Environmental Engineering Reference
In-Depth Information
•
The rates of use of renewable resources do not exceed their rates of generation.
•
The rates of use of non-renewable resources do not exceed the rate at which sus-
tainable renewable substitutes are developed.
•
The rates of pollution emission do not exceed the assimilative capacity of the
environment.
Air transport, as currently practised, fails outright to satisfy the first two conditions
and, probably, also the third. In the longer term (perhaps 2050+), global air trans-
port is not sustainable on any basis because there is, as yet, no feasible substitute for
oil, hydrogen-based fuels being the only apparent possibility.
Public opposition to aviation, which is situationally determined, tends to focus
primarily upon noise. Whereas modern aircraft are quieter than their predecessors, it
is the volume of traffic - both airside and landside - that compounds public expo-
sure to noise, particularly for residents who live near major airports. In general terms,
internationally negotiated and implemented noise controls have largely realized the
potential returns from aircraft engine noise reduction, and the principal future gains
are likely to come from advances in airframe technology. Noise, however, dominates
at the scale of the individual airport and its relationship with its local community,
leading to a plethora of, often stringent, local operating regulations constraining air-
craft operations.
It is becoming more widely recognized, however, that the most serious sustain-
ability impacts of air transport are from atmospheric pollution at both global and
local scales. These include the, as yet, poorly understood effects of contrails in the upper
atmosphere, and carbon dioxide (CO
2
) pollution and nitrogen oxide (NO
x
) emis-
sions, all of which contribute to global warming. It has been estimated that because
of aviation's growth and the lack of alternatives to fossil fuels, the sector's current 3
per cent contribution to global warming may increase to between 10 and 20 per cent
of the total by 2005. In addition, ground-level emissions at airports, both from air-
craft and surface vehicles, are increasing - the trend exacerbated by the development
of airports as major activity economic centres and intermodal transportation hubs.
In general terms, although again technology has been successful in reducing atmo-
spheric and ground emissions per aircraft and vehicle, the technological returns are
diminishing and being offset by aviation's growth.
It must be emphasized, however, that in addition to concerns with environmen-
tal carrying capacity, sustainability also invokes connotations of long-term economic
development, social needs and equity. Such targets, especially when applied to more
peripheral or disadvantaged regions, demand accessibility to core regions as mea-
sured by time and cost, while the access of isolated areas to wider networks is a basic
social equity objective. Firms also require accessibility to factors of production and
markets. However, the infrastructure created to enhance accessibility also encourages
mobility, which is essentially a behavioural attribute and, moreover, one easily manip-
ulated by price. Arguably, it is mobility provision, best exemplified here by low-cost
airlines, which provides the basic challenge to sustainability.
In the US, the sustainable transport initiative has largely been confined to strat-
egies that mitigate the environmental impacts of transportation without infringing
upon the individual freedom to travel. Most of the effort has targeted motor vehicles
and their impacts at the metropolitan scale. Interest in air transport and sustainability
