper and are likely to 

encourage their development. In addition, while fuel efficiency and 

emissions reductions may be important to airlines, so are a number of 

other factors, including safety, performance, local air quality, and noise 

levels, and trade-offs may exist between these factors. 

Experts Believe 

Future Technological 

and Operational 

Improvements Are 

Likely to Help Reduce 

Emissions from 

Commercial Aircraft, 

but Likely Not by 

Enough to Fully 

Offset Estimated 

Market Growth 

Experts Believe That 

Although Many 

Technologies Are 

Expected to Help Reduce 

Emissions Growth in the 

Future, They Involve 

Trade-offs 

Improvements to aircraft engines have played a primary role in increasing 

fuel efficiency and reducing engine emission rates; experts we interviewed 

expect them to do so in the future—one study estimates that 57 percent of 

improvements in aircraft energy intensity between 1959 and 1995 were due 

to improvements in engine efficiency.35 Such improvements have resulted 

from increasing engine pressure and temperatures (which increases their 

efficiency and decreases fuel usage) and improving the “bypass ratio,” a 

Aircraft Engine Improvements 

 

35Joosung J. Lee, Stephen P. Lukachko, Ian A. Waitz, and Andreas Schafer, “Historical and 

Future Trends in Aircraft Performance, Cost, and Emissions,” Annual Reviews on Energy 

and Environment, vol. 26 (2001). 

Page 22 GAO-09-554 Aviation and Climate Change
 

measure of airflow through the engine.36 However, according to experts 

we surveyed, further advances in these technologies may face hi

development costs (see table 2), and some may not be available for 

commercial use any time soon because engineers still face challenges in 

improving engine technology. 

gh 

Table 2: Selected Potential Aircraft Engine Improvements to Reduce Emissions 

Improvement 

Potential 

reduction in 

carbon 

dioxide 

emissionsa

 

Potential 

research and 

development 

costsa

Estimated 

time frame for 

commercial 

useb

Potential for 

public 

acceptancea

Geared turbofan 

engine—more 

fuel efficient 

engine 

Medium Medium Short-medium High 

Open rotor 

engine—engine 

fan blades not 

enclosed 

High High Medium Low-medium 

Distributed 

propulsion 

systems—many 

small engines 

instead of few 

large ones 

Medium High Long High 

Source: GAO survey of experts. 

Note: Between 8 and 13 experts responded to each of our questions about technological 

improvements. 

a

We did not provide definitions for “low,” “medium,” or “high” in these cases. 

b

Short timeframe (<5 years); medium timeframe (5-15 years); long timeframe (>15 years). 

Some technologies may be available sooner than others, but all present a 

range of challenges and tradeoffs: 

• One latest-generation aircraft engine, the geared turbofan engine, is likely 

to be available for use in certain aircraft in the next few years; promises to 

reduce emissions according to its manufacturer, Pratt & Whitney; and may 

 

36The higher the bypass ratio, the more air bypasses the engine, providing extra propulsion 

for the engine fan blades and increasing the engine’s efficiency. 

Page 23 GAO-09-554 Aviation and Climate Change
 

face few challenges to widespread adoption.37 According to Pratt & 

Whitney, this engine design is estimated to reduce fuel burn and emissions 

by 12 percent, compared with similar engines now widely used, in part due 

to an increase in the engine’s bypass ratio. The geared turbofan engine is 

the result of research conducted by NASA and Pratt & Whitney.38

• Another engine technology, which could be introduced in the next 5 to 15 

years, is the “open rotor” engine. It may deliver even greater emissions 

reductions but may face consumer-related challenges. The open rotor 

engine holds the engine fan blades on the outside of the engine case, 

thereby increasing the air flow around the engine, the effective bypass 

ratio, and the efficiency of the engine’s propulsion. However, this engine 

may be noisy and its large, visible engine blades could raise consumer 

concerns according to experts we surveyed. Research in the United States 

is currently a joint effort of NASA and General Electric. Rolls-Royce is also 

pursuing this technology. 

• In the longer term, despite some engineering challenges, distributed 

propulsion technologies also hold promise for reducing aircraft emissions. 

Distributed propulsion systems would place many small engines 

throughout an aircraft instead of using a few large engines, as today’s 

aircraft do. Experts we interviewed said that engineering challenges must 

be overcome with distributive propulsion, including determining the best 

and most efficient way to distribute power and store fuel. NASA is 

currently involved in distributed propulsion research. 

Aircraft improvements also have played a role in reducing emissions rates 

in the past and experts we interviewed expected them to continue to do 

so. Through improvements in materials used to build aircraft and other 

improvements that increase aerodynamics and reduce drag, aircraft have 

become more fuel efficient over time. In the short term, improvements in 

aircraft materials, leading to decreased weight, and improvements in 

aerodynamics will help reduce fuel consumption and, thus, emissions 

rates. In the longer term, new aircraft designs, primarily a blended wingbody aircraft, hold potential for greater reductions in emissions rates. 

However, new aircraft concepts face engineering and consumer 

Aircraft Improvements 

 

37In addition, General Electric is developing a new fuel-efficient engine, the GEnx. 

According to General Electric, this engine will improve fuel burn by 15 percent, while also 

reducing NOx emissions, compared with General Electric’s previous generation of engine 

technologies. 

38The U.S. Air Force also is conducting research into more fuel efficient engines through its 

ADVENT program, a joint effort with engine manufacturers that Air Force officials told us 

is expected to have commercial applications. 

Page 24 GAO-09-554 Aviation and Climate Change
 

acceptance challenges and new technologies are likely to incur high 

development costs (see table 3). 

Table 3: Selected Aircraft Improvements to Reduce Emissions 

Improvement 

Potential 

reduction in 

carbon dioxide 

emissionsa

 

Potential 

research 

and 

development 

costsa

Estimated 

time frame for 

commercial 

useb

Potential for 

public 

acceptancea

Blended wing-body—

Fuselage and wings 

as part of one 

airframe 

High High Long Low-medium 

Lightweight 

composite 

airframes—

Lightweight materials 

Medium Medium Medium High 

Winglets—Wing 

attachments to 

reduce drag 

Low Low Shortc High 

Source: GAO survey of experts. 

Note: Between 11 and 14 experts responded to each of our questions about technological 

improvements. 

a

We did not provide definitions for “low,” “medium,” or “high” in these cases. 

b

Short timeframe (<5 years); medium timeframe (5-15 years); long timeframe (>15 years). 

c

Winglets are already available and used by a number of airlines. 

The following improvements to aircraft should help reduce aircraft fuel 

consumption and emissions in the long term, despite costs and challenges: 

• The use of lightweight composite materials in aircraft construction has led 

to weight and fuel burn reductions in the past and is expected to continue 

to do so in the future. Over time, aircraft manufacturers have increasingly 

replaced more traditional materials such as aluminum with lighter-weight 

composite materials in airframe construction. For example, according to 

Boeing, 50 percent of the weight of the airframe of the Boeing 787, 

expected to be released in 2010, will be attributable to composite 

materials, compared with 12 percent composites in a currently available 

Boeing 777. According to Airbus, it first began using composite materials 

in airframe construction in 1985, and about 25 percent of the airframe 

weight of an A380 manufactured in 2008 was attributable to composites. 

By reducing the weight of the airframe, the use of composites reduces 

aircraft weight, fuel burn, and emissions rates. 

• Retrofits such as winglets—wing extensions that reduce drag—can be 

made to aircraft to make them more aerodynamic but may have limited 

Page 25 GAO-09-554 Aviation and Climate Change
 

potential for future emissions reductions according to experts we 

surveyed. By improving airflow around wings, winglets reduce drag and 

improve fuel efficiency, thus reducing emissions by a modest amount. 

Boeing estimates that the use of winglets on a 737 reduces fuel burn by 3.5 

percent to 4 percent on trips of over 1,000 nautical miles. Many new 

aircraft can be purchased with winglets, and existing aircraft also can be 

retrofitted with them. However winglets have already become very 

common on U.S. commercial airline aircraft and provide limited benefit 

for short-haul flights. According to experts we surveyed, there is low 

potential for future fuel consumption and emissions reductions from 

winglets. 

• Redesigned aircraft, such as a blended wing-body aircraft—that is, an 

aircraft in which the body and wings are part of one airframe—hold 

greater potential for reducing emissions, according to experts we 

surveyed, though these face challenges as well. Several public and private 

organizations, including NASA and Boeing are conducting research on 

such aircraft. Many experts expect that blended wing-body aircraft will 

reduce emissions through improved aerodynamics and lighter weight. 

Estimates for potential emissions reductions include 33 percent compared 

with currently available aircraft according to NASA. However, these new 

designs face challenges; notably, according to experts we interviewed, 

development costs are likely to be substantial, their radically different 

appearance may pose consumer acceptance issues, and they may require 

investments in modifying airports.39

Experts Also Expect 

Operational Improvements 

to Help Reduce Aircraft 

Emissions in the Future, 

but Reductions May Be 

Limited 

Airlines have already taken a number of steps to improve fuel efficiency 

over time; however, the potential for future improvements from these 

measures may be limited. Airlines have increased their load factors (the 

percentage of seats occupied on flights), increasing the fuel efficiency of 

aircraft on a per-passenger basis. Load factors were about 80 percent for 

U.S. carriers in 2008, compared with about 65 percent in 1995. However, 

some experts we interviewed said the potential for additional future 

emissions reductions from increasing load factors may be small because 

they are already so high. Airlines also have removed many unnecessary 

items from aircraft and minimized supplies of certain necessary items, 

such as water, carried on board. As a result, according to some experts we 

interviewed, there may be little additional improvement in reducing 

emissions by reducing on-board weight. Airlines also have made other 

 

39However, National Aeronautics and Space Administration staff told us that no such 

investments will be necessary. 

Page 26 GAO-09-554 Aviation and Climate Change
 

voluntary operational changes to reduce emissions, such as reducing 

speeds on certain routes, which reduces fuel use, and washing aircraft 

engines to make them cleaner and more efficient. Airlines also have retired 

less-fuel-efficient aircraft and replaced them with more-fuel-efficient 

models. For example, in 2008, American Airlines announced it was 

replacing more of its fuel-inefficient MD-80 aircraft with more efficient 

Boeing 737-800 aircraft. In addition, Continental Airlines, in 2008, replaced 

regional jets with turboprop planes on many routes. Still other 

improvements also are available for airlines to reduce emissions in the 

future, but the experts we interviewed ranked the potential for emissions 

reductions and consumer acceptance of these improvements as low (see 

table 4). 

Table 4: Selected Operational Improvements to Reduce Emissions 

Improvement 

Potential 

reduction in 

carbon 

dioxide 

emissionsa

 

Potential 

research and 

development 

costsa

Estimated time 

frame for 

commercial 

useb

Potential for 

public 

acceptancea

Air-to-air refueling—

Air tankers fueling 

aircraft in flight 

Low High Long Low 

Engine washing—

To improve engine 

performance 

Low Low Short High 

Formation flying—

Multiple aircraft 

flying close together 

to reduce drag 

Low Medium-high Medium-long Low 

Multi-stage long 

distance flights—

Use of fueling stops 

on long-distance 

flights 

Low-medium Low Short Low 

Source: GAO survey of experts. 

Note: Between 9 and 12 survey respondents answered each of our questions about operational 

improvements to reduce emissions. 

a

We did not provide definitions for “low,” “medium,” or “high” in these cases. 

b

Short timeframe (<5 years); medium timeframe (5-15 years); long timeframe (>15 years). 

Airlines could make other operational changes to reduce fuel burn and 

emissions but are unlikely to do so, because the potential for consumer 

acceptance of such changes is low according to experts we surveyed. For 

example, aircraft could fly in formation to improve airflow and reduce fuel 

Page 27 GAO-09-554 Aviation and Climate Change
 

burn. More specifically, rather than flying individually, several aircraft 

could fly in proximity to one another, reducing drag of aircraft and 

subsequently fuel use. However, aircraft would fly closer to one another 

than FAA’s regulations currently allow and additional technological and 

aerodynamics research needs to be done. Another potential option, 

currently used for military purposes, is air-to-air refueling. Under this 

option, aircraft would be fueled in flight by tanker aircraft, reducing the 

amount and weight of fuel needed for the flight. However, DOT staff told 

us that air-to-air refueling may pose safety risks similar to those posed by 

formation flying. Some experts also have suggested that airlines make inroute on-ground fueling stops on long-haul flights, so they could reduce 

the amount of fuel they carry. However, more fueling stops could have 

negative effects on air quality at airports used for these stops as well as on 

air traffic operations. 

Air Traffic Management 

Improvements through 

NextGen Will Incorporate 

Technological and 

Operational Improvements 

to Help Reduce Aircraft 

Emissions According to 

Experts 

According to FAA, some of the air traffic management improvements that 

are part of NextGen—the planned air traffic management system designed 

to address the impacts of future traffic growth—can help reduce aircraft 

fuel consumption and emissions in the United States. Besides improving 

air traffic management, NextGen has environmental goals, which include 

accelerating the development of technologies that will lower emissions 

and noise. According to FAA, it is conducting a review to develop a set of 

NextGen goals, targets and metrics for climate change, as well as for noise 

and local air quality emissions. NextGen has the potential to reduce 

aircraft fuel burn by 2025, according to FAA, in part through technologies 

and procedures that reduce congestion and create more direct routing. 

Some procedures and technologies of NextGen have already been 

implemented and have already led to emissions reductions. Similarly, in 

Europe through the Single European Sky Air Traffic Management 

Research Program (SESAR), air traffic management technologies and 

procedures will be upgraded and individual national airspace systems will 

be merged into one, helping to reduce emissions per flight by 10 percent 

according to EUROCONTROL, the European Organization for the Safety 

of Air Navigation. However, some experts we met with said that because 

some of SESAR’s technologies and procedures have already been 

implemented, future fuel savings might be lower. Table 5 provides 

information on selected components of NextGen that hold potential for 

reducing aircraft emissions. 

Page 28 GAO-09-554 Aviation and Climate Change
 

Table 5: Selected Air Traffic Management Improvements to Reduce Emissions 

Improvement 

Potential 

reduction in 

carbon 

dioxide 

emissionsa 

Potential 

research and 

development 

costsa

Estimated 

time frame for 

commercial 

useb

Potential for 

public 

acceptancea

Required navigation 

performance—More 

precise routes 

Medium Medium Medium High 

Automatic 

Dependent 

SurveillanceBroadcast—

Satellite navigation 

system 

Medium Medium Short High 

Continuous 

Descent Arrival—

More fuel efficient 

landings 

Low-Medium Medium Short High 

NextGen NetworkEnabled Weather—

Advanced real-time 

weather data 

Medium Medium Medium High 

Source: GAO survey of experts, 

Note: 7 to 13 experts answered each of our survey questions about NextGen improvements 

a

We did not provide definitions for “low,” “medium,” or “high” in these cases. 

b

Short timeframe (<5 years); medium timeframe (5-15 years); long timeframe (>15 years) 

NextGen has the potential to reduce fuel consumption and emissions 

through technologies and operational procedures: 

• NextGen makes use of air traffic technologies to reduce emissions. For 

example, the Automatic Dependent Surveillance-Broadcast (ADS-B) 

satellite navigation system is designed to enable more precise control of 

aircraft during flight, approach, and descent, allowing for more direct 

routing and thus reducing fuel consumption and emissions. Also, Area 

Navigation (RNAV) will compute an aircraft’s position and ground speed 

and provide meaningful information on the flight route to pilots, enabling 

them to save fuel through improved navigational capability. NextGen 

Network-Enabled Weather will provide real-time weather data across the 

national airspace system, helping reduce weather-related delays and 

allowing aircraft to best use weather conditions to improve efficiency. 

