Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
calculations, the authors of Chapter 4 set uncertainty limits on these results. For ozone changes
resulting from the impact of the subsonic fleets, the uncertainty was taken to be a factor of two times
the difference obtained by the Oslo 3-D model for scenarios (B-A), (D-C), and (F-E) defined in Table
4-4. The quoted uncertainties are taken as the 67% likelihood range. We believe that uncertainty in
the calculation of ozone percentage changes is by far the greatest uncertainty in the determination of
percentage changes in UVery; accordingly, we have not added additional uncertainties to the range
supplied by Chapter 4. In addition, our assessment of the confidence in these calculations is as given
by Chapter 4-that is, "fair" for 2015 and "poor" for 2050.
Chapter 4 considered three components in assessing the uncertainty for the impact of the hybrid fleet
on ozone: The spread obtained by a number of models for a range of plausible scenarios,
uncertainties in chemical rate coefficients, and uncertainties introduced by inaccurate treatment of
atmospheric circulation in the models. Chapter 4 concluded that the annually averaged impact on
ozone for the Northern Hemisphere of a hybrid fleet in 2050 (including 1,000 HSCTs) would be in the
range of -3.5 to +1% when compared with the impact of the subsonic fleet and that the best estimate
is -1 % given by the AER 2-D model. The uncertainty range again represents the 67% likelihood range
with a confidence in this
uncertainty range of "fair." As with estimated subsonic impacts, we believe that the uncertainty in the
change in ozone caused by the hybrid fleet is much greater than any other uncertainties in the
calculation of changes in UVery. Chapter 4 has provided only an annually averaged Northern
Hemisphere value because it is not possible at present to assign uncertainty factors as functions of
latitude, altitude, and season. The large variations in ozone changes predicted by a range of models
as functions of latitude, altitude, and season (see Figures 4-6c, 4-6d, 4-12a, and 4-12b) are clear
indications of shortcomings inherent in current models.
Given that the predicted change in UVery is primarily a function of changes in the ozone column and
is less sensitive to the exact altitude dependence of the ozone change, an estimate of the uncertainty
for changes in ozone columns as a function of latitude and season should be sufficient. This chapter
uses the subjective estimates of uncertainties from Chapter 4 and defines the 67% likelihood range
for changes in ozone columns at each latitude and season as follows. If the column change predicted
by the AER 2-D model at latitude (Q) and time of year (T) is a(Q,T)%, the uncertainty range in percent
column ozone change at that latitude and time of year is given by [a(Q,T) -3]% to [a(Q,T) +2]%. The
same definition will be adopted for fleet sizes of either 500 or 1,000 HSCTs. These estimates are very
subjective; although the confidence attached to these uncertainties for the tropics is "good," outside
the tropics the confidence can be considered only "fair." In the absence of a rigorous method of
obtaining uncertainties, this chapter also assumes that there is a 5% range in estimated uncertainties
for change in UVery; this range is given by [b(Q,T) -2]% to [b(Q,T) +3]%, where b(Q,T)% is the
percent change in UVery corresponding to a(Q,T)% change in ozone column. In summary,
uncertainties in the impact of the subsonic fleet on UVery may be obtained from any of the diagrams
in this chapter that report this change simply by doubling or halving the change shown in the diagram.
For example, in the top panel of Figure 5-9, the change in UVery shown for the subsonic impact for
http://www.ipcc.ch/ipccreports/sres/aviation/060.htm (3 von 6)08.05.2008 02:42:42
Figure 5-7: Calculated ozone and UVery at 45°N in January
referred to the calculated background values for 1970.