Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
the use of fossil fuel alone. For comparison, in the IS92a scenario, the RFI for all human
activities is about 1; for greenhouse gases alone it is about 1.5, and it is much higher for sectors
emitting CH4 and N2O without significant fossil fuel use.
6.6.6. Aviation and Anthropogenic Change
Figure 6-17: Predicted change in global mean surface
temperature (K) from 1990 (defined as 0) to 2050 for
the IS92a emission scenario (solid line) and for the
same scenario without aircraft (Fa1, dotted line).
The overall positive anthropogenic RF today, leading toward global warming, is caused primarily by an increase in anthropogenic emissions of long-lived greenhouse
gases, countered in part by short-lived aerosols. Much of this radiative forcing has built up since the industrial revolution. Emissions from aviation are a relatively new
contributor to this RF, although they are potentially a growing sector. In evaluating climate change forced by aviation, as well as that by other industrial sectors, the RFI
provides a useful indicator. With an RFI of about 3, aviation's role in climate change involves several important climate perturbations beyond that from its release of
fossil carbon alone.
This report presents the first thorough IPCC climate assessment of any industrial or agricultural sector. It includes all known climate forcings, many of which are
important and not currently represented by indices such as GWP. Comparison of aviation to other industries must await an equally thorough evaluation of the summed
effects of human activities by sector that is not available in IPCC (1996) but is anticipated for IPCC's Third Assessment Report in 2001.
The range of technology options that would attempt to reduce the impact of aviation on climate did not significantly change radiative forcing by the year 2050. A lesson
taken from the Second Assessment Report (IPCC, 1996, Figure 6a) is that changes in total radiative forcing, even the wide range of emissions for the IS92a-f
scenarios, do not appear much before year 2050. Thus, subsequent climate assessments of 21st century options for civil aviation need to carry out projected changes
in greenhouse gases and aerosols, and all chemical and climate feedbacks, to the year 2100.
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