Aviation and the Global Atmosphere

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Three-dimensional (latitude, longitude, altitude) global inventories of civil and military aircraft fuel burned and emissions have been developed for the United States National Aeronautics and Space Administration (NASA) for the years 1976, 1984, and 1992, and by the European Abatement of Nuisances Caused by Air Transport (ANCAT)/European Commission (EC) Working Group and the Deutsches Zentrum für Luft- und Raumfahrt (DLR) for 1991/92. For 1992, the results of the inventory calculations are in good agreement, with total fuel used by aviation calculated to be 129.3 Tg (DLR), 131.2 Tg (ANCAT), and 139.4 Tg (NASA). Total emissions of NOx (as NO2) in 1992 were calculated to range from 1.7 Tg (NASA) to 1.8 Tg (ANCAT and DLR).

Forecasts of air travel demand and technology developed by NASA and ANCAT for 2015 have been used to create three-dimensional (3-D) data sets of fuel burn and NOx emissions for purposes of modeling the near-term effects of aircraft. The NASA 2015 forecast results in a global fuel burn of 309 Tg, with a NOx emission of 4.1 Tg (as NO2); the global emission index, EI(NOx) (g NOx/kg fuel), is 13.4. In contrast, the ANCAT 2015 forecast results in lower values-a global fuel burn of 287 Tg, an emission of 3.5 Tg of NOx, and a global emission index of 12.3. The differences arise from the distribution of air travel demand and technology assumptions.

Long-term emission scenarios for CO2 and NOx from subsonic aviation in 2050 have been constructed by the International Civil Aviation Organization (ICAO) Forecasting and Economic Support Group (FESG); the United Kingdom Department of Trade and Industry (DTI); and the Environmental Defense Fund (EDF), whose projections extend to 2100. The FESG and EDF scenarios used the Intergovernmental Panel on Climate Change (IPCC) IS92 scenarios for economic growth to project future air traffic demand, though with different approaches to the relative importance of gross domestic product (GDP) and population. Each group also makes different assumptions about projected improvements in fleet fuel efficiency and NOx reduction technology. In addition, the Massachusetts Institute of Technology (MIT) has projected emissions from a "high speed" sector that includes aviation, and the World Wide Fund for Nature (WWF) has published a projection of aviation emissions for the year 2041.

All future scenarios were constructed by assuming that the necessary infrastructure (e.g., airports, air traffic control) will be developed as needed and that fuel supplies will be available. System capacity constraints, if any, have not been evaluated.

Future scenarios predict fuel use and NOx emissions that vary over a wide range, depending on the economic growth scenario and model used for the calculations. Although none of the scenarios are considered impossible as outcomes for 2050, some of the EDF high-growth scenarios are believed to be less plausible. The FESG low-growth scenarios, though plausible in terms of achievability, use traffic estimates that are very likely to be exceeded given the present state of the industry and planned developments.

The 3-D gridded outputs from all of the FESG 2050 scenarios and from the DTI 2050 scenario are suitable for use as input to chemical transport models and may also be used to calculate the effect of aviation CO2 emissions. The FESG scenarios project aviation fuel use in 2050 to be in the range of 471-488 Tg, with corresponding NOx emissions of 7.2 and 5.5 Tg (as NO2) for IS92a, depending on the technology scenario; 268-277 Tg fuel and NOx of 4.0 and 3.1 Tg for IS92c; and 744-772 Tg fuel and NOx of 11.4 and 8.8 Tg for IS92e. (For all of the individual FESG IS92-based scenarios, higher fuel usage-thus CO2 emissions-were a result of the more aggressive NOx reduction technology assumed). The DTI scenario projects aviation fuel use in 2050 to be 633 Tg, with NOx emissions at 4.5 Tg.

As a result of higher projected fuel usage, EDF projections of CO2 emissions are all higher than those of FESG by factors of approximately 2.4 to 4.3 for IS92a, 3.1 to 5.7 for IS92c, and 1.7 to 3.1 for IS92e. Results from EDF scenarios based on IS92a and IS92d are suitable for use in calculating the effect of CO2 emissions as sensitivity analyses; the latter scenario projects CO2 emissions levels from aviation 2.2 times greater in 2050 than the highest of the FESG scenarios.

The effects of a fleet of high-speed civil transport (HSCT) aircraft on fuel burned and NOx emissions in the year 2050 were calculated using the FESG year 2050 subsonic inventories as a base. A fleet of 1,000 HSCTs operating with a program goal EI(NOx) of 5 in 2050 was calculated to increase global fuel burned by 12-18% and reduce global NOx by 1-2% (depending on the scenario chosen), assuming that low-NOx HSCTs displace traffic from the higher NOx subsonic fleet. A fleet of 1,000 HSCT aircraft was chosen to evaluate the effect of a large fleet; it does not constitute a forecast of the size of an HSCT fleet in 2050.

The simplifying assumptions used in calculating all of the historical and present-day 3-D inventories (1976 through 1992)-great circle routing, no winds, standard temperatures, no cargo payload-cause a systematic underestimate of fuel burned (therefore emissions produced) by aviation on the order of 15%, so calculated values were scaled up accordingly. By 2015, we assume that the introduction of advanced air traffic management systems will reduce this underestimate to approximately 5%. Full implementation of these systems by 2050 should reduce the error somewhat further, but given the wide range of year 2050 scenario projections, adjustments to calculated fuel values in 2050 were not considered to be necessary.

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