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Quantification of constrained scenarios on aviation and emissions

Exploitable results

For the study period of the EU-funded project 'Constrained scenarios on aviation and emissions' (Consave) up until 2050, the cost/'Revenue tonne-kilometres' (RTK) (unit costs) for airlines will increase for all scenarios, with higher growth rates between 2020 and 2050. The effects of the scenario-specific constraints on unit costs were lowest for the 'Unlimited skies' (ULS) scenario (increase from USD 0.71/tonne-km in 1992 to USD 1.15 in 2050) and highest for the two sub-scenarios of the 'Regulatory push & pull' (RPP) scenarios, kerosene fleet with global USD 2 fuel tax and hydrogen fleet rollover (increase to USD 2.10, respectively to USD 2.14 in 2050). The effects of the characteristic constraints of the 'Fractured world' (FW) on unit costs were also relatively high (USD 1.91 in 2050), whereas the pressure on costs was more moderate in the 'Down to Earth' (DtE) scenario. The pattern of the increase of the revenue/RTK was similar to that of the cost/RTK. Thus, the development of the operating results for airlines mirrors the scenario specific levels of air transport demand. Costs and revenues for airlines were higher in the high-growth scenarios and slightly decreasing in all scenarios over time. The profitability was high in the ULS scenario and low in the DtE scenario, while in the scenarios 'Regulatory push & pull' (RPP) and FW, values were within the historical range of 4 % to 6 %. The comparatively good profitability in FW was explained by differences in the regional development - some regions, especially North America and Eurasia seemed to be able to adjust to the assumed fragmentation in the long run, dividing the world into winners and losers of a FW. One has to keep in mind that this conclusion was only valid for the estimated time horizon and under the assumption that the potential for conflicts and security problems - typically very high in this scenario - did not reach a 'wild card' level such as another world war.
Four 'Constrained scenarios on aviation and emissions' (Consave) project scenarios with alternative approaches were designed, to be able to cover a broad range of possible future situations. This permits a straightforward, direct discussion of the key study questions, in particular those related to future challenges and constraints for aviation and its emissions. The four scenarios were qualitatively described using storylines with assumptions and then quantified by means of key information, calculated using 'Aviation emissions and evaluation of reduction options' (AERO)-model and scenario-specific sets of inputs. These are: - 'Unlimited skies' (ULS); global, dominant actor: market; -'Regulatory push & pull' (RPP); global, dominant actor: policy; - 'Fractured world' (FW); regional, dominant actors depending on regions; -'Down to Earth' (DtE); global, dominant actor: society. Each Consave aviation situation was drawn up using a related Consave background scenario. The scenario was quantified for gross domestic product (GDP), population, and key energy issues, applying the respective figures calculated for the 'partner' scenarios in the intergovernmental panel on climate change /special reports on emission scenarios (IPCC/SRES) exercise (on the basis of a total of six reviewed quantification models). This work is an important step going beyond existing scenario work, delivering a foundation for short-, medium-, and long-term planning, enabling more efficient consideration of possible future situations and consideration of the implications for technological development and other possible responses. Rather than looking for mixed 'realistic' futures developing along 'most-likely' paths, the concept of Consave was to design a set of 'pure', even extreme, scenarios, allowing the definition of robust boundaries for the range of possible growth of aviation and its emissions until 2050 This approach provides essential information for the policy and regulation community, the aviation industry, and for researchers including climatologists, and is a valuable input for further RTD activities within FP7. It was of interest to compare the selection of scenarios made by Consave with those considered to be the most important external (long-term) aviation scenario activities: Acare/Astera and Eurocontrol long-term forecast. Both the 'Advisory council for aeronautics research in Europe' (Acare)/'Aeronautical research and technological areas' (Astera) and Eurocontrol long-term forcasts had designed scenarios with the time horizon of 2020. Three of the Consave scenarios have very similar counterparts in the sets of scenarios developed by these external activities. But both Acare/Astera and Eurocontrol long-term forecasts did not have any equivalent to the fourth Consave scenario 'Down to Earth'. Related to their specific goals, these activities preferred the inclusion of a 'base case' respectively a 'business as usual'-scenario. By implementing intensive contacts and interactions especially with Acare/Astera and Eurocontrol, the project has been able to successfully contribute to the development of a common European understanding of critical aspects of the long-term development of aviation and its related emissions.
