Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
anthropogenic or natural emissions of aerosol or aerosol precursors at the ground might also influence cirrus cloud formation (Plantico et al., 1990; Hansen et al.,
1996; Hasselmann, 1997). Cirrus trend values deduced from surface observations may also be influenced by a variety of issues. For example, reported cirrus
frequencies depend in an unknown manner on how observers classify contrails as cirrus. Reliable cloud observations are obtained mainly during daytime periods
(Hahn et al., 1995), which do not always correlate with the main air traffic periods. The significance of the statistical relationship between cloud changes and air traffic
is limited because of the limited duration of satellite and surface cloud observations and the brief period of aircraft emissions in comparison to long-term climate
variations. Thus, existing studies are not complete enough to conclude that aircraft-induced contrails and cloudiness have caused observable changes in surface and
tropospheric temperatures or other climate parameters.
Table 3-6: Instantaneous TOA radiative flux changes averaged over a day for shortwave (SW), longwave (LW), and net (= SW + LW) radiation for 100%
contrail cover in various regions and seasons, with prescribed surface albedo, contrail ice water content (IWC), and computed optical depth t of contrail at
0.55 µm. Results are for spherical particles (model M, upper values) and hexagons (four-stream version of model FL, lower values).a
Region
Surface
Albedo
IWC
(mg m -3 ) t
Mid-latitude summer continent, 45°N 0.2 21 0.52 -13.4
-22.0
Mid-latitude winter continent, 45°N 0.2 7.2 0.18 -4.2
-4.6
Mid-latitude winter continent with snow, 45°N 0.7 7.2 0.18 -2.3
-2.0
North Atlantic summer ocean, 55°N 0.05 21 0.52 -21.5
-32.7
Tropical ocean (Equator, June) 0.05 23 0.57 -16.0
-25.9
Subarctic summer ocean, 62°N 0.05 28.2 0.70 -30.8
-45.3
Subarctic winter ocean ice, 62°N 0.7 7.2 0.18 -0.6
-0.7
http://www.ipcc.ch/ipccreports/sres/aviation/039.htm (5 von 6)08.05.2008 02:42:06
SW
(W m -2 )
LW
(W m -2 )
51.6
51.5
18.4
18.3
18.4
18.3
53.3
50.9
63.0
57.4
55.7
49.1
14.6
13.2
Net
(W m -2 )
38.2
29.5
14.2
13.7
16.1
16.3
31.8
18.2
47.0
31.5
24.9
3.7
14.0
12.5