• NextGen also relies on operational changes that have demonstrated the 

potential to reduce fuel consumption and emissions rates. Continuous 

Descent Arrivals (CDA) allow aircraft to remain at cruise altitudes longer 

Page 29 GAO-09-554 Aviation and Climate Change
 

as they approach destination airports, use lower power levels, and 

therefore produce lower emissions during landings. CDAs are already in 

place in a number of U.S. airports and according to FAA, the use of CDAs 

at Atlanta Hartsfield International Airport reduces carbon dioxide 

emissions by an average of about 1,300 pounds per flight. Required 

Navigation Performance (RNP) also permits an aircraft to descend on a 

more precise route, reducing its consumption of fuel and lowering its 

carbon dioxide emissions. According to FAA, over 500 RNAV and RNP 

procedures and routes have been implemented. Funding and other 

challenges, however, affect FAA’s implementation of these various 

NextGen procedures and technologies.40

Alternative Fuel Sources 

Have Potential for 

Reducing Aircraft 

Greenhouse Gas 

Emissions, but Challenges 

Exist 

The use of alternative fuels, including those derived from biological 

sources (biofuels), has the potential to reduce greenhouse gas emissions 

from aircraft in the future; however, these fuels also present a number of 

challenges and environmental concerns. While the production and use of 

biofuels result in greenhouse gas emissions, the extent to which they 

provide a reduction in greenhouse gas emissions depends on whether their 

emissions on an energy-content basis are less than those resulting from 

the production and use of fossil fuels.41 To date, some assessments of 

biofuels have shown a potential reduction in greenhouse gas emissions 

when compared with fossil fuels, such as jet fuel. However, researchers 

have not agreed on the best approach for determining the greenhouse gas 

effects of biofuels and the magnitude of any greenhouse gas reductions 

attributable to their production and use.42 FAA, EPA, and U.S. Air Force 

officials we met with said that quantifying the life-cycle emission of 

 

40For more information on challenges in NextGen implementation see GAO, Next 

Generation Air Transportation System: Issues Associated with Midterm Implementation 

of Capabilities and Full System Transformation, GAO-09-481T (Washington, D.C.: Mar. 

25, 2009). 

41Although plants converted into biofuels remove carbon dioxide from the air during 

growth, the biofuel production process is not emissions-free. For instance, nitrous oxide—

a powerful greenhouse gas—may be emitted when nitrogen-based fertilizers are applied to 

soils to increase yields of important biofuel feedstocks such as corn. In addition, fossil 

fuels are burned during the harvesting, transporting and refining of biofuel feedstock 

plants. Finally, researchers have raised concerns that increased biofuel production could 

result in additional greenhouse gas impacts due to the conversion of lands not previously 

used for biofuel crop production. 

42On May 26, 2009, EPA issued a Notice of Proposed Rulemaking regarding the renewable 

fuel standard, as required by the Energy Independence and Security Act of 2007 (EISA). 

When finalized, the proposed rule would implement EISA’s changes to the renewable fuel 

standard. 74 Fed. Reg. 24904 (May 26, 2009).

Page 30 GAO-09-554 Aviation and Climate Change
 

biofuels is difficult, but work in this area is currently under way.43 For 

example, according to EPA, the agency has developed a comprehensive 

methodology to determine the life-cycle emissions, including both direct 

and indirect emissions, of a range of biofuels. This methodology, which 

involved extensive coordination with experts outside of and across the 

federal government, was included in the recent notice of proposed 

rulemaking on the renewable fuel standard. Non-oil-energy sources, such 

as hydrogen, have potential for providing energy for ground transport, but 

many experts we met with said that such sources are unlikely to have use 

for commercial aircraft given technological, cost, and potential safety 

issues.44

According to experts we interviewed, a variety of sources could be used to 

produce biofuels for aircraft, including biomasses such as switchgrass and 

forest and municipal waste; and oils from jatropha (a drought-resistant 

plant that can grow in marginal soil), algae, camelina (a member of the 

mustard family that can grow in semiarid regions), palm, and soy. 

However, many experts claim that some of these crops are unsuitable for 

use as biofuels because they may have negative environmental and 

economic consequences, such as potentially reducing the supply and 

quality of water, reducing air quality and biodiversity, and limiting global 

food supplies. For example, cultivating palm for biofuel production might 

lead to deforestation, thereby increasing both greenhouse gas emissions 

and habitat loss. In addition, jatropha has been identified as an invasive 

species in some regions and, because of its aggressive growth, may have 

the potential to reduce available habitat for native species. According to 

experts we met with, algae, on the other hand, are seen as a potentially 

viable source: they can be grown using saltwater and in a variety of other 

environments. In addition, according to DOT, camelina appears to be a 

potential biofuel source in the short term as it is not currently used for 

food and uses limited water for development. 

 

43In addition, FAA and the U.S. Air Force, through the Partnership for AiR Transportation 

Noise and Emissions Reduction (PARTNER) program—an FAA-NASA-Transport Canadasponsored Center of Excellence, is sponsoring a project that aims to develop a tool that 

can estimate the life-cycle environmental impact from alternative jet fuels. The U.S. Air 

Force is leading an interagency working group including EPA, FAA, the Department of 

Energy and researchers to develop a document of life-cycle analysis best practices. 

44While in 2008 Boeing conducted a test flight of a small aircraft powered by hydrogen fuel 

cells, the manufacturer indicated it does not expect that large aircraft will be able to derive 

their primary energy from such sources. 

Page 31 GAO-09-554 Aviation and Climate Change
 

However, many experts we interviewed raised questions about the 

availability of future supplies of biofuels. According to the experts, large 

investments in fuel production facilities will likely be needed because little 

industrial capacity and compatible infrastructure currently exist to create 

biofuels.45 The cost of current algae conversion technology has, for 

example raised obstacles to the commercial-scale production needed to 

obtain significant supplies in the future. Given that future alternative fuels 

will have many uses, airlines will compete with other sources, including 

road transportation, for those limited supplies. Compared with the market 

for ground transport, the market for fuels for commercial aviation is small, 

leading some experts to believe that fuel companies are more likely to 

focus their biofuel efforts on the ground transport market than on the 

commercial aviation market. Some experts we met with said that given the 

relatively small size of the market, limited biofuel supplies should be 

devoted to road transportation since road transportation is the largest 

contributor of emissions from the transportation sector.46

A large number of industry and government participants, including 

airlines, fuel producers, and manufacturers, are currently conducting 

research and development on alternative fuels for aircraft. One effort is 

the Commercial Aviation Alternative Fuels Initiative, whose members 

include FAA, airlines, airports, and manufacturers. The goal of this 

initiative is to “promote the development of alternative fuels that offer 

equivalent levels of safety and compare favorably with petroleum-based jet 

fuel on cost and environmental bases, with the specific goal of enhancing 

security of energy supply.” Any developed biofuel will be subject to the 

same certification as petroleum-based jet fuel to help ensure its safety. In 

addition, other government efforts are under way, most notably the 

Biomass Research and Development Initiative. This initiative is a 

multiagency effort to coordinate and accelerate all federal biobased 

products and bioenergy research and development. The Department of 

Transportation is one of the initiative’s participants. 

 

45For a discussion of biofuel production see GAO, Biofuels: DOE Lacks a Strategic 

Approach to Coordinate Increasing Production with Infrastructure Development and 

Vehicle Needs GAO-07-713 (Washington, D.C.: June 8, 2007). 

46However, according to DOT, it could also be argued that because aircraft do not face the 

potential for non-liquid fuel sources of energy—for example, electricity—and because 

there is a proportionally higher premium for refining jet fuel, aviation may be a more 

certain consumer of biofuel supplies. 

Page 32 GAO-09-554 Aviation and Climate Change
 

Finally, the aviation industry has conducted a number of test flights using 

a mixture of biofuels and jet fuel. These test flights have demonstrated 

that fuel blends containing biofuels have potential for use in commercial 

aircraft. In February 2008, Virgin Atlantic Airlines conducted a 

demonstration flight of a Boeing 747 fueled by a blend of jet fuel (80 

percent) and coconut- and babassu-oil-based fuels (20 percent). In 

December 2008, Air New Zealand conducted a test flight of a Boeing 747 

fueled by a blend consisting of an equal mixture of jet fuel and jatropha oil. 

In January 2009, Continental Airlines conducted a test flight using a fuel 

blend of 50 percent jet fuel, and a jatropha and algae biofuel blend on a 

Boeing 737.47 In January 2009, Japan Airlines conducted a test flight of a 

Boeing 747 fueled by a blend including camelina oil. According to the 

airlines, the results of all these tests indicate that there was no change in 

performance when engines were fueled using the biofuel blends. For 

example, the pilot of the Air New Zealand test flight noted that both onground and in-flight tests indicated that the aircraft engines performed 

well while using the biofuel. 

Improvements to Reduce 

Emissions from Aircraft 

Face Challenges and 

According to Experts 

Adopting Them May Not 

Be Enough to Offset 

Future Market and 

Emissions Growth 

Future fuel prices are likely to be a major factor in influencing the 

development of low-emissions technologies for commercial aviation. 

According to the airline industry, fuel costs provide an incentive for 

airlines to reduce fuel consumption and emissions. However, according to 

some experts we interviewed, short-term increases in fuel prices may not 

provide enough of an incentive for the industry to adopt certain lowemission improvements. For example, the commercial airlines would have 

greater incentive to adopt fuel saving technologies if the projected fuel 

savings are greater than the improvement’s additional life-cycle cost. The 

higher existing and projected fuel prices are, the more likely airlines 

would undertake such improvements, all else the same. One expert said 

that if fuel costs were expected to consistently exceed $140 per barrel in 

the future, much more effort would be made to develop a finished open 

rotor engine quickly. The price of fuel as a factor in providing an incentive 

for the development and adoption of low-emission technologies is seen in 

some historical examples in NASA research. While winglets were first 

developed through a NASA research program in the 1970s, they were not 

used commercially until a few years ago when higher fuel prices justified 

their price. Additionally, although NASA currently is sponsoring research 

into open rotor engines, the agency also did so in the 1980s in response to 

 

47Algae-based biofuel composed only 2.5 percent of the fuel blend. 

Page 33 GAO-09-554 Aviation and Climate Change
 

high fuel prices. That research was discontinued before the technology 

could be matured, however, when fuel prices dropped dramatically in the 

late 1980s. 

In addition, the current economic recession has impacted commercial 

airlines and may cause some airlines to cut back on purchases of newer 

and more fuel-efficient aircraft. For example, the U.S. airline industry lost 

about $3.7 billion in 2008, and while analysts are uncertain about its 

profitability 2009, some analysts predict industry profits of around $4 

billion to $10 billion. In addition, Boeing has reported a number of recent 

cancellations of orders for the fuel-efficient 787 Dreamliner. According to 

one expert we met with, when airlines are low on cash, they are unlikely 

to undertake improvements that will reduce their fuel consumption and 

emissions, even if the savings from fuel reductions will ultimately be 

greater than the cost of the improvement because they have so little cash. 

This expert said, for example, that although it may make financial sense 

for airlines to engage in additional nonsafety-related engine maintenance 

to reduce fuel burn and emissions, they may not do so because they lack 

sufficient cash. 

Although some airlines may adopt technologies to reduce their future 

emissions, these efforts may not be enough to mitigate the expected 

growth in air traffic and related increase in overall emissions through 

2050. Although IPCC’s forecast, as mentioned earlier, assumes future 

technological improvements leading to annual improvements in fuel 

efficiency, it excludes or doesn’t account for the possibility that some 

airlines might adopt biofuels or other potential breakthrough technologies. 

Nonetheless, even if airlines adopt such technologies, some experts 

believe that emissions will still be higher in 2050 under certain conditions 

than they were in 2000. One expert we met with did a rough estimate of 

future emissions from aircraft assuming the adoption of many low-carbon 

technologies such as blended wing-body, operational improvements, and 

biofuels. He used IPCC’s midrange forecast of emissions to 2050 as a 

baseline for future traffic and found that even assuming the introduction 

of these technologies, global emissions in 2050 would continue to exceed 

Page 34 GAO-09-554 Aviation and Climate Change
 

2000 emissions levels.48 Had a lower baseline of emissions been used, 

forecasted emissions may have been lower. He acknowledged that more 

work needs to be done in this area. Another study by a German research 

organization modeled future emissions assuming the adoption of 

technological improvements, as well as biofuels, to reduce emissions. This 

study assumed future traffic growth averaging 4.8 percent between 2006 

and 2026 and 2.6 percent between 2027 and 2050.49 While this study 

forecasted improvements in emissions relative to expected market growth, 

it estimated that by 2050 total emissions would still remain greater than 

2000 emissions levels. 

Governments have a number of policy options—including policies that set 

a price on emissions, market-based measures like a cap-and-trade program 

or a tax, regulatory standards, and funding for research and 

development—they could use to help reduce greenhouse gas emissions 

from commercial aviation and other sectors of the economy. The social 

benefits (for example, resulting from emissions reductions) and costs 

associated with each option vary, and the policies may affect industries 

and consumers differently. However, economic research indicates that 

market-based policies are more likely to better balance the benefits and 

costs of achieving reductions in greenhouse gases and other emissions (or, 

in other words, to be more economically efficient). In addition, research 

and development spending could complement market-based measures or 

standards to help facilitate the development and deployment of lowemissions technologies. However, given the relatively small current and 

forecasted percentage of global emissions generated by the aviation 

sector, actions taken to reduce aviation emissions alone, and not 

Governments Can Use 

a Variety of Policy 

Options to Help 

Reduce Commercial 

Aircraft Emissions, 

but the Costs and 

Benefits of Each Vary 

 

48This analysis assumed that biofuels are first available in 2015 and their usage increases at 

a rate of 2 percent per year, and through life-cycle carbon emissions, biofuels emit 20 

percent the carbon dioxide as jet fuel. For blended-wing body aircraft, the analysis 

assumed an 18 percent fuel burn reduction and introduction of the aircraft into global 

fleets in 2025 with a 30-year time frame to achieve a penetration of 33 percent of global 

aircraft fleets. The analysis also assumed the adoption of other improvements, including 

the use of lightweight materials, open rotor engines, formation flying, and multistage longdistance travel. We did not review the reliability of this analysis. 

49A lower assumed traffic growth rate would have reduced the study’s forecast of 

emissions. With respect to biofuels, this study assumed that biofuels would be used 

between 2010 and 2050 (at which time they would represent 25 percent of aviation fuels) 

and would produce 10 percent of the carbon dioxide emissions of fossil fuels. We did not 

review the reliability of this analysis. 

Page 35 GAO-09-554 Aviation and Climate Change
 

emissions from other sectors, could be costly and have little potential 

impact on reducing global greenhouse gas emissions.50

Market-Based Policies 

Could Be Used to Provide 

Airlines and Other Sources 

with an Economic 

Incentive to Reduce 

Greenhouse Gas 

Emissions 

Economists and other experts we interviewed stated that establishing a 

price on greenhouse gas emissions through market-based policies, such as 

a cap-and-trade program or a tax on emissions from commercial aircraft 

and other sources, would provide these sources with an economic 

incentive to reduce their emissions. Generally, a cap-and-trade program or 

an emissions tax (for example, on carbon dioxide) can achieve emissions 

reductions at less cost than other policies because they would give firms 

and consumers the flexibility to decide when and how to reduce their 

emissions. Many experts we surveyed said that establishing a price on 

emissions through a cap-and-trade program or a tax would help promote 

the development and adoption of a number of low-emissions technologies 

for airlines, including open rotor engines and blended wing-body aircraft. 

Another market-based policy, subsidy programs, such as a payment per 

unit of emissions reduction, can in principle provide incentives for firms 

and consumers to reduce their greenhouse gas emissions. However, 

subsidy programs need to be financed—for example through existing 

taxes or by raising taxes—and can create perverse incentives resulting in 

higher emissions. 

One market-based option for controlling emissions is a cap-and-trade 

program. Also known as an emissions trading program, a cap-and-trade 

program would limit the total amount of emissions from regulated 

sources. These sources would receive, from the government, allowances 

to emit up to a specific limit—the “cap.” The government could sell the 

allowances through an auction or provide them free of charge (or some 

combination of the two). In addition, the government would establish a 

market under which the regulated sources could buy and sell allowances 

with one another. Sources that can reduce emissions at the lowest cost 

could sell their allowances to other sources with higher emissions 

reduction costs. In this way, the market would establish an allowance 

price, which would represent the price of carbon dioxide (or other 

greenhouse gas) emissions. Generally, according to economists, by 

Cap-and-Trade Program 

 

50For a comprehensive discussion of the economics of policy options to address climate 

change as well as discussion of a combination of such options, see GAO, Climate Change: 

Expert Opinion on the Economics of Policy Options to Address Climate Change, 

GAO-08-605 (Washington, D.C.: May 9, 2008). 

