Aviation and the Global Atmosphere

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From the implied 2050 fleet sizes, it is likely that more airports will be required to support the growth in traffic and flight operations. The number of new airports required will depend on the total fleet, the number of airports now capable of handling jet operations, and the number of gates available at each airport. Table 9-26 shows the number of new airports required, assuming the lowest and highest growth cases for the passenger fleet and total fleet (from model by Campbell-Hill Aviation Group, 1998). The present inventory of airports was taken as the number of airports now having one or more jet departures per day, thereby obviously capable of handling large jet transport aircraft, and the total number of airports in the OAG-that is, airports with scheduled air service (many not presently capable of handling large jet transport aircraft). For example, if all of the airports now having one or more jet departures per day had 15 or more gates, no new airports would be needed to handle the fleet in the lowest growth case. Conversely, the highest growth case would require more than 1,300 new airports of 15 gates each (two new airports per month for 60 years) even if all 3,750 airports now listed in the OAG had 15 gates and were capable of handling large jet transport aircraft (which they do not and are not). This analysis ignores infrastructure location and the problems associated with its provision. In populous parts of the world, where civil aviation is established, the addition of airport capacity is often difficult given local environmental pressures such developments create. However, in developing countries, where much of the future traffic growth is anticipated, new infrastructure might encounter less environmental sensitivity and therefore be more readily provided. Nonetheless, the infrastructure projects required to satisfy the highest growth scenarios are unprecedented in scope. Fuel Availability

All of the 2050 scenarios imply large increases in fuel consumption by aircraft. In the highest FESG scenario (Fe2), aircraft fuel consumption increases from 139 to 772 Tg yr-1 over the period 1992 to 2050. In the highest EDF scenario (Eeh), the increase is from 179 Tg yr-1 in 1990 to 2,297 Tg yr-1 in 2050. Because both scenarios are based on the IS92e scenario, it is appropriate to compare these figures to total energy use in the IS92e scenario. According to scenario Fe2, aircraft will account for 13% of the total transportation energy usage in 2050 and require 15% of the world's liquid fossil fuel production. The EDF scenario (Eeh) implies that aircraft account for 39% of the transportation energy usage and require 45% of the world's liquid fuel production. These comparisons assume that aircraft do not use biomass fuels or fuels derived from natural gas.

Under either scenario, the world will be straining the limits of conventional oil resources by 2050. Total remaining resources of conventional petroleum, discovered and undiscovered, have been estimated at between one trillion (Campbell and Laherrere, 1998) and two trillion barrels (Masters et al., 1994-based on the optimistic 5% probability estimate of undiscovered oil). The IS92e scenario implies cumulative production of liquid fuels of 1 trillion barrels by 2025 and 2 trillion barrels by 2050. Cumulative consumption by 2050 by aircraft alone amounts to 0.15 trillion barrels in the Fe2 scenario and 0.35 trillion barrels in the Eeh scenario. However, production of liquid fuels is not necessarily limited by conventional oil resources. Liquid fuels can be produced from heavy oil, tar sands, oil shale, or even coal, albeit with significantly greater environmental consequences and at higher costs. High fuel prices would violate the explicit assumptions used in developing the scenarios. Manufacturing Capability and Trends in Aircraft Capacity

In 1997, the global aircraft manufacturing capability delivered 634 passenger jet aircraft, bringing the global jet passenger fleet to approximately 10,000 aircraft. The rate of new aircraft deliveries has followed a generally increasing trend since the mid-1950s, and this trend must continue over the scenario period to satisfy predicted demand for new and replacement aircraft. For the demand cases examined above, deliveries of new aircraft are estimated to reflect the schedule given in Table 9-27.

The delivery rate for the Fa1 and Fa2 scenarios would be achievable with existing manufacturing capacity. The delivery rate required by the highest scenario, Eeh, implies a considerable increase in manufacturing capacity-approximately six times that existing today. Although this level is not impossible, such an expansion of aircraft manufacturing capability is likely to be difficult to achieve and sustain during the period. The Eab scenario implies a delivery rate that is approximately three times the level existing today, which is not implausible for 2050.

One assumption intrinsic to the fleet size analysis was that the average number of seats per aircraft will increase by 1% each year, reflecting current trends. This assumption has a large effect on fleet size estimates, particularly for high-demand cases. As a sensitivity analysis, the factor was changed to 2% per year for the Eeh high scenario and for the Fa1 and Fa2 scenarios. Such a change may reflect potential market pressures for larger aircraft, which is not inappropriate for a high traffic growth scenario. The results are given in Table 9-28.

As this analysis shows, a different assumption in aircraft size growth has a significant effect on the estimated future fleet. The projected numbers of the largest aircraft types (between 625 and 799 seats) in future fleets are particularly sensitive in this analysis, which suggests that there might be more than 7,000 such aircraft in the fleet by 2050 in the Eeh scenario (compared with about 10,000 passenger aircraft of all sizes today) or about 4,000 additional aircraft for the more conservative Fa1 and Fa2 scenarios.

Increased capacity can be supplied by additional aircraft, increased flying hours (i.e., more efficient use of the fleet), larger aircraft, or a combination of these factors. The high aircraft growth assumption used as a sensitivity analysis here suggests that about 70% of future capacity growth will be supplied by an increase in aircraft size. Although such an industry trend is not impossible, it is unlikely to occur in such a prescriptive manner if the industry remains relatively deregulated. Deregulation tends to favor increased frequency and direct flights with smaller aircraft between departure and destination. However, it is likely that some markets would favor the proliferation of very large aircraft, especially those with dense traffic flows. The size of the fleets suggested by the 2% per year aircraft size growth assumption must therefore be regarded as toward the low end of the range. Synthesis of Plausibility Analyses

Given the range of estimates for traffic, fuel consumption, and emissions from the 2050 aircraft scenarios available to this assessment, it is necessary to comment on the plausibility of the results-not least to demonstrate that results used in subsequent analyses are bounded by sensible limits within which the aviation industry is currently envisaged to develop.

The foregoing analyses suggest that although none of the scenarios considered for 2050 is impossible, some of the high-growth scenarios (e.g., Eah and Eeh) are probably less plausible. The fleet size and infrastructure implications suggest radical developments that are likely to be beyond the scope of changes observed in the industry thus far (or anticipated for the future). Similarly, the low-growth scenarios-though plausible in terms of achievability-give traffic estimates that are likely to be exceeded given the present state of the industry and planned developments. Although all of the FESG scenarios discount the possibility of truly radical developments in technology over the next 50 years, they are considered to fall within a plausible range of outcomes and suggest achievable developments for the industry.

The 3-D gridded output from scenarios Fa-Fe (with T1 and T2 technology scenarios) and from DTI are suitable for use as input to chemical transport models and may be used to calculate the effect of aviation CO2 emissions. Scenarios Eab and Edh are suitable for use in Chapter 6 to calculate the effect of CO2 emissions as sensitivity analyses because the latter scenario projects CO2 emissions levels from aviation that are 2.2 times greater in 2050 than the highest of the FESG scenarios. Table 9-29 provides a summary of all of the long-term scenarios examined in the chapter.

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