Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
This factor inhibits the prospect of further reducing CO 2 by changing fuels. The use of kerosene is addressed in some detail in Section 7.8, as is the question of fuel
effects on emissions. Looking further ahead, Section 7.8 also considers briefly the use of alternative fuels in the longer term-beyond 2050.
The later sections of the chapter concentrate on the smaller numbers of special category aircraft in the global fleet. The first of these categories is "small aircraft" as
used in the regional sector of air transport. Generally, these aircraft fly at lower altitudes than their larger counterparts and therefore have a much lower potential
impact on the climate. However, growth in this sector is expected to continue; for completeness, therefore, Section 7.9 reports on the particular problems and
differences of these aircraft now and in the future. Section 7.10 is concerned with the significant technical and operational issues that differentiate supersonic aircraft
from the subsonic fleet. These aircraft are small in numbers now and are likely to remain so until 2015 or later. Beyond that time frame, a significant rise in the numbers
of such aircraft could present a more challenging environmental problem because of the altitude at which they fly-a matter discussed in Chapter 2. This prospect has
spawned research programs addressing the particular problems arising from high-speed, high-altitude operations.
Section 7.11 discusses the effects of military priorities that influence trends in the technology applied to aircraft. Although operational effectiveness in combat will
continue to be the key consideration in engine design, Section 7.11 also points out why military operators' interest in the composition of exhaust is similar to that for
civil engines. This section has links with Chapter 9, which shows how, in relative terms, the impact of military fleets will fall partly because of the anticipated slight
reduction in their numbers but mainly because of the predicted steep rise of global civil fleets over the next 50 years.
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