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7. Issues for the Future
This report has assessed the potential climate and ozone changes
due to aircraft to the year 2050 under different scenarios. It recognizes
that the effects of some types of aircraft emissions are well understood.
It also reveals that the effects of others are not, because of the many
scientific uncertainties. There has been a steady improvement in characterizing
the potential impacts of human activities, including the effects of
aviation on the global atmosphere. The report has also examined technological
advances, infrastructure improvements, and regulatory or market-based
measures to reduce aviation emissions. Further work is required to reduce
scientific and other uncertainties, to understand better the options
for reducing emissions, to better inform decisionmakers, and to improve
the understanding of the social and economic issues associated with
the demand for air transport.
There are a number of key areas of scientific uncertainty that limit
our ability to project aviation impacts on climate and ozone:
- The influence of contrails and aerosols on cirrus clouds
- The role of NOx in changing ozone
and methane concentrations
- The ability of aerosols to alter chemical processes
- The transport of atmospheric gases and particles in the upper troposphere/lower
stratosphere
- The climate response to regional forcings and stratospheric perturbations.
There are a number of key socio-economic and technological issues that
need greater definition, including inter alia the following:
- Characterization of demand for commercial aviation services, including
airport and airway infrastructure constraints and associated technological
change
- Methods to assess external costs and the environmental benefits
of regulatory and market-based options
- Assessment of the macroeconomic effects of emission reductions in
the aviation industry that might result from mitigation measures
- Technological capabilities and operational practices to reduce emissions
leading to the formation of contrails and increased cloudiness
- The understanding of the economic and environmental effects of meeting
potential stabilization scenarios (for atmospheric concentrations
of greenhouse gases), including measures to reduce emissions from
aviation and also including such issues as the relative environmental
impacts of different transportation modes.
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