Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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6.6.5. Climate Change
Other reports in this collection
The ranges of aircraft perturbations to climate change examined in this report are, of course, small compared to the overall increase in RF expected throughout the
next century. Climate modeling of this transient change over the next 50 years cannot readily evaluate aircraft, or any equally small RF, in terms of specific climate
changes because of problems in separating "signal" from "noise." Climate parameters that might be attributed to aircraft, such as the increase in global mean surface
air temperature, are calculated here using a simple model consistent with previous IS92a relationships.
The predicted change in global mean surface temperature is shown in Figure 6-17 for total
warming in accord with IS92a (solid) and for the case in which all of aviation's contribution to
global warming (scenario Fa1) is cut off (dotted line). Of total global warming of 0.9 K anticipated
in 2050, about 0.05 K would be attributable to aviation. The Eab case anticipates a larger
aviation component (0.09 K). One caveat is that aircraft may produce a different climate
signature, one that is not represented by an increase in global mean temperature.
To evaluate individual energy sectors as part of overall climate forcing, it is necessary to
compare their summed radiative forcing from all atmospheric perturbations, not just that from
their use of fossil-fuel carbon alone. The radiative forcing index-defined here as the ratio of total
radiative forcing to that from CO 2 emissions alone-is a measure of the importance of aircraft-
induced climate change relative to that from an equivalent sector with the same fossil fuel use
but without any effect other than CO 2 (see also Section 6.2.3). In 1992, the RFI for aircraft was
about 2.7, with an uncertainty of at least ±1.5. The RFI changes to 3.0 by 2015 then drops to 2.6
for the Fa1 scenario (see Table 6-1). This index ranges from 2.2 to 3.4 in the year 2050 for the
various E- and F-type scenarios for subsonic aviation and technical options considered here.
The RFI increases from 2.6 to 3.4 with the addition of HSCT aircraft (scenario Fa1H), as a result
of the effects of stratospheric water vapor. Thus, aircraft-induced climate change with RFI > 1
points to the need for a complete scientific assessment rather than basing the climate impact on
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