Environmental Engineering Reference
In-Depth Information
been a number of significant events. NASA has ceased support of the HSCT research
efforts as Boeing withdrew its intention to develop a large civil SST. At the same
time, NASA dramatically reduced its funding of research into effects of subsonic air-
craft in its Subsonic Assessment Programme (SASS). In Europe, however, there has
been a strong research programme put into place both in the environment and tech-
nology areas, particularly regarding the areas of emissions, particle and contrail effects,
and potential trade-offs. Other recent events in technology development include the
intention of Airbus Industries to develop and build the A380, a competitor product
to the Boeing 747, and Boeing's announcement of the development of the Sonic
Cruiser. The environmental impacts of such developments have not yet been assessed.
The policy response to the IPCC report is effected mainly through ICAO's Com-
mittee on Aviation and Environmental Protection (CAEP) work programmes. Cur-
rently, only domestic aviation emissions of CO
2
are accounted for in greenhouse gas
emission inventories and therefore in the Kyoto Protocol. However, the Kyoto Pro-
tocol makes allowance for inclusion of international aviation and the United Nations
Framework Convention on Climate Change (UNFCCC), through its Subsidiary Body
on Scientific and Technological Advice (SBSTA), has requested that ICAO's CAEP
look at methods by which international aviation may be brought under the Kyoto
Protocol. One favoured route is through CO
2
emissions trading (Gander and Helme,
1999). However, this ignores that fact that aviation has effects other than CO
2
on
climate (see Figure 5.3) and that purchases by the aviation industry may
increase
total radiative forcing, not decrease it (Lee and Sausen, 2000).
In parallel to the issue of emissions trading is that of emissions allocations. Since
aviation is, by its nature, international, the allocation of emissions is not so straight-
forward - though a number of allocation methodologies have been suggested by the
UNFCCC (1996). Before emissions of CO
2
can be traded, there must be some sort
of allocation. Currently, these allocations are not known, although initial work has
begun (D S Lee, 2002, pers comm), which shows that approximately 40 per cent of
global civil aircraft emissions in 1992 were domestic and 60 per cent were interna-
tional. Attribution by country by two of the commonly accepted allocation method-
ologies is also calculated in this work.
There is much work yet to be done before we can have higher confidence in assess-
ments of the impacts of aviation on climate and establish methods by which these
effects might be ameliorated. Trade-offs between the different effects is the theme of
a major European Commission research effort. In this project (TRADEOFF) cli-
mate impacts are being examined, as well as those of simple changes in operational
practices.
2
For example, it has already been shown by Sausen et al (1998) that flying
1km lower or higher affects contrails in different ways, increasing contrail coverage
for a 1km downwards shift in parts of Eurasia and the NAFC, but decreasing it in
the tropics and North America. However, the effects on fuel efficiency and NO
x
emissions were not considered. It has been calculated that a 2km shift downwards may
increase CO
2
and NO
x
emissions by approximately 4 per cent (Lee et al, 2002b). A
downward shift in cruise altitudes may decrease O
3
production, and thus radiative
forcing (Grewe et al, 2002); however, contrails at lower altitudes may have stronger
radiative properties because of their higher water content (Meerkötter et al, 1999).
Thus, it can be seen that potential operational changes have complex environmental
responses that are not yet fully understood. It is premature to even begin thinking
