Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Under the IS92a scenario (the IPCC base case), the base-demand level in 2050 is higher than
the 1990 level by a factor of 10.7 and has an average annual demand growth rate of 4.03% over
the 60-year forecast period (forecasts to 2100 are given by Vedantham and Oppenheimer,
1998). For the base-demand set, the range of traffic demand expected for different population
and GNP estimates spans a factor of almost 5 in 2050; the full range across all 10 scenarios
spans a factor of more than 20. Assumptions about rates of expansion and maturity have a
sizable impact: The high-demand projection for the IS92a scenario in 2050 is 78% higher than
the base-demand value.
The 10 demand scenarios produced by the EDF model are synthesized with expectations for
fuel efficiency improvement and changes in emissions indices to produce fuel use, CO2 emissions, and NOx emissions scenarios.
Although fuel efficiency has increased steadily over the past few decades, improvements in fuel
efficiency are becoming less dramatic over time. The technology projections of the EDF model
use a constant-capacity logistic that extrapolates Greene's (1992) forecast for a base-case
annual increase of 1.3% in fleet-wide fuel efficiency from 1989 to 2010. Significant differences in
fuel efficiency exist today across regions, and there may be a tendency toward higher fuel
efficiency in wealth ier regions. The EDF model assumes differences in fuel efficiency across
economic groups and builds projections on the assumption that the technology gap between
wealthier and poorer nations will close over time.
The NOx emissions scenarios reflect changes in EI(NOx ) based on a constant-capacity logistic
that extrapolates a best-fit approximation to the 1993 NASA numbers for EI(NOx ) in 1990 and
2015 (Stolarski and Wesoky, 1993). The model does not reflect specific technology choices for
fuel efficiency or changes in EI(NOx ), although the fleet EI(NOx ) of 6.9 that results from the
extrapolation is in the ultra-low technology regime. Results for all scenarios are summarized in
Table 9-19.
Figure 9-21 shows CO 2 emissions scenarios [which assume a constant EICO 2 ) of 3.16]. Under
the base IS92a scenario, CO 2 emissions grow at an annual rate of 3.2% to reach 983 Tg C in
2050-an increase of a factor of 6.6. For all scenarios, projected CO 2 emissions climb rapidly
after 2015. For the IS92c scenario (which reflects low population and GNP growth) under both
demand sets, the level of CO 2 emissions in 2100 is lower than that in 2050, reflecting a
successful catch-up effect whereby technological improvements have compensated for demand
growth (Vedantham and Oppenheimer, 1998). Comparing the EDF scenarios for aviation's CO2 emissions projections with the IPCC scenarios for total anthropogenic CO2 emissions (including
Figure 9-21: EDF CO 2 emissions projections.
Figure 9-22: EDF NO x emissions projections.
emissions from energy consumption and deforestation) provides a benchmark measure of the environmental importance of the aviation sector. For the base-demand
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