Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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9.6. Evaluation and Assessment of Long-Term Subsonic Scenarios
9.6.1. Difficulties in Constructing Long-Term Scenarios
Other reports in this collection
Long-term (beyond 20 years) projections of aviation traffic demand, fleet fuel burned, and fleet emissions are inevitably speculative. Difficulty in forecasting
technological developments that might be appropriate for the long term, possible shifts in traffic demand, and myriad uncertainties resulting from human society's
development over the period in question all conspire to make long-term projections unreliable-sometimes astoundingly so. Given the state of the aviation industry 50
years ago (in 1947), it is doubtful that either the technology or the scope of the industry in 1997 could have been forecast. However, because the transport aviation
market and aviation technology seem to be maturing, a plausible way of making projections far into the future is to make reasonable extrapolations based on our
knowledge of present trends in the world and in the aviation industry. These extrapolations are termed scenarios, rather than forecasts, as outlined in Section 9.1.
9.6.2. Structure and Assumptions
Before we review the outcomes of the scenario studies in the following section, we consider
some differences and similarities between the models. This comparison is restricted to the EDF,
DTI, and FESG models. Although the MIT model provides an interesting insight into future travel
options based on the thesis of invariant travel time and travel expenditure budgets, it is excluded
from this comparison because it provides only a highly aggregated scenario for the future
mobility of total motorized passenger traffic; air traffic is only one-albeit important-portion of this
picture, and the aircraft component cannot be identified. The WWF aviation scenario for 2041
provides aggregated fuel burned and CO 2 emissions projections but does not provide regionally
distributed NO x emissions estimates.
Of the long-term scenarios considered, the EDF, FESG, and DTI studies allow assessment of
the impacts of CO 2 from aviation. However, only the results from the DTI and the FESG models
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