Page 36 GAO-09-554 Aviation and Climate Change
 

allowing sources to trade allowances, policy makers can achieve 

emissions reductions at the lowest cost. 

A cap-and-trade program can be designed to cap emissions at different 

points in the economy. For example, a cap-and-trade program could be 

designed to cap “upstream” sources like fuel processors, extractors, and 

importers. Under this approach, a cap would be set on the emissions 

potential that is inherent in the fossil fuel. The upstream cap would 

restrain the supply and increase the prices of fossil fuels and thus the price 

of jet fuel relative to less carbon-intensive alternatives. Alternatively, 

under a “downstream” program, direct emitters, such as commercial 

airlines, would be required to hold allowances equal to their total carbon 

emissions each year. (See fig. 9.) However, economic research indicates 

that both types of programs would provide commercial airlines with an 

incentive to reduce their fuel consumption in the most cost-effective way 

for each airline, such as by reducing weight, consolidating flights, or using 

more fuel-efficient aircraft, if they were included in such a program. To the 

extent that airlines would pass along any program costs to customers 

through higher passenger fares and shipping rates, travelers and shippers 

could respond in various ways, including by traveling less frequently or 

using a different, cheaper transportation mode.51

 

51However, to the extent that a cap-and-trade program regulates other transportation 

sectors as well, costs of using alternative transportation modes are likely to be higher as 

well. 

Page 37 GAO-09-554 Aviation and Climate Change
 

Figure 9: A Potential Cap-and-Trade Program Regulating Airlines and Other Emissions Sources 

Free allowances

Auctioned allowances

Free allowances

Government

Source: GAO.

Auctioned allowances

$$ $ Free

allowances

Free

allowances

Auctioned

allowances

Auctioned

allowances

Allowances

$

Airline A Airline B Factory

Allowances

$

Airline A 

exceeds

their 

emissions

allowances and purchases

allowances from other 

airlines and industries

Airline B 

makes

low-cost 

emissions

reductions and sells its

excess allowances to 

airline A

This

factory 

makes

low-cost 

emissions reductions

and sells its excess

allowances to airline A

The effectiveness of a cap-and-trade program in balancing the benefits and 

costs of the emission reductions could depend on factors included in its 

design. Generally, by establishing an upper limit on total emissions from 

regulated sources, a cap-and-trade program can provide greater certainty 

than other policies (for example, an emissions tax) that emissions will be 

reduced to the desired level. Regulated sources would be required to hold 

allowances equal to their total emissions, regardless of the cost. However, 

allowance prices could be volatile, depending on factors such as changes 

Page 38 GAO-09-554 Aviation and Climate Change
 

in energy prices, available technologies, and weather,52 making it more 

expensive for sources to meet the cap. To limit price volatility, a costcontainment mechanism called a “safety valve” could be incorporated into 

the cap-and-trade program to establish a ceiling on the price of 

allowances. For example, if allowance prices rose to the safety-valve price, 

the government could sell regulated sources as many allowances as they 

would like to buy at the safety-valve price.53 Although the safety valve 

could limit price spikes, the emissions cap would be exceeded if the safety 

valve were triggered. 

In addition, the baseline that is used to project future emissions and set 

the emissions cap can affect the extent to which a cap-and-trade program 

will contain or reduce emissions.54 The point in time on which a baseline is 

set also can influence the environmental benefits of a cap-and-trade 

program. For example, some environmental interest groups in Europe 

have claimed that the environmental benefits of including aviation in the 

EU ETS will be minimal, since the emissions cap will be based on the 

mean average of aviation emissions from 2004 through 2006, leading to 

minimal future emissions reductions.55

In addition, industry groups and other experts have raised concerns that a 

cap-and-trade program could be administratively burdensome to the 

government, which would need to determine how to allocate the 

allowances to sources, oversee allowance trading, and monitor and 

enforce compliance with the program. Generally speaking, an upstream 

 

52For example, the demand for energy may increase during unexpectedly hot or cold 

periods, leading to price spikes and making it more expensive for sources to meet the cap. 

53The safety valve would help prevent the price of allowances from exceeding the expected 

benefits of the emissions reductions. Under a cap-and-trade program, the emissions cap 

could be set at a level that balances the expected marginal cost of meeting the cap with an 

estimate of the marginal benefits. The safety valve price could be set just above the 

expected marginal costs to avoid the possibility that the cap is overly stringent. 

54We have reported on the importance of setting an emissions baseline. For example, 

setting a baseline with poor historical data could lead to the creation of a baseline that is 

above actual emissions, leading to no emission reductions. See GAO, Climate Change 

Science: High Quality Greenhouse Gas Emissions Data Are a Cornerstone of Programs 

to Address Climate Change, GAO-09-423T (Washington, D.C.: Feb. 24, 2009). 

55However, some interest groups have expressed concern that an emissions cap does not 

take into account emissions reductions that airlines have achieved in recent years and 

claim that it unfairly penalizes those airlines that have reduced emissions. 

Page 39 GAO-09-554 Aviation and Climate Change
 

program may have lower administrative costs than a downstream program 

because it would likely involve fewer emissions sources. 

Some members of the aviation industry have said they view open and 

global cap-and-trade programs positively, although they report that not all 

types of cap-and-trade programs will work for them. For instance, ICAO 

and other industry organizations have said they would prefer an open capand-trade program (in which airlines are allowed to trade allowances with 

other sectors and sources) to a closed one (in which airlines are allowed 

to trade emissions allowances only with one another) because an open 

program would give airlines more flexibility in meeting their emissions 

cap. Staff we met with at the Association of European Airlines expressed 

willingness for aviation to participate in a cap-and-trade program as long 

as it is global in scope, is an open system, is not in addition to similar 

taxes, and does not double-count emissions.56 In addition, some industry 

groups and government agencies we met with said that a global program 

would best ensure that all airlines would take part in reducing emissions. 

Cap-and-Trade Plans and Legislation 

Some countries are planning to address aviation emissions through capand-trade programs. The European Union originally implemented the EU 

ETS in 2005, covering industries representing about 50 percent of its 

carbon dioxide emissions.57 The EU is planning on including all covered 

flights by aircraft operators flying into or out of EU airports, starting in 

2012.58 Please see appendix I for more details on the EU ETS, including a 

comprehensive discussion of the potential legal implications and 

 

56For example, Association of European Airlines expressed a concern that because some 

countries in Europe have taxes on aircraft carbon dioxide emissions, airlines may be 

subject to those taxes as well as the ETS, meaning that their emissions would be counted 

twice by two different regulations. 

57We have reported on lessons learned from the EU ETS. See GAO, International Climate 

Change Programs: Lessons Learned from the European Union’s Emissions Trading 

Scheme and the Kyoto Protocol’s Clean Development Mechanism, GAO-09-151

(Washington, D.C.: Nov. 18, 2008). 

58With respect to aircraft, the ETS currently regulates only carbon dioxide emissions. 

However, according to the European Commission, it has agreed to address nitrogen oxide 

emissions from aircraft through a separate legislative measure. As of May 2009, no EU 

legislative proposal has specifically addressed nitrogen oxide emissions from aircraft. 

Page 40 GAO-09-554 Aviation and Climate Change
 

stakeholders’ positions on this new framework. Other countries are 

considering cap-and-trade programs that would affect the aviation sector.59

In addition, the United States is currently considering and has previously 

considered cap-and-trade programs: 

• H.R. 2454, the American Clean Energy and Security Act of 2009, 111th 

Cong. (2009), would create a cap-and-trade program for greenhouse gas 

emissions for entities responsible for 85 percent of emissions in the United 

States. The current language proposes to regulate producers and 

importers of any petroleum-based liquid fuel, including aircraft fuel, as 

well as other entities, and calls for an emissions cap in 2050 that would be 

83 percent lower than 2005 emissions. The bill also calls for the emissions 

cap in 2012 to be 3 percent below 2005 levels, and in 2020 to be 20 percent 

below 2005 levels. In addition, the Obama Administration’s fiscal year 2010 

budget calls for the implementation of a cap-and-trade program to regulate 

emissions in the United States. The budget calls for emissions reductions 

so that emissions in 2020 are 14 percent below 2005 levels and emissions 

in 2050 are 83 percent below 2005 levels. 

• Additionally in this Congress, the Cap and Dividend Act,60 also proposes a 

cap-and-trade program for carbon dioxide emissions beginning in 2012, 

which would include jet fuel emissions. This program’s covered entities 

would include entities that would make the first sale in U.S. markets of oil 

or a derivative product used as a combustible fuel, including jet fuel. The 

bill would require the Secretary of the Treasury, in consultation with the 

EPA Administrator, to establish the program’s emission caps in 

accordance with the following targets: the 2012 cap would equal 2005 

emissions; the 2020 cap would equal 75 percent of 2005 emissions; the 

2030 cap would equal 55 percent of 2005 emissions; the 2040 cap would 

equal 35 percent of 2005 emissions; and the 2050 cap would equal 15 

percent of 2005 emissions. 

• A number of bills creating a cap-and-trade program also were introduced 

in the 110th Congress but did not pass. For example, a bill sponsored by 

Senators Boxer, Warner, and Lieberman would have established a cap-andtrade program that covered petroleum refiners and importers, among 

other entities.61 The costs of the regulation would have been borne by 

 

59For example, Japan is considering creating a voluntary cap-and-trade program and Japan 

Airlines already has indicated that it will participate in the scheme, but only based on its 

domestic flights. 

60H.R. 1862, 111th Cong. (2009). 

61S. 3036, 110th Cong. (2008). 

Page 41 GAO-09-554 Aviation and Climate Change
 

these refiners and importers who would likely have passed on those costs 

to airlines through increases in the price of jet fuel. 

An emissions tax is another market-based policy that could be used to 

reduce emissions from commercial aviation and other emissions sources. 

Under a tax on carbon dioxide (or other greenhouse gas), the government 

would levy a fee for every ton of carbon dioxide emitted. Similar to a capand-trade program, a tax would provide a price signal to commercial 

airlines and other emission sources, creating an economic incentive for 

them to reduce their emissions. A carbon tax could be applied to 

“upstream” sources such as fuel producers, which may in turn pass along 

the tax in the form of higher prices to fuel purchasers, including 

commercial airlines. Similar to a cap-and-trade program, emissions taxes 

would provide regulated sources including commercial airlines with an 

incentive to reduce emissions in the most cost-effective way, which might 

include reducing weight, consolidating flights, or using more fuel-efficient 

aircraft. 

Emissions Taxes 

According to economic theory, an emissions tax should be set at a level 

that represents the social cost of the emissions.62 Nonetheless, estimates 

of the social costs associated with greenhouse gas emissions vary. Fo

example, IPCC reported that the social costs of damages associated with 

greenhouse gas emissions average about $12 per metric ton

r 

 

63 of carbon 

dioxide (in 2005 dollars) with a range of $3 to $95 per ton (in 2005 dollars). 

Economic research indicates that an emissions tax is generally a more 

economically efficient policy tool to address greenhouse gas emissions 

than other policies, including a cap-and-trade program, because it would 

better balance the social benefits and costs associated with the emissions 

reductions. In addition, compared to a cap-and-trade program, an 

emissions tax would provide greater certainty as to the price of emissions. 

However, it would in concept provide less certainty about emissions 

62For example, the social cost of carbon reflects the present value of economic damages 

caused by an additional quantity of emissions. Under an economically optimal policy, the 

price would be set at a point where the marginal damages from global warming equal the 

marginal cost of controlling emissions. 

63A metric ton equals 2,205 pounds. 

Page 42 GAO-09-554 Aviation and Climate Change
 

reductions because the reductions would depend on the level of the tax 

and how firms and consumers respond to the tax.64

Subsidies are another market-based instrument that could, in principle, 

provide incentives for sources to reduce their emissions. For example, 

experts we met with said that the government could use subsidies to 

encourage industry and others to adopt existing low-emissions 

technologies and improvements, such as winglets. In addition, some 

experts told us that NextGen-related technologies are candidates for 

subsidies because of the high costs of the technologies and the benefits 

that they will provide to the national airspace system. According to IPCC, 

subsidies can encourage the diffusion of new low-emissions technologies 

and can effectively reduce emissions. For example, as newer, more fuelefficient engines are developed and become commercially available, 

subsidies or tax credits could lower their relative costs and encourage 

airlines to purchase them. 

Subsidies 

Although subsidies are similar to taxes, economic research indicates that 

some subsidy programs can be economically inefficient, and need to be 

financed (for example, using current tax revenue or by raising taxes). For 

example, although some subsidy programs could lead to emissions 

reductions from individual sources, they may also result in an overall 

increase by encouraging some firms to remain in business longer than they 

would have under other policies such as an emissions tax. 

Both a cap-and-trade program and an emissions tax would impose costs 

on the aviation sector and other users of carbon-based fuels. The extent to 

which the costs associated with an emissions control program are 

incurred by commercial airlines and passed on will depend on a number of 

economic factors, such as the level of market competition and the 

responsiveness of passengers to changes in price. Officials of some 

industry organizations we met with said that because airlines are in a 

competitive industry with a high elasticity of demand,65 they are 

constrained in passing on their costs, and the costs to industry likely will 

Distribution of Costs under 

Market-based Measures 

 

64The extent to which a cap-and-trade program would provide greater certainty about 

emissions reductions depends on the design of the particular program. For example, some 

programs may include cost containment measures that allow total emissions to exceed the 

cap under certain conditions. 

65Price elasticity of demand is a measure of the responsiveness in quantity demanded as a 

result of a change in price. Goods and services with a high elasticity of demand will see 

larger changes in the quantity demanded than the change in price. 

Page 43 GAO-09-554 Aviation and Climate Change
 

be large. The Association of European Airlines reported that airlines will 

have very limited ability to pass on the costs of the EU ETS. Furthermore, 

the International Air Transport Association has estimated that the costs to 

the industry of complying with the EU ETS will be €3.5 billion in 2012,66

with annual costs subsequently increasing.67 Others we interviewed, 

however, stated that airlines will be able to pass on costs, and the 

increases in ticket prices will not be large. For example, the EU estimates 

that airlines will be able to pass on most of the costs of their compliance 

with the EU ETS, which will result in an average ticket price increase of €9 

on a medium-haul flight.68 However, the revenue generated by the tax or by 

auctioning allowances could be used to lessen the overall impact on the 

economy, or the impact on certain groups (for example, low income) or 

sectors of the economy by, for example, reducing other taxes.69

Finally, according to some airline industry representatives, a program to 

control greenhouse gas emissions would add to the financial burden the 

aviation industry and its consumers already face with respect to other 

taxes and fees. For example, passenger tickets in the United States are 

subject to a federal passenger ticket tax of 7.5 percent, a segment charge 

of $3.40 per flight segment, and fees for security and airport facilities (up 

to $4.50 per airport). In addition, international flights are subject to 

departure taxes and customs-related fees. However, none of these taxes 

and fees attempt to account for the cost of greenhouse gas emissions, as a 

tax or cap-and-trade program would do. In addition, the revenue generated 

from an emissions tax or by auctioning allowances under a cap-and-trade 

program, could be used to offset other taxes, thereby lessening the 

economic impact of the program. 

 

66Equivalent to about $4.5 billion based on exchange rates on Apr. 20, 2009. 

67According to industry interests groups we met with, to the extent that airlines incur the 

costs of a tax or for cap-and-trade allowances, their resources for upgrading their fleets 

with more fuel-efficient aircraft and for implementing other emissions-reduction measures 

will be more limited. 

68Equivalent to about $11.60 based on exchange rates on April 20, 2009. 

69Some organizations we met believe that revenues collected through the auctions of 

allowances should be used for climate change mitigation and adaptation as well as to help 

fund low-emissions technologies. 

