Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
Table of contents | Previous page | Next page
3.7. Parameters of Future Changes in Aircraft-Produced Aerosol and Cloudiness
Other reports in this collection
The future effects of aircraft depend on trends in climate and air traffic amount and changes in the technical properties of aircraft. Our current understanding of the
formation of aviation-induced aerosol and cloudiness can be used to estimate how future changes may affect the impacts of aviation and to identify mitigation options
that would be effective in reducing these impacts.
3.7.1 Changes in Climate Parameters
If climate change occurs in the future, atmospheric parameters related to aerosols and contrails will also have changed. Of particular importance to aviation-induced
aerosol and cloudiness are changes in temperature and humidity in the upper troposphere and lower stratosphere; changes in the height, temperature, and humidity of
the tropopause region; changes in the abundance of particles; and changes in cloudiness. Table 3-10 summarizes how changes in these parameters may be reflected
in aviation-related impacts. General circulation models of the atmosphere predict that the climate of 2050 will reflect global warming from the accumulation of
greenhouse gases. In this new climate, models predict increases in the amounts of cirrus clouds, the height of the tropopause, and upper tropospheric temperature
(IPCC, 1996; Timbal et al., 1997). A higher tropopause would cause more contrails, at least at high latitudes. Observed temperature changes (e.g., Parker et al., 1997)
do not reveal the expected temperature increase in the upper troposphere. Some models predict a higher tropopause if the surface temperature increases (about 200m
altitude increase for 1 K surface temperature increase) (Thuburn and Craig, 1997). Increases on the order of 100 m were analyzed in polar regions and at midlatitudes
(Hoinka, 1998; Steinbrecht et al., 1998). Such changes may be forced by cooling of the lower stratosphere as a result of changes in ozone concentration
(Hansen et al., 1997) and increases in moisture as a result of increasing methane concentrations. Stratospheric temperatures between 50 and 100 hPa have
decreased by about 1 to 2 K since 1980 (Ramaswamy et al., 1996; Halpert and Bell, 1997). An increase in water vapor concentration has been observed in the lower
stratosphere, with the largest trend (0.8%/yr) in the 18- to 20-km region (Oltmans and Hofmann, 1995). Because few contrails currently form in the lower stratosphere,
small changes in stratospheric conditions will not create significant changes in contrail abundance. Aerosol loading in the troposphere and lower stratosphere may
increase because of changed climate conditions and increased surface emissions. Surface emissions from fossil fuel burning were projected to grow by a factor of 1.5
to 2.1 from 1990 to 2040 (Wolf and Hidy, 1997).
3.7.2. Changes in Subsonic Aircraft
http://www.ipcc.ch/ipccreports/sres/aviation/041.htm (1 von 5)08.05.2008 02:42:11