Air Travel, Life-Style, Energy Use and Environmental Impact
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Air travel, life-style, energy use and environmental impact Stefan Kruger Nielsen Ph.D. dissertation September 2001 Financed by the Danish Energy Agency’s Energy Research Programme Department of Civil Engineering Technical University of Denmark Building 118 DK-2800 Kgs. Lyngby Denmark http://www.bvg.dtu.dk 2001 DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document Report BYG DTU R-021 2001 ISSN 1601-2917 ISBN 87-7877-076-9 Executive summary This summary describes the results of a Ph.D. study that was carried out in the Energy Planning Group, Department for Civil Engineering, Technical University of Denmark, in a three-year period starting in August 1998 and ending in September 2001. The project was funded by a research grant from the Danish Energy Research Programme. The overall aim of this project is to investigate the linkages between energy use, life style and environmental impact. As a case of study, this report investigates the future possibilities for reducing the growth in greenhouse gas emissions from commercial civil air transport, that is passenger air travel and airfreight. The reason for this choice of focus is that we found that commercial civil air transport may become a relatively large energy consumer and greenhouse gas emitter in the future. For example, according to different scenarios presented by Intergovernmental Panel on Climate Change (IPCC), commercial civil air transport's fuel burn may grow by between 0,8 percent a factor of 1,6 and 16 between 1990 and 2050. The actual growth in fuel consumption will depend on the future growth in airborne passenger travel and freight and the improvement rate for the specific fuel efficiency. As a central mid-term estimate the IPCC foresees that the fuel consumption may grow by around 3 percent per year until 2015. The average specific C02 emissions per revenue passenger kilometre transported by the World’s aircraft fleet is lower than the C02 intensity of an average Danish passenger car with one occupant. But because aircraft can travel over long distances within a relatively short period of time, one air trip can contribute considerably to the total yearly C02 emissions of air travellers. For example, on a long haul return flight (12400 kilometres) between Copenhagen and New York in a modern aircraft (for example a B767-300ER), around 300-500 kilograms of jet fuel may be burned per passenger emitting around 0,9-1,6 tonnes of C02. The lower figure represents a calculation where the fuel consumption that may be attributable to belly-hold freight is subtracted on an equal weight basis. Note that this estimate may change between types of aircraft and is dependent on the actual load factor. Furthermore, it should be taken into consideration that aircraft engine emissions per amount of fuel burned at I high altitude may contribute 2-4 times as much to climate change as emissions from fuel burned in for example passenger cars at sea level. Note also that there is currently relatively high uncertainty connected to this estimate. The relative importance of one such long-haul return trip can be exemplified by comparing to the average emissions of C02 from combustion of fossil energy sources per capita. On average, the World’s citizens emit around 4 tonnes of C02 in a year, although the number is much higher in many industrialised countries and much lower in many developing countries. There are considerable differences between the energy intensity of different types of aircraft and also between airlines. Old aircraft are generally less fuel-efficient than newer types, and aircraft used at short-haul are generally more fuel intensive than aircraft used at medium-haul and long haul. Therefore, airlines that operate new fuel- efficient aircraft over relatively long distances and at relatively high load factors are the most fuel-efficient. European charter carriers that operate aircraft with a high-density seat-configuration at close to the optimum passenger load factor while only carrying insignificant amounts of freight are the most fuel-efficient passenger carriers in the airline industry. Conversely, the most fuel-intensive airlines are to be found among the regional carriers that operate relatively small aircraft at below average load factors at short-haul routes. Aircraft used at long haul routes consume more fuel per available seat kilometre than the most fuel- efficient aircraft operated at medium-haul. However, if taking into account that passenger aircraft used at long haul routes by scheduled carriers generally transport relatively high loads of belly-hold freight, the fuel intensity per revenue passenger kilometre, or per revenue tonne kilometre, is also relatively low on these routes. The division of the fuel consumed by passenger aircraft between passenger and freight loads is not straightforward, and different methodologies can be used. Air traffic growth by far overrides the efficiency gains attained