Page 44 GAO-09-554 Aviation and Climate Change
 

Mandating the use of certain technologies or placing emissions limits on 

aircraft and aircraft engines are also potential options for governments to 

address aircraft emissions. Standards include both technology standards, 

which mandate a specific control technology such as a particular fuelefficient engine, and performance standards, which may require polluters 

to meet an emissions standard using any available method. The flexibility 

in the performance standards reduces the cost of compliance compared 

with technology-based standards and, according to DOT, avoids potential 

aviation safety implications that may occur from forcing a specific 

technology across a wide range of operations and conditions. 

Emissions Standards 

Could Limit Emissions 

from Specific 

Technologies, but Are 

Generally Not an 

Economically Efficient 

Approach for Reducing 

Greenhouse Gas 

Emissions 

For example, by placing a strict limit on aircraft emissions, a standard 

would limit the emissions levels from an engine or aircraft. Regulations on 

specific emissions have been used to achieve specific environmental goals. 

ICAO’s nitrogen oxide standards place limits on nitrogen oxide emissions 

from newly certified aircraft engines. These standards were first adopted 

in 1981 and became effective in 1986. Although no government has yet 

promulgated standards on aircraft carbon dioxide emissions or fuel 

economy, emissions standards are being discussed within ICAO’s 

Committee on Aviation Environmental Protection and, in December 2007, 

a number of environmental interest groups filed petitions with EPA asking 

the agency to promulgate regulations for greenhouse gas emissions from 

aircraft and aircraft engines. In addition, the American Clean Energy and 

Security Act of 2009 would require EPA to issue standards for greenhouse 

gas emissions from new aircraft and new engines used in aircraft by 

December 31, 2012.70

Although standards can be used to limit greenhouse gas emissions levels 

from aircraft, economic research indicates that they generally are not as 

economically efficient as market-based instruments because they do not 

effectively balance the benefits and costs associated with the emissions 

reductions.71 For example, unlike market-based instruments, technology 

standards would give engine manufacturers little choice about how to 

reduce emissions and may not encourage them to find cost effective ways 

 

70H.R. 2454, § 221(b), 111th Cong. (2009). 

71Emissions standards typically do not equalize marginal costs across sources, a basic 

condition for efficiency. In the case of greenhouse gas emissions, emissions are uniformly 

mixed and abatement costs vary widely across sources. These characteristics favor marketbased instruments, which can achieve significant cost savings by encouraging low-cost 

sources to make the bulk of the emissions reductions. 

Page 45 GAO-09-554 Aviation and Climate Change
 

of controlling emissions.72 In addition, according to IPCC, because 

technology standards may require emissions to be reduced in specified 

ways, they may not provide the flexibility to encourage industry to search 

for other options for reducing emissions. However, according to EPA, 

performance standards to address certain emissions from airlines, such as 

those adopted by ICAO and EPA, gave manufacturers flexibility in 

deciding which technologies to use to reduce emissions.73 Nonetheless, 

although performance standards can provide greater flexibility and 

therefore be more cost-effective than technology standards, economic 

research indicates that standards generally provide sources with fewer 

incentives to reduce emissions beyond what is required for compliance, 

compared to market-based approaches. Moreover, standards typically 

apply to new, rather than existing, engines or aircraft, making new engines 

or aircraft more expensive, and as a result, the higher costs may delay 

purchases of more fuel-efficient aircraft and engines. 

Current international aviation standards also may require international 

cooperation. Because ICAO sets standards for all international aviation 

issues, it may be difficult for the U.S. government, or any national 

government, to set a standard that is not adopted by ICAO, although 

member states are allowed to do so. Industry groups we met with said that 

any standards should be set through ICAO and then adopted by the United 

States and other nations and, as mentioned earlier, some environmental 

groups have petitioned EPA to set such standards. 

 

72According to FAA and EPA, existing aircraft engine standards do not mandate specific 

technologies and are developed on the basis of technological practicability. 

73According to EPA, well designed standards could give aircraft engine manufacturers the 

flexibility to make cost-effective reductions. In addition, according to an official in EPA’s 

Office of Air and Radiation, with the projected increase in jet fuel consumption and related 

emissions, addressing greenhouse gas emissions will require consideration of technology 

measures and market-based measures. However, under a market-based program such as 

cap-and-trade, emissions caps set the total emissions level and sources would need to 

determine how to accommodate business growth while complying with the cap. Such an 

approach gives sources an incentive to innovate and search for low-cost ways to reduce 

emissions. 

Page 46 GAO-09-554 Aviation and Climate Change
 

Government-sponsored research into low-fuel consumption and lowemissions technologies can help foster the development of such 

technologies, particularly in combination with a tax or a cap-and-trade 

program. Experts we surveyed said that increased government research 

and development could be used to encourage a number of low-emissions 

technologies, including open rotor engines and blended wing-body 

aircraft. According to the Final Report of the Commission on the Future 

of the United States Aerospace Industry, issued in 2002, the lack of longterm investments in aerospace research is inhibiting innovation in the 

industry and economic growth. This study also asserted that national 

research and development on aircraft emissions is small when compared 

with the magnitude of the problem and the potential payoffs that research 

drives. Experts we met with said that government sponsorship is crucial, 

especially for long-term fundamental research, because private companies 

may not have a sufficiently long-term perspective to engage in research 

that will result in products for multiple decades into the future. According 

to one expert we interviewed, the return on investment is too far off into 

the future to make it worthwhile for private companies. NASA officials 

said that private industry generally focuses only on what NASA deems the 

“next generation conventional tube and wing technologies,” which are 

usually projected no more than 20 years into the future. Furthermore, 

raising fuel prices or placing a price on emissions through a tax or capand-trade program is likely to encourage greater research by both the 

public and private sectors into low-emissions technologies because it 

increases the pay off associated with developing such technologies. 

Government-Sponsored 

Research and 

Development Can Help 

Encourage the 

Development and 

Adoption of LowEmissions Technologies, 

but May Be Costly to 

Governments 

Various U.S. federal agencies, including NASA and FAA, have long been 

involved in research involving low-emissions technologies.74 For example, 

NASA’s subsonic fixed-wing research program is devoted to the 

development of technologies that increase aircraft performance, as well as 

reduce both noise levels and fuel burn. Through this program, NASA is 

researching a number of different technologies to achieve those goals, 

including propulsion, lightweight materials, and drag reduction. The 

subsonic fixed-wing program is looking to develop three generations of 

aircraft with increasing degrees in technology development and fuel burn 

improvements—the next-generation conventional tube and wing aircraft, 

the unconventional hybrid wing-body aircraft, and advanced aircraft 

 

74In addition, the U.S. Air Force conducts research that has potential for applicability for 

commercial aviation. For example, through the ADVENT program, the Air Force is 

researching fuel-efficient engine technologies. 

Page 47 GAO-09-554 Aviation and Climate Change
 

concepts.75 NASA follows goals set by the National Plan for Aeronautics 

Research and Development and Related Infrastructure for fuel efficiency 

improvements76 for each of these generations (see table 6).77

Table 6: NASA’s Subsonic Fixed-Wing Research Fuel-Reduction Goals 

Research generation 

Next generation 

tube and wing 

Unconventional 

hybrid wing-body 

Advanced aircraft 

concepts 

Aircraft fuel burn 

reduction goal 

33 percent fuel 

reduction (relative to 

Boeing 737) 

40 percent fuel 

reduction (relative to 

Boeing 777) 

Better than 70 

percent fuel 

reduction 

Time frame 2015 2020 2030-2035 

Source: NASA. 

However, budget issues may affect NASA’s research schedule. As we have 

reported, NASA’s budget for aeronautics research was cut by about half in 

the decade leading up to fiscal year 2007, when the budget was $717 

million.78 Furthermore, NASA’s proposed fiscal year 2010 budget calls for 

significant cuts in aeronautics research, with a budget of $569 million. As 

NASA’s aeronautics budget has declined, it has focused more on 

fundamental research and less on demonstration work. However, as we 

have reported, NASA and other officials and experts agree that federal 

research and development efforts are an effective means of achieving 

emissions reductions in the longer term.79 According to NASA officials, the 

research budget for its subsonic fixed-wing research program, much of 

which is devoted to technologies to reduce emissions and improve fuel 

efficiency, will be about $69 million in 2009. 

 

75NASA refers to the three generations of technologies as N+1, N+2, and N+3. 

76The plan also sets goals for future noise levels and nitrogen oxide emissions. 

77National Science and Technology Council, National Plan for Aeronautics Research and 

Development and Related Infrastructure (Washington, D.C., Jan. 18, 2008). 

78GAO, Aviation and the Environment: FAA’s and NASA’s Research and Development 

Plans for Noise Reduction Are Aligned, but the Prospects of Achieving Noise Reduction 

Goals Are Uncertain, GAO-08-384 (Washington, D.C., Feb. 15, 2008). 

79GAO, Aviation and the Environment: NextGen and Research and Development Are Keys 

to Reducing Emissions and Their Impact on Health and Climate, GAO-08-706T

(Washington, D.C., May 6, 2008). 

Page 48 GAO-09-554 Aviation and Climate Change
 

FAA has proposed creating a new research consortium to focus on 

emissions and other issues. Specifically, FAA has proposed the 

Consortium for Lower Energy, Emissions, and Noise, which would fund, 

on a 50-50 cost share basis with private partners, research and advanced 

development into low-emissions and low-noise technologies, including 

alternative fuels, over 5 years. FAA plans that the consortium will mature 

technologies to levels that facilitate uptake by the aviation industry. The 

consortium contributes to the goal set by the National Plan for 

Aeronautics, Research and Development and Related Infrastructure to 

reduce fuel burn by 33 percent compared with current technologies. The 

House FAA Reauthorization Bill (H.R. 915, 111th Cong. (2009)) would 

provide up to $108 million in funding for the consortium for fiscal years 

2010 through 2012. 

Lastly, the EU has two major efforts dedicated to reducing aviation 

emissions. The Advisory Council for Aeronautics Research in Europe 

(ACARE) is a collaborative group of governments and manufacturers 

committed to conducting strategic aeronautics research in Europe. 

According to officials with the European Commission Directorate General 

of Research, about €150 million to €200 million per year80 is devoted to 

basic research through ACARE. Another research effort in Europe is the 

Clean Sky Joint Technology Initiative, which will provide €1.6 billion81 over 

7 years to fund various demonstration technologies. 

We provided a draft copy of this report to the Department of Defense, the 

Department of State, the Department of Transportation, the National 

Aeronautics and Space Administration, and the Environmental Protection 

Agency for their review. 

Agency Comments 

and Our Evaluation 

The Department of Defense had no comments. The Department of State 

provided comments via email. These comments were technical in nature 

and we incorporated them as appropriate. 

The Department of Transportation provided comments via email. Most of 

these comments were technical in nature and we incorporated them as 

appropriate. In addition, DOT stated that our statements indicating that 

the use of future technological and operational improvements may not be 

 

80About $200 million to $267 million per year based on exchange rates on Apr. 29, 2009. 

81Equivalent to approximately $2.1 billion based on exchange rates on Mar. 31, 2009. 

Page 49 GAO-09-554 Aviation and Climate Change
 

enough to offset expected emissions growth is not accurate given the 

potential adoption of alternative fuels. We agree that alternative fuels do 

have potential to reduce aircraft emissions in the future; to the extent that 

a low-emission (on a life-cycle basis) alternative fuel is available in 

substantial quantities for the aviation industry, emissions from the aviation 

industry are likely to be less than they otherwise would be. However, we 

maintain that given concerns over the potential environmental impacts of 

alternative fuels, including their life-cycle emissions, as well as the extent 

to which such fuels are available in adequate supplies at a competitive 

price, there may be a somewhat limited potential for alternative fuel use to 

reduce emissions from commercial aircraft in the future, especially the 

short term. DOT also suggested that we clarify the sources for our 

discussion about policy options that can be used to address aviation 

emissions. As much of that discussion is based on economic research and 

experience with market-based instruments and other policies, we clarified 

our sources where appropriate. 

NASA provided a written response (see app. V) in which they stated that 

our draft provided an accurate and balanced view of issues relating to 

aviation and climate change. NASA also provided technical comments that 

were incorporated as appropriate. EPA provided technical comments via 

email that were incorporated as appropriate and also provided a written 

response. (see app. VI). 

EPA was concerned that characterizing aircraft emissions standards as 

being economically inefficient especially compared to market-based 

measures, might lead readers to believe that emissions standards cannot 

be designed in a manner that fosters technological innovations and 

economic efficiency. EPA officials explained that, based on their 

experience, standards can be designed to optimize technical responses, 

provide regulated entities with flexibility for compliance and that studies 

show that EPA regulations have generated benefits in excess of costs. We 

agree that allowing regulated sources more flexibility in how they meet 

emissions standards can reduce the costs associated with achieving the 

emissions reductions. However, economic research indicates that for 

addressing greenhouse gas emissions, market-based measures such as 

emissions taxes or cap-and-trade programs would be economically 

efficient (that is, would maximize net benefits) compared to other 

approaches, in part because market-based measures can give firms and 

consumers more flexibility to decide when and how to reduce their 

emissions. Emissions standards, for example, generally give regulated 

sources fewer incentives to reduce emissions beyond what is required for 

compliance. The ultimate choice of what specific policy option or 

Page 50 GAO-09-554 Aviation and Climate Change
 

combination of options governments might use and how it should be 

designed is a complex decision and beyond the scope of our discussion. 

Finally, EPA was concerned that our draft report did not adequately 

discuss the increases in fuel consumption and emissions that have resulted 

from high rates of market growth and expected continued growth. We 

believe that our report adequately discusses fuel efficiency as well as fuel 

consumption and emissions output. In addition, our report discusses that 

aviation emissions are expected to grow in the long term, despite the 

potential availability of a number of technological and operational options 

that can help increase fuel efficiency. In response to this comment, we 

added additional information on forecasted fuel use by U.S.-based 

commercial airlines. 

We are sending copies of this report to the Secretaries of Defense, State, 

and Transportation and the Administrators of the Environmental 

Protection Agency and the National Aeronautics and Space 

Administration. This report is also available at no charge on the GAO Web 

site at http://www.gao.gov. 

If you or your staffs have any questions concerning this report, please 

contact me at (202) 512-2834 or flemings@gao.gov. Contact points for our 

Offices of Congressional Relations and Public Affairs may be found on the 

last page of this report. Staff members making key contributions to this 

Susan Fleming 

report are listed in appendix VII. 

Director, Physical Infrastructure Issues 

Page 51 GAO-09-554 Aviation and Climate Change
 

List of Congressional Requesters 

The Honorable Bart Gordon 

Chairman 

The Honorable Ralph Hall 

Ranking Member 

Committee on Science and Technology 

House of Representatives 

The Honorable James L. Oberstar 

Chairman 

The Honorable John L. Mica 

Ranking Member 

Committee on Transportation and Infrastructure 

House of Representatives 

The Honorable Jerry F. Costello 

Chairman 

The Honorable Thomas E. Petri 

Ranking Member 

Subcommittee on Aviation 

Committee on Transportation and Infrastructure 

House of Representatives 

Page 52 GAO-09-554 Aviation and Climate Change
A

Unio

ppendix I: Legal Implications of European 

n Emissions Trading Scheme 

Page 53 GAO-09-554 

Appendix I: Legal Implications of European 

Union Emissions Trading Scheme 

The European Union’s recent decision to include aviation in the European 

Union’s Emissions Trading Scheme (EU ETS), which includes U.S. carriers 

flying in and out of Europe, is a complex and controversial matter. 

Preparations by U.S. carriers are already underway for 2012, the first year 

aircraft operators will be included in the ETS. The inclusion of aviation in 

the current EU ETS implicates a number of international treaties and 

agreements and has raised concerns among stakeholders both within and 

outside the United States. Many stakeholders within the United States 

have posed that the inclusion of aviation in the ETS violates provisions of 

these international agreements and is contrary to international resolutions. 

Others, primarily in Europe, disagree and find aviation’s inclusion in the 

current ETS to be well within the authority set forth in these agreements. 

In light of these disagreements, the EU may confront a number of hurdles 

in attempting to include U.S. carriers in the current EU ETS framework. 

