Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
A study by WWF addresses future aviation demand by analyzing load factors and capacity
constraints, particularly in the freight market (Barrett, 1994). Analysis of historical data shows
that increases in the number of seats per aircraft have begun to level off. The study examines
the effects of pollution control strategies such as phasing out of air freight and policies to
encourage intermodal shifts to road and rail. Technological options for reducing the
environmental impact of aviation (such as operational improvements, changes in cruise altitude
and alternative fuel sources) are examined. In particular, these models consider the feasibility
that increases in load factors (percentage of total passenger seats that are occupied) could
increase fuel efficiency per seat-km for aviation. The model evaluates a wide range of policy and
operational choices, including a 100% load factor and a 100% fuel tax.
The model includes explicit assumptions of fixed growth rates in leisure travel, business travel,
average trip length for passenger and freight traffic, and freight tonnage. It assumes that
passenger load factors rise to 75% by 2020 in the base case. Constant rates of improvement are
assumed for aircraft size, airframe efficiency, and EI(NO x ).
With an annual growth rate of 5.2%, demand rises by a factor of more than 12 between 1991
and 2041 in the "business-as-usual" case. Proposed policies, including changes in load factor,
and technological improvements result in a forecast for demand increase of about a factor of 3 in
the "demand management" case. Carbon emissions in 2041 constitute 550 Tg C, and aviation's
share of global carbon emissions rises to 15% by 2041.
9.4.5. Massachusetts Institute of Technology Long-Term Scenarios
A study of the long-term future mobility of the world population has been undertaken at MIT. This
study constructed scenarios based on the simple yet powerful assumption that time spent and
share of expenditures on travel remain constant (Zahavi, 1981), on average, over time and
across regions of the globe (Schafer and Victor, 1997). Stability of average time budgets for
travel (motorized and nonmotorized) is substantiated by a considerable amount of aggregate
historical data. Although there is some variability in travel budgets from poorer to richer nations,
within each society travel budgets have generally followed a predictable pattern-rising with
income and motorization and stabilizing at 10-15%.
Using the constant travel budget hypothesis, Schafer and Victor (1997) produced global
passenger mobility scenarios for 11 world regions and four transport modes for the period 1990-
2050. Adding estimates of changes in the energy intensity of transportation modes, they also
generated scenarios of CO 2 emissions from passenger transport (see Table 9-20).
The high-speed travel category includes aviation, but the aviation portion of high-speed travel is
not explicitly characterized. Results of this model projection therefore cannot be used directly in
evaluations of the effect of aviation on the atmosphere, nor can they be directly compared to
other long-term projections of emissions from aviation.
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Figure 9-23: Flight tracks above 13-km altitude for a
fleet of 500 high-speed civil transports (Baughcum and
Henderson, 1998).