Aviation and the Global Atmosphere

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6.1. How Do Aircraft Cause Climate Change?

Figure 6-1: Schematic of possible mechanisms whereby
aircraft emissions impact climate. Climate impact is
represented by changes in global mean surface
temperature (�Ts) and global mean sea level rise (�msl).

Aircraft perturb the atmosphere by changing background levels of trace gases and particles and by forming condensation trails (contrails). Aircraft emissions include greenhouse gases such as CO2 and H2O that trap terrestrial radiation and chemically active gases that alter natural greenhouse gases, such as O3 and CH4. Particles may directly interact with the Earth's radiation balance or influence the formation and radiative properties of clouds. Figure 6-1 portrays a causal chain whereby the direct emissions of aircraft accumulate in the atmosphere, change the chemistry and the microphysics, and alter radiatively active substances in the atmosphere, which change radiative forcing and hence the climate.

Chapters 2 and 3 link the direct emissions of aircraft today to changes in radiatively active substances, and Chapter 4 projects these atmospheric changes into the future for a range of aviation scenarios. This chapter presents calculations of radiative forcing from aircraft-related atmospheric changes and discusses implications concerning the role of aircraft in a changing climate. This section begins with the concept of "dangerous climate change," as defined within the mandate of the United Nations Framework Convention on Climate Change (FCCC), then presents the IS92 scenarios for future climate change associated with the Second Assessment Report (IPCC, 1996). Section 6.1 also summarizes aviation's potential role in climate change and its proportion of fossil fuel use. Section 6.2 discusses the concepts of radiative forcing (RF) and global warming potential (GWP). Section 6.3 provides calculations of radiative forcing from aircraft perturbation of greenhouse gases, and Section 6.4 presents calculations of RF from aircraft perturbations of aerosols and contrails. Section 6.5 examines how radiative forcing can be used as a predictor of climate change and presents some case studies of climate change patterns that might be induced by aviation. Finally, Section 6.6 presents the summed radiative forcing, and associated climate change, for a range of projected scenarios and technological options in future aviation.

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