Aviation and Climate Change: Aircraft Emissions Expected to Grow, but Technological and Operational Improvements and Government Policies Can Help Control Emissions
Published: 2009-06-08T00:00:00

Fast Facts:

Highlights:
section_title: Why GAO Did This Study
paragraphs: 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.
section_title: What GAO Found
paragraphs: According to IPCC, aviation currently accounts for about 2 percent of human-generated 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 medium-range 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 cap-and-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.

section_title: Letter
paragraphs: 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  during the 2008 through 2012 commitment period. 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.” Finally, some  governments have taken actions designed to control aviation emissions.  For example, in 2003, the European Union (EU) established a cap-and- trade 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.
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,  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.
subsections: section_title: Background
paragraphs: 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.
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. According to the FAA, in 2006  the civil aviation industry in the United States directly and indirectly  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.
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. 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,  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.
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.
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.
To develop a better understanding of the effects of human-induced climate  change and identify options for adaptation and mitigation, 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  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,  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); 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 engines and has adopted emission standards matching those for  aircraft set by ICAO. While neither ICAO nor EPA has established  standards for aircraft engine emissions of carbon dioxide, ICAO is  currently discussing proposals for carbon dioxide emissions standards and  considering a global goal for fuel efficiency. 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.
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. 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. The Protocol  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.  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.
section_title: Aviation Emissions Represent a Small but Growing Share of All Emissions
paragraphs: 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 forcing 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  300 leading and contributing authors and experts worldwide and is  internationally accepted and used for policy making.
subsections: section_title: Aviation Contributes about 2 Percent of Global Carbon Dioxide Emissions
paragraphs: According to IPCC, global aviation contributes about 2 percent of the  global carbon dioxide emissions caused by human activities. 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. In the United  States, domestic aviation contributes about 3 percent of total carbon  dioxide emissions, according to EPA data.
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. 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  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.
section_title: Aviation Contributes about 3 Percent of All Human- Generated Emissions
paragraphs: 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  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.
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  percent 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.
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. 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  from aviation emissions is estimated to be approximately two times that of  carbon dioxide alone.
section_title: Global Aviation Emissions Are Expected to Grow but Forecasts Vary, Primarily Reflecting Different Economic Growth Assumptions
paragraphs: IPCC generated three scenarios that forecasted the growth of global  aviation carbon dioxide emissions from the near-term (2015) to the long- term (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.
subsections: section_title: Forecasts of Global Economic Growth and Air Traffic Primarily Drive IPCC’s Emissions Estimates
paragraphs: 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.
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. 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.
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  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. 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. 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. 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. To account for some uncertainties in FAA’s emissions  forecasting, FAA officials said they are working on creating future  scenarios for the U.S. aviation sector to assess the influence of a range of  technology and market assumptions on future emissions levels.
section_title: Other Forecasts Show Continued Long-term Growth, but Emissions Could Fall below Estimated Levels during the Current Economic Downturn
paragraphs: 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. 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  decline.
section_title: Assumptions about Other Factors Could Affect IPCC’s Forecasts
paragraphs: In developing its forecasts, IPCC made assumptions about factors other  than economic growth that also affected its for experts we interviewed, and FAA have noted:  ecast results, as IPCC itself,  IPCC assumed that advances in aircraft technology and the introduction new aircraft would increase fuel efficiency by 40 percent to 50 percent  from 1997 through 2050.
IPCC assumed that an ideal air traffic management system w place worldwide by 2050, reducing congestion and delays.
However, the forecast doesn’t account for the possibility that some airlines might adopt  low-carbon alternative fuels.
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.
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.
section_title: 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
paragraphs: 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.
subsections: section_title: Experts Believe That Although Many Technologies Are Expected to Help Reduce Emissions Growth in the Future, They Involve Trade-offs
subsections: section_title: Aircraft Engine Improvements
paragraphs: 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. Such improvements have resulted  from increasing engine pressure and temperatures (which increases their  efficiency and decreases fuel usage) and improving the “bypass ratio,” a  measure of airflow through the engine. However, according to experts  we surveyed, further advances in these technologies may face hi gh  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.
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  face few challenges to widespread adoption. 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.
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.
section_title: Aircraft Improvements
paragraphs: 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 wing- body aircraft, hold potential for greater reductions in emissions rates.  However, new aircraft concepts face engineering and consumer  acceptance challenges and new technologies are likely to incur high  development costs (see table 3).