Within the 'Aviation emissions and evaluation of reduction options' (AERO)-model, the dominant features for the quantification of the development of global passenger demand were 'gross domestic product' (GDP) and population as external factors (taken from 'Intergovernmental panel on climate change' /'Special reports on emission scenarios' (IPCC/SRES)), air transport-related assumptions on elasticities and saturation effects, and (calculated) ticket prices. The results for passenger demand (in terms of passenger-kilometres) within the constrained 'Constrained scenarios on aviation and emissions' (Consave) scenarios 'Regulatory push & pull' (RPP), 'Fractured world' (FW), and 'Down to Earth' (DtE) for the year 2020 were in line with what would be expected - that is lower than the actual forecasts for the year 2020 from the 'International Civil Aviation Organization' (ICAO), Airbus, Boeing, 'Forecasting and Economic Analysis Support Group' 'Forschungseinrichtung Satellitengeodäsie' (FESG). These forecasts are all close to the outcomes for the Consave 'Unlimited skies' (ULS) scenario. Compared to the outcomes from the FESG demand scenarios Fa, Fc, Fe (1999) for (2020 and 2050), the ranges of passenger demand for both sets of scenarios were very much the same, with the exception of the DtE scenario which was characterised by lower development. Although AERO2k does not report passenger-kilometres, a comparison with forecast results of this study was possible on the basis of aircraft-kilometres from the year 2025, the AERO2k values for 2025 being in the middle of the range for the four Consave scenarios The number of passengers within the four scenarios grew with rates very similar to those for the demand in passenger-kilometres, with one exception: for the FW scenario the growth rates for passengers were remarkably higher with respect to the number of passengers than with respect to passenger-kilometres, as within this scenario a decrease in long-range flights between blocks was combined with a compensatory higher air traffic activity within the blocks. The project also reported figures for the development of air transport within and between the 14 'International Air Transport Association' (IATA) regions, used for the AERO-model system. Scenario-specific traffic flows for major route groups (in billions of passenger-kilometres) and the number of passengers of the IATA regions (in millions of passenger-kilometres) have been calculated up to 2050. The highest increases in absolute numbers were in all scenarios for the Intra Asia airline, followed by Intra Central & South America as they are the largest markets with respect to population. As a consequence, the dominance of air transport within North America and within Europe will be remarkably reduced. The growth factors differed significantly within the scenarios and the regions, dependant on the combinations of reasons, described in the study. Intra Africa, as a so far underdeveloped market, showed the highest growth factor (F) in all scenarios. In contrast, Intra North America, Intra Europe, and the Intra South Pacific market will have the lowest growth factors: They all will reach a high level of saturation. Regional growth rates for passenger demand between 2000 and 2050 ranged from 0.1 % up to about 9 %, being quite different depending on the scenarios and the various regions. The regional differences for the number of air passenger trips per capita (n) decreased over time until 2050, but for the region with the highest number of annual trips per capita (Southwest Pacific, n = 4.88 for ULS, n = 3.48 for RPP, n = 2.26 for FW, n = 1.35 for DtE) and the region with the lowest per capita air traffic (Eastern Africa, n = 0.54 for ULS, n = 0.37 for RPP, n = 0.21 for FW, n = 0.05 for DtE), the difference still remained very high, with a ratio (r) of the order of r = 10 for all scenarios (even higher for DtE).
