6.1.3. Aviation Scenarios Adopted for Climate Assessment

A few, detailed, three-dimensional (3-D) emission inventories for three specific years-1992, 2015, and 2050-are presented in Chapter 9 and are studied with 3-D atmospheric models: NASA-1992, NASA-2015, and the ICAO-developed FESGa and FESGe scenarios for 2050. The FESG scenarios include three economic options, a/c/e, corresponding to economic growth assumed in IS92a/c/e. Each of the FESG scenarios has technology option 1 assuming typical, market-driven advances in engine/airframe technology and technology option 2 with advanced engine technology (i.e., a 25% reduction in NOx emission index with a 3.5% increase in fuel use; see Chapter 9). Between these fixed-year scenarios, linear interpolation is used to derive continuous scenarios-Fa1, Fa2, Fc1, and Fe1 (see Table 6-3)-that extend from 1990 to 2050. CO2 increases are derived from carbon-cycle models (see notes to Tables 6-1 and 6-2). Two scenarios based on EDF projections for the years 2015 and 2050 (Vedantham and Oppenheimer, 1998) provide only global CO2 and NOx emissions: the EDF-a-base (Eab) and EDF-d-high (Edh) cases. The Edh scenario was not adopted for its relationship to any underlying population or economic scenario, but because it is a smooth extrapolation of recent growth rates. Atmospheric changes other than CO2 for Eab and Edh are scaled from the Fa1 and Fe1 scenarios (see notes to Table 6-1). The continuous scenarios are summarized in Table 6-3.

a The scenarios in boldface were studied in atmospheric models with defined 3-D emission patterns; the others were scaled to these scenarios. The NASA-1992* aviation scenario has been scaled here by 1.15, and the NASA-2015* scenario by 1.05, to account for inefficiencies in flight routing.
b Low/High give likely (67% probability) range.
c In FESG scenarios, tech 1 is standard, and tech 2 reduces EI(NOx) by 25% with a few percent additional fuel use.
d Throughout the table and this report, NOx emissions (Mt yr-1) and indices (EI) use the NO2 molecular weight.
e In the EDF 2015 scenarios, the fuel burns have been revised to 374 (a-base) and 592 (d-high) Mt yr-1, which would increase the added CO2 by 2050 to 10.0 (a-base) and 14.7 (d-high) ppmv.
f CO2 is largely cumulative and depends on the assumed previous history of the emissions; CH4 perturbations are decadal in buildup time; all other perturbations reach steady-state balance with emissions in a few years. All except CO2 are assumed here to be instantaneous. Thus, CO2 concentrations are based on complete history of fuel burn-for example, scenario Fa1 = NASA-1992* ' NASA-2015* ' FESGa (tech1) 2050; and scenario Eab = NASA-1992* ' EDFa-base 2015 ' EDFa-base 2050, all with linear interpolation between 1992, 2015, and 2050 (see also Section 6.1.3).
g The O3 and CH4 RFs are scaled to NOx emissions for non-bold scenarios.
h As for note g, stratospheric H2O, sulfate, and BC aerosols scale with fuel burn.
i Contrails do not scale with fuel burn as the fleet and flight routes evolve (see Chapter 3). The contrail RF here is from line-shaped contrail cirrus only. Additional induced cirrus cover RF is positive, and may be of similar magnitude, but no best estimate can be given yet.

The total fuel in Gt C used by aviation from 1950 to 1992 is shown in Figure 6-6. It also shows two projections to 2050 (Fa1 and Eab; see Tables 6-1 and 6-2), comparing them with projected total fossil carbon emissions for a similar economic scenario (IS92a). Note the logarithmic scale in Figure 6-6. For scenario F1a, fuel use parallels that of IS92a, but for Eab it grows faster than total fossil fuel use. In converting aviation fuel to CO2 emissions, we adopt a carbon fraction by weight of 86%. Aviation fuel use prior to 1992 is based on International Energy Agency data (IEA, 1991; for table, see Sausen and Schumann, 1999). To account for systematic underestimation of fuel use (see Chapter 9), we have increased NASA-1992 and NASA-2015 emissions by 15% and 5%, respectively, to form the inventories NASA-1992* and NASA-2015*. Figure 6-7 gives an expanded linear scale of aviation fuel use from 1990 to 2050 for scenarios Fc1, Fa1, Fa1H, Fe1, Eab, and Edh, in order of increasing fuel use by 2050.

Chapter 4 studies the impact of a fleet of high-speed civil transport (HSCT, i.e., supersonic) aircraft using a range of 3-D emission scenarios with atmospheric chemistry models. These calculations form a parametric range that covers changes in fleet size, NOx emissions, cruise altitude, sulfate aerosol formation, and future atmospheres. The present chapter combines those results into a continuous scenario for the HSCT fleet, designated Fa1H: On top of the Fa1 scenario it assumes that HSCT aircraft come into service in 2015, grow at 40 planes per year to a final capacity of 1,000 aircraft by 2040, continue operation to 2050, and displace equivalent air traffic from the subsonic fleet (~11% of Fa1 in 2050). This Mach 2.4 HSCT fleet cruises at 18-20 km altitude and deposits most of its emissions in the stratosphere. It has new combustor technology that produces very low emissions of 5 g NO2 per kg fuel. Table 6-1 gives the breakdown of RF from two specific HSCT studies in Chapter 4: 500 HSCTs in a 2015 background atmosphere and 1,000 HSCTs in a 2050 background atmosphere (e.g., chlorine loading, methane, nitrous oxide). The likely interval for the RF here combines the uncertainty in calculating the ozone or water vapor perturbation with that from calculating the radiative imbalance.

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