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  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.
section_title: Experts Also Expect Operational Improvements to Help Reduce Aircraft Emissions in the Future, but Reductions May Be Limited
paragraphs: 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  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).
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  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 in- route 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.
section_title: Air Traffic Management Improvements through NextGen Will Incorporate Technological and Operational Improvements to Help Reduce Aircraft Emissions According to Experts
paragraphs: 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.
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  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.
section_title: Alternative Fuel Sources Have Potential for Reducing Aircraft Greenhouse Gas Emissions, but Challenges Exist
paragraphs: 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. 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. FAA, EPA, and U.S. Air Force  officials we met with said that quantifying the life-cycle emission of  biofuels is difficult, but work in this area is currently under way. 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.
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.
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. 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.
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.
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. 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 on- ground and in-flight tests indicated that the aircraft engines performed  well while using the biofuel.
section_title: 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
paragraphs: 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 low- emission 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  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  2000 emissions levels. 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. 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.
section_title: Governments Can Use a Variety of Policy Options to Help Reduce Commercial Aircraft Emissions, but the Costs and Benefits of Each Vary
paragraphs: 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 low- emissions 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  emissions from other sectors, could be costly and have little potential  impact on reducing global greenhouse gas emissions.
subsections: section_title: Market-Based Policies Could Be Used to Provide Airlines and Other Sources with an Economic Incentive to Reduce Greenhouse Gas Emissions
paragraphs: 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.
subsections: section_title: Cap-and-Trade Program
paragraphs: 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  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.
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  in energy prices, available technologies, and weather, making it more  expensive for sources to meet the cap. To limit price volatility, a cost- containment 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. 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. 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.
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  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 cap- and-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. 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.
Some countries are planning to address aviation emissions through cap- and-trade programs. The European Union originally implemented the EU  ETS in 2005, covering industries representing about 50 percent of its  carbon dioxide emissions. The EU is planning on including all covered  flights by aircraft operators flying into or out of EU airports, starting in  2012. Please see appendix I for more details on the EU ETS, including a  comprehensive discussion of the potential legal implications and  stakeholders’ positions on this new framework. Other countries are  considering cap-and-trade programs that would affect the aviation sector.
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, 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-and- trade program that covered petroleum refiners and importers, among  other entities. The costs of the regulation would have been borne by  these refiners and importers who would likely have passed on those costs  to airlines through increases in the price of jet fuel.
section_title: Emissions Taxes
paragraphs: 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 cap- and-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.
According to economic theory, an emissions tax should be set at a level  that represents the social cost of the emissions. Nonetheless, estimates  of the social costs associated with greenhouse gas emissions vary. For  example, IPCC reported that the social costs of damages associated with  greenhouse gas emissions average about $12 per metric ton 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  reductions because the reductions would depend on the level of the tax  and how firms and consumers respond to the tax.
section_title: Subsidies
paragraphs: 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 fuel- efficient engines are developed and become commercially available,  subsidies or tax credits could lower their relative costs and encourage  airlines to purchase them.
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.
section_title: Distribution of Costs under Market-based Measures
paragraphs: 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, they are  constrained in passing on their costs, and the costs to industry likely will  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,  with annual costs subsequently increasing. 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. 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.
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.
section_title: Emissions Standards Could Limit Emissions from Specific Technologies, but Are Generally Not an Economically Efficient Approach for Reducing Greenhouse Gas Emissions
paragraphs: 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 fuel- efficient 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.
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.
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. 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  of controlling emissions. 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. 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.
section_title: Government-Sponsored Research and Development Can Help Encourage the Development and Adoption of Low- Emissions Technologies, but May Be Costly to Governments
paragraphs: Government-sponsored research into low-fuel consumption and low- emissions 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 long- term 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 cap- and-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.
Various U.S. federal agencies, including NASA and FAA, have long been  involved in research involving low-emissions technologies. 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  concepts. NASA follows goals set by the National Plan for Aeronautics  Research and Development and Related Infrastructure for fuel efficiency  improvements for each of these generations (see table 6).
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. 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. 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.
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 year is devoted to  basic research through ACARE. Another research effort in Europe is the  Clean Sky Joint Technology Initiative, which will provide €1.6 billion over  7 years to fund various demonstration technologies.
section_title: Agency Comments and Our Evaluation
paragraphs: 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.