EU ETS Law In 2005, the EU implemented its ETS, a cap-and-trade program to control 

carbon dioxide emissions from various energy and industrial sectors. On 

December 20, 2006, the European Commission set forth a legislative 

proposal to amend the law, or directive, which established the ETS so as 

to include aviation in the ETS.1

 On July 8, 2008, the European Parliament 

adopted the legislative resolution of the European Council and on 

October, 24, 2008, the Council adopted the directive, signaling its final 

approval.2

 The directive was published in the Official Journal on January 

13, 2009, and became effective on February 2, 2009.3

Under the amended ETS Directive, beginning on January 1, 2012, a cap will 

be placed on total carbon dioxide emissions from all covered flights by 

 

1

The European Commission initiates the legislative process by drafting specific pieces of 

legislation and proposing them to the Council of the European Union and European 

Parliament, who together serve as the EU’s legislative branch. 

2

Under the EU’s co-decision procedure, the legislative procedure for environmental and 

certain other types of laws, both the Council of the European Union and European 

Parliament must approve legislation in order to enact a law. Once both bodies approve 

identical texts of the legislation, it must be published in the Official Journal of the 

European Union. The law goes into force 20 days after publication. Thereafter, each 

member state has 1 year to transpose the directive into national law. 

3

Directive 2008/101/EC, 2009 O.J. (L 8) 3. The directive was amended on Mar. 26, 2009. 

 Aviation and Climate Change 
Appendix I: Legal Implications of European 

Union Emissions Trading Scheme 

aircraft operators flying into or out of an EU airport.4 Emissions will be 

calculated for the entire flight.5

 For 2012, the cap for all carbon dioxide 

emissions from covered flights will be set at 97 percent of historical 

aviation emissions.6

 For the 2013-2020 trading period and subsequent 

trading periods, the cap will be set to reflect annual emissions equal to 95 

percent of historical aviation emissions.7

The cap represents the total quantity of emissions allowances available for 

distribution to aircraft operators. In 2012 and each subsequent trading 

period, 15 percent of allowances must be auctioned to aircraft operators; 

the remaining allowances will be distributed to these aircraft operators for 

free based on a benchmarking process.8

 Individual member states, in 

accordance with the EU regulation, will conduct the auctions for aircraft 

operators assigned to that member state.9

 The auction of allowances will 

be open for anyone to participate. The number of allowances each 

member state has to auction depends on its proportionate share of the 

 

4

Some flights are excluded from the cap, including military flights, flight operations for 

emergency purposes, such as firefighting, as well as airlines with very limited operations. 

See 2008/101/EC, 2009 O.J. (L 8) 3, Annex I. 

5

For instance, a flight from Los Angeles to London will have to surrender allowances for its 

travel in U.S. airspace, international airspace, and U.K. airspace. 

6

Historical aviation emissions is defined as the mean average of the annual emissions in 

calendar years 2004, 2005, and 2006. This will be the baseline for emissions reductions. See 

Directive 2008/101/EC, 2009 O.J. (L8) 3, art. 3c. 

7

See Directive 2008/101/EC, art. 3(c) (establishing the cap). The cap for subsequent trading 

periods can be adjusted by an amendment to the directive. See also Proposal for a Directive 

COM(2008) 16 (extending the trading periods to 8 years from 5 years). Although both the 

European Parliament and the European Council have signaled final approval of the 

proposed directive, final, formal approval had not occurred as of June 2, 2009. 

8

Three percent of the total quantity of allowances to be allocated will be set aside in a 

special reserve for new aircraft operators or aircraft operators with rapid growth. Eligible 

aircraft operators must apply to their assigned member states to obtain free allowances 

from the special reserve. The European Commission will determine how the allowances in 

the special reserve will be distributed. Any unallocated allowances will be auctioned. 

9

Aircraft operators will be assigned to the member state that either: (1) issued its operating 

license or (2) has the greatest estimated emissions from flights performed by that aircraft 

operator in 2006 or the operator’s first year of operation. See Directive 2008/101/EC, 2009 

O.J. (L 8) 3, art. 18(a). These assignments were made in February 2009 and most U.S. 

airlines were assigned to the United Kingdom. According to the Directorate-General of the 

Environment (DG Environment), the auctions will be open to anyone to participate and the 

Commission is currently developing the regulation containing detailed provisions for 

member state auctions. 

Page 54 GAO-09-554 Aviation and Climate Change
Appendix I: Legal Implications of European 

Union Emissions Trading Scheme 

total verified aviation emissions for all member states for a certain year.10

The member states will be able to use the revenues raised from auctions in 

accordance with the amended directive.11 For each trading period, aircraft 

operators can apply to their assigned member state to receive free 

allowances. Member states will allocate the free allowances in accordance 

with a process the European Commission establishes for each trading 

period. 

After the conclusion of each calendar year, aircraft operators must 

surrender to their assigned member state a number of allowances equal to 

their total emissions in that year. If an aircraft operator’s emissions exceed 

the number of free allowances it receives, it will be required to purchase 

additional allowances at auction or on the trading market for EU ETS 

allowances.12 In addition, in 2012, aircraft operators will be able to submit 

certified emissions reductions (CER) and emission reduction units 

(ERU)—from projects in other countries undertaken pursuant to the 

Kyoto Protocol’s Clean Development Mechanism and Joint 

Implementation—to cover up to 15 percent of their emissions in lieu of 

ETS allowances. For subsequent trading periods, aircraft operators’ use of 

CERs and ERUs depends in part on whether a new international 

agreement on climate change is adopted. However, regardless of whether 

such an agreement is reached, in the 2013 through 2020 trading period, 

 

10For 2012, each member state’s total allowances will be based on verified 2010 emissions. 

In subsequent years, the total allowances will be based on verified emissions from 2 years 

prior. 

11According to the 2008 directive, it shall be for member states to determine the use to be 

made of revenues generated from the auctioning of allowances. Those revenues should be 

used to tackle climate change in the EU and third countries, inter alia; to reduce 

greenhouse gas emissions; to adapt to the impacts of climate change in the EU and third 

countries, especially developing countries; to fund research and development for 

mitigation and adaptation, including in particular in the fields of aeronautics and air 

transport; to reduce emissions through low-emission transport; and to cover the cost of 

administering the Community scheme. 

12Alternatively, if an aircraft operator has excess emissions allowances, it will be able to 

sell those excess allowances on the market. 

Page 55 GAO-09-554 Aviation and Climate Change
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Union Emissions Trading Scheme 

each aircraft operator will be allowed to use CERs and ERUs to cover at 

least 1.5 percent of their emissions.13

If a country not participating in the EU ETS adopts measures for reducing 

the climate change impact of flights to participating countries, then the 

European Commission, in consultation with that country, will consider 

options to provide for “optimal interaction” between the ETS and that 

country’s regulatory scheme—for example, the Commission may consider 

excluding from the ETS flights to participating EU ETS countries from that 

country.14 Although 2012 is the first year aircraft operators must comply 

with the ETS law, preparations in the EU15 and from U.S. carriers16 began 

soon after the law went into force. 

Legal Implications of the 

ETS 

The inclusion of aviation in the newly amended EU ETS implicates a 

number of international agreements, policy statements, and a bilateral 

agreement specific to the United States, including the United Nations 

Framework Convention on Climate Change (UNFCCC), the Kyoto 

Protocol to the UNFCCC, the Convention on International Civil Aviation 

(the ‘Chicago Convention’), Resolutions of the International Civil Aviation 

Organization, and the U.S.-EU Air Transport Agreement (the ‘U.S.-EU 

Open Skies Agreement’). 

 

13The European Commission will determine the exact percentage of CERs and ERUs that 

aircraft operators can use in the 2013 through 2020 trading period. In determining the 

percentage of CERs and ERUs that each covered sector can use in the 2012 through 2020 

trading period, the Commission will ensure that overall CER and ERU usage does not 

exceed 50 percent of the emissions reductions achieved in Phase II (2007 through 2012), 

measured from a baseline of 2005 emissions levels. 

14According to the DG Environment, draft legislation and a number of bills proposed in the 

110th Congress would have triggered such consideration. See McCain-Lieberman, S. 280, 

110th Cong. (2007); Lieberman-Warner, S. 2191, 110th Cong. (2007); Dingell-Boucher, draft 

bill; and Waxman-Markey, H.R. 1590, 110th Cong. (2007), H.R. 6186, 110th Cong. (2008). 

15On Feb. 11, 2009, the Commission adopted the Preliminary List of Aircraft Operators and 

their administering Member States, Commission Notice Pursuant to Article 18a(3)(a) of 

Directive 2003/87/EC, C(2009) 866. Additional preparations have included holding a 

number of stakeholder workshops to discuss implementing this directive and development 

of guidelines for monitoring, reporting, and verification of emissions, according to the DG 

Environment. 

16All operators must submit their monitoring plan by the end of August 2009, according to 

the DG Environment. 

Page 56 GAO-09-554 Aviation and Climate Change
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The UNFCCC, a multilateral treaty on global warming that was signed in 

1992 and has been ratified by 192 countries, including the United States, 

seeks to “achieve stabilization of greenhouse gas concentrations in the 

atmosphere at a level that would prevent dangerous anthropogenic 

interference with the climate system.”17 Although the UNFCCC required 

signatory states to formulate a national response to climate change,18 its 

mitigation provisions did not require mandatory national emissions 

targets.19

In order to strengthen the commitments articulated in the UNFCCC, the 

Kyoto Protocol was developed within the UNFCCC’s framework and 

adopted in 1997. The Protocol entered into force in February 2005.20 The 

Kyoto Protocol established binding greenhouse gas emissions targets for a 

number of industrialized nations21 and the European Economic 

Community (EEC).22 Notably, the agreement required these industrialized 

nations and the EEC to pursue “limitations or reduction of emissions of 

greenhouse gases ... from aviation ... working through the International 

Civil Aviation Organization.”23 As of January 2009, 183 countries had 

ratified the Kyoto Protocol, but not the United States. 

Further, the Convention on International Civil Aviation, commonly known 

as the Chicago Convention, signed on December 7, 1944, sets forth rules 

on airspace, issues of sovereignty, aircraft licensing and registration, and 

general international standards and procedures, among others.24 Notably, 

 

17United Nations Framework Convention on Climate Change, 1992, Article 2, GE.05-62220. 

(E) 200705. 

18Id. at Article 4(1)(b). 

19Id. at Article 4. 

20Kyoto Protocol to the United Nations Framework Convention on Climate Change, 1999 

[hereinafter Kyoto Protocol]. 

21The Kyoto Protocol recognized that industrialized nations are the largest contributors to 

greenhouse gas emissions and therefore divided the signatory countries into two groups—

Annex I countries that are industrialized nations subject to binding targets, either emission 

reduction or limitation requirements, and Non-Annex I countries that are not subject to 

binding targets. 

22Kyoto Protocol, supra note 20, art. 3(1). 

23Id. at art. 2(2). 

24Convention on International Civil Aviation, Dec. 7, 1944, Ninth ed., 2006, 61 Stat. 1180, 15 

U.N.T.S. 295 [hereinafter Chicago Convention]. 

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the treaty sets forth sovereignty provisions, recognizing that a contracting 

state has exclusive sovereignty over airspace above its own territory.25

Provisions potentially applicable to the recent amendment incorporating 

aviation into the ETS include Article 11,26 Article 12,27 Article 15,28 and 

Article 24.29

Established by the Chicago Convention in 1944, the International Civil 

Aviation Organization (ICAO) is an agency of the United Nations and is 

tasked with fostering the planning and development of international 

aviation. ICAO has issued a number of Assembly Resolutions, which are 

statements of policy rather than law, including a nonbinding ICAO 

Resolution A36-22 relating to environmental protection and aviation 

emissions.30 This resolution, which supersedes ICAO Resolution A35-5 

which had endorsed the further development of an open emissions trading 

scheme for international aviation, calls for mutual agreement between 

contracting states before implementation of an emissions trading 

scheme.31 Additionally, the Resolution formed a new Group on 

 

25See Id. at art. 1. 

26Article 11 provides that “[S]ubject to the provisions of this Convention, the laws and 

regulations of a contracting State relating to the admission to or departure from its 

territory of aircraft engaged in international navigation . . . shall be applied to the aircraft of 

all contracting States without distinction as to nationality, and shall be complied with by 

such aircraft upon entering or departing from or while within the territory of that State.” 

27Article 12 states that “[e]ach contracting State undertakes to adopt measures to insure 

that every aircraft flying over or maneuvering within its territory and that every aircraft 

carrying its nationality mark, wherever such aircraft may be, shall comply with the rules 

and regulations relating to the flight and maneuver of aircraft there in force. . . . Over the 

high seas, the rules in force shall be those established under this Convention, . . .” 

28Article 15 provides in part that “[n]o fees, dues or other charges shall be imposed by any 

contracting State in respect solely of the right of transit over or entry into or exit from its 

territory of any aircraft of a contracting State or persons or property thereon.” Moreover, 

charges that may be imposed must be non-discriminatory. 

29Article 24 covers customs and related duties for aircraft of contracting states and includes 

the provision that “[f]uel . . . on board an aircraft of a contracting State, on arrival in the 

territory of another contracting State and retained on board on leaving the territory of that 

State shall be exempt from customs duty, inspection fees or similar national or local duties 

and charges.” 

30Consolidated Statement on Continuing ICAO Policies and Practices Related to 

Environmental Protection, ICAO Res. A36-22, 36th Session, Appendix L, 1(b)(1)(2007) 

[hereinafter ICAO Res. A36-22]. 

31Many positions referred to in this article cite to ICAO Resolution A35-5 rather than the 

A36-22. 

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International Aviation and Climate Change (GIACC) that was tasked with 

developing and recommending to the ICAO Council a program of action to 

address international aviation and climate change.32 GIACC is due to 

report to the Council later this year. 

 

Finally, the U.S.-EU Air Transport Agreement,33 signed on April 25 and 30, 

2007, and provisionally applied as of March 30, 2008, provided greater 

flexibility for flights between the United States and the EU, authorizing 

every U.S. and every EU airline to: operate without restriction on the 

number of flights, aircraft, and routes, set fares according to market 

demand; and enter into cooperative arrangements, including codesharing, 

franchising, and leasing. It includes enhanced opportunities for EU 

investment in carriers from almost 30 non-EU countries, and enhanced 

regulatory cooperation in regard to competition law, government 

subsidies, the environment, consumer protection, and security.34 Among 

the provisions potentially applicable to the newly amended EU ETS is 

Articles 12 relating to charges for use of airports and related facilities and 

services and Article 3 which prohibits a party from unilaterally limiting 

service or aircraft type.35

Although a number of international agreements, policy statements, and 

bilateral agreements are in place currently, climate change policies are 

constantly changing. In December 2009, the Conference of the Parties to 

the UNFCCC will meet in Copenhagen to discuss and negotiate an “agreed 

outcome” in order to implement the UNFCCC “up to and beyond 2012.”36

Stakeholder Positions on 

Legal Issues 

A number of stakeholders have expressed concern as to the legal basis for 

aviation’s inclusion in the EU ETS. In the United States, within the EU 

community, and in countries throughout the world, public and private 

entities, as well as legal scholars, have expressed opinions as to whether 

the inclusion of aviation into the ETS is in compliance with international 

law. 

32ICAO Res. A36-22, supra note 30, Appendix K. 

33This also is referred to as the U.S.-EU Open Skies Agreement. 

34See generally Id. 

35Id. at art. 12, 3. 

36Bali Action Plan, Decision 1/CP.13, 1 (FCCC/CP/2007/6/Add.1). 

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Stakeholders within the United States, such as the executive branch, 

members of Congress, and the Air Transport Association (ATA), have 

weighed in on the legality of the newly amended EU ETS which requires 

compliance by U.S. carriers. 