in the specific fuel consumption and emissions per revenue tonne kilometre performed by commercial civil aircraft. For example, the number of revenue tonne kilometres transported by the American air carriers grew by a factor of 3,8 between 1973 and 1997. In the same period, the specific fuel consumption per revenue tonne kilometre was reduced by 55%, leading to an increase in the total fuel consumption by a factor of 1,7. The major part of the reduction in the specific fuel consumption was achieved in the early part of II the period while the yearly improvements have slowed down in the later part of the period. Even though the yearly growth rates in passenger air travel and freight have slowed down in the last decades, as compared to the earlier decades, many scenario studies expect that commercial civil air transport will continue growing faster than most other energy services. Furthermore, the yearly reduction of the fuel intensity is expected to slow down further in the future. Therefore, in a business as usual scenario, commercial civil air transport is likely to become a bigger source of greenhouse gas emissions in the future and its share of the total emissions is likely to rise. The yearly improvement rate for the aircraft fleets ’ fuel efficiency can to some extent be speeded up by implementing new measures to promote development of new and more fuel-efficient aircraft as well as the phasing out of older and more fuel intensive aircraft. For example, a tax on jet fuel or emissions or voluntary agreements between governments and the airline industry on future goals for the reduction of the fuel intensity, may lead airlines to scrap some of the 5000 operating jets that are more than 23 years old earlier than what can otherwise be expected. Furthermore, on the longer term, the aircraft producers may choose to develop radically more fuel-efficient types of aircraft configurations, such as flying-wing aircraft, that are designed for cruising at lower speed and altitude, thereby perhaps also being less greenhouse gas intensive per amount of fuel burnt. Likewise, new fuel-efficient types of propulsion technologies, such as propfan engines, could be further developed to substitute current turbofans that seem to have reached a plateau in fuel-efficiency improvements. However, at the current fuel price a rather high kerosene tax may be needed to make such radically improved technologies economically attractive to airlines. And because the development cycles in aeronautical engineering tend to be relatively long, it may take several decades before such technologies can come into use in civil passenger aircraft. Furthermore, a tax on jet fuel or emissions could potentially contribute by making current plans for developing GHG intensive high-speed and high-altitude aircraft types, such as sonic cruisers or a new generation of supersonics, less economically attractive to airlines. Currently, the major American aircraft producer Boeing considers launching the so-called sonic cruiser that will be able to cruise at higher speed and altitude than current state-of-the-art subsonic aircraft. Ill Alternative fuels, such as liquefied hydrogen or synthetic jet fuel produced from biomass, could theoretically also be used in commercial civil air transport, but development and implementation poses large technical and economical challenges. Most aviation experts seem to consider that alternative fuels will not be technically or economically viable in the next decades. Furthermore, the current knowledge about the impact on climate change of burning hydrogen at high altitude is relatively poor and highly uncertain. There is also potential for using more efficient air traffic management systems and for improving the load factors. However, technical and operational efforts to improve the specific fuel consumption and the related emissions are not envisioned to be sufficient to keep pace with the growth in the air traffic volume at current growth rates. The strong growth in passenger air travel and airfreight is generated by social, technical, political and economic changes. People living in industrialised countries have become accustomed to travel by air and the building up of a large socio-technical system surrounding commercial civil air transport facilitates air travel growth. Airport and aircraft capacity is constantly enlarged, while the real cost of air travel is reduced. The building up of commercial civil air transport ’s socio-technical system is furthered by government subsidies, which again contribute to reduce airfares. National interests and geopolitics play important roles in the subsidisation of commercial civil air transport’ s socio-technical system. National governments support local airports, airlines and aerospace industries to maintain and increase the relatively large number of people employed in these industries. Further aspects are the prestige and power connected to maintaining aeronautical and military leadership as well as the prestige connected to operating national flag carriers.