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  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  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.
section_title: Appendix I: Legal Implications of European Union Emissions Trading Scheme
paragraphs: 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.
subsections: section_title: EU ETS Law
paragraphs: 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. 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. The directive was published in the Official Journal on January  13, 2009, and became effective on February 2, 2009.
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  aircraft operators flying into or out of an EU airport. Emissions will be  calculated for the entire flight. For 2012, the cap for all carbon dioxide  emissions from covered flights will be set at 97 percent of historical  aviation emissions. 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.
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. Individual member states, in  accordance with the EU regulation, will conduct the auctions for aircraft  operators assigned to that member state. 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  total verified aviation emissions for all member states for a certain year.  The member states will be able to use the revenues raised from auctions in  accordance with the amended directive. 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. 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,  each aircraft operator will be allowed to use CERs and ERUs to cover at  least 1.5 percent of their emissions.
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. Although 2012 is the first year aircraft operators must comply  with the ETS law, preparations in the EU and from U.S. carriers began  soon after the law went into force.
section_title: Legal Implications of the ETS
paragraphs: 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’).
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.” Although the UNFCCC required  signatory states to formulate a national response to climate change, its  mitigation provisions did not require mandatory national emissions  targets.
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. The  Kyoto Protocol established binding greenhouse gas emissions targets for a  number of industrialized nations and the European Economic  Community (EEC). 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.” 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. Notably,  the treaty sets forth sovereignty provisions, recognizing that a contracting  state has exclusive sovereignty over airspace above its own territory.  Provisions potentially applicable to the recent amendment incorporating  aviation into the ETS include Article 11, Article 12, Article 15, and  Article 24.
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. 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. Additionally, the Resolution formed a new Group on  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. GIACC is due to  report to the Council later this year.
Finally, the U.S.-EU Air Transport Agreement, 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. 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.
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.”
section_title: Stakeholder Positions on Legal Issues
paragraphs: 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.
subsections: section_title: Stakeholder Positions within the United States
paragraphs: 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.
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. While  the executive branch has not articulated a position on this issue since mid- 2008, it has expressed the importance of climate change and developing a  solution on a global level.
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.  ATA argues that imposition of the ETS on U.S.-based carriers is contrary  to Articles 1, 12, 11, 15 and potentially, in the alternative, Article 24. 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, is  violated by the EU’s extraterritorial reach which covers emissions of non- EU airlines in another states’ airspace. Further, Article 12, which requires  contracting states to ensure that aircraft under its jurisdiction are in  compliance with rules and regulations relating to the flight and maneuver  of aircraft, 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  nt  coverage of non-agreeing-EU airlines over the high seas is inconsiste with ICAO’ 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 15 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. ATA has  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.
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. 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.” The bill recommends working through ICAO  to address these issues.
section_title: Stakeholder Positions outside the United States
paragraphs: 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.  IETA  supports the inclusion of aviation in the EU ETS from a policy perspective,  but has not opined on the legality of its inclusion. 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. However,  the organization has expressed concerns over a number of issues, some of  which include access to project credits, amount of allowances available  for auctioning, and allocation calculation.
Id. at 170-73. consequently, Article 15 is inapplicable. Finally, Article 24 of the  Convention does not apply to the Emissions Trading System because  trading allowances are “fundamentally different from customs duties.”  Additionally, the opinion finds policy support for these legal findings in  ICAO Resolution A35-5 and bilateral air transport agreements.
Additionally, countries outside the European Community have joined the  United States in an expression of concerns regarding the imposition of the  r  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. The letter asks that the EU ETS not include no aircraft unless done by mutual consent. 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. 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. The letter closes with a  n” nter to  reservation of right to take appropriate measures under international law if the ETS is imposed.
section_title: Legal Scholar/Researcher Views
paragraphs: Given the controversial nature and complexity of aviation’s inclu the EU ETS, a number of scholars in the legal community, both within the  United States and the EU, have provided explanatory articles or position  papers on the issue of the consistency of the EU’s plans with its  international legal obligations.
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.” This  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 and  legal challenges. 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 … .” Finally, Reagan argues that pursuing an emissions  reduction regime through ICAO could avoid likely legal challenges which  present themselves under the current ETS, as ICAO could facilitate a  common understanding of contentious provisions. In conclusion, he  proposes that the EU should channel the energy for implementation of the  current regime into holding ICAO accountable for fulfilling environmental  duties.
