Environmental Engineering Reference
In-Depth Information
troposphere and lower stratosphere acts as a powerful 'greenhouse gas', potentially
contributing to climate warming. However, more recently, other effects such as those
of contrails (condensation trails) have been studied intensively. Contrails are line-
shaped ice clouds caused by the emission of water vapour and particles from the aircraft
exhaust. Depending (principally) upon the particular conditions of temperature and
humidity, contrails may be very short lived or persistent, sometimes spreading by wind
shear, sedimentation and diffusion into cirrus-like clouds that are ultimately unrec-
ognizable as having been caused by aircraft. Other effects on climate from associated
particle emissions and the enhancement of cirrus clouds have also been discussed.
Research into the potential effects of aviation on the upper atmosphere was
recently synthesized in a special report of the Intergovernmental Panel on Climate
Change (IPCC) -
Aviation and the Global Atmosphere
(IPCC, 1999). This report
was a landmark in that it was the first sectoral examination by the IPCC and that esti-
mates of radiative forcing of climate from various aircraft emissions and their effects
were made.
Besides the IPCC report, other assessments and syntheses have been made (eg
Brasseur et al, 1998; Friedl et al, 1997; Rogers et al, 2002; Schumann, 1994). This chap-
ter does not attempt to duplicate such reviews; rather, it provides the non-specialist
with an overview of the global impacts of aircraft emissions and points the way to more
detailed literature for the interested reader. In the next section, a very brief overview
of climate change in relation to aircraft is given. Following this, we briefly review air-
craft emissions and their development over time, and the effects of subsonic and super-
sonic aviation. Lastly, more recent research since the publication of the IPCC (1999)
report is reviewed and an overall chapter summary is provided.
C
LIMATE
CHANGE
Given that much recent discussion has focused upon the estimates of radiative forc-
ing from aircraft emissions given by IPCC (1999) for 1992 and 2050, it is pertinent
to introduce some of the basic concepts of climate change. In such a short chapter, a
complete and comprehensive overview is impossible, but the basic concepts and
suitable references are provided.
'Climate' is, of course, different to 'weather', weather being the more-or-less instan-
taneous meteorological conditions, whereas climate describes weather conditions typ-
ical of a region or site (eg McIlveen, 1992). Climate
change
is a long-term systematic
change. That climate has changed over the last 100 years or so is almost beyond doubt,
although some of the scientific issues remain contentious. The IPCC was set up jointly
by the World Meteorological Organization and the United Nations Environment
Programme (UNEP) in order to provide authoritative international statements of sci-
entific opinion on climate change, and it has delivered major reports in 1990, 1995
and 2001.
In order to describe climate change quantitatively, some sort of metric is required.
The components of climate that change as a result of external or varying influences
are multifarious. However, the most often - and, indeed, obvious - cited manifesta-
tion is surface temperature. However, it is extremely difficult to simulate or predict
changes in surface temperature except with highly sophisticated three-dimensional
