Several conclusions can be derived from this special issue's
contributions. A number of technology options exist that can
substantially mitigate aircraft fuel burn (and thus CO2 emissions),
NO
x emissions, and aircraft noise. However, if air travel demand
continues to increase as anticipated by industry projections, the
only realistic achievement can be mitigating the growth rate of
impacts due to the lack of sufficiently strong mitigation options on
a sufficiently large scale, at least over the next 20 years. Capacity
constraints at key airports would mainly shift the traffic away from
more congested toward less constrained airports and affect the
growth in total traffic only marginally.
The key aviation-related impacts include noise, air quality, and
climate change. Due to the large scale of the air transportation
system, the related annual global damages are likely in excess of
one billion US$ in terms of noise and up to ten times as large for
climate change. On an aggregate level, damages due to climate
change dominate, but aircraft noise damages are very location
specific: for people living at airport boundaries, costs related to
aircraft noise are highest, while climate change related costs are
highest to those living further away from airports.
There is no single solution that effectively addresses noise, air
quality, and climate change impacts. Various options exist that can
address each of the impacts individually or at most two of the
impacts simultaneously at different degrees. For example, second
generation biofuels have the potential to significantly mitigate
both CO2 and to some extent local air quality related emissions,
but do not affect aircraft noise. Significant and financially risky
aircraft design changes would be necessary to also significantly
mitigate aircraft noise.
The shift toward the best available technology, changes in new
aircraft technology, and advances in air traffic management can be
combined in terms of CO2 emissions reduction. Assuming a 0.2%
per year reduction due to a shift towards the best available
technology (9% reduction over 40 years), a perhaps optimistic 1%
per year decline in fleet fuel burn due to change in and rapid
penetration of new aircraft technology, and a 0.3% reduction due
to improvements in air traffic management (10% reduction over 40
years), the combined (multiplicative) total reduction of CO2 emissions results in 1.5% per year. Taking into account the projected
annual growth of 5% per year in air transportation, CO2 emissions
would continue to rise by 3.5% per year. To achieve a CO2-neutral