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. article presents the case that neither existing traffic rights in member  states, bilateral air transport agreements, nor the Chicago Convention  pose any legal obstacles. He argues, in fact, that the EU has a mandate  under the UNFCCC and the Kyoto Protocol to implement climate change  policies which include aviation. First, the article sets forth that the  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 discrimination on  the basis of nationality, as required by Article 11. 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 certain  aircraft operations. Article 15, which covers charges, is similarly  inapplicable because emissions allowances on the free market or through  the auctioning process do not constitute a charge. Finally, Article 24 is  inapposite as well because the emissions trading system does not  constitute a customs duty.
Additionally, Schwarze argues that the bilateral air transport agreements  with various nations, such as the Open Skies Agreement with the Unite d  States, do not pose any legal barriers to inclusion of aviation in ETS.
Id. at 12-13.
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. The article argues so long as the ETS operates without discrimination, it is in conformity  with the principle of a sound and economic operation of air services and  therefore satisfies the fairness clause. Finally, since the ETS gives only  incentive to reduce emissions, it does not regulate the amount of air  traffic.
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, recognizing that  this can be done “jointly with other parties.” Additionally, the Kyoto  Protocol, which sought to strengthen UNFCCC, required Annex 1 parties  to pursue “limitations or reduction of emissions of greenhouse gases …  from aviation … working through the International Civil Aviation  Organization.” And finally, although not legally binding, ICAO Resolution  A35-5 endorses the development of an open emissions trading system for  international aviation.
section_title: Potential Legal Challenges and Dispute Resolution
paragraphs: A  re  actions under international law if the ETS is imposed. If challenges are  brought forth, they could potentially be brought forth under the Chicag o  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 he Convention (Settlement of Disputes) is  invoked. Article 84 provides that if there is a disagreement by two or more  contracting states which cannot be settled by negotiation, it will be  decided upon by the Council. 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.
Air service agreements additionally have dispute resolution procedures  and the U.S.-EU Air Transport Agreement is no exception. Article 19 of the  U.S.-EU Air Transport Agreement provides that parties to a dispute may  submit to binding arbitration through an ad hoc tribunal if negotiations  fail. 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.
section_title: Appendix II: List of Experts
section_title: Appendix III: Detailed Survey Results
paragraphs: 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.
Instructions for Completing This Tool  You can answer most of the questions by checking boxes or filling in  blanks.  A few questions request short narrative answers.  Please note that  these blanks will expand to fit your answer.   ease use your mouse to na Pl on the field or checkin or “Enter” keys, bec g the box you ish to fill in. ause doing so ay cause for m ut the do   D ma cum ing  o not use the “Tab tting prob ms. le ”
To select a box, click on  it once; to d select a box, double click on it.
If you prefer, you may pr fax.  Please use ext questions.
We ask that you complet Rosenberg  your desktop or hard drive and  by January 9, 2009.  Plea  save the com leted document to  e-mail it as an attachment to  RosenbergMC@gao.gov.  If you complete this tool by hand, please fax the  completed tool to Matthew Rosenberg at GAO at 312-220-7726.
If you have any quest Analyst, at 3 Assistant Director, at 312 enior  12-220-7645 or RosenbergMC@gao.gov or Cathy Colwell,  ions, please co act Matthew senberg v. help.
subsections: section_title: Part 1: Technology Options
paragraphs: 1.  How would you rate y our overall knowledge of technological  options to reduc as aircraft  costs of  e aircraft carbon dioxide ( O) emissions, such  engines and aircraft design technologies, and the  those technologies?
SKIP TO QUESTION #9  0 None    SKIP TO QUESTION #9  6 Minimal  4 Basic    CONTINUE TO QUESTION #2  1 Proficient    CONTINUE TO QUESTION #2   TO QUESTION #2  7 Advanced    CONTINUE2.  In your expert opinio n, what is the potential for futur  fuel  savings and CO3.  In your expert opinion, what would be the potential R&D costs to develop the following options for commercial use? a.  Open rotor engines  b.  Geared Turbo Fan  (Composites) e.
4.
Given your answer to question two, what would be the potential  costs to the air transport industry to procure, operate and  maintain the following options to achieve those fuel savings an CO emissions reductions?
Medium costs  High costs Don’t know a.  Open rotor engines  b.  Geared Turbo Fan  ) e.
5.  In your expert opinion, what is the level of public acceptance  for the following conceptual options? a.  Open rotor engines  b.  Geared Turbo Fan  (Composites) e.
6.