Stakeholder Positions within 

the United States 

In 2007 and 2008, the executive branch expressed the view that the 

imposition of the ETS was inconsistent with international law, specifically, 

the Chicago Convention and the U.S.-EU Air Transport Agreement.37 While 

the executive branch has not articulated a position on this issue since mid2008, it has expressed the importance of climate change and developing a 

solution on a global level.38

The Air Transport Association (ATA), a trade association representing 

principle U.S. airlines, also has concluded that the EU ETS’s inclusion of 

aviation violates international law, specifically the Chicago Convention.39

ATA argues that imposition of the ETS on U.S.-based carriers is contrary 

to Articles 1, 12, 11,40 1541 and potentially, in the alternative, Article 24.42 In 

summary, ATA argues that the ETS, as amended, violates Article 1 and 

Article 12 provisions of sovereignty and authority. Article 1, which 

provides contracting states exclusive sovereignty over their airspace,43 is 

violated by the EU’s extraterritorial reach which covers emissions of nonEU airlines in another states’ airspace. Further, Article 12, which requires 

 

37Letter of U.S. Ambassador Kristen Silverberg to Jos Delbeke, Acting Director General 

General, Environment Directorate General, Oct. 30, 2008; and letter from the Ambassadors 

of Australia, Canada, China, Japan, Korea and the United States to Ambassador Peter Witt 

of Germany, Apr. 6, 2007 [hereinafter Ambassador Letter]. 

38See statement of Secretary Clinton: “President Obama and I recognize that the solutions 

to this crisis are both domestic and global, that all nations bear responsibility and all 

nations must work together to find solutions.” See also statement of Special Envoy Stern: 

“Yet we can only meet the climate challenge with a response that is genuinely global. 

Eighty percent of greenhouse gas emissions are produced outside the United States, and a 

rapidly growing percentage is produced in emerging market countries.” 

39ATA’s analysis is contained in a non-public Legal Analysis Summary provided to GAO. 

40Chicago Convention, supra note 24, art. 11. 

41Id. at art. 15. 

42Article 24 provides that “fuel...on board an aircraft of a contracting State, on arrival in the 

territory of another... shall be exempt from customs duty, inspection fees or similar 

national or local duties and charges.” 

43Chicago Convention, supra note 24, art. 1. Article 1 provides that every contracting state 

has “complete and exclusive sovereignty over the airspace above its territory.” 

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contracting states to ensure that aircraft under its jurisdiction are in 

compliance with rules and regulations relating to the flight and maneuver 

of aircraft,44 also is violated. ATA argues that Article 12 gives ICAO 

primary authority, under the Convention, to set rules for the “flight and 

maneuver of aircraft” over the “high seas,” which precludes the applicatio

of rules by one state over the airlines of another state to the extent 

inconsistent with ICAO rules. Thus, because ICAO has stated that one 

state can apply emissions trading to the airlines of another state only 

through mutual consent, ATA contends that the EU’s emissions trading 

coverage of non-agreeing-EU airlines over the high seas is inconsiste

with ICAO’

n 

nt 

s authority. 

 

Additionally, with respect to Article 11, ATA argues that although Article 

11 provides authority to states to establish certain rules for admission and 

departure of aircraft, the authority is limited. States may only establish 

admission and departure rules consistent with the remainder of the 

Chicago Convention, which prevents the EU from arguing that Article 11 

authorizes EU action. In any event, ATA contends that any rules may only 

apply “upon entering or departing from or while within the territory of that 

State,” whereas the European scheme reaches outside European territory. 

Further, ATA finds that the ETS is contrary to Article 1545 of the Chicago 

Convention because it imposes a de facto charge for the right to enter or 

exit an EU member state. In the alternative, ATA argues that there could 

be a violation of Article 24 of the Convention, which exempts fuel on 

board an aircraft from duties, fees, and charges. Because the law 

calculates emissions based on fuel consumption, the purchase of 

greenhouse gas permits may constitute a “similar ... charge” of fuel on 

board, according to ATA. Additionally, Article 24 mirrors Article 11 of the 

U.S.-EU Air Transport Agreement but extends the freedom from 

taxation/charges on fuel to that purchased in the EU. Thus, ATA argues, 

the prohibition against the EU levying a fuel tax applies to fuel already on 

board as well as fuel purchased in the EU. 

ATA has publicly expressed harsh opposition to the ETS’s inclusion of 

aviation and has stated that there will be a number of legal challenges 

from around the globe, including from the United States.46 ATA has 

44Id. at art. 12. 

45Id. at art. 15. 

46See Josh Voorhees, Greenwire, EU brings airlines into climate scheme; industry vows 

court fight (2008), at http://www.eenews.net/Greenwire/2008/07/08/archive/3. 

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additionally expressed discontent with the newly amended ETS law as a 

matter of policy, as it siphons money out of aviation which is 

counterproductive from reinvesting in improving technologies that reduce 

emissions.47

Finally, the Congress is considering the House FAA Reauthorization Bill, 

H.R. 915, 111th Cong. (2009), which includes an expression of the Sense of 

the Congress with respect to the newly amended EU ETS.48 The bill states 

that the EU’s imposition of the ETS, without working through ICAO, is 

inconsistent with the Chicago Convention, other relevant air service 

agreements, and “antithetical to building cooperation to address 

effectively the problem of greenhouse gas emissions by aircraft engaged in 

international civil aviation.”49 The bill recommends working through ICAO 

to address these issues.50

Stakeholders in the EU community and a not-for-profit business 

organization have expressed both legal and policy views on the newly 

amended ETS, as well. An independent contractor for the European 

Commission’s Directorate-General of the Environment (DG Environment) 

as well as the International Emissions Trading Association (IETA) have 

both issued opinions in support of aviation’s inclusion in the ETS. 51 IETA 

supports the inclusion of aviation in the EU ETS from a policy perspective, 

but has not opined on the legality of its inclusion.52 From a policy 

standpoint, IETA supports aviation’s inclusion on both EU and non-EU 

carriers so as to share the burden to combat climate change.53 However, 

the organization has expressed concerns over a number of issues, some of 

Stakeholder Positions outside 

the United States 

 

47Press Release, Air Transport Association Chief Executive Says European Aviation 

Emissions Trading Scheme ‘Contrary to International Law and Bad Policy’ (Oct. 30, 2008), 

available at http://www.airlines.org/news/releases/2008/news_10-30-08.htm. 

48A “Sense of the Congress” is not legally binding if passed. 

49H.R. 915, Sec. 514(1), 111th Cong. (2009). 

50Id. at Sec. 514(2). 

51The legal assessment was conducted by an independent contractor for the DG 

Environment. 

52IETA, IETA’s position on the Inclusion of Aviation in the EU ETS, available at 

www.ieta.org/ieta/www/pages/getfile.php?docID=2413. 

53Id. at 2. 

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which include access to project credits, amount of allowances available 

for auctioning, and allocation calculation.54

From a legal perspective, an independent contractor for the DG 

Environment55 has issued an opinion supporting aviation’s inclusion in the 

EU ETS.56 The opinion states that alongside a state’s inherent right to 

enact legislation and the provisions of the EC Treaty for collective actio

by member states, the legal basis for action is contained in the UNFCCC

requirement for developed countries to take measures to mitigate climate 

change, in the Kyoto Protocol which reinforces this position, and under 

EU law (the EC Treaty), which provides the basis for the EU to act by 

including aviation in the ETS.

n 

’s 

 

57 Further, the opinion articulates that the 

ETS does not violate Articles 11,58 12,59 15,60 or 2461 of the Chicago 

Convention. First, Article 11 is consistent with the newly amended ETS 

law so long as the “laws and regulations” established do not “discriminate 

as to nationality of aircraft.”62 Further, Article 12 is inapplicable because 

emissions trading does not affect the flight or maneuver of aircraft but 

merely the terms for admission to and departure from EU territory. 

Additionally, the opinion stated that Article 15 is inapplicable because the 

coverage of aviation cannot be seen as an “airport charge or similar 

charge.” Even if payment were to occur under an auction system, the 

allowances are not designed as compensation for the costs of operation 

and management of airports and air navigation facilities, and 

57

58

60

61

62

54Id.

55The legal assessment was conducted by an independent contractor for the DG 

Environment. 

56Giving Wings to Emissions Trading, Inclusion of Aviation under the European 

emissions trading system (ETS): Design and Impacts (The Delft Report), Report to the 

European Commission, DG Environment, No.ENV.C.2./ETU/2004/0074r, July 2005 

[hereinafter Delft Report]. This report was prepared for and endorsed by the European 

Commission. 

Id. at 170-73. 

Chicago Convention, supra note 24, art. 11. 

59Article 12 requires contracting states to ensure that aircraft under their jurisdiction are in 

compliance with rules and regulations relating to the flight and maneuver of aircraft. 

Chicago Convention, supra note 24, art. 15. 

Id. at art. 24. 

The Delft Report at 175-77. 

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consequently, Article 15 is inapplicable.63 Finally, Article 24 of the 

Convention does not apply to the Emissions Trading System because 

trading allowances are “fundamentally different from customs duties.”64

Additionally, the opinion finds policy support for these legal findings in 

ICAO Resolution A35-565 and bilateral air transport agreements.66

r 

n” 

n-EU 

e 

nter to 

 

Additionally, countries outside the European Community have joined the 

United States in an expression of concerns regarding the imposition of the 

ETS on non-EU carriers. In an April 2007 letter to the German Ambassado

to the European Union, the United States, Australia, China, Japan, South 

Korea, and Canada conveyed a “deep concern and strong dissatisfactio

for the then-proposal to include international civil aviation within the 

scope of the EU ETS.67 The letter asks that the EU ETS not include no

aircraft unless done by mutual consent.68 Although supportive of the 

reduction of greenhouse gas emissions, the ascribing parties argue that th

“unilateral” imposition of the ETS on non-EU carriers would potentially 

violate the Chicago Convention and bilateral aviation agreements with the

parties to the letter.69 Moreover, they write, the proposal runs cou

the international consensus that ICAO should handle matters of 

international aviation, which was articulated with the ICAO Assembly and 

the ICAO Council in 2004 and 2006, respectively.70 The letter closes with a 

 7 

pendix 1 (2004) [hereinafter 

ns 

l opportunity to participate in the ETS is already covered under the 

e 

er to the German Presidency regarding Commission proposal to extend ETS to 

aviation (Apr. 6, 2007). 

63Id. at 176-7

64Id. at 177. 

65Consolidated statement of continuing ICAO policies and practices related to 

environmental protection, ICAO Res. A35-5, 35th Session, Ap

ICAO Res. A35-5]. “ICAO endorses an open emission system for international aviation” and 

requests council focus on two areas under this framework. 

66The Delft Report further elaborates: “the operation of an ETS does not unilaterally limit 

the volume of traffic ... or aircraft types, as it only provides incentives to reduce emissio

over time; fair and equa

Chicago Convention’s non-discrimination clause and this must be adhered to under th

ETS.” See pp. 179-181. 

67Lett

68Id. 

69Id. 

70Id. 

Page 64 GAO-09-554 Aviation and Climate Change
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reservation of right to take appropriate measures under international law

if the ETS is imposed.

sion in 

s in the legal community, both within the 

United States and the EU, have provided explanatory articles or position 

”73 This 

 and 

lly 

s 

 understanding of contentious provisions.76 In conclusion, he 

proposes that the EU should channel the energy for implementation of the 

71

Given the controversial nature and complexity of aviation’s inclu

the EU ETS, a number of scholar

papers on the issue of the consistency of the EU’s plans with its 

international legal obligations.72

One U.S. law review article by Daniel B. Reagan argues that international 

aviation emission reductions should be pursued through ICAO given the 

“political, technical, and legal implications raised by the regulation.

article sets forth that politically, ICAO is the appropriate body because it 

can work towards uniformity in a complex regulatory arena, incidentally 

resulting in increased participation from a variety of stakeholders, 

reduction of resentment, and a reduced likelihood of non-compliance

legal challenges.74 Further, ICAO has the expertise necessary to technica

design aviation’s emission reduction regime and is in a position to 

consider the “economic, political, and technical circumstances of its 

member states ... .”75 Finally, Reagan argues that pursuing an emission

reduction regime through ICAO could avoid likely legal challenges which 

present themselves under the current ETS, as ICAO could facilitate a 

common

current regime into holding ICAO accountable for fulfilling environmental 

duties.77

 

For brevity’s sake, we have not included explanatory articles because they are repetitive 

an, Putting International Aviation Into the European Union Emissions 

ading Scheme: Can Europe Do It Flying Solo?, 35 B.C. Envtl. Aff. L. Rev. 349 (2008). 

74Id. at 380-81. 

75Id. at 381-82. 

76Id. at 382. 

Legal Scholar/Researcher 

Views 

71Id. 

72

of what is contained in this appendix. Here we highlight those articles which set forth legal

positions on the issue. 

73Daniel B. Reag

Tr

77Id. at 383. 

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In contrast, a law review article published in the European Environmen

Law Review in 2007 by Gisbert Schwarze argues that bringing aviation in

the EU ETS falls clearly within existing law and is, in fact, mandated.

tal 

to 

policies which include aviation. First, the article sets forth that the 

ther 80

ation on 

 certain 

, which covers charges, is similarly 

inapplicable because emissions allowances on the free market or through 

d 

 

78 The 

article presents the case that neither existing traffic rights in member 

states, bilateral air transport agreements, nor the Chicago Convention 

pose any legal obstacles.79 He argues, in fact, that the EU has a mandate 

under the UNFCCC and the Kyoto Protocol to implement climate change 

inclusion of aviation does not restrict existing traffic rights or allow or 

disallow certain aircraft operations in different member states, but ra

merely brings the amount of emissions into the decision-making process.

Further, Schwarze explains that imposing the ETS on carriers flying in and

out of the EU is well within the Chicago Convention. Article 1 of the 

Convention provides contracting states exclusive sovereignty over their 

airspace which provides the EU with the authority to impose obligations 

relating to arrival and departures, so long as there is no discrimin

the basis of nationality, as required by Article 11.81 Additionally, the article 

sets forth that Article 12, regarding the flight and maneuver of aircraft, is

not applicable because, as argued above, the ETS does not regulate

aircraft operations. Article 15

the auctioning process do not constitute a charge.82 Finally, Article 24 is 

inapposite as well because the emissions trading system does not 

constitute a customs duty.83

Additionally, Schwarze argues that the bilateral air transport agreements 

with various nations, such as the Open Skies Agreement with the Unite

States, do not pose any legal barriers to inclusion of aviation in ETS.84

78Gisbert Schwarze, Including Aviation into the European Union Emissions Trading 

ean Environmental Law Review (2007). 

In the alternative, as argued, even if this did constitute a charge, Article 15’s only 

Gisbert Schwarze, Including Aviation into the European Union Emissions Trading 

3-14, European Environmental Law Review (2007). 

t 14. 

Scheme, Europ

79Id. at 12-15. 

80Id. at 12-13. 

81Id. at 13-14. 

82

applicability is to discrimination as to nationality. Id. 

83

Scheme, p. 1

84Id. a

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These agreements contain a prohibition of discrimination similar to Art

11 of the Chicago Convention and a fair competition clause which require

fair competition among signatories in international aviation as well as 

prohibits a party from unilaterally limiting traffic.

icle 

s 

 that 

s the ETS operates without discrimination, it is in conformity 

with the principle of a sound and economic operation of air services and 

g that 

 reduction of emissions of greenhouse gases ... 

from aviation ... working through the International Civil Aviation 

rganization.”89 And finally, although not legally binding, ICAO Resolution 

nges 

A 

re 

es 

 

85 The article argues

so long a

therefore satisfies the fairness clause.86 Finally, since the ETS gives only 

incentive to reduce emissions, it does not regulate the amount of air 

traffic.87

Finally, Schwarze argues that not only is the inclusion of aviation into the

EU ETS legally sound, the UNFCCC and Kyoto Protocol mandate its 

inclusion. The UNFCCC requires all parties to the treaty to adopt national

policies and take corresponding measures on the mitigation of climate 

change consistent with the objective of the convention, recognizin

this can be done “jointly with other parties.”88 Additionally, the Kyoto 

Protocol, which sought to strengthen UNFCCC, required Annex 1 parties 

to pursue “limitations or

O

A35-5 endorses the development of an open emissions trading system for 

international aviation.90

Implementation of the new ETS directive will likely face legal challe

before 2012, the first year aircraft operators will be included in the ETS. 

number of stakeholders, including ATA, have publicly expressed that the

will be “government-to-government legal challenges” and potentially a 

“multilateral challenge from around the world.”91 Further, countri

outside the EU community have joined in support of taking appropriate 

limate Change, supra note 17, art. 4(2)(a). 

