provide the conclusions and also present avenues
how to reduce or even to avoid air traffic emissions
changing climate.
Emissions of Climatically Relevant
Substances by Aviation
The estimates of climate effects of air traffic
depend totally on a reliable time-dependent emission inventory on global scale for the past, the
present, and the future. The major research project
QUANTIFY of the European Union’s Sixth
Framework Research Programme (finished very
recently) has established such a consistent global
three-dimensional air transport emission inventory for greenhouse gases, particles, and precursor
gases of other greenhouse gases and for aerosol
particles for the year 2000 (also for all other
modes of transport), and has developed estimates
of future emissions for the years 2020, 2050, and
2100. The example for air traffic is shown in Fig. 1
and Table 1, taken from [25].
Since different substances in the aircraft
exhaust have very different concentrations and
also very different radiative properties, a common
scale must be created for a just assessment of the
environmental burden caused by different aircraft
and flight types. The next subsection will deal
with it.
Creating a Common Scale for the Climate
Effects of Air Traffic Emissions
The entire motorized transport sector (road traffic,
shipping, rail, aviation) emits a wide variety of
gases and aerosols into the atmosphere, with different characteristics, which either influence climate directly by their radiative properties or
indirectly via chemical and physical processes
influencing concentrations of other climatically
relevant substances. We need metrics that allow
these emissions to be placed on a common scale in
terms of their impact on global climate. The applications of such metrics are manifold: First, they
have served and will serve as basic information in
negotiations for international agreements and
emission trading schemes (see section “The
European Directive to Include Air Traffic into
the Emission Trading Scheme”); second, they
allow the assessment of trade-offs between
changes in emissions resulting from technological
or operational developments; third, they serve for
comparisons of different environmental impacts
caused by the different transport sectors and thus
help in traffic policy making. Usually, the CO 2
emission, common to all transport sectors, is used
as a reference. Therefore, all other emissions have
to be transformed into their “CO 2 -equivalents.”
Ideally, the same equivalent CO 2 emissions
should produce the same climate effect, regardless
of their shares in the exhaust or after chemical
transformation in the atmosphere. This is, however, only an approximation of reality, because
most of the non-CO 2 emissions from the different
transport sectors, and especially aviation, are
short-lived substances with often rather regionalized concentrations. In addition, these short-lived
substances are all not included in the Kyoto Protocol basket of solely long-lived greenhouse
gases.
The challenges in developing generally
accepted metrics are strongly magnified by the
inclusion of short-lived species. One first difficulty concerns the choice of an appropriate structure for the metric. Should effects of an emission
today be integrated over 10, 20, 50, 100, or even
200 years? Or should the impact, e.g., the global
mean surface temperature increase after a certain
time period, be used as a measure? The first
approach is the most frequently used one, characterized by the global warming potential (GWP)
and the one adopted in the Kyoto Protocol. The
second one, called global temperature change
potential (GTP), strongly reduces the influence
of short-lived emissions if the same long time
horizon is used as typically for GWP. In view of
the lifetime (defined as the time for the decay of
the concentration of an emitted pulse of a substance to 1/e) in the atmosphere of an anthropogenic addition of CO 2 , which is well above
100 years, 100 years have been chosen for the
Kyoto Protocol, although there was no specific
argument put forward for this time horizon by
IPCC. A further challenge is the quantification
of input parameters for the metric, originating in
the uncertainty of atmospheric processes. For
Aviation and Atmosphere
329
how to reduce or even to avoid air traffic emissions
changing climate.
Emissions of Climatically Relevant
Substances by Aviation
The estimates of climate effects of air traffic
depend totally on a reliable time-dependent emission inventory on global scale for the past, the
present, and the future. The major research project
QUANTIFY of the European Union’s Sixth
Framework Research Programme (finished very
recently) has established such a consistent global
three-dimensional air transport emission inventory for greenhouse gases, particles, and precursor
gases of other greenhouse gases and for aerosol
particles for the year 2000 (also for all other
modes of transport), and has developed estimates
of future emissions for the years 2020, 2050, and
2100. The example for air traffic is shown in Fig. 1
and Table 1, taken from [25].
Since different substances in the aircraft
exhaust have very different concentrations and
also very different radiative properties, a common
scale must be created for a just assessment of the
environmental burden caused by different aircraft
and flight types. The next subsection will deal
with it.
Creating a Common Scale for the Climate
Effects of Air Traffic Emissions
The entire motorized transport sector (road traffic,
shipping, rail, aviation) emits a wide variety of
gases and aerosols into the atmosphere, with different characteristics, which either influence climate directly by their radiative properties or
indirectly via chemical and physical processes
influencing concentrations of other climatically
relevant substances. We need metrics that allow
these emissions to be placed on a common scale in
terms of their impact on global climate. The applications of such metrics are manifold: First, they
have served and will serve as basic information in
negotiations for international agreements and
emission trading schemes (see section “The
European Directive to Include Air Traffic into
the Emission Trading Scheme”); second, they
allow the assessment of trade-offs between
changes in emissions resulting from technological
or operational developments; third, they serve for
comparisons of different environmental impacts
caused by the different transport sectors and thus
help in traffic policy making. Usually, the CO 2
emission, common to all transport sectors, is used
as a reference. Therefore, all other emissions have
to be transformed into their “CO 2 -equivalents.”
Ideally, the same equivalent CO 2 emissions
should produce the same climate effect, regardless
of their shares in the exhaust or after chemical
transformation in the atmosphere. This is, however, only an approximation of reality, because
most of the non-CO 2 emissions from the different
transport sectors, and especially aviation, are
short-lived substances with often rather regionalized concentrations. In addition, these short-lived
substances are all not included in the Kyoto Protocol basket of solely long-lived greenhouse
gases.
The challenges in developing generally
accepted metrics are strongly magnified by the
inclusion of short-lived species. One first difficulty concerns the choice of an appropriate structure for the metric. Should effects of an emission
today be integrated over 10, 20, 50, 100, or even
200 years? Or should the impact, e.g., the global
mean surface temperature increase after a certain
time period, be used as a measure? The first
approach is the most frequently used one, characterized by the global warming potential (GWP)
and the one adopted in the Kyoto Protocol. The
second one, called global temperature change
potential (GTP), strongly reduces the influence
of short-lived emissions if the same long time
horizon is used as typically for GWP. In view of
the lifetime (defined as the time for the decay of
the concentration of an emitted pulse of a substance to 1/e) in the atmosphere of an anthropogenic addition of CO 2 , which is well above
100 years, 100 years have been chosen for the
Kyoto Protocol, although there was no specific
argument put forward for this time horizon by
IPCC. A further challenge is the quantification
of input parameters for the metric, originating in
the uncertainty of atmospheric processes. For
Aviation and Atmosphere
329