In your expert opinion, given our best knowledge about future  market conditions, and abt government intervention, how sen long would it take for technolo  the private sector to adopt these  gies? timeframe (< 5 years)
Medium  timeframe  (5 - 15  years)
Long  timeframe  (> 15  a.  Open rotor engines  b.  Geared Turbo Fan  (Composites) e. a.  Open rotor engines  b.  Geared Turbo Fan Engines  c.  d. (Composites) e.  f.
section_title: Part 2: Operational Options
paragraphs: 9.  How would you rate your overall knowledge of operational  options to reduce aircraft fuel usage and CO?
11. In your expert opinion, what would be the potential R&D costs  to develop the following options for commercial use?
12. Given your answer to question ten, what would be the potentia costs to the air transport in options to achieve those fuel savings and CO  emissions  reductions? dustry to adopt the following  13. In your expert opinion, what is the level of public acceptance  for the following options?
Limited use of paint on airframes  Use of APU on ground at gate  Automatic Dependent Surveillance –  Broadcast (ADS-B)
Required Navigation Performance  (RNP)
Continuous Descent Arrivals (CDA)
14. In your expert opinion, given our best knowledge about future  market conditions, and absent government intervention, how  long would it take for the priva e sector to adopt these t technologies?
S timefr (< 5 years)
Medium  meframe ti (5 -15 years) (> 15 years) Never a.  Reduction of on-board  c.  Limited use of paint on  d.  f.  Use of APU on ground  Surveillance –  Broadcast (ADS-B)
Performance (RNP) a.  b.  c.  d.  e.  f.  Use of APU on ground at gate  g.  Automatic Dependent Surveillance –  Broadcast (ADS-B)  (RNP)  i.  Continuous Descent Arrivals (CDA )
section_title: Part 3: Alternative Fuel Options
paragraphs: 17. How would you rate your overall knowledge of alternative fuel  options to reduce aircraft COemissions, such as biofu els?
1 None  7 Minimal  2 Basic  8  3 Proficient    CON 8  5 Advanced    CONTINUE TO QUESTION #18    SKIP TO QUESTION #25   SKIP TO QU   CONTINUE TO QU TION #1ES TINUE TO QU TION #1ES 18. In your exp ert opinion, compared to jet fuel currently in use,  what is the potentia a life-cycle ba l for future reduction of sis) for the following options?
CO 19. In your expert opinion, what would be the potential R&D costs  to develop the following options for commercial use? a.  Coal to liquid  f.  Hydrotreated Palm and Soy  i.
20. In your expert opinion, what is the level of p for the following options? a.  Coal to liquid  f.  Hydrotreated Palm and Soy  i.
21. In your expert opinion, given our best knowledge about fu market conditions, and absent government inter long would it take for the private sector to adopt these  technologies? ti (<10years)
Medium  timeframe  (10-20  years) (> 20 years) a. Coal to li i. a.  Coal to liquid  f.  Hydrotreated Palm and Soy Oils  i.
24. What other government actions, if any, should be undertaken  address greenhouse gas emissions from commercial aircraft ?  25. Do you have any other comments about anything covered in th rating tool?  If so, please comment here.
section_title: Appendix IV: Scope and Methodology
paragraphs: To address our objectives, we interviewed selected officials  knowledgeable about the aviation industry, the industry’s impact on the  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 and  reviewed relevant documentation, studies, and articles related to our  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 authoritative  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 the  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,  economics, environmental science, and transportation policy. 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  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 assessment tool that instructed the experts to  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  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  as having “low potential”, “medium potential”, or “high potential”  for fuel savings and carbon dioxide emissions reductions. 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 rcraft and  to assess the potential of technological options, such as new ai ls  engine designs, we asked them to assess the potential of alternative fue to reduce carbon dioxide emissions. Furthermore, for operational opti ons  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,” “ responses. We then determined an overall, or group, answer for each  q uestion based on the response the experts most commonly selected for  each option and dimension. However, if approximately the same number  o 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  medium,” and “high”  f experts selected a second response, then we chose both responses as  selected all responses, then we determined that there was no consensus  on that question and reported the result as such.
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, government- sponsored 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).
section_title: Appendix V: Comments from the National Aeronautics and Space Administration
section_title: Appendix VI: Comments from the Environmental Protection Agency
section_title: Appendix VII: GAO Contact and Staff Acknowledgments
subsections: section_title: GAO Contact
section_title: Staff Acknowledgements
paragraphs: 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.