In contrast with some other sectors, voluntary agreements within the aviation industry to meet environmental targets without recourse to regulatory standards have been rare. In its consultation paper on air transport and the environment, the European Commission has recommended that the industry examine options for establishing voluntary environmental agreements. A further recommendation was that better information should be provided to consumers about the environmental performance of alternative air travel options (European Commission, 1998). A similar consultative process is occurring in the United States, where the White House Climate Change Task Force is seeking voluntary reductions in greenhouse gas emissions from many industries, including aviation.
In addition, the Kyoto Protocol and the following Conferences of Parties have stimulated interest in the possible role of other voluntary measures (such as carbon sequestration) as a further way to mitigate the effects of CO2 emissions. At present, there is no clear picture of the role such measures could play in joint implementation and other mechanisms that may have international significance in the limitation of CO2 emissions.
One additional potential mitigation measure is encouragement of surface transport-principally rail-in place of air travel, through the use of economic instruments or restrictions on the use of air travel on certain routes. Intermodal substitution is considered in Section 8.3.3 of this report, where it is noted that the scope for substituting other modes for air is up to 10%. Moreover, comparison of carbon emissions among different modes of transport is highly dependent on the type of aircraft, train, or car and the type of service.
Interactions between emissions and climate effects are not fully understood; research efforts on the environmental impact of aircraft emissions can assist the decisionmaking process. Research relating to the atmospheric effects of aircraft emissions and their mitigation through technological and operational measures is taking place throughout the world. The European Commission and the U.S. government sponsor substantial programs. These efforts are also complemented with aviation-focused scientific assessments that are cited in other chapters of this report.
Based on full consideration of mitigation options available to policymakers to influence aviation emissions, if needed, and underlying information requirements, the main areas that require future research follow:
. Uncertainties over future trends in traffic, technology, and therefore
emissions, depending on the scenarios chosen. Factors underlying this uncertainty
include uncertainties about the pace of introduction of CNS/ ATM and the impact
of infrastructure constraints in limiting growth in demand. These future projections
and scenarios form the base case against which policy measures are considered.
. The impact of aviation emissions on the environment and the monetary value associated with the benefits of mitigating those impacts. There is uncertainty about the appropriate level at which any environmental levy should be set.
. The impact of deregulation and subsidies to airlines on fuel consumption and emissions.
. The environmental benefits of ICAO engine emissions stringency standards.
. How the "best available" technology concept used in other sectors might be applied in aviation.
. The impact of various options on encouraging adoption of technological changes.
. The applicability of various market options to the circumstances of countries not included in Annex 1 to the UNFCCC.
. Practical experience with emissions trading at the global level.
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