Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
impact of the combined effect of a stratospheric ozone decrease and a tropospheric ozone
increase from an assumed sub- and supersonic aircraft fleet for the year 2015. An equilibrium
climate simulation leads to a general stratospheric cooling of a few tenths of a Kelvin, combined
with a warming of the lower stratosphere in northern polar regions as a result of altered
atmospheric circulation (Figure 6-11). The globally averaged surface temperature change was
found to be not statistically significant compared with climatic variability.
As another example, Figure 6-12 shows the equilibrium annual, zonal mean temperature change
from ECHAM4/MLO (Ponater et al., 1998) due to ozone perturbations resulting from 1992 air
traffic (Dameris et al., 1998), which differ slightly from the 1992 ozone perturbations reported in
this assessment. The overall pattern of temperature change is statistically significant. The RF
associated with this case is 0.04 W m-2, and the resulting equilibrium change of global mean
surface temperature is 0.06 K, resulting in a climate sensitivity parameter l of about 1.5 K/(W m-
2). Note that a climate sensitivity calculated for such small perturbations is associated with large
uncertainty.
For comparison, Figure 6-13 shows the equilibrium climate change associated with the
anthropogenic increase of well-mixed greenhouse gases CO2 , CH4, etc.) from 1990 to 2015
according to IS92a as simulated with the same model. The associated global mean surface
temperature change is 0.9 K, and the RF is 1.1 W m-2 . The resulting climate sensitivity
parameter, about 0.8 K/(W m-2), is smaller than for the aircraft-induced ozone perturbation.
Temperature change patterns are quite different for well-mixed greenhouse gases than for the
aircraft-induced ozone perturbation.
These and related experiments with the GISS and ECHAM4 models showed that: The aircraftrelated
climate change pattern and the aircraft-related climate sensitivity parameters are modeldependent,
and the climate response for aircraft-induced ozone changes is different from that for
conventional greenhouse gases. Internal feedback processes within and between climate
models appear to work differently. The exact nature of the climate feedback differences to
different pattern of RF remains to be investigated. Thus, the climate factors of human interest,
especially the regional climate change for these regional perturbations, await further
development of climate models. The details of the climate response to the contrail radiative
imbalance, which is spatially heterogeneous on the smallest scales, is likewise unknown.
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Figure 6-12: Equilibrium change of annual, zonal
mean temperature (K) caused by ozone perturbation
due to NO x emissions of 1991-92 air traffic (DLR-2),
as simulated with the ECHAM4/MLO model (Ponater
et al., 1998). This result is similar to, but not based on,
the scenarios analyzed here.
Figure 6-13: Equilibrium change of annual, zonal
mean temperature (K) resulting from the