Aviation and the Global Atmosphere

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8.1. Introduction

The air transport industry has grown rapidly over recent years, and growth is expected to continue. An effect of this growth is an increasing amount of emitted exhaust gases and consequential environmental impact. Chapter 9 discusses aspects of this growth.

Chapter 8 is the second of two chapters that assess what is known about means of addressing adverse environmental impacts associated with aircraft engine emissions. Whereas Chapter 7 considers how aircraft and their engines might be improved, this chapter assesses what is known about measures that might be, or have been, taken to change aircraft operations and improve air traffic management (ATM) systems and procedures to reduce the amount of fuel consumed, which would have the effect of reducing emissions. Aircraft operations and measures that could be taken to improve efficiency are well understood, but only limited knowledge exists on the potential environmental impact of many of these measures.

Section 8.2 describes the constraints and limitations of the conventional ATM system and changes that are presently being implemented through new technology and improved procedures, as well as changes anticipated for the future designed to create a more integrated, global system of air traffic management. Whereas inefficient routings, cruising at less than optimum flight levels, and airborne holdings that characterize the present system result in unnecessary amounts of emissions injected into the atmosphere, new systems and procedures could result in fuel savings, hence reductions of emissions for a given demand for air transportation.

Section 8.3 discusses potential fuel reductions from other (non-ATM) operational factors, including improvement of aircraft utilization, optimization of speed, reductions in weight and nonessential fuel on board, limiting the use of auxiliary power units, and reduced taxiing. The airlines' need to contain fuel costs already provide a powerful incentive for progressive improvements in these areas. Application of these measures is restricted to some degree, however, by safety and regulatory aspects.

To answer the question of whether emissions reductions could be achieved by substituting other modes of travel for air transport, several studies have compared fuel burn and carbon dioxide emissions from different modes of transport. This comparison between carbon dioxide emissions for different modes of transport is discussed in Section 8.3.

Throughout this chapter, the assumption is made that improvements in operations and fuel efficiency will lead to reductions in emissions. Improved efficiency however, may result in attracting additional air traffic, although no studies providing evidence on the existence of this so-called rebound effect have been identified. In this respect, the scenarios presented in Chapter 9 have assumed an optimized air traffic management system. As a consequence, Chapter 9 includes the effects of an optimized ATM system for air transport demand and related emissions. Chapter 8 discusses the relation between improved operational efficiency and emissions for a given demand for air transport.

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