The summarised scenario-dependent results for flight-kilometres, fuel use and emissions from civil aviation are: Resulting growth factors (F) for carbon dioxide (CO2) and nitrogen oxides (NOx) for the scenarios 'Unlimited skies' (ULS); 'Regulatory push & pull' (RPP); 'Fractured world' (FW) from 2000 to 2050 are F = 4.6 / 3.3, 3.1 / 2.2 and 1.8 / 1.2 respectively. For these scenarios the progress in technology does not fully compensate for the increase in transport volume. For the 'Down to earth' (DtE) scenario CO2 grew with a factor of F = 1.4 until 2050, whereas NOx was reduced by F = 0.5, reflecting the scenario-specific assumption that within the DtE world strong emphasis is given globally to the reduction of NOx. The rollover to the hydrogen technology in the RPP- Cryoplane scenario will result in a strong decrease of CO2 in 2050 of 86 % (i.e. F = 0.14) compared to 2000 (although it is important to recognise that CO2 produced during the production process of hydrogen was not included in this figure). However, there was a significant increase in the release of water vapour emissions, and the climate effect of water vapour relative to effects from CO2 emissions is still under discussion. (Reacting with other aviation emissions, water vapour can cause the formation of contrails and cirrus clouds.). The differences in NOx emissions from the hydrogen fleet, compared to a kerosene-fuelled fleet, emanated from three sources: a lower NOx emission index, an approximately 2.8 times higher energy per unit mass (partly offset by a greater fuel consumption), and a modernisation effect (as - due to the scenario assumptions - the hydrogen fleet in 2050 is a comparably extremely young fleet, produced almost entirely between 2040 and 2050). Due to further improvements in fuel efficiency in ULS and RPP the specific fuel consumption (kg fuel per ac-km) will be reduced in these scenarios by approximately 30 % until 2050. Although technology advances in the FW were only in some regions of the globe comparable to those in ULS and RPP, FW even showed a somewhat higher reduction of the specific fuel consumption (-36 %), as the average flight distance in this scenario was significantly lower (and therefore e.g. the take-off-weight relatively lower for the same aircraft). The lowest consumption of fuel per aircraft will be in the RPP H2 sub-scenario (-46 %), mainly as the energy density of hydrogen was higher than the energy density of kerosene. For all scenarios, 3-dimensional emissions' inventories for civil aviation addressing aircraft-kilometres fuel use, CO2, water (H2O), NOx, carbon monoxide (CO), unburned hydrocarbons (CxHy) with a grid scale of 5° x 5° x1 km are available at the Consave project website: ( Within the Consave 2050 project, military aviation was not addressed. However (as for 'Global aircraft emissions data project for climate impacts evaluation' (AERO2k)) the assumption was made that in the future the total volumes for fuel used and for emissions will increase with very low growth rates or will even oscillate around present values - with some differences among the four scenarios. As there is no reliable information on the future development of military aviation emissions, it was assumed that the respective absolute values for military aviation for 2020 and 2050 are in the order of those, given by AERO2k for the year 2002. The four Consave aviation scenarios can be regarded as being consistently embedded in the Consave background scenarios. The four Consave background scenarios were quantified using the quantified results for key factors of 'partner' scenarios of the 'Intergovernmental panel on climate change /Special reports on emission scenarios' (IPCC/SRES) exercise with scenario characteristics closest to those of the four Consave scenarios. As the IPCC scenarios are related to emissions from all human activities, the contribution from civil aviation to these total emissions can be estimated by comparing the results for the Consave scenarios with the figures calculated for the 'partner' scenario of the IPCC/SRES work. For CO2 and NOx, contributions from aviation compared to the respective emissions from all human activities were determined for the years 2020 and 2050. The AERO-model was modified to allow for some results concerning the Airport air quality (AAQ) and noise aspects of air traffic. Around 65 cities are selected world wide, emphasising the larger airports in the western hemisphere. For each of these cities (or airports) the average changes were calculated for fuel consumption and for NOx, as the emission species from aircraft are most relevant for 'Airport air quality' (AAQ). For three of the four basic scenarios - ULS, RPP (kerosene), and FW - NOx emissions around airports will increase until the year 2050: Compared to the present levels NOx emissions from aircraft will increase with average factors of about 2.4/1.6/1.5 for the three scenarios with variance values for the whole selected sample of 65 cities of approximately 5.4/3.9/3.3, respectively. One of the basic scenarios, the DtE scenario, shows a reduction of the average NOx emissions from aircraft around airports. In the RPP Cryoplane sub-scenario aircraft NOx emissions around airports will be significantly reduced until 2050 also.

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