have not been altered significantly [25]. There is,
however, a discussion about a new potential influence of aviation on cloudiness, the so-called soot
cirrus (as already discussed above), relating to
effects of changed optical properties of ice clouds
into which soot from aircraft exhaust is mixed and
which may act after transformations in the atmosphere as ice nuclei. The related model estimates
[26, 29] diverge so strongly (see also the values
given for soot cirrus in Table 2) and they are not
backed by observations that much more research
is needed before conclusions on a changed aviation policy could be drawn. In this context, it is too
early to ask whether aviation’s influence on radiative forcing might even change the sign.
Man-made changes in cirrus cloud cover can be
detected by comparing cirrus trends over adjacent
regions with dense and nearly no air traffic. Some
exemplary long-term trends are shown in Fig. 6,
taken from QUANTIFY [30]. It is evident that cirrus
cloud coverage increases more or decreases less in
regions with dense air traffic compared to regions
with little air traffic. This could be considered a
signature of increasing air traffic in the past
20 years. Such preliminary estimates from the differences in cirrus cloud cover, however, suggest an
effect on radiative forcing of the order of only
6 mW/m for an assumed optical thickness of 0.4
for the cirrus clouds with air traffic influence.
Much better information on the statistics of optical thicknesses of single contrails, including the
variation over their life cycle, can be obtained now
from a contrail tracking algorithm that has been
developed during QUANTIFY [34, 35]. The combination of such a tracking algorithm, based on
satellite data from a polar orbiter (MODIS on
NASA’s Aqua and Terra satellites) and a geostationary one (MSG operated by EUMETSAT), with a
numerical contrail plume model for which first
developments have been made in the project allows
to extend the observable fraction of a contrail life
cycle in both directions, that is, from formation up to
its end. There are, however, not yet trends available
for a larger area with intense air traffic over Europe.
Changes of Air Chemistry by Air Traffic
The present and future impacts of emissions from
aviation are typically evaluated using several
global atmospheric chemistry models in order to
obtain not only a quantification of the impact of a
specific transport sector on global atmospheric
composition but also an estimate of the associated
model uncertainties. For the QUANTIFY project
such an assessment included chemistry transport
models and chemistry-climate models. For these
simulations the global emission inventory
Aviation and Atmosphere, Table 2 Year 2000 radiative forcing (in mWm
À2
) for each transport sector and each
forcing mechanism relative to pre-industrial times, together with uncertainties. SWV is stratospheric water vapor
Road
Ship
Air
Rail
CO 2
131 Æ 15
34 Æ 6
2 0 Æ 3
2 3 Æ 7
Ozone
32 Æ 9
2 4 Æ 6
1 8 Æ 3
2 Æ 0.4
CH 4 lifetime
À7 Æ 4
À19 Æ 2
À5 Æ 1
À1 Æ 0.4
CH 4 – ozone
À3 Æ 2
À8 Æ 1
À2 Æ 0.5
À0.3 Æ 0.2
SWV methane
À1 Æ 0.7
À3 Æ 0.7
À1 Æ 0.3
À0.1 Æ 0.1
SWV direct
1 Æ 0.2
CFCs/HFCs
28 Æ 3
Stratospheric ozone
À2 Æ 4
Sulphate aerosol
À9 Æ 4
À26 Æ 11
À1 Æ 0.4
À1 Æ 0.3
Black carbon aerosol
44 Æ 17
2 Æ 1
0.3 Æ 0.1
1 Æ 0.3
Organic carbon aerosol
À2 Æ 1
À1 Æ 0.5
À0.5 Æ 0.3
Indirect aerosol effect
6 Æ 111
À49 Æ 209
À127 Æ 128
0.5 Æ 10
Contrails
7 (À4, +6)
Aviation induced cirrus
21 (À9, +17)
338
Aviation and Atmosphere
however, a discussion about a new potential influence of aviation on cloudiness, the so-called soot
cirrus (as already discussed above), relating to
effects of changed optical properties of ice clouds
into which soot from aircraft exhaust is mixed and
which may act after transformations in the atmosphere as ice nuclei. The related model estimates
[26, 29] diverge so strongly (see also the values
given for soot cirrus in Table 2) and they are not
backed by observations that much more research
is needed before conclusions on a changed aviation policy could be drawn. In this context, it is too
early to ask whether aviation’s influence on radiative forcing might even change the sign.
Man-made changes in cirrus cloud cover can be
detected by comparing cirrus trends over adjacent
regions with dense and nearly no air traffic. Some
exemplary long-term trends are shown in Fig. 6,
taken from QUANTIFY [30]. It is evident that cirrus
cloud coverage increases more or decreases less in
regions with dense air traffic compared to regions
with little air traffic. This could be considered a
signature of increasing air traffic in the past
20 years. Such preliminary estimates from the differences in cirrus cloud cover, however, suggest an
effect on radiative forcing of the order of only
6 mW/m for an assumed optical thickness of 0.4
for the cirrus clouds with air traffic influence.
Much better information on the statistics of optical thicknesses of single contrails, including the
variation over their life cycle, can be obtained now
from a contrail tracking algorithm that has been
developed during QUANTIFY [34, 35]. The combination of such a tracking algorithm, based on
satellite data from a polar orbiter (MODIS on
NASA’s Aqua and Terra satellites) and a geostationary one (MSG operated by EUMETSAT), with a
numerical contrail plume model for which first
developments have been made in the project allows
to extend the observable fraction of a contrail life
cycle in both directions, that is, from formation up to
its end. There are, however, not yet trends available
for a larger area with intense air traffic over Europe.
Changes of Air Chemistry by Air Traffic
The present and future impacts of emissions from
aviation are typically evaluated using several
global atmospheric chemistry models in order to
obtain not only a quantification of the impact of a
specific transport sector on global atmospheric
composition but also an estimate of the associated
model uncertainties. For the QUANTIFY project
such an assessment included chemistry transport
models and chemistry-climate models. For these
simulations the global emission inventory
Aviation and Atmosphere, Table 2 Year 2000 radiative forcing (in mWm
À2
) for each transport sector and each
forcing mechanism relative to pre-industrial times, together with uncertainties. SWV is stratospheric water vapor
Road
Ship
Air
Rail
CO 2
131 Æ 15
34 Æ 6
2 0 Æ 3
2 3 Æ 7
Ozone
32 Æ 9
2 4 Æ 6
1 8 Æ 3
2 Æ 0.4
CH 4 lifetime
À7 Æ 4
À19 Æ 2
À5 Æ 1
À1 Æ 0.4
CH 4 – ozone
À3 Æ 2
À8 Æ 1
À2 Æ 0.5
À0.3 Æ 0.2
SWV methane
À1 Æ 0.7
À3 Æ 0.7
À1 Æ 0.3
À0.1 Æ 0.1
SWV direct
1 Æ 0.2
CFCs/HFCs
28 Æ 3
Stratospheric ozone
À2 Æ 4
Sulphate aerosol
À9 Æ 4
À26 Æ 11
À1 Æ 0.4
À1 Æ 0.3
Black carbon aerosol
44 Æ 17
2 Æ 1
0.3 Æ 0.1
1 Æ 0.3
Organic carbon aerosol
À2 Æ 1
À1 Æ 0.5
À0.5 Æ 0.3
Indirect aerosol effect
6 Æ 111
À49 Æ 209
À127 Æ 128
0.5 Æ 10
Contrails
7 (À4, +6)
Aviation induced cirrus
21 (À9, +17)
338
Aviation and Atmosphere