 Res. A35-5, supra note 66, Appendix I Nr. 2(c)(1). 

Potential Legal Challenges 

and Dispute Resolution 

85Id. 

86Id. 

87Id. 

88United Nations Framework Convention on C

89Kyoto Protocol, supra note 20, art. 2(2). 

90Schwarze at 13. See also ICAO

91See Voorhees, supra note 46.

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actions under international law if the ETS is imposed.92 If challenges are 

brought forth, they could potentially be brought forth under the Chicag

Convention, air service agreements (e.g., U.S.- EU Air Transport 

Agreement) or potentially in individual member state courts. Each o

has its own dispute resolution procedure. 

If a challenge is brought forth under the Chicago Convention after fai

negotiations, Article 84 of t

o 

ption 

led 

he Convention (Settlement of Disputes) is 

invoked. Article 84 provides that if there is a disagreement by two or more 

t Agreement is no exception. Article 19 of the 

U.S.-EU Air Transport Agreement provides that parties to a dispute may 

ns 

 days, 

efits which 

In addition to bringing legal challenges under international treaties, 

carriers could potentially mount legal challenges in member states’ 

 

contracting states which cannot be settled by negotiation, it will be 

decided upon by the Council.93 A decision by the Council can be appealed 

to an agreed-upon ad hoc tribunal or to the Permanent Court of 

International Justice (now the International Court of Justice) whose 

decision will be binding.94

Air service agreements additionally have dispute resolution procedures 

and the U.S.-EU Air Transpor

submit to binding arbitration through an ad hoc tribunal if negotiatio

fail.95 If there is noncompliance with the tribunal’s decision and a 

subsequent agreement between the parties is not reached within 40

the other party may suspend the application of comparable ben

arise under the agreement.96

 

ting 

penalties are 

ion. Alternatively, a challenge 

could potentially be brought against a carrier. If a carrier chooses to move forward and not 

action could be brought under the Chicago Convention Article 87 and 

he airline to cease operations over any contracting state. 

Id. at art. 19(7). 

92See Ambassadors Letter, supra note 37. 

93Chicago Convention, supra note 24, art. 84. The Council is composed of 36 contrac

states elected by the Assembly. See Id. at art. 50. When a disagreement is submitted to the 

Council, the Council will invoke the Rules of the Settlement of Differences, established in 

1957, which sets forth procedures for disputes. 

94Id. at art. 84. Additional requirements for settlement of disputes and 

contained in Articles 85, 86, 87 and 88 of the Chicago Convent

comply with the ETS, 

force t

95See U.S.-EU Air Transport Agreement, art. 19. 

96See 

Page 68 GAO-09-554 Aviation and Climate Change
Appendix I: Legal Implications of Europ

Union Emissions Trading Scheme 

ean 

Page 69 GAO-09-554 Aviation and Climate Change

national courts, according to some legal scholars.97 Additionally, a 

on authority in the state’s 

 

European state will potentially be able to take action against a 

noncompliant carrier under their civil aviati

courts.98

97See Aimee Turner, Flight Global, EU warns ICAO it will go it alone if no progress is 

made with ETS (2007), available at www.flightglobal.com. 

98Id. 
Appendix II: List of Experts Appendix II: List of Experts 

Gerald Bernstein, Stanford Transportation Group 

Dennis Bushnell, National Aeronautics and Space Administration 

Kenneth Button, George Mason University 

nthony Dean, General Electric 

 Faber, CE Delft (Netherlands) 

i, GRA, Incorporated 

James Hileman, Massachusetts Institute of Technology 

ennifer Holmgren, Universal Oil Products 

chester Metropolitan University (United Kingdom) 

Peter Morrell, Cranfield University (United Kingdom) 

A

Robert Deering, American Airlines 

Christian Dumas, Airbus (France) 

Jasper

Richard Golaszewsk

Preston Henne, Gulfstream Aerospace Corporation 

J

David Lee, Man

Andreas Schafer, University of Cambridge (United Kingdom) 

Agam Sinha, MITRE Corporation 

Julian Tishkoff, United States Air Force 

Ian Waitz, Massachusetts Institute of Technology 

Donald Wuebbles, University of Illinois 

Page 70 GAO-09-554 Aviation and Climate Change 
Appendix III: Detailed Survey Results Appendix III: Detailed Survey Results 

The survey tool used to assess options for reducing commercial aircraft 

emissions is below, complete with detailed results. We do not include the 

responses for open-ended questions. 

Uni

Off

Aviatio

Ranking To raft Greenhouse Gas Emissions 

ted States Government Accountability 

ice 

n and Climate Change 

ol for Options to Reduce Airc

ntroduction 

ation emissions that were identified 

rough our interviews with you and other experts, or by GAO. We have 

pla ptions in three categories—technologies, operations, and 

alte ert opinion on them. We 

ask that you rate th viding comments 

where appropriate. 

Instructions for Completing This Tool 

ese blanks will expand to fit your answer. 

• ease use your mouse to na ougho cum lick

g the box you ish to fill in. o not use the “Tab

ause doing so ay cause for tting prob ms.

it once; to d select a box, double click on it. 

int this tool, complete it by hand, and return it by 

ra paper as neces plete the open-ended 

e and retur this documen o Matthew

by January 9, 2009. Plea save the com leted document to 

e-mail it as an attachment to 

I

This rating tool follows up on our recent interview with you on 

commercial aviation and greenhouse gas emissions. The tool contains 

options for reducing commercial avi

th

ced the o

rnative fuels—and are interested in your exp

e options across several factors, pro

You can answer most of the questions by checking boxes or filling in 

blanks. A few questions request short narrative answers. Please note that 

th

Pl vigate thr ut the do ent by c ing 

on the field or checkin w D ” 

or “Enter” keys, bec m ma le

• To select a box, click on e

If you prefer, you may pr

fax. Please use ext sary to com

questions. 

Deadline 

We ask that you complet n t t

Rosenberg 

your desktop or hard drive and 

se p

Page 71 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

RosenbergMC@gao.gov. If you complete this tool by hand, please fax the 

completed tool to Matthew Rosenberg at GAO at 312-220-7726. 

Contact Information 

ions, please co act Matthew senberg enior 

12-220-7645 or RosenbergMC@gao.gov or Cathy Colwell, 

-220-7655 o v. 

help. 

our overall knowledge of technological 

e aircraft carbon dioxide ( O2) emissions, such 

engines and aircraft design technologies, and the 

those technologies?

0 None Æ SKIP TO QUESTION #9 

 TO QUESTION #2 

2. In your expert opinio e

ons for the following options? 

Low 

potenti

Medium 

potentia

High 

potential

Don’t 

kno

If you have any quest

Analyst, at 3

nt Ro , S

Assistant Director, at 312 r ColwellC@gao.go

Thank you for your 

1. How would you rate y

options to reduc

as aircraft 

C

costs of 

Part 1: Technology 

Options 

6 Minimal Æ SKIP TO QUESTION #9 

4 Basic Æ CONTINUE TO QUESTION #2 

1 Proficient Æ CONTINUE TO QUESTION #2 

7 Advanced Æ CONTINUE

n, what is the potential for futur fuel 

savings and CO2 emissions reducti

al l w

a. Open rotor engines 0 5 8 1

b. Geared Turbo Fan

Engines 

2 7 3 2

c. Distributive Propulsi

systems 

on 2 2 5 5

d. Lighter airframes 

(Composites) 

2 5 6 1

e. Increased Laminar 

Flow Control 

2 6 3 2

f. Blended wing-body 

aircraft 

0 5 81

g. Winglets 8 3 3 0

h. Riblets 9 1 0 4

Page 72 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

3. In your expert opinion, what would be the potential R&D costs

to develop the following options for commercial use? 

 Lowco edi sts M um costs High c Don’t osts know

a. Open rotor engines 1 6 6 1

b. Geared Turbo Fan 

Engines 

3 7 3 1

c. Distributive Propulsion 0 1 76

systems 

d. Lighter airframes 1 6 61

(Composites) 

e. Increased Laminar 0 4 73

Flow Control 

f. Blended wing-body 1 1 12 0

aircraft 

g. Winglets 14 0 0 0

h. Riblets 7 3 0 4

4.

co

Given your answer to question two, what would be the potential 

d 

Medium costs High costs Don’t know

sts to the air transport industry to procure, operate and 

maintain the following options to achieve those fuel savings an

CO2 emissions reductions? 

 Lowcosts

a. Open rotor engines 2 7 3 2

b. Geared Turbo Fan 

Engines 

2 9 1 2

c. Distributive Propulsion 

systems 

0 2 6 6

d. Lighter airframes 

) 

3 6 32

(Composites

e. Increased Laminar 

Flow Control 

1 4 54

f. Blended wing-body 

aircraft 

2 3 90

g. Winglets 14 0 0 0

h. Riblets 9 1 0 4

Page 73 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

5. In your expert opinion, what is the level of public acceptance 

for the following conceptual options? 

Medium 

acceptance 

High 

acceptance

Don’t 

ac know

Low 

ceptance

a. Open rotor engines 6 7 0 1

b. Geared Turbo Fan 

Engines 

0 2 11 1

c. Distributive Propulsion 

systems 

2 2 46

d. Lighter airframes 

(Composites) 

0 3 92

e. Increased Laminar Flow 0 4 82

Control 

f. Blended wing-body 4 5

aircraft 

2 3

g. Winglets 0 0 13 1

h. Riblets 0 1 9 4

6.

market conditions, and ab

In your expert opinion, given our best knowledge about future 

s t government intervention, how 

 the private sector to adopt these 

gies? 

Short 

timeframe

(< 5 years)

Medium 

timeframe 

(5 - 15 

years) 

Long 

timeframe 

(> 15 

years) Never

Don’t 

know

en

long would it take for

technolo

a. Open rotor engines 1 9 3 0 1

b. Geared Turbo Fan 

Engines 

6 6 00 2

c. Distributive 

Propulsion systems 

0 0 62 6

d. Lighter airframes 

(Composites) 

3 9 10 1

e. Increased Laminar 

Flow Control 

2 4 50 3

f. Blended wing-body 

aircraft 

0 2 102 0

g. Winglets 14 0 0 0 0

h. Riblets 5 3 1 0 5a

Page 74 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

Page 75 GAO-09-554 Aviation and Climate Change 

7. What major challenges exist to widespread use of ... 

a. Open rotor engines 

b. Geared Turbo Fan Engines 

c. Distributi ulsion systems ve Prop

d. Lighter airfra (Composites) mes

e. Increased ar Flow Control Lamin

f. Blended wing- dy aircraft bo

g. Winglets 

h. Riblets 

8. What actions could the U.S. federal government undertake to 

promote the development and/or t adop ion of ...

a. Open rotor engines 

b. Geared Turbo Fan Engines 

c. Distributive Propulsion systems 

d. Lighter airframes (Composites) 

e. Increased Laminar Flow Control 

f. Blended wing-body aircraft 

g. Winglets 

h. Riblets 
Appendix III: Detailed Survey Results 

Aviation and Climate Change

9. How would you rate your overall knowledge of operational 

options to reduce aircraft fuel usage and CO2 emission

a

s, such as 

ir traffic management and airline operations? 

0 None Æ SKIP TO QUEST 7 

 QUESTION 7 

Æ CONTINUE TO QUE ION #10

 TO QUE ION #10

E TO QUE ION #10

hat is the future po ntial fo fuel 

ductions for the llowing ptions

Lo

potential

Mediu

potential 

Hig

potential

Don’t 

know

ION #1

5 Minimal Æ SKIP TO #1

7 Basic ST

4 Proficient Æ CONTINUE ST

2 Advanced Æ CONTINU ST

10. In your expert opinion, w te r 

savings and CO2 emissions re fo o ? 

w m h 

a. Reduction of on-board weight 7 4 2 0

b. Engine washing 8 4 0 1

c. Limited use of paint on airframes 9 3 0 1

d. Increased engine maintenance 8 3 1 1

e. Single engine taxing 7 6 0 0

f. Use of APU on ground at gate 10 2 0 1

g. Automatic Dependent Surveillance 

– Broadcast (ADS-B) 2 6 1 4

h. Required Navigation Performan

(RNP) 

ce 

2 4 2 5

i. Continuous Descent Arrivals 

(CDA) 5 5 2 1

j. NEXTGEN Weather 3 5 1 4

k. Enhanced vision systems 6 3 0 4

l. Synthetic vision systems 6 2 0 5

m. Reduced Vertical Separation 3 8 1 1

n. Flying at slower speeds 5 5 3 0

o. Formation flying 5 2 2 4

p. Air to air refueling 7 1 0 5

q. Reduced flight frequency with 

larger aircraft 6 3 3 1

r. Multi-stage long distance travel 6 4 1 2

Part 2: Operational 

Options 

Page 76 GAO-09-554 
Appendix III: Detailed Survey Results 

11. In your expert opinion, what would be the potential R&D costs 

to develop the following options for commercial use? 

Low 

Costs 

Medium 

Costs 

High 

Costs

Don’t 

know

a. Reduction of on-board weight 8 4 1 0

b. Engine washing 11 0 0 2

c. Limited use of paint on airframes 13 0 0 0

d. Increased engine maintenance 11 2 0 0

e. Single engine taxing 13 0 0 0

f. Use of APU on ground at gate 11 0 0 2

g. Automatic Dependent Surveillance 

– Broadcast (ADS-B) 

1 6 1 5

h. Required Navigation Performance 

(RNP) 

3 4 0 6

i. Continuous Descent Arrivals (CDA) 4 7 0 2

j. NEXTGEN Weather 1 4 3 5

k. Enhanced vision systems 2 5 1 5

l. Synthetic vision systems 2 5 1 5

m. Reduced Vertical Separation 9 1 1 2

n. Flying at slower speeds 13 0 0 0

o. Formation flying 3 3 4 3

p. Air to air refueling 0 3 5 5

q. Reduced flight frequency with 1

larger aircraft 

2 0 1 0

r. Multi-stage long distance travel 11 0 1 1

Page 77 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

12. Given your answer to question ten, what would be the potentia

costs to the air transport in

o

l 

dustry to adopt the following 

ptions to achieve those fuel savings and CO emissions 

reductions? 

Low 

costs 

Medium 

costs 

Hig

cos

Don’t 

kno

2

h 

ts w

a. Reduction of on-board weight 8 5 0 0

b. Engine washing 8 4 0 1

c. Limited use of paint on airframes 11 2 0 0

d. Increased engine maintenance 5 6 1 1

e. Single engine taxing 13 0 0 0

f. Use of APU on ground at gate 10 1 0 2

g. Automatic Dependent Surveillance 

– Broadcast (ADS-B) 

2 4 2 5

h. Required Navigation Performance 4 

(RNP) 

3 0 6

i. Continuous Descent Arrivals (CDA) 8 3 0 1

j. NEXTGEN Weather 2 3 1 6

k. Enhanced vision systems 1 5 2 5

l. Synthetic vision systems 1 6 1 5

m. Reduced Vertical Separation 9 2 0 2

n. Flying at slower speeds 11 2 0 0

o. Formation flying 2 4 2 5

p. Air to air refueling 0 4 5 4

q. Reduced flight frequency with 

larger aircraft 

9 1 3 0

r. Multi-stage long distance travel 5 4 2 2

Page 78 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

13. In your expert opinion, what is the level of public acceptance 

for the following options? 

Low 

acceptance

Medium 

acceptance 

High 

acceptance

Don’t 

know

Reduction of on-board weight 0 5 8 0

Engine washing 0 0 11 2

Limited use of paint on airframes 1 2 10 0

Increased engine maintenance 0 0 12 1

Single engine taxing 0 2 11 0

Use of APU on ground at gate 0 2 9 2

Automatic Dependent Surveillance – 0 0 94

Broadcast (ADS-B) 

Required Navigation Performance 0 0 85

(RNP) 

Continuous Descent Arrivals (CDA) 0 1 12 0

NEXTGEN Weather 0 1 8 4

Enhanced vision systems 0 1 9 3

Synthetic vision systems 1 1 8 3

Reduced Vertical Separation 1 6 6 0

Flying at slower speeds 7 5 1 0

Formation flying 8 3 1 1

Air to air refueling 10 1 0 2

Reduced flight frequency with larger 7 5 1

aircraft 

0

Multi-stage long distance travel 8 3 0 1

Page 79 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

14. In your expert opinion, given our best knowledge about future 

market conditions, and absent government intervention, how 

e priva e sector to adopt these 

hort 

ame 

(< 5 years)

Medium 

meframe 

(5 -15 years) 

Long 

timeframe 

(> 15 years) Never

Don’t 

know

long would it take for th t

technologies?

S

timefr ti

a. Reduction of on-board 

weight 

8 5 00 0

b. Engine washing 11 1 0 0 1

c. Limited use of paint on 

airframes 

9 4 00 0

d. Increased engine 12

maintenance 

1 0 0 0

e. Single engine taxing 13 0 0 0 0

f. Use of APU on ground 

at gate 

8 3 00 2

g. Automatic Dependent 

Surveillance – 

Broadcast (ADS-B) 

3 5 00 5

h. Required Navigation 6 1 00 6

Performance (RNP) 

i. Continuous Descent 7 5 00 1

Arrivals (CDA) 

j. NEXTGEN Weather 2 5 0 0 6

k. Enhanced vision 

systems 

2 5 10 5

l. Synthetic vision 

systems 

1 4 30 5

m. Reduced Vertical 

Separation 

5 6 10 1

n. Flying at slower 

speeds 

11 0 2 0 0

o. Formation flying 2 4 4 2 1

p. Air to air refueling 0 1 8 1 3

q. Reduced flight 

frequency with larger 

aircraft 

8 3 11 0

r. Multi-stage long 

distance travel 

6 1 22 2

Page 80 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

15. What major challenges exist to widespread use of ... 

a. Reduction of on-board weight 

b. Engine washing 

c. Limited use of paint on airframes 

d. Increased engine maintenance 

e. Single engine taxing 

f. Use of APU on ground at gate 

g. Automatic Dependent Surveillance – 

Broadcast (ADS-B) 

h. Required Navigation Performance 

(RNP) 

i. Continuous Descent Arrivals (CDA) 

j. NEXTGEN Weather 

k. Enhanced vision systems 

l. Synthetic vision systems 

m. Reduced Vertical Separation 

n. Flying at slower speeds 

o. Formation flying 

p. Air to air refueling

q. Reduced flight frequency with larger 

aircraft 

r. Multi-stage long distance travel 

Page 81 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

16. What actions could the U.S. federal government undertake to 

promote the adoption of ... 

a. Reductio board weight n of onb. Engine washing 

c. Limited u aint on airframes se of p

d. Increased eng e maintenance in

e. Single engine xing ta

f. Use of APU on ground at gate 

g. Automatic Dependent Surveillance – 

Broadcast (ADS-B) 

h. Required Navigation Performance 

(RNP) 

i. Continuous Descent Arrivals (CDA ) 

j. NEXTGEN Weather 

k. Enhanced vision systems 

l. Synthetic vision systems 

m. Reduced Vertical Separation 

n. Flying at slower speeds 

o. Formation flying 

p. Air to air refueling 

q. Reduced flight freque

aircraft 

ncy with larger 

r. Multi-stage long distance travel 

Page 82 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

Aviation and Climate Change

17. How would you rate your overall knowledge of alternative fuel 

options to reduce aircraft CO2 emissions, such as biofu Part 3: Alternative els? 

1 None Æ SKIP TO QUESTION #25

7 Minimal Æ SKIP TO QU

Æ CONTINUE TO QU TION #1

TINUE TO QU TION #1

ert opinion, compared to jet fuel currently in use, 

l for future reduction of 2 emis ns (on

sis) for the following options? 

No 

potential

w 

potential 

Medium 

potential 

High 

potential

Don’t 

know

Fuel Options 

ESTION #25 

2 Basic ES 8 

3 Proficient Æ CON

5 Advanced Æ CONTINUE TO QUESTION #18 

ES 8 

18. In your exp

what is the potentia

a life-cycle ba

 CO sio

Lo

a. Coal to liquid 7 1 2 0 0

b. Fischer-Tropsch-treate

 such as 

d 

s 

1 3 

feedstocks

switchgras

3 3 0

c. Fischer-Tropsch-treated 

forest waste 

1 3 3 3 0

d. Fischer-Tropsch-treated 1 5 1 3 0

municipal waste 

e. Hydotreated algae 0 3 1 6 0

f. Hydrotreated Palm and 

Soy Oils 

2 3 3 1 1

g. Hydrotreated camelina 1 2 3 2 2

h. Hydrotreated jatropha 0 3 3 2 2

i. Fuel cells 6 1 1 0 1

j. Hydrogen 4 2 1 1 1

Page 83 GAO-09-554 
Appendix III: Detailed Survey Results 

19. In your expert opinion, what would be the potential R&D costs 

to develop the following options for commercial use? 

 Low costs

Medium 

costs Highcosts

Don’t 

know

a. Coal to liquid 3 3 3 1

b. Fischer-Tropsch-treated 

feedstocks such as 

switchgrass 

1 3 4 2

c. Fischer-Tropsch-treated 4

forest waste 

1 3 2

d. Fischer-Tropsch-trea

municipal wa

ted 

ste 

0 4 42

e. Hydotreated algae 0 4 6 0

f. Hydrotreated Palm and Soy 

Oils 

2 3 3 2

g. Hydrotreated camelina 2 3 2 3

h. Hydrotreated jatropha 2 3 2 3

i. Fuel cells 0 1 7 2

j. Hydrogen 0 1 8 1

20. In your expert opinion, what is the level of p lic accep nce 

for the following options? 

s

Don’t 

know

ub ta

 Low costs

Medium 

costs 

High 

cost

a. Coal to liquid 5 3 0 2

b. Fischer-Tropsc

fe

h-treated 0 3 6 1

edstocks such as 

switchgrass 

c. Fischer-Tropsch-treated 

forest waste 

0 4 5 1

d. Fischer-Tropsch-treated 0 3 6 1

municipal waste 

e. Hydotreated algae 0 1 7 2

f. Hydrotreated Palm and Soy 5 1 2 2

Oils 

g. Hydrotreated camelina 0 5 2 3

h. Hydrotreated jatropha 0 3 4 3

Aviation and Climate Change

i. Fuel cells 1 4 3 2

j. Hydrogen 5 2 0 3

Page 84 GAO-09-554 
Appendix III: Detailed Survey Results 

21. In your expert opinion, given our best knowledge about fu

market conditions, and absent government inter

ture 

vention, how 

long would it take for the private sector to adopt these 

s? 

hort 

mef ame 

(<10years)

Medium 

timeframe 

(10-20 

years) 

Long 

timeframe 

(> 20 years)

Don’t 

know

technologie

 Never

S

ti r

a. Coal to liquid 7 2 0 0 1

b. Fischer-Tropsch-treated 

feedstocks such as 

switchgrass 

5 40 01

c. Fischer-Tropsch-treate

te 

d 5 40 01

forest was

d. Fischer-Tropsc

municipal w

h-treated 

aste 

5 40 01

e. Hydotreated algae 3 4 2 0 1

f. Hydrotreated Palm and 5 30 02

Soy Oils 

g. Hydrotreated camelina 4 3 0 0 3

h. Hydrotreated jatropha 4 3 0 0 3

i. Fuel cells 0 3 6 0 1

j. Hydrogen 1 0 7 1 1

22. What major challenges exist to widespread use of ... 

a. Coal to liquid 

b. Fischer-Tropsch-treated feedstocks 

such as switchgrass 

c. Fischer-Tropsch-treated forest waste 

d. Fischer-Tropsch-treated municipal 

waste 

e. Hydotreated algae 

f. Hydrotreated Palm and Soy Oils 

g. Hydrotreated camelina 

h. Hydrotreated jatropha 

i. Fuel cells 

j. Hydrogen 

Page 85 GAO-09-554 Aviation and Climate Change
Appendix III: Detailed Survey Results 

Page 86 GAO-09-554 Aviation and Climate Change

23. What actions could the federal government underta

promote the development and/or adoption of ... 

a. Coal to liquid 

ke to 

b. Fischer-Tropsch-treated feedstocks 

such as switchgrass 

c. Fischer-Tropsch-treated forest waste 

d. Fischer-Tropsch-treated municipal 

waste 

e. Hydotreated algae 

f. Hydrotreated Palm and Soy Oils 

g. Hydrotreated camelina 

h. Hydrotreated jatropha 

i. Fuel cells 

j. Hydrogen 

24. What other government actions, if any, should be undertaken 

address greenhouse gas emissions from commercial aircraft

to 

? 

25. Do you have any other comments about anything covered in this 

rating tool? If so, please comment here. 
Appendix IV: Scope and Methodology 

Page 87 GAO-09-554 

Appendix IV: Scope and Methodology 

To address our objectives, we interviewed selected officials 

knowledgeable about the aviation industry, the industry’s impact on th

production of greenhouse gas and other emissions that have an impact on

the climate, and options for reducing these emissions. We interviewed 

federal officials from the Environmental Protection Agency (EPA), FAA, 

the National Aeronautics and Space Administration (NASA) and the 

Departments of Defense and State. We also met with representatives of 

ICAO—a United Nations agency. We interviewed representatives of 

industry groups, environmental groups, airlines, aircraft manufacturers, 

aircraft engine manufacturers, alternative fuels manufacturers, 

economists, and academics. We interviewed officials based in the United 

States and abroad. We interviewed representatives of the EU and 

associations about the EU ETS. We completed a literature search

reviewed relevant documentation, studies, and articles related

objectives. To specifically address commercial aviation’s contribution to 

emissions, we asked our interviewees to identify the primary studies that 

estimate current and future emissions. As a result, we reviewed and 

summarized the findings of the 1999 International Panel of Climate Change 

Aviation and the Environment report and its 2007 Fourth Assessment

Report, which were most frequently named as the most authoritati

sources on global aviation emissions. 

To specifically address technological and operational options to reduce 

commercial aviation’s contribution to greenhouse gases and other 

emissions that can have an impact on the climate, we contracted with t

National Academy of Sciences to identify and recruit experts in aviation 

and environmental issues. We interviewed 18 experts identified by the 

Academy, including those with expertise in aeronautics, air traffic 

management, atmospheric science, chemistry, climate change modeling, 

e 

 and 

 to our 

ve 

he 

economics, environmental science, and transportation policy1

. In 

conducting these interviews, we used a standardized interview guide to 

obtain consistent answers from our experts and had the interviews 

recorded and transcribed. Based on these interviews, we assembled a list 

nt tool that instructed the experts to 

, 

 

of options for reducing aviation emissions, and we asked our experts to 

assess these options on several dimensions. We provided each of our 

experts with a standardized assessme

assess the potential of each technological and operational option on the 

following dimensions: potential fuel savings and emissions reductions

potential research and development costs, potential cost to the airline

 r a list of the experts we interviewed. 1

See Appendix II fo

 Aviation and Climate Change 
Appendix IV: Scope and Methodology 

industry, potential for public acceptance, and time frames for adoption. 

For each dimension, we asked the experts to assess each option on a 

three-point scale. For example, we asked the experts to rate each option 

xperts 

f 

ller 

s 

rcraft and 

ls 

ons 

e 

medium,” and “high” 

responses. We then determined an overall, or group, answer for each 

uestion based on the response the experts most commonly selected for 

each option and dimension. However, if approximately the same number 

f experts selected a second response, then we chose both responses as 

the group answer. For example, rather than reporting that the experts 

rated a particular option as having “high” potential, we instead reported 

that they rated it as having “medium-high” potential if approximately the 

same number of experts selected the “high” response as selected the 

“medium” response. Finally, if approximately the same number of experts 

 

as having “low potential”, “medium potential”, or “high potential” 2

 for fuel

savings and carbon dioxide emissions reductions.3

 We directed the e

not to answer questions about areas in which they did not have specific 

knowledge or expertise. As a result, throughout our report, the number o

expert responses discussed for each emissions reduction option is sma

than 18, the number of experts we interviewed. Besides asking the expert

to assess the potential of technological options, such as new ai

engine designs, we asked them to assess the potential of alternative fue

to reduce carbon dioxide emissions4

. Furthermore, for operational opti

we asked the experts to assess included options that the federal 

government must implement, such as air traffic management 

improvements, as well as options that the airlines can exercise to reduc

fuel burn. We analyzed and summarized the experts’ responses in order to 

identify those technological and operational options that the experts 

collectively identified as holding the most promise for reducing emissions. 

To analyze the results, for each option and dimension, we counted the 

numbers of experts that selected the “low,” “

q

o

2

We did not provide specific definitions for “low,” “medium,” and “high” and let each 

respondent determine what it meant to them. 

3

See app. III for a copy of the assessment tool that we asked the experts to complete as 

well as complete results. Additionally, we asked the experts to describe the major 

challenges to the widespread use of the options and the actions that the U.S. federal 

government could take to promote the development and/or adoption of any of these 

options. 

4

For alternative fuel options, we used a four-point scale to assess each option’s potential to 

reduce carbon dioxide emissions (“no potential,” “low potential,” “medium potential “or 

“high potential”). 

Page 88 GAO-09-554 Aviation and Climate Change
Appendix IV: Scope and Methodology 

Page 89 GAO-09-554 Aviation and Climate Change

selected all responses, then we determined that there was no consensus 

on that question and reported the result as such5

. 

In order to determine government options for reducing aviation emissions, 

we interviewed relevant experts, including those 18 recruited by the 

National Academy of Sciences, about the potential use and the costs and 

benefits of these options. We asked our interviewees to provide opinions 

and information on a variety of governmental options, including carbon 

taxes, cap-and-trade programs, aircraft and engine standards, governmentsponsored research, and governmental subsidies. We looked at 

governmental actions that have been taken in the past and at those that 

have been proposed. We reviewed economic research on the economic 

impact of policy options for addressing greenhouse gas emissions. Our 

review focused on whether policy options could achieve emissions 

reductions from global sources in an economically efficient manner (for 

example, maximize net benefits). We interviewed EU officials to understand 

how the EU ETS will work and to determine issues related to this scheme, 

which is slated to include certain flights into and out of EU airports starting 

in 2012. Additionally, we reviewed and summarized the EU ETS and the 

legal implications of the scheme (see app. I). 

 

5

We defined “approximately the same number of experts” as being either the exact same 

number of experts or as one fewer or one more expert. 
Appendix V: Comments from the National Appendix V: Comments from the N Aeronautics and Space Administration ational 

Aeronautics and Space Administration 

Page 90 GAO-09-554 Aviation and Climate Change 
Appendix VI: Comments from the Appendix VI: Comments from the Environmental Protection Agency 

Environmental Protection Agency 

Page 91 GAO-09-554 Aviation and Climate Change
Appendix VI: Comments from the 

Environmental Protection Agency 

Page 92 GAO-09-554 Aviation and Climate Change
Appendix VI: Comments from the 

Environmental Protection Agency 

Page 93 GAO-09-554 Aviation and Climate Change
Appendix VII: GAO Contact and Staff 

Acknowledgments 

Page 94 GAO-09-554 Aviation and Climate Change 

Appendix VII: GAO Contact and Staff 

Acknowledgments 

Susan Fleming, (202) 512-4431 or flemings@gao.gov

In addition to the contact above, Cathy Colwell and Faye Morrison 

(Assistant Directors), Lauren Calhoun, Kate Cardamone, Brad Dubbs, 

Elizabeth Eisenstadt, Tim Guinane, Michael Hix, Sara Ann Moessbauer,

Josh Ormond, Tim Persons (Chief Scientist), Matthew Rosenberg, and 

Amy Rosewarne made key contributions to this report. 

GAO Contact 

The GAO staff that worked on this report dedicate it to their late 

colleague, Jacqueline McFarlane, in recognition of the valuable 

contributions she made 

Staff 

Acknowledgements 

(541042) 
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