Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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6.6. The Role of Aircraft in Climate Change-Evaluation of Sample Scenarios
The overall impact of aviation on climate change in the next 50 years is evaluated here for a
range of scenarios (see Section 6.1.3 and Table 6-3) in air traffic and potential options in
civil aviation (e.g., low-NOx combustors, high-speed civil transport). Aviation's role is
considered within the context of climate change already being forced by greenhouse gases
and expected to continue from growth of the world's economies (e.g., IPCC's IS92a
scenario; see IPCC, 1992). The impact of air travel and climate change as a whole on
society is beyond this scientific assessment of the role of aviation in physical climate
change.
This section combines the aviation impacts from Sections 6.3 and 6.4 evaluated for the
fixed-year scenarios (defined in Table 6-1) and places them in a continuous time sequence
(defined in Table 6-3) to compare with overall climate changes expected under IS92a. We
assume that RFs are additive, so the issue of different climate sensitivities-for example, for
aircraft-induced ozone perturbations versus those from co 2 (as discussed in Section 6.5)-
introduces some additional error/ uncertainty when we use summed RF to deduce climate
change. We have no alternative but to use RF as a metric of climate change because
differences in forcing between the various subsonic options would not be reliably detected
above the natural climate variability in many models. The summed RF, however, should
provide a relative ranking of the different options discussed below.
6.6.1. Individual Components of Radiative Forcing
Figure 6-14a (IPCC, 1996) shows a bar chart of individual components of RF for all
anthropogenic change for the 1990 atmosphere. This figure can be compared with 1992
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Figure 6-14a: Bar charts of radiative forcing from all perturbations in
1990 (from IPCC, 1996). Note scale change from (a) to (b). In (b),
best estimate (bars) and high-low 67% probability intervals (whiskers)
are given. No best estimate is shown for the cirrus clouds; rather, the
dashed line indicates a range of possible